Patent Publication Number: US-6705526-B1

Title: Automated method of and system for dimensioning objects transported through a work environment using contour tracing, vertice detection, corner point detection, and corner point reduction methods on two-dimensional range data maps captured by an amplitude modulated laser scanning beam

Description:
CROSS-REFERENCE TO RELATED US APPLICATIONS 
     This is a Continuation of application Ser. No. 09/327,756 filed Jun. 7, 1999 now abandoned, which is a Continuation-in-Part of application Ser. No. 09/305,896 filed May 5, 1999 now U.S. Pat. No. 6,287,946, which is a Continuation-in-Part of application Ser. No. 09/275,518 filed Mar. 24, 1999, now U.S. Pat. No. 6,457,642, which is a Continuation-in-Part of application Ser. No. 09/274,265 filed Mar. 22, 1999 now U.S. Pat. No. 6,382,515; Ser. No. 09/243,078 filed Feb. 2, 1999 now U.S. Pat. No. 6,354,505; Ser. No. 09/241,930 filed Feb. 2, 1999 now U.S. Pat. No. 6,422,467; Ser. No. 09/157,778 filed Sep. 21, 1998; Ser. No. 09/047,146 filed Mar. 24, 1998 now U.S. Pat. No. 6,360,947, Ser. No. 08/949,915 filed Oct. 14, 1997 now U.S. Pat. No. 6,158,659; Ser. No. 08/854,832 filed May 12, 1997 now U.S. Pat. No. 6,085,978; Ser. No. 08/886,806 filed Apr. 22, 1997 now U.S. Pat No. 5,924,185; Ser. No. 08/726,522 filed Oct. 7, 1996 now U.S. Pat. No. 6,073,846; and Ser. No. 08/573,949 filed Dec. 18, 1995 now abandoned, each said application being commonly owned by Assignee, Metrologic Instruments. Inc. of Blackwood, N.J., and incorporated herein by reference as it fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates generally to an automated tunnel-type laser scanning package identification and measuring system arranged about a high-speed conveyor structure used in diverse package routing and transport applications, and also a method of identifying and measuring packages labeled with bar code symbols. 
     2. Brief Description of the Prior Art 
     In many environments, there is a great need to automatically identify and measure objects (e.g. packages, parcels, products, luggage, etc.) as they are transported along a conveyor structure. While over-the-head laser scanning systems are effective in scanning upwardly-facing bar codes on conveyed objects, there are many applications where it is not practical or otherwise feasible to ensure that bar code labels are upwardly-facing during transportation under the scanning station. 
     Various types of “tunnel” scanning systems have been proposed so that bar codes can be scanned independently of their orientation within scanning volume of the system. One such prior art tunnel scanning system is disclosed in U.S. Pat. No. 5,019,714 to Knowles. In this prior art scanning system, a plurality of single scanline scanners are orientated about a conveyor structure in order to provide a limited degree of omni-directional scanning within the “tunnel-like” scanning environment. Notably, however, prior art tunnel scanning systems, including the system disclosed in U.S. Pat. No. 5,019,714, are incapable of scanning bar code systems in a true omni-directional sense, i.e. independent of the direction that the bar code faces as it is transported along the conveyor structure. At best, prior art scanning systems provide omni-directional scanning in the plane of the conveyor belt or in portions of planes orthogonal thereto. However, true omnidirectional scanning along the principal planes of a large 3-D scanning volume has not been hitherto possible. 
     Also, while numerous systems have been proposed for automatically identifying and measuring the dimensions and weight of packages along a high-speed conveyor, prior art systems have been very difficult to manufacture, maintain, and operate in a reliable manner without the use of human supervision. 
     Thus, there is a great need in the art for an improved tunnel-type automated laser scanning package identification/measuring system and a method of identifying and measuring packages transported along a high-speed conveyor system, while avoiding the shortcomings and drawbacks of prior art scanning systems and methodologies. 
     OBJECTS AND SUMMARY OF THE PRESENT INVENTION 
     Accordingly, a primary object of the present invention is to provide a novel tunnel-type automated package identification and measuring system that is free of the shortcomings and drawbacks of prior art tunnel-type laser scanning systems and methodologies. 
     Another object of the present invention is to provide a fully automated package identification and measuring system, wherein an omni-directional laser scanning tunnel is used to read bar codes on packages entering the tunnel, while a package dimensioning subsystem is used to capture information about the package prior to entry into the tunnel. 
     Another object of the present invention is to provide such an automated package identification and measuring system, wherein Laser Detecting And Ranging (LADAR-based) scanning methods are used to capture two-dimensional range data maps of the space above a conveyor belt structure, and two dimensional image contour tracing methods are used to extract package dimension data therefrom. 
     Another object of the present invention is to provide a fully automated package identification and measuring system, wherein the package dimensioning subsystem is realized as a LADAR-based package imaging and dimensioning unit (i.e. subsystem) supported above the conveyor belt structure of the system. 
     Another object of the present invention is to provide such an automated package identification and measuring system, wherein the LADAR-based imaging and dimensioning subsystem produces a synchronized amplitude-modulated laser beam that is automatically scanned across the width of the conveyor belt structure and, during each scan thereacross, detects and processes the reflected laser beam in order to capture a row of raw range (and optionally reflection-intensity) information that is referenced with respect to a polar-type coordinate system symbolically-embedded within the LASAR-based imaging and dimensioning subsystem. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the rows of range data captured by the LADAR-based imaging and dimensioning subsystem are continuously loaded into a preprocessing data buffer, one row at a time, and processed in real-time using window-type convolution kernels that smooth and edge-detect the raw range data and thus improve its quality for subsequent dimension data extraction operations. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically subtracts detected background information (including noise) from the continuously updated range data map as to accommodate for changing environmental conditions and enable high system performance independent of background lighting conditions. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically buffers consecutively captured rows of smoothed/edge-detected range data to provide a range data map of the space above the conveyor belt, and employs two-dimensional image contour tracing techniques to detect image contours within the buffered range data map, indicative of packages being transported through the laser scanning tunnel system. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically processes the indices (m,n) of the computed contours in order to detect vertices associated with polygonal-shaped objects extracted from the range data map, which are representative of packages or like objects being transported through the laser scanning tunnel system. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically processes the m and n indices of the detected vertices associated with the computed contours in order to detect candidates for corner points associated with the corners of a particular package being transported through the laser scanning tunnel system. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically processes the m and n indices of detected corner point candidates in order to reduce those corner point candidates down to those most likely to be the corners of a regular-shaped polygonal object (e.g. six sided box). 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically processes the m and n indices of the corner points extracted from the range data map in order to compute the surface area of the package represented by the contours traced therein. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically processes the m and n indices of the corner points extracted from the range data map in order to compute the x, y and z coordinates corresponding to the corners of the package represented by the contours traced therein, referenced relative to a Cartesian-type global coordinate reference system symbolically embedded within the automated package identification and measuring subsystem. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem automatically processes the m and n indices of the corner points extracted from the range data map in order to compute the average height of the package represented by the contours traced therein, referenced relative to the Cartesian-type global coordinate reference system. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem employs a polygonal-type laser scanning mechanism for scanning an amplitude-modulated laser beam across the width of the conveyor belt. 
     Another object of the present invention is to provide such an automated package identification and measuring subsystem, wherein the LADAR-based imaging and dimensioning subsystem employs a holographic-type laser scanning mechanism for scanning an amplitude-modulated laser beam across the width of the conveyor belt. 
     Another object of the present invention is to provide a fully automated package identification and measuring system, wherein corner-projected orthogonal laser scanning patterns employed therein provide for enhanced reading of ladder and picket fence oriented bar codes on packages moving through the tunnel. 
     Another object of the present invention is to provide a fully automated package identification and measuring system, wherein mathematical models are created on a real-time basis for both the geometry of the package and the position of the laser scanning beam used to read the bar code symbol thereon. 
     Another object of the present invention is to provide a fully automated package identification and measuring system, wherein the mathematical models are analyzed to determine if collected and queued package identification data is spatially and/or temporally correlated with package measurement data using vector-based ray-tracing methods, homogeneous transformations, and objectoriented decision logic so as to enable simultaneous tracking of multiple packages being transported through the scanning tunnel. 
     Another object of the present invention is to provide such a system, in which a plurality of holographic laser scanning subsystems are mounted from a scanner support framework, arranged about a high-speed conveyor belt, and arranged so that each scanning subsystem projects a highly-defined 3-D omni-directional scanning volume with a large depth-of-field, above the conveyor structure so as to collectively provide omni-directional scanning with each of the three principal scanning planes of the tunnel-type scanning system. 
     Another object of the present invention is to provide such a system, in which each holographic laser scanning subsystem projects a highly-defined 3-D omni-directional scanning volume that has a large depth-of-field and is substantially free of spatially and temporally coincident scanning planes, to ensure substantially zero crosstalk among the numerous laser scanning channels provided within each holographic laser scanning subsystem employed in the system. 
     Another object of the present invention is to provide such a system, in which a split-type conveyor is used with a gap disposed between its first and second conveyor platforms, for mounting of an omni-directional projection-type laser scanning subsystem that is below the conveyor platforms and ends substantially the entire width of the conveyor platform. 
     Another object of the present invention is to provide such a system, wherein a plurality of holographic laser scanners are arranged about the conveyor system as to produce a bidirectional scanning pattern along the principal axes of a three-dimensional laser scanning volume. 
     A further object of the present invention is to provide a system, in which each holographic laser scanner employed in the system projects a three-dimensional laser scanning volume having multiple focal planes and a highly confined geometry extending about a projection axis extending from the scanning window of the holographic scanner and above the conveyor belt of the system. 
     Another object of the present invention is to provide an automated package identification and measuring system, wherein singulated packages can be detected, dimensioned, weighed, and identified in a fully automated manner without human intervention, while being transported through a laser scanning tunnel subsystem using a package conveyor subsystem. 
     Another object of the present invention is to provide such a system, wherein a package detection and dimensioning subsystem is provided on the input side of its scanning tunnel subsystem, for detecting and dimensioning singulated packages passing through the package detection and dimensioning subsystem. 
     Another object of the present invention is to provide such a system, wherein a data element queuing, handling and processing subsystem is provided for queuing, handling and processing data elements representative of package identification, dimensions and/or weight, and wherein a moving package tracking queue is maintained so that data elements comprising objects, representative of detected packages entering the scanning tunnel, can be tracked along with dimensional and measurement data collected on such detected packages. 
     Another object of the present invention is to provide such a system, wherein a package detection subsystem is provided on the output side of its scanning tunnel subsystem. 
     Another object of the present invention is to provide such a system, wherein the tunnel scanning subsystem provided therein comprises a plurality of laser scanning subsystems, and each such laser scanning subsystem is capable of automatically generating, for each bar code symbol read by the subsystem, accurate information indicative of the precise point of origin of the laser scanning beam and its optical path to the read bar code symbol, as well as produced symbol character data representative of the read bar code symbol. 
     Another object of the present invention is to provide such a system, wherein the plurality of laser scanning subsystems generated an omnidirectional laser scanning pattern within a 3-D scanning volume, wherein a bar code symbol applied to any one side of a six-sided package (e.g. box) will be automatically scanned and decoded when passed through the 3-D scanning volume using the conveyor subsystem. 
     Another object of the present invention is to provide such a system, wherein the laser scanning subsystems comprise holographic laser scanning subsystems, and also polygonal-type laser scanning subsystems for reading bar code symbols facing the conveyor surface. 
     Another object of the present invention is to provide such a system, wherein each holographic laser scanning subsystem employed in the tunnel scanning subsystem comprises a device for generating information specifying which holographic scanning facet or holographic facet sector (or segment) produced the laser scan data used to read any bar code symbol by the subsystem. 
     Another object of the present invention is to provide such a system, wherein each non-holographic (e.g. polygonal-type) laser scanning subsystem employed in the tunnel scanning subsystem comprises a device for generating information specifying which mirror facet or mirror sector produced the laser scan data used to read any bar code symbol by the subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a scan beam geometry modeling subsystem for producing, relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem, coordinate information comprising a geometric model of each laser scanning beam used to read a particular bar code symbol for which symbol character data has been produced by the laser scanning subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a first homogeneous transformation module for converting the coordinate information comprising the geometric model of each laser scanning beam used to read a particular bar code symbol on a detected package, from the local coordinate reference system symbolically embedded within the laser scanning subsystem, to a global coordinate reference system symbolically embedded within the tunnel-type scanning system. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a package surface modeling subsystem for producing, relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem, coordinate information comprising a geometric model of each surface on each package detected by the package detection and dimensioning subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a second homogeneous transformation module for converting the coordinate information comprising the geometric model of each surface on a detected package, from the local coordinate reference system symbolically embedded within the laser scanning subsystem, to a global coordinate reference system symbolically embedded within the tunnel-type scanning system. 
     Another object of the present invention is to provide such a system, wherein a laser scan beam and package surface intersection determination subsystem is provided for determining which detected package was scanned by the laser scanning beam that read a particular bar code symbol, and for linking (i.e. correlating) package measurement data associated with the detected package with package identification data associated with the laser scanning beam that read a bar code symbol on a detected package. 
     Another object of the present invention is to provide such a system with a package velocity measurement subsystem for measuring the velocity of the package as it moves from the package detection and dimensioning subsystem through the laser scanning tunnel subsystem of the system. 
     Another object of the present invention is to provide such a system, wherein the package velocity measurement subsystem is realized using a pair of spaced-apart laser beams projected over the conveyor so that when a package interrupts these laser beams, electrical pulses are automatically generated and processed using a clock in order to compute the instantaneous velocity of each and every package transported along the conveyor belt subsystem. 
     Another object of the present invention is to provide such a system, wherein the package detection and dimensioning subsystem provided on the input side of the laser scanning tunnel subsystem comprises a first pair of light transmitting and receiving structures arranged to transmit a plurality of light beams along a direction parallel to the conveyor belt in order to collect data and measure the height of each singulated package passing through the package detection and dimensioning subsystem, and a second pair of light transmitting and receiving structures arranged to transmit a plurality of light beams along a direction perpendicular to the conveyor belt in order to collect data and measure the width of each singulated package passing through the package detection and dimensioning subsystem. 
     Another object of the present invention is to provide such a system, wherein the package detection and dimensioning subsystem provided on the input side of the laser scanning tunnel subsystem further comprises a height data processor for processing arrays of height profile data collected from the first pair of light transmitting and receiving structures in order to detect stacked arrangements of packages transported through the package detection and dimensioning subsystem, and width data processor for processing arrays of width profile data collected from the second pair of light transmitting and receiving structures in order to detect side-by-side arrangements of packages transported through the package detection and dimensioning subsystem, an d upon detecting either a stacked configuration of packages or a side-by-side configuration of packages, automatically generating an unique data element indicative of such multiple package arrangements along the conveyor belt, and placing this unique data element in the moving package tracking queue in the data element queuing, handling and processing subsystem so that this subsystem can cause an auxiliary subsystem to reroute such multiple packages through a singulation unit and then return to pass once again through the system of the present invention. 
     Another object of the present invention is to provide such a system, wherein a package weighing-in-motion subsystem is provided for weighing singulated packages moving through the package detection and dimensioning subsystem, and producing weight measurement information for assignment to each detected package. 
     Another object of the present invention is to provide an automated package identification and measuring system, wherein singulated packages can be detected, dimensioned, weighed, and identified in a fully automated manner without human intervention, while being transported through a laser scanning tunnel subsystem using a package conveyor subsystem. 
     Another object of the present invention is to provide such a system, wherein a package detection and dimensioning subsystem is provided on the input side of its scanning tunnel subsystem, for detecting and dimensioning singulated packages passing through the package detection and dimensioning subsystem. 
     Another object of the present invention is to provide such a system, wherein a data element queuing, handling and processing subsystem is provided for queuing, handling and processing data elements representative of package identification, dimensions and/or weight, and wherein a moving package tracking queue is maintained so that data elements comprising objects, representative of detected packages entering the scanning tunnel, can be tracked along with dimensional and measurement data collected on such detected packages. 
     Another object of the present invention is to provide such a system, wherein a package detection subsystem is provided on the output side of its scanning tunnel subsystem. 
     Another object of the present invention is to provide such a system, wherein the tunnel scanning subsystem provided therein comprises a plurality of laser scanning subsystems, and each such laser scanning subsystem is capable of automatically generating, for each bar code symbol read by the subsystem, accurate information indicative of the precise point of origin of the laser scanning beam and its optical path to the read bar code symbol, as well as produced symbol character data representative of the read bar code symbol. Another object of the present invention is to provide such a system, wherein the plurality of laser scanning subsystems generated an omnidirectional laser scanning pattern within a 3-D scanning volume, wherein a bar code symbol applied to any one side of a six-sided package (e.g. box) will be automatically scanned and decoded when passed through the 3-D scanning volume using the conveyor subsystem. 
     Another object of the present invention is to provide such a system, wherein the laser scanning subsystems comprise holographic laser scanning subsystems, and also polygonal-type laser scanning subsystems for reading bar code symbols facing the conveyor surface. 
     Another object of the present invention is to provide such a system, wherein each holographic laser scanning subsystem employed in the tunnel scanning subsystem comprises a device for generating information specifying which holographic scanning facet or holographic facet sector (or segment) produced the laser scan data used to read any bar code symbol by the subsystem. 
     Another object of the present invention is to provide such a system, wherein each non-holographic (e.g. polygonal-type) laser scanning subsystem employed in the tunnel scanning subsystem comprises a device for generating information specifying which mirror facet or mirror sector produced the laser scan data used to read any bar code symbol by the subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a scan beam geometry modeling subsystem for producing, relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem, coordinate information comprising a geometric model of each laser scanning beam used to read a particular bar code symbol for which symbol character data has been produced by the laser scanning subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a first homogeneous transformation module for converting the coordinate information comprising the geometric model of each laser scanning beam used to read a particular bar code symbol on a detected package, from the local coordinate reference system symbolically embedded within the laser scanning subsystem, to a global coordinate reference system symbolically embedded within the tunnel-type scanning system. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a package surface modeling subsystem for producing, relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem, coordinate information comprising a geometric model of each surface on each package detected by the package detection and dimensioning subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a second homogeneous transformation module for converting the coordinate information comprising the geometric model of each surface on a detected package, from the local coordinate reference system symbolically embedded within the laser scanning subsystem, to a global coordinate reference system symbolically embedded within the tunnel-type scanning system. 
     Another object of the present invention is to provide such a system, wherein a laser scan beam and package surface intersection determination subsystem is provided for determining which detected package was scanned by the laser scanning beam that read a particular bar code symbol, and for linking (i.e. correlating) package measurement data associated with the detected package with package identification data associated with the laser scanning beam that read a bar code symbol on a detected package. 
     Another object of the present invention is to provide such a system with a package velocity measurement subsystem for measuring the velocity of the package as it moves from the package detection and dimensioning subsystem through the laser scanning tunnel subsystem of the system. 
     Another object of the present invention is to provide such a system, wherein the package velocity measurement subsystem is realized using an roller wheel engaged in direct contact with the conveyor belt as it moves, generating electrical pulses as an optical encoder attached to the shaft of the roller wheel is caused to complete one revolution, during which the conveyor belt traveled one linear foot, and counting these generated electrical pulses with reference to a clock in order to compute the instantaneous velocity of the conveyor belt, and thus each and every package transported therealong without slippage. 
     Another object of the present invention is to provide such a system, wherein the package detection and dimensioning subsystem provided on the input side of the laser scanning tunnel subsystem comprises a laser scanning mechanism that generates an amplitude modulated laser scanning beam that is scanned across the width of the conveyor structure in the package conveyor subsystem while the scanning beam is disposed substantially perpendicular to the surface of the conveyor structure, and light reflected from scanned packages is collected, detected and processed to produce information representative of the package height profile across the width of the conveyor structure for each timing sampling instant carried out by the package detection and dimension subsystem. 
     Another object of the present invention is to provide such a system, wherein the package detection and dimensioning subsystem provided on the input side of the laser scanning tunnel subsystem further comprises a height data processor for processing arrays of height profile data collected from the first pair of light transmitting and receiving structures in order to detect stacked arrangements of packages transported through the package detection and dimensioning subsystem, and width data processor for processing arrays of width profile data collected from the second pair of light transmitting and receiving structures in order to detect side-by-side arrangements of packages transported through the package detection and dimensioning subsystem, and upon detecting either a stacked configuration of packages or a side-by-side configuration of packages, automatically generating a unique data element indicative of such multiple package arrangements along the conveyor belt, and placing this unique data element in the moving package tracking queue in the data element queuing, handling and processing subsystem so that this subsystem can cause an auxiliary subsystem to reroute such multiple packages through a singulation unit and then returned to pass once again through the system of the present invention. 
     Another object of the present invention is to provide such a system, wherein a package weighing-in-motion subsystem is provided for weighing singulated packages moving through the package detection and dimensioning subsystem, and producing weight measurement information for assignment to each detected package. 
     Another object of the present invention is to provide an automated package identification and measuring system, wherein multiple packages, arranged in a side-by-side, stacked and/or singulated configuration, can be simultaneously detected, dimensioned, weighed, and identified in a fully automated manner without human intervention, while being transported through a laser scanning tunnel subsystem using a package conveyor subsystem. 
     Another object of the present invention is to provide such a system, wherein a package detection and dimensioning subsystem is provided on the input side of its scanning tunnel subsystem, for simultaneously detecting and dimensioning multiple packages passing through the package detection and dimensioning subsystem, and wherein the package detection and dimensioning subsystem employs multiple moving package tracking queues simultaneously maintained therein for spatially different regions above the conveyor belt so order that data objects, representative of packages detected in such spatially different regions, can be produced and tracked along with dimensional and measurement data collected on such detected packages. 
     Another object of the present invention is to provide such a system, wherein a data element queuing, handling and processing subsystem is provided for queuing, handling and processing data elements representative of package identification, dimensions and/or weight, and wherein multiple moving package tracking queues are simultaneously maintained for spatially different regions above the conveyor belt so that data elements comprising objects, representative of detected packages entering the scanning tunnel, can be tracked along with dimensional and measurement data collected on such detected packages. 
     Another object of the present invention is to provide such a system, wherein a multiple package detection and dimensioning subsystem is provided on the output side of its scanning tunnel subsystem, and multiple moving package tracking queues are simultaneously maintained therein for spatially different regions above the conveyor belt in order that data elements comprising objects, representative of detected packages exiting the scanning tunnel, can be tracked along with dimensional and measurement data collected on such detected packages. 
     Another object of the present invention is to provide such a system, wherein the tunnel scanning subsystem provided therein comprises a plurality of laser scanning subsystems, and each such laser scanning subsystem is capable of automatically generating, for each bar code symbol read by the subsystem, accurate information indicative of the precise point of origin of the laser scanning beam and its optical path to the read the bar code symbol, as well as symbol character data representative of the read bar code symbol. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a scan beam geometry modeling subsystem for producing, relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem, coordinate information comprising a geometric model of each laser scanning beam used to read a particular bar code symbol for which symbol character data has been produced by the laser scanning subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a first homogeneous transformation module for converting the coordinate information comprising the geometric model of each laser scanning beam used to read a particular bar code symbol on a detected package, from the local coordinate reference system symbolically embedded within the laser scanning subsystem, to a global coordinate reference system symbolically embedded within the tunnel-type scanning system. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a package surface modeling subsystem for producing, relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem, coordinate information comprising a geometric model of each surface on each package detected by the package detection and dimensioning subsystem. 
     Another object of the present invention is to provide such a system, wherein the data element queuing, handling and processing subsystem provided therein further comprises a second homogeneous transformation module for converting the coordinate information comprising the geometric model of each surface on a detected package, from the local coordinate reference system symbolically embedded within the laser scanning subsystem, to a global coordinate reference system symbolically embedded within the tunnel-type scanning system. 
     Another object of the present invention is to provide such a system, wherein a laser scan beam and package surface intersection determination subsystem is provided for determining which detected package was scanned by the laser scanning beam that read a particular bar code symbol, and for linking (i.e. correlating) package measurement data associated with the detected package with package identification data associated with the laser scanning beam that read a bar code symbol on a detected package. 
     Another object of the present invention is to provide such a system with a package velocity measurement subsystem for measuring the velocity of the package as it moves from the package detection and dimensioning subsystem through the laser scanning tunnel subsystem of the system. 
     Another object of the present invention is to provide such a system, wherein the package velocity measurement subsystem is realized using an roller wheel engaged in direct contact with the conveyor belt as it moves, generating electrical pulses as an optical encoder attached to the shaft of the roller wheel is caused to complete one revolution, during which the conveyor belt traveled one linear foot, and counting these generated electrical pulses with reference to a clock in order to compute the instantaneous velocity of the conveyor belt, and this each and every package transported therealong without slippage. 
     Another object of the present invention is to provide such a system, wherein the package detection and dimensioning subsystem provided on the input side of the laser scanning tunnel subsystem comprises a laser scanning mechanism that generates an amplitude modulated laser scanning beam that is scanned across the width of the conveyor structure in the package conveyor subsystem while the scanning beam is disposed substantially perpendicular to the surface of the conveyor structure, and light reflected from scanned packages is collected, detected and processed to produce information representative of the package height profile across the width of the conveyor structure for each timing sampling instant carried out by the package detection and dimension subsystem. 
     Another object of the present invention is to provide such a system, wherein the package detection and dimensioning subsystem provided on the input side of the laser scanning tunnel subsystem comprises a stereoscopic camera subsystem which captures stereoscopic image pairs of packages being transported through the package detection and dimensioning subsystem, and also a real-time stereoscopic image processor which is programmed to detect multiple images present in the field of view of stereoscopic imaging subsystem, and compute the vertices and dimensions of each such detected package. 
     Another object of the present invention is to provide such a system, wherein a package weighing-in-motion subsystem is provided for weighing simultaneously weighing each package, or arrangement of side-by-side and/or stacked packages moving through the package detection and dimensioning subsystem, and producing weight measurement information. for assignment to each detected package, or apportioned to each arrangement of side-by-side and/or stacked packages, based on relative volumetric measurements. 
     Another object of the present invention is to provide an improved tunnel-type scanning system, wherein bar code symbols downwardly facing the conveyor belt can be automatically scanned as they are transported through the system in a high-speed manner. 
     Another object of the present invention is to provide a novel corner-mounted laser scanning system which uses at least two (2) pairs of opposed VLD/scanning stations in order to produce an orthogonal set of raster-type scan patterns projected over a conveyor belt structure. 
     Another object of the present invention is to provide such a corner-mounted laser scanning system, wherein its laser scanning pattern has at least three depth-of-field (DOF) regions, identifiable as DOF 1 , DOF 2  and DOF 3 , which are neither overlapping nor contiguous. 
     Another object of the present invention is to provide such a corner-mounted laser scanning system, which can read bar codes on the front of items on a conveyor belt when the bar codes are generally in a picket fence orientation (i.e. bar elements are arranged vertically relative to the conveyor belt surface) or ladder orientation (i.e. the bar elements are arranged horizontally relative to the conveyor belt surface), or nearly so. 
     Another object of the present invention is to provide a bar code symbol scanning system which is designed to be installed on side of the conveyor belt, so that the focused spot size normal to the beam is considerably smaller than the minimum resolution element of the bar code to be scanned. 
     Another object of the present invention is to provide a complete omni-directional scanning system, wherein the scanning pattern comprises a n orthogonal set of laser scanning, including vertical or horizontal oriented rastered sets of laser scanning planes for reading bar code symbols having either a picket fence orientation or a ladder orientation, respectively. 
     Another object of the present invention is to provide a novel laser scanning system, comprising a set of scanners that are placed at an angle close to 45 degrees relative to the direction of item travel so as to assure that that at least one scanner can read bar codes on item surfaces that are facing in the direction of item travel and also toward the side of the conveyor belt, while minimizing the shadow effect yet ensuring good reading on the front surfaces. 
     Another object of the present invention is to provide such a laser scanning system, which further comprises side scanners that can read bar codes placed on the sides of items, rather than of on the front sides thereof. 
     Another object of the present invention is to provide such a laser scanning system, wherein the laser scan lines are optimally separated and tilted to assure that at least one scanner can read bar codes that are not in perfect picket fence or ladder orientations, yet provide some small degree of omni-directional scanning. 
     Another object of the present invention is to provide such a laser scanning system, wherein the relatively small focused spot of the laser scanning beam, required by the tilt of the scanner, reduces the depth of field for each focal group of the multiple-focal-plane scanning system. 
     Another object of the present invention is to provide such a laser scanning system, wherein the depth of field regions of the individual focal groups (DOF 1 , DOF 2 , DOF 3 ) do not need to be contiguous due to the fact that the scanner is mounted at an angle off to the side of the conveyor belt. 
     Another object of the present invention is to provide such a laser scanning system, wherein the laser scanning lines in each focal groups are carefully separated to guarantee reading across the desired scan width while using only three focal zones, whereas in contrast, when using contiguous, or overlapping, focal zones would require as many as seven focal zones. 
     Another object of the present invention is to provide such a laser scanning system, wherein the laser scanning pattern produced thereby has a reduced number of focal zones to produce a scan pattern that is denser and which results in more effective scanning of bar code symbols on the front and back surfaces of objects. 
     Another object of the present invention is to provide such a laser scanning system, wherein each corner-located scanner is a holographic scanning subsystem having a laser scanning disc having twenty-one scanning facets which produce seven scan lines in each focal group. 
     Another object of the present invention is to provide a novel method of analyzing the laser scanning pattern produced by a pair of corner-based laser scanners. 
     Another object of the present invention is to provide such a method of laser scan pattern analysis, wherein a complete picture of the effectiveness of a proposed scan pattern (called a time-lapsed composite “scan coverage plot”) is composed by taking multiple exposures of the item surface as it progresses through the scan volume. 
     Another object of the present invention is to provide such a method, wherein the x-axis of the scan coverage plot is the dimension parallel to the belt width, and the y-axis thereof is the height dimension for a box being scanned through the scan volume. 
     Another object of the present invention is to provide a novel laser scanning system which uses different optics in the laser beam production modules associated with the four laser scanning stations that generate the two sets of horizontally oriented scanning planes, and the two laser scanning stations that generate the two sets of vertically oriented scanning planes. 
     Another object of the present invention is to provide such a laser scanning system, wherein the nominal (normal to the scanning beam) resolution of the horizontal scan lines is greater than that of the vertical lines to compensate for the elongation of the horizontal scan lines in the direction of scan at the label. 
     Another object of the present invention is to provide such a laser scanning system, wherein the vertical scan lines are also elongated, but not in the scan direction. 
     Another object of the present invention is to provide such a laser scanning system, wherein the beam diameter at the disk is greater for the horizontal VLD stations than for the vertical VLD stations. 
     Another object of the present invention is to provide such a laser scanning system, wherein different optics are used for the two sets of stations in order to optimize the performance of the two sets of scan lines. 
     Another object of the present invention is to provide a novel corner-mounted laser scanning system, for use in reading bar code symbols on tubs and trays moving along a conveyor belt, as well as a “train” in which cars have bar codes placed on the front or back surfaces thereof. 
     Another object of the present invention is to provide a novel “corner” scanner that produces a laser scanning pattern that is predisposed to reading codes in orthogonal orientations, in contrast with conventional Omni, Raster, or Linear scanning patterns. 
     Another object of the present invention is to provide such a laser scanning t pattern, wherein the scanlines in the laser scanning pattern generated therefrom are not necessarily orthogonal to the scan codes. 
     Another object of the present invention is to provide such a laser scanning system, wherein a definite degree of angular tolerance is provided, so that bar codes scanned at plus or minus 20 degrees of code orientation pose no problem during decoding with or without stitching). 
     Another object of the present invention is to provide such a laser scanning system, wherein optimal scanning occurs for bar code symbols oriented at about +/−10 degrees off the ladder or picket fence orientation of the system. 
     Another object of the present invention is to provide a corner-mounted laser scanning system that is designed to read mainly ladder and picket fence orientation labels on the front (or back) of tubs and trays on a moving conveyor belt. 
     Another object of the present invention is to provide such a corner-mounted laser scanning system which projects over a conveyor belt, a laser scanning pattern that is optimized for reading bar code symbols on surfaces that are oriented at about 45 degrees to the nominal direction of propagation of the laser scanning beams, unlike prior art scanners that have been optimized for reading bar code symbols on surfaces that are oriented at about 90 degrees to the nominal direction of propagation of the laser scanning beams. 
     Another object of the present invention is to provide a LADAR-based package imaging and dimensioning subsystem for imaging and/or profiling packages transported thereby a substantially constant velocity. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein a synchronized amplitude-modulated laser beam is automatically produced and scanned across the width of a conveyor belt structure and, during each scan thereacross, detects and processes the reflected laser beam in order to capture a row of raw range (and optionally reflection-intensity) information that is referenced with respect to a polar-type coordinate system symbolically-embedded within the LASAR-based imaging and dimensioning subsystem. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein captured rows of range data are continuously loaded into a preprocessing data buffer, one row at a time, and processed in real-time using window-type convolution kernels that smooth and edge-detect the raw range data and thus improve its quality for subsequent dimension data extraction operations. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein detected background information (including noise) is automatically subtracted from consecutively captured rows of smoothed/edge-detected range data to provide a range data map of the space above the conveyor belt, for use in carrying out package dimension data extraction operations involving the same. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein two-dimensional image contour tracing techniques are used to detect image contours within the buffered range data map, indicative of packages being transported thereby. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem automatically processes the indices (m,n) of the computed contours in order to detect possible vertices associated with polygonal-shaped objects extracted from the range data map, which are representative of packages or like objects being transported by the subsystem. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein the m and n indices of the vertices associated with the computed contours are automatically processed in order to detect candidates for corner points associated with the corners of packages transported by the subsystem. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein the m and n indices of detected corner point candidates are automatically processed in order to reduce those corner point candidates down to those most likely to be the corners of a regular-shaped polygonal object (e.g. six sided box). 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein the m and n indices of the corner points extracted from the range data map are automatically processed in order to compute the surface area of the package represented by the contours traced therein. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein the m and n indices of the corner points extracted from the range data map are automatically processed in order to compute the x, y and z coordinates corresponding to the corners of the package represented by the contours traced therein, referenced relative to a Cartesian-type global coordinate reference system symbolically embedded within the automated package identification and measuring subsystem. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein the m and n indices of the corner points extracted from the range data map are automatically processed in order to compute the average height of the package represented by the contours traced therein, referenced relative to the Cartesian-type global coordinate reference system. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein a polygonal-type laser scanning mechanism is used to scan an amplitude-modulated laser beam across the width of the conveyor belt. 
     Another object of the present invention is to provide such a LADAR-based imaging and dimensioning subsystem, wherein a holographic-type laser scanning mechanism is used to scan an amplitude-modulated laser beam across the width of the conveyor belt. 
     These and other objects of the present invention will become apparent hereinafter and in the Claims to Invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, the following Detailed Description of the Illustrative Embodiment should be read in conjunction with the accompanying Drawings, wherein: 
     FIG. 1 is a perspective view of an automated tunnel-type laser scanning package identification and measurement (e.g. dimensioning and weighing) system constructed in accordance with the first illustrated embodiment of the present invention; 
     FIG. 1A is an end elevated view of the system shown in FIG. 1; 
     FIG. 1B is a first perspective view of the tunnel-type package identification and measurement system of the first illustrative embodiment of the present invention; 
     FIG. 1C is an elevated side view of the tunnel-type package identification and measurement system of the first illustrative embodiment, removed from the scanner support framework, in order to clearly show the O-ring conveyor platform for staggering packages prior to entering the 3-D scanning volume, the light curtain associated with the packaging dimensioning subsystem for determining the total volume of the package, and whether there are multiple packages entering the 3-D scanning volume, a scanner management computer system (i.e. Station) with a graphical user interface (GUI) for easily configuring the scanning subsystems within the system and monitoring the flow of packages into the scanning tunnel, and an exit sensor for detecting the exit of each scanned package within the scanning tunnel; 
     FIG. 1D is a perspective view of the tunnel-type laser scanning system of the first illustrative embodiment of the present invention, shown in greater detail, detached from a portion of its roller-based conveyor subsystem and scanner management subsystem; 
     FIG. 1E is a perspective view of the split-section conveyor subsystem and its bottom-mounted laser scanning projection subsystem, and user-interface/workstation, shown detached from the scanner support framework shown in FIGS. 1,  1 A and  1 B; 
     FIG. 2A is a perspective view of the split-conveyor subsystem removed from scanner support framework of the system of the first illustrative embodiment, showing a coordinate reference framework symbolically embedded within the conveyor subsystem and shown with graphical indications describing the directions of yaw, pitch and roll of each triple-scanning disc holographic scanner supported from the scanner support framework of the tunnel scanning system shown in FIGS. 1 and 1A; 
     FIG. 2B is a perspective view of the split-conveyor subsystem removed from scanner support framework of the package identification and measurement system of the first illustrative embodiment, showing a coordinate reference framework symbolically embedded within the conveyor system and schematically depicted with graphical indications describing the directions of yaw, pitch and roll of each single-scanning disc holographic scanner supported from the scanner support framework of the tunnel scanning subsystem shown in FIGS. 1 and 1A; 
     FIG. 2C is a table setting forth data specifying the position and orientation of the sixteen omni-directional holographic laser scanners mounted within the tunnel scanning subsystem of the first illustrative embodiment of the present invention, wherein the position of each single-disc holographic scanner is specified with respect to the center of the holographic scanning disc contained within each such scanning unit, and the position of each triple-disc holographic scanner is specified with respect to the center of the middle holographic scanning disc contained within each such scanning unit; 
     FIG. 3 is a schematic block diagram illustrating that the holographic and fixed-projection laser scanning subsystems, the package dimensioning/measurement subsystem, package velocity and length measurement subsystem, the package-in-tunnel indication subsystem, the package-out-of-tunnel subsystem, the package weighing-in-motion subsystem, the data-element queuing, handling and processing subsystem, the input/output port multiplexing subsystem, and the conveyor belt subsystem integrated together within the automated tunnel-type package identification an d measurement system of the first illustrative embodiment of the present invention; 
     FIG.  4 A 1  is a plan view of the triple-disc holographic scanning subsystem (e.g. indicated as Front, Back, Top/Front, Top/Back, Left Side/Front, Left Side/Back, Right Side/Front and Right Side/Back in FIG.  1 B and the Scanner Positioning Table shown in FIG.  2 C), mounted on the top and sides of the tunnel-type scanning system of the first illustrative embodiment, showing three holographic scanning discs mounted on an optical bench with about a 15.0 inches spacing between the axis of rotation of each neighboring holographic scanning disc, and each holographic scanning disc mounted therein being surrounded by five beam folding mirrors, five parabolic light collection mirrors, five laser beam production modules, five photodetectors, and five analog and digital signal processing boards mounted on the optical bench of the subsystem; 
     FIG.  4 A 2  is a perspective view of one of the laser scanning stations mounted about each holographic laser scanning disc in the holographic laser scanning subsystem shown in FIG.  4 A 1 , 
     FIG.  4 A 3  is a cross-sectional view of the triple-disc holographic laser scanning subsystem shown in FIG.  4 A 2 , taken along line  4 A 3 — 4 A 3  thereof, showing its holographic scanning disc rotatably supported by its scanning motor mounted on the optical bench of the subsystem; 
     FIG.  4 A 4  is a schematic representation of the layout of the volume-transmission type holographic optical element (HOEs) mounted between the glass support plates of each holographic scanning disc employed within the triple-disc holographic scanning subsystem shown in FIG.  4 A 1 ; 
     FIG.  4 A 5  is a table setting forth the design parameters used to construct each holographic disc within the single-disc holographic scanning subsystem employed in the tunnel scanning system of the first illustrative embodiment; 
     FIGS.  4 A 6 A through  4 A 6 C, taken together, show the subcomponents configured together on the analog signal processing boards, decode signal processing boards and within the housing of the single-disc holographic laser scanning subsystems of the first illustrative embodiment of the present invention; 
     FIG.  4 A 7 A is an elevated view of the home-pulse mark sensing module of the present invention deployed about each holographic scanning disc in the system of the first illustrative embodiment of the present invention; 
     FIG.  4 A 7 B is a plan view of the home pulse mark sensing module shown i n FIG.  3 A 8 A; 
     FIGS.  4 A 7 C 1  and  4 A 7 C 2 , taken together, set forth a schematic diagram of an analog signal processing circuit which can be used to implement the home-pulse detector employed in the holographic laser scanning subsystems of the first illustrative embodiment of the present invention; 
     FIG.  4 A 8 A is a schematic representation of the 3-D laser scanning volume produced from the triple-disc holographic laser scanning subsystem of FIG.  4 A 1  (indicated as “Penta 3”), indicating the physical dimensions of the 3-D scanning volume, as well as the minimum bar code element width resolutions that the subsystem can achieve over three identified subregions within the scanning volume; 
     FIG.  4 A 8 B is a schematic representation of the 3-D laser scanning volume produced from a double-disc embodiment of the holographic laser scanning subsystem of FIG.  4 A 1  (indicated as “Penta 2”), indicating the physical dimensions of the 3-D scanning volume, as well as the minimum bar code element width resolutions that the subsystem can achieve over three identified subregions within the scanning volume; 
     FIG.  4 A 8 C is a schematic representation of the 3-D laser scanning volume produced from a single-disc embodiment of the holographic laser scanning subsystem of FIG.  4 A 1  (indicated as “Penta 1”), indicating the physical dimensions of the 3-D scanning volume, as well as the minimum bar code element width resolutions that the subsystem can achieve over three identified subregions within the scanning volume; 
     FIG.  4 A 8 D is a scanner specification table setting forth operational specifications for the holographic laser scanning subsystems shown in FIGS.  4 A 8 A,  4 A 8 B and  4 A 8 C, for the Penta 3, Penta 2 and Penta 1 scanners, respectively; 
     FIG.  4 A 9  is a schematic representation of all the laser scan lines produced by a single scanning platform within the laser scanning subsystem of FIG.  4 A 1 , projected into the respective focal planes of such laser scan lines; 
     FIG.  4 A 10  is a schematic representation of all the laser scan lines produced by all three of the laser scanning platforms within the laser scanning subsystem of FIG.  4 B 1 , projected into the respective focal planes of such laser scan lines; 
     FIG.  4 B 1 A is an enlarged plan view of one of the laser scanning subsystems (i.e. platforms) in the subsystem shown in FIG.  4 B 1 , showing the angular position of each laser scanning station (LS 1  through LS 6 ) relative to the home pulse gap detector; 
     FIG.  4 B 1  is a plan view of the triple-disc holographic laser scanning subsystem (e.g. indicated as L/F Corner # 1 , L/F Corner # 2 , L/B Corner # 1 , L/B Corner # 2 , R/F Corner # 1 , R/F Corner # 2 , R/B Corner # 1  and R/B Corner # 2  in FIG.  1 B and the Scanner Positioning Table shown in FIG.  2 C), mounted within the corners of the tunnel-type scanning system of the first illustrative embodiment, showing each holographic scanning disc mounted therein being spaced apart from adjacent discs by about 13.0 inches and surrounded by six beam folding mirrors, six parabolic light collection mirrors, six laser beam production modules, six photodetectors, and six analog and digital signal processing boards mounted on the optical bench of the subsystem; 
     FIG.  4 B 2  is a schematic representation of the layout of the volume-transmission type holographic optical element (HOEs) mounted between the glass support plates of each holographic scanning disc employed within the triple-disc holographic scanning subsystem of FIG.  4 B 1 ; 
     FIGS.  4 B 3 A and  4 B 3 B shown a table setting forth the design parameters used to construct each holographic disc within the triple-disc holographic scanning subsystem of FIG.  4 B 1 ; 
     FIGS.  4 B 4 A through  4 B 4 C, taken together, show the subcomponents configured together on the analog signal processing boards, decode signal processing boards and within the housing of the triple-disc holographic laser scanning subsystems of FIG.  4 B 1 ; 
     FIG.  4 B 5 A is a schematic representation of the 3-D laser scanning volume produced from the triple-disc holographic laser scanning subsystem of FIG.  4 B 1  (indicated as “Ortho 3”), indicating the physical dimensions of its 3-D scanning volume and the clearance between the scanner housing and the 3-D scanning volume; 
     FIG.  4 B 5 B is a schematic representation of the 3-D laser scanning volume produced from a double-disc embodiment of the holographic laser scanning subsystem of FIG.  4 B 1  (indicated as “Ortho 2”), indicating the physical dimensions of its 3-D scanning volume and the clearance between the scanner and the 3-D scanning volume; 
     FIG.  4 B 5 C is a schematic representation of the 3-D laser scanning volume produced from a single-disc embodiment of the holographic laser scanning subsystem of FIG.  4 A 1  (indicated as “Ortho 1”), indicating the physical dimensions of the 3-D scanning volume and the clearance between the scanner housing and the 3-D scanning volume; 
     FIG.  4 B 5 D is a scanner specification table setting forth operational specifications for the holographic laser scanning subsystems shown in FIGS.  4 B 5 A,  4 B 5 B and  4 B 5 C, for the Ortho 3, Ortho 2 and Ortho 1 scanners, respectively; 
     FIG.  4 B 6  is a plan view schematic representation of the 3-D laser scanning volume generated from the triple-disc holographic laser scanning subsystem of FIG.  4 B 1 , showing the scanning volume projected over a conveyor belt structure transporting a package moving through the scanning tunnel of the system of FIG. 1; 
     FIG.  4 B 7  is a plan view schematic representation of the 3-D laser scanning volume generated from the triple-disc holographic laser scanning subsystem of FIG.  4 B 1 , showing the orthogonal (i.e. horizontal and vertical) and horizontal scanning regions within each spatially-separated focal zone FZ 1 , FZ 2  and FZ 3  of the subsystem; 
     FIG.  4 B 8  is a schematic representation of all the laser scan lines produced by a single scanning platform within the laser scanning subsystem of FIG.  4 B 1 , projected into the respective focal planes of such laser scan lines; 
     FIG.  4 B 9  is a schematic representation of all the laser scan lines produced by all three of the laser scanning platforms within the laser scanning subsystem of FIG.  4 B 1 , projected into the respective focal planes of such laser scan lines; 
     FIG.  4 B 10  is a graphical representation plotting (i) the spot-size of a laser beam produced from a laser scanning station within the subsystem of FIG.  4 B 1  which generates laser scanning lines oriented to read “picket-fence” oriented bar code symbols on packages transported along the conveyor belt, versus (ii) the distance of the scanned bar code symbol from the holographic scanning disc; 
     FIG.  4 B 11  is a graphical representation plotting (i) the spot-size of a laser beam produced from a laser scanning station within the subsystem of FIG.  4 B 1  which generates laser scanning lines oriented to read “ladder” oriented bar code symbols transported along the conveyor belt, versus (ii) the distance of the scanned bar code symbol from the holographic scanning disc; 
     FIG.  4 B 12  is a graphical representation of the composite time-lapsed “scan coverage pattern” provided by each corner-mounted laser scanning subsystem in the first illustrative embodiment shown in FIG. 1; 
     FIG.  4 B 13  is a plan view schematic representation showing the scanning areas covered by four corner-mounted triple-disc laser scanning subsystems of FIG.  4 B 1 , as well as the orthogonal and omni-directional scanning regions projected over a moving conveyor belt structure; 
     FIG.  4 B 14  is a plan view schematic representation showing the scanning areas covered by eight corner-mounted triple-disc laser scanning subsystems employed in the tunnel scanning system of FIGS. 1 through 1C, as well as the orthogonal and omni-directional scanning regions projected over a moving conveyor belt structure thereof; 
     FIG.  4 C 1  is an exploded diagram of the fixed laser projection scanner mounted beneath the conveyor belt surface of the system and between the first and second conveyor belt platforms of the conveyor subsystem employed in the tunnel scanning system of the first illustrative embodiment of the present invention, showing the optical bench upon which eight fixed projection-type laser scanning subsystems are mounted and enclosed within a scanner housing having a rugged glass scanning window bridging the gap provided between the first and second conveyor belt platforms; 
     FIG.  4 C 2  is a perspective diagram of the projection-type laser scanning subsystem mounted within the bottom-mounted fixed projection scanner shown in FIG.  4 C 1 , showing an eight-sided polygon scanning element rotatably mounted closely adjacent to a stationary mirror array comprised of four planar mirrors, and a light collecting mirror centrally mounted for focusing light onto a photodetector disposed slightly beyond the polygon scanning element; 
     FIG.  4 C 3  is a plan view of the eight fixed-projection laser scanning subsystems mounted on the optical bench of the bottom-mounted laser scanner shown in FIG.  4 C 1 ; 
     FIG.  4 C 3  is an elevated end view of the eight fixed-projection laser scanning subsystems mounted on the optical bench of the bottom-mounted laser scanner shown in FIG.  4 C 1 , so that the scanning window(s) of the fixed projection laser scanning subsystems (i.e. platforms or benches) are disposed at about a 28° angle with respect to the optically transparent extending across the width extent of the plane of the conveyor belt structure of the system; 
     FIG.  4 C 3 A is a side end view of the polygonal bottom scanning subsystem depicted in FIG.  4 C 3 ; 
     FIG.  4 C 4  is a schematic representation of the partial scanning pattern produced by the eight-sided polygon scanning element and two stationary mirrors mounted adjacent to the central plane of each fixed-projection laser scanning subsystem mounted on the optical bench of the bottom-mounted laser scanner shown in FIG.  4 C 1 ; 
     FIG.  4 C 5  is a schematic representation of the partial scanning pattern produced by the eight-sided polygon scanning element and two outer stationary mirrors mounted adjacent to the two inner-located stationary mirrors in each fixed-projection laser scanning subsystem mounted on the optical bench of the bottom-mounted laser scanner shown in FIG.  4 C 1 ; 
     FIG.  4 C 6  is a schematic representation of the complete scanning pattern produced by the eight-sided polygon scanning element and four stationary mirrors mounted about the central plane of each fixed-projection laser scanning subsystem mounted on the optical bench of the bottom-mounted laser scanner shown in FIG.  4 C 1 ; 
     FIG.  4 C 7  is a schematic representation of the resultant (collective) omni-directional scanning pattern produced through the conveyor-mounted scanning window, by the eight fixed-projection laser scanning subsystems mounted on the optical bench of the bottom-mounted laser scanner shown in FIG.  4 C 1 ; 
     FIG. 5A is a schematic diagram showing the directions of omni-directional scanning provided in the X-Y plane of the 3-D scanning volume of the tunnel scanning system of the first illustrative embodiment of the present invention, by the Front and Back holographic laser scanning subsystems, and bottom-mounted fixed projection scanning subsystem employed therein; 
     FIG. 5B is a schematic diagram showing the direction of omni-directional scanning provided in the Y-Z plane of the 3-D scanning volume of the tunnel scanning system of the first illustrative embodiment, by the bottom-mounted fixed-projection laser scanning subsystem employed therein; 
     FIG. 6 is a schematic diagram showing the direction of omni-directional scanning provided in the X-Y plane of the 3-D scanning volume of the tunnel scanning system of the first illustrative embodiment, by the Left Side Front, Left Side Back, Right Side Front and Right Side Back holographic laser scanning subsystems employed therein; 
     FIG. 7 is a schematic diagram showing the direction of omni-directional scanning provided in the Y-Z plane of the 3-D scanning volume of the tunnel scanning system of the first illustrative embodiment, by the Front and Back holographic laser scanning subsystems employed therein; 
     FIG. 8A is a schematic diagram showing the direction of omni-directional scanning provided in the Y-Z plane of the 3-D scanning volume of the tunnel scanning system of the first illustrative embodiment of the present invention, by the holographic laser scanning subsystems (indicated by R/B Corner # 1 , R/B Corner # 2 , L/F Corner # 1  and R/B Corner # 2 ) employed therein; 
     FIG. 8B is a schematic diagram showing the direction of omni-directional scanning provided in the X-Y plane of the 3-D scanning volume of the tunnel scanning system of the first illustrative embodiment of the present invention, by the holographic laser scanning subsystems (indicated by R/B Corner # 1 , R/B Corner # 2 , R/F Corner # 1  and RIB Corner # 2 ) employed therein; 
     FIG. 9A is a schematic diagram showing the direction of omni-directional scanning provided in the Y-Z plane of the 3-D scanning volume of tunnel scanning system of the first illustrative embodiment of the present invention, by the holographic laser scanning subsystems (indicated by L/B Corner # 1 , L/B Corner # 2 , L/F Corner # 1  and L/B Corner # 2 ) employed therein; 
     FIG. 9B is a schematic diagram showing the direction of omni-directional scanning provided in the X-Y plane of the 3-D scanning volume of tunnel scanning system of the first illustrative embodiment of the present invention, by the holographic laser scanning subsystems (indicated by L/B Corner # 1 , L/B Corner # 2 , L/F Corner # 1  and L/B Corner # 2 ) employed therein; 
     FIG. 10 is a schematic representation of the components on the control board and decode processing boards associated with holographic scanning disc employed within the tunnel scanning subsystem of the first illustrative embodiment of the present invention, showing the home-pulse detector and home-offset pulse (HOP) generator on the control board, and the start-of-facet-sector pulse (SOFSP) generator, digitizer circuitry, decode signal processor and ROM containing relative timing information about each SOFSP in relation to the HOP sent to the decode processing board from the control board of the present invention; 
     FIG. 10A is a schematic representation of the start-of-facet-sector pulse (SOFSP) generator employed on each decode board associated with a holographic laser scanning subsystem in the system of the first illustrative embodiment of the present invention; 
     FIG. 10B is a first table containing parameters and information that are used within the SOFP generation module of the SOFSP generator shown in FIG. 10A; 
     FIG. 10C is a schematic representation of the operation of the start-of-facet pulse (SOFP) generator employed within each SOFSP generator of the present invention, wherein start of facet pulses are generated within the SOFP generator relative to the home-offset pulse (HOP) received from the HOP generator on the control board associated with each holographic scanning disc; 
     FIG. 10D is a second table containing parameters and information that are used within the SOFSP generation module of the SOFSP generator shown in FIG. 10A; 
     FIGS.  10 E 1  and  10 E 2  set forth a table containing a set of production rules used within the SOFSP generation module of the SOFSP generator shown in FIG. 10A, to generate start-of-facet-sector pulses therewithin; 
     FIG. 10F is a schematic representation of the operation of the start-of-facet-sector pulse (SOFSP) generator of the present invention, wherein start of facet sector pulses (SOFSPs) are generated within the SOFSP generator relative to the home-offset pulse (HOP) received from the HOP generator on the control board associated with each holographic scanning disc; 
     FIGS.  11 A 1  and  11 A 2 , taken together, set forth a schematic diagram of the digitizing circuit shown in FIG. 10, using a pair of dual FIFO memory storage buffers to synchronously track digital scan data and information about the facet-sectors on the optically-encoded holographic scanning disc of FIG. 12 used to generate the laser scanning beam that was used to collect such digital scan data from a bar code symbol on a package transported through the tunnel scanning subsystem of the first illustrative embodiment of the present invention; 
     FIG. 11B is a schematic diagram showing in greater detail the digitizing circuit shown in FIG. 10; 
     FIGS.  11 C 1 ,  11 C 2  and  11 D set forth tables containing parameters and information that are used within the decode processor of the present invention shown in FIG. 11B in order to recover digital count data from time-based facetsector related information, and generate decoded symbol character data and the minimum and maximum facet sector angles that specify the facet sector on a particular holographic scanning disc used to generate the laser scanning beam/plane that collects the scan data associated with the decoded bar code symbol; 
     FIG. 11E is a high level flow chart describing the steps of the process carried out by the decode processor of the present invention shown in FIG. 11B; 
     FIG. 12A is a schematic diagram of the holographic scanning disc that contains an optically-encoded home-pulse mark as well as a series of start-offacet-sector marks about the outer edge thereof for indicating where each facet sector along the disc begins, relative to the home pulse mark; 
     FIG. 12B is a schematic representation of the components on the control board and decode processing boards associated with an optically-encoded holographic scanning disc which can be employed within the tunnel scanning subsystem of the present invention, showing the home-pulse detector and homeoffset pulse (HOP) generator on the control board, and the start-of-facet-sector pulse (SOFSP) generator, digitizer circuitry, decode signal processor and ROM containing relative timing information about each SOFSP in relation to the HOP sent to the decode processing board from the control board of the present invention; 
     FIG. 12C is a schematic representation of the start-of-facet-sector pulse (SOFSP) generator employed on each decode board shown in FIG. 12B; 
     FIG. 12D is a table containing parameters and information that are used within the SOFSPgeneration module of the SOFSP generator shown in FIG. 12C; 
     FIG. 12E is a schematic representation of the operation of the start-of-facet sector pulse (SOFSP) generator shown FIG. 12C, wherein start of facet sector pulses are generated therewithin relative to the home-offset pulse (HOP) received from the HOP generator on the control board associated with each holographic scanning disc; 
     FIGS.  13 A 1  and  13 A 2 , taken together, set forth a schematic diagram of the digitizing circuit shown in FIG. 12B using a pair of dual FIFO memory storage buffers to synchronously track digital scan data and information about the facet-sectors on a holographic scanning disc used to generate the laser scanning beam that was used to collect such digital scan data from a bar code symbol on a package transported through the tunnel scanning subsystem hereof; 
     FIG. 13B is a schematic diagram showing the digitizing circuit of FIGS.  13 A 1  and  13 A 2  in greater detail; 
     FIGS.  13 C 1  and  13 C 2  are tables containing parameters and information that are used within the decode processor of the present invention shown in FIG.  13 A 1  and  13 A 2  in order to recover digital count data from time-based facet-sector related information, and generate decoded symbol character data and the minimum and maximum facet sector angles that specify the facet sector on a particular holographic scanning disc used to generate the laser scanning beam/plane that collect the scan data associated with the decoded bar code symbol; 
     FIG. 13D is a high level flow chart describing the steps of the process carried out by the decode processor of the present invention shown in FIG. 12B; 
     FIG. 14A is a schematic representation of the components on the control board and decode processing boards associated with a holographic scanning disc employed within an alternative embodiment of the holographic scanning subsystems in the tunnel scanning subsystem of the first illustrative embodiment of the present invention, showing the home-pulse detector and home-offset pulse (HOP) generator on the control board, and the start-of-facet-sector pulse (SOFSP) generator, digitizer circuitry, and decode signal processor. 
     FIG. 14B is a schematic representation of the start-of-facet-sector pulse (SOFSP) generator employed on each decode board associated with a holographic laser scanning subsystem depicted in FIG. 14A; 
     FIG. 14C is a flow chart describing the operation of the HOP generator on the control board associated with each holographic scanning disc, wherein home offset pulses (HOPs) are automatically generated from the HOP generator aboard the control board in each holographic laser scanning subsystem independent of the angular velocity of the holographic scanning disc employed therein; 
     FIG. 14D is a flow chart describing the operation of the SOFSP generator aboard each decode board, wherein start of facet pulses (SOFPs) are automatically generated within the SOFP generation module relative to the home-offset pulse (HOP) received by the control module in the SOFSP generator independent of the angular velocity of the holographic scanning disc of the subsystem, and wherein start of facet sector pulses (SOFSPs) are automatically generated within the SOFSP generation module relative to SOFPs generated by the SOFP generation module, independent of the angular velocity of the holographic scanning disc of the subsystem; 
     FIG. 15 is a schematic representation of the package velocity and length measurement subsystem of the present invention configured in relation to the tunnel conveyor and package height/width profiling subsystems of the system of the first illustrative embodiment of the present invention; 
     FIG. 15A is a schematic representation showing the dual-laser based package velocity and measurement subsystem installed in a “direct transmit/receive” configuration at the location of the vertical and horizontal light curtains employed in the package height/width profiling subsystem of the present invention; 
     FIG.  15 A 1  is a schematic representation of the signals received by the photoreceivers of the dual-laser based package velocity and measurement subsystem shown in FIG. 15; 
     FIG.  15 A 2  is a schematic representation of the signals generated by the photoreceiving circuitry and provided as input to the signal processor of the dual-laser based package velocity and measurement subsystem shown in FIG. 15; 
     FIG.  15 A 3  is a schematic diagram of circuitry for driving the dual laser diodes used in the dual-laser based package velocity and measurement subsystem of FIG. 15A; 
     FIGS.  15 A 4 A and  15 A 4 B is a schematic diagram of circuitry for conditioning the signals received by the photoreceivers employed in the dual-laser based package velocity and measurement subsystem of FIG. 15A; 
     FIG. 15B is a schematic representation showing the dual-laser based package velocity and measurement subsystem installed in a “retro-reflection” configuration at the location of the vertical and horizontal light transmitting/receiving structures employed in the package height/width profiling subsystem of the present invention; 
     FIG.  15 B 1  is a schematic diagram of electronic circuitry adapted for automatically generating a pair of laser beams at a known space-part distance, towards a retroflective device positioned on the opposite side of the conveyor belt of the system of the first illustrative embodiment of the present invention, and automatically detecting the retroflected beams and processing the same so as to produce signals suitable for computing the length and velocity of a package passing through the transmitted laser beams within the dual-laser based package velocity and measurement subsystem of FIG. 15B; 
     FIGS.  15 C through  15 C 2 , taken together, set forth a flow chart describing the steps carried out by the signal processor used in the dual-laser based package velocity and measurement subsystems of FIGS.  15  and FIG. 15B, so as to compute the velocity (v) and length (L) of the package transported through the laser beams of the dual-laser based package velocity and measurement subsystem hereof; 
     FIG. 16 is a perspective view of the automated package identification and measurement system of the present invention, showing the location of the package height/width profiling subsystem (and package-in-tunnel signaling subsystem) in relation thereto and the global coordinate reference system R global  symbolically embedded within the structure thereof, as shown; 
     FIG. 16A is a schematic representation of the horizontally and vertically arranged light transmitting and receiving structures and subcomponents employed in the package height/width profiling subsystem in the system of the first illustrative embodiment of the present invention; 
     FIG. 17A is an elevated side view of a pair of packages, arranged in a side-by-side configuration, and about to be transported through the package height/width profiling subsystem of FIG. 16; 
     FIG. 17B is a plan view of a pair of packages, arranged in a side-by-side configuration, and about to be transported through the package height/width profiling subsystem of FIG. 16; 
     FIG. 17C is an elevated side view of a pair of package, arranged in a side-by-side configuration, and being transported through and thus profiled by the package height/width profiling subsystem of FIG. 16; 
     FIG. 18A is an elevated side view of a pair of stacked packages conveyed along the conveyor belt subsystem, wherein one package is being transported through and thus profiled by the package height/width profiling subsystem of FIG. 16, while the other package has not yet been profiled by the subsystem; 
     FIG. 18B is an elevated side view of a pair of stacked packages conveyed along the conveyor belt subsystem, wherein both packages are being transported through and thus profiled by the package height/width profiling subsystem of FIG. 16; 
     FIG. 18C is an elevated side view of a pair of stacked packages conveyed along the conveyor belt subsystem, wherein one package is being transported through and thus profiled by the package height/width profiling subsystem of FIG. 16, while the other package has already been profiled by the subsystem; 
     FIG. 19 is a schematic diagram of an improved third-order finite-impulse-response (FIR) digital filter system that can be used to filter data streams produced from the width and height profiling data channels of the package height/width profiling subsystem of FIG. 16, in order to detect sudden changes in width and height profiles along the conveyor belt, within the context of a method of simultaneous package detection and tracking being carried out on a real-time basis in accordance with the principles of the present invention; 
     FIG. 19A is a flow chart describing the operation of the FIR digital filter system of FIG.  19  and how it detects sudden changes in the width and height data streams produced by the package height/width profiling subsystem of FIG. 16; 
     FIG. 19B is a flow chart describing the method of simultaneously detecting “side-by-side” configurations of packages along a conveyor belt using the FIR digital filter system of FIG. 19 to detect sudden changes in the width data streams produced by the package height/width profiling subsystem of FIG. 16; 
     FIG. 19C is a flow chart describing the method of simultaneously detecting “stacked” configurations of packages along a conveyor belt using the FIR digital filter of FIG. 19 to detect sudden changes in the height data streams produced by the package height/width profiling subsystem of FIG. 16; 
     FIG. 20A is an elevated side schematic view of the in-motion weighing subsystem employed in the system of the first illustrative embodiment of the present invention, wherein the scale and data processing subcomponents thereof are shown arranged about the package height/width profiling subsystem of FIG. 16; 
     FIG. 20B is a plan view of the in-motion weighing subsystem shown in FIG. 20A, wherein a moving package is shown being weighed on the scale component as it is transported along the conveyor belt of the system of the first illustrative embodiment; 
     FIG. 21 is a schematic diagram of the package-in-tunnel signaling subsystem employed in the automated package identification and measuring system of the first illustrative embodiment of the present invention; 
     FIGS.  22 A 1 ,  22 A 2  and  22 B, taken together provide a schematic representation of the data element queuing, handling and processing subsystem of the present invention shown in FIG. 4; 
     FIGS.  23 A 1  and  23 A 2  set forth a table of rules used to handle the data elements stored in the system event queue in the data element queuing, handling and processing subsystem of FIGS.  22 A 1  and  22 A 2 ; 
     FIG. 24 is a schematic representation of the surface geometry model created for each package surface by the package surface geometry modeling subsystem (i.e. module) deployed with the data element queuing, handling and processing subsystem of FIGS.  22 A 1  and  22 A 2 , illustrating and showing how each surface of each package (transported through package dimensioning/measuring subsystem and package velocity/length measurement subsystem) is mathematically represented (i.e. modeled) using at least three position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global , and a normal vector drawn to the package surface indicating the direction of incident light reflection therefrom; 
     FIG. 24A is a table setting forth a preferred procedure for creating a vector-based surface model for each surface of each package transported through the package dimensioning/measuring subsystem and package velocity/length measurement subsystem of the system hereof; 
     FIGS.  25 A through  25 A 1  is schematic representation of a diffraction-based geometric optics model, created by the scan beam geometry modeling subsystem (i.e. module) of FIGS.  22 A 1  and  22 A 2 , for the propagation of the laser scanning beam (ray) emanating from a particular point on the facet, towards its point of reflection on the corresponding beam folding mirror, towards to the focal plane determined by the focal length of the facet, created within the scan beam geometry modeling module shown in FIGS.  22 A 1  and  22 A 2 ; 
     FIGS.  25 B 1  through  25 B 3  set forth a table of parameters used to construct the diffraction-based geometric optics model of the scanning facet and laser scanning beam shown in FIGS.  25 A and  25 A 1 ; 
     FIGS.  25 C 1  and  25 C 2 , taken together, set forth a table of parameters used in the spreadsheet design of the holographic laser scanning subsystems of the present invention, as well as in real-time generation of geometrical models for laser scanning beams using 3-D ray-tracing techniques; 
     FIG. 26 is a schematic representation of the laser scanning disc shown in FIGS.  25 A and  25 A 1 , labeled with particular parameters associated with the diffraction-based geometric optics model of FIGS.  25 A and  25 A 1 ; 
     FIG. 27 is a table setting forth a preferred procedure for creating a vector-based ray model for laser scanning beams which have been produced by a holographic laser scanning subsystem of the system hereof, that may have collected the scan data associated with a decoded bar code symbol read thereby within the tunnel scanning subsystem; 
     FIG. 28 is a schematic representation of the vector-based 2-D surface geometry model created for each candidate scan beam by the scan surface modeling subsystem (i.e. module) shown in FIG. 22B, and showing how each omni-directional scan pattern produced from a particular polygon-based bottom scanning unit is mathematically represented (i.e. modeled) using four position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global , and a normal vector drawn to the scanning surface indicating the direction of laser scanning rays projected therefrom during scanning operations; 
     FIG. 29 is a schematic representation graphically illustrating how a vector-based model created within a local scanner coordinate reference frame R localscannerj  can be converted into a corresponding vector-based model created within the global scanner coordinate reference frame R global  using homogeneous transformations; 
     FIG. 30 is a schematic representation graphically illustrating how a vector-based package surface model created within the global coordinate reference frame R global  at the “package height/width profiling position” can be converted into a corresponding vector-based package surface model created within the global scanner coordinate reference frame R global  at the “scanning position” within the tunnel using homogeneous transformations, and how the package travel distance (d) between the package height/width profiling and scanning positions is computed using the package velocity (v) and the difference in time indicated by the time stamps placed on the package data element and scan beam data element matched thereto during each scan beam/package surface intersection determination carried out within the data element queuing, handling and processing subsystem of FIGS.  22 A 1 ,  22 A 2  and  22 B; 
     FIGS. 31A and 31B, taken together, provide a procedure for determining whether the scan beam (rays) associated with a particular scan beam data element produced by a holographic scanning subsystem intersects with any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system; 
     FIGS. 32A and 32B, taken together, provide a procedure for determining whether the scanning surface associated with a particular scan beam data element produced by a non-holographic (e.g. polygon-based) bottom-located scanning subsystem intersects with any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system; 
     FIG. 33 is a perspective view of a “dual-lane” automated tunnel-type laser scanning package identification and weighing system constructed in accordance with the second illustrated embodiment of the present invention; 
     FIG. 33A is a plan view schematic representation showing the scanning areas covered by four corner-mounted triple-disc laser scanning subsystems of FIG. 33, as well as the orthogonal and omni-directional scanning regions projected over the moving conveyor belt structure of the system; 
     FIG. 34 is a schematic block diagram illustrating the holographic laser scanning subsystems, the package-in-tunnel indication subsystem, the package velocity measurement subsystem, the package-out-of-tunnel subsystem, the package weighing-in-motion subsystem, the data-element queuing, handling and processing subsystem, the input/output port multiplexing subsystem, and the conveyor belt subsystem; 
     FIGS. 35A through 35C, taken together, set forth a flow chart describing the computational process used by the conveyor belt velocity measurement subsystem employed in FIG. 33, so as to compute the velocity of the conveyor belt of the system of the second illustrative embodiment of the present invention; 
     FIGS. 36A and 36B, taken together, set forth a schematic representation of the data element queuing, handling and processing subsystem employed in the system of the second illustrative embodiment of the present invention, illustrated in FIG. 33; 
     FIGS. 37A and 37B set forth a table of rules used to handle the data elements stored in the system event queue in the data element queuing, handling and processing subsystem of FIG. 36A and 36B; 
     FIG. 38 is a schematic representation of the system and method used herein to create vector-based models of each package location region within the tunnel scanning system of the second illustrative embodiment; 
     FIGS. 39A and 39B provide a flow chart setting forth a preferred procedure for creating a vector-based model for each package location region within the tunnel scanning system of the second illustrative embodiment; 
     FIG. 40 is a schematic representation graphically illustrating how a vector-based scanning beam model created within a local scanner coordinate reference frame R localscannerj  can be converted into a corresponding vector-based model created within the global scanner coordinate reference frame R global  using homogeneous transformations; 
     FIG. 41 is a flow chart setting forth a preferred procedure for determining whether the scan beam (rays) associated with a particular scan beam data element produced by a holographic scanning subsystem within the system of FIG. 33 intersects with the package location region associated with package scanned at the scanning position associated with the scan beam data element, and thus whether to correlate a particular package identification data element with a particular package measurement data element or like token acquired by the system; 
     FIG. 42 is a perspective view of an automated tunnel-type laser scanning package identification and weighing system constructed in accordance with the third illustrated embodiment of the present invention, wherein multiple packages, arranged in stacked and/or side-by-side configurations, are transported along a high speed conveyor belt, dimensioned, weighed and identified in a fully automated manner without human intervention; 
     FIG. 43 is schematic block diagram of the system of FIG. 42, showing the subsystem structure thereof as comprising a scanning tunnel including holographic and non-holographic laser scanning subsystems, a first simultaneous multiple-package detection and dimensioning subsystem installed on the input side of the tunnel scanning subsystem, a second simultaneous multiple-package detection and dimensioning subsystem installed on the output side of the tunnel scanning subsystem, a package/belt velocity measurement subsystem, a package weighing-in-motion subsystem, a data-element queuing, handling and processing subsystem, an input/output (I/O) subsystem, a conveyor belt subsystem, and a master clock for establishing a global time reference when time-stamping data elements generated throughout the system; 
     FIG. 44 is a schematic representation of the first simultaneous multiple-package detection and dimensioning subsystem installed on the input side of the tunnel scanning subsystem, showing its various constituent subcomponents, namely a LADAR-based imaging and dimensioning subsystem for producing package dimension (PD) data elements, a package-in-the-tunnel (PIT) detection subsystem for automatically detecting the entry of multiple packages into the scanning tunnel and generating PIT data elements, a data element controller for receiving the PD and PIT data elements, date-stamping the same, and loading these data elements into and unloading the same from a plurality of moving package tracking queues assigned to different spatial regions above the conveyor belt, located on the input side of the tunnel scanning subsystem; 
     FIG. 44A is a schematic block diagram of the LADAR-based imaging and dimensioning subsystem employed in the simultaneous multiple-package detection and dimensioning subsystem shown in FIG. 44; 
     FIG. 44B is a schematic representation of a first illustrative embodiment of the LADAR-based imaging and dimensioning subsystem of the present invention, having an eight-sided polygonal scanning element, mounted on an optical bench within the subsystem housing, for scanning an amplitude modulated laser beam along a single scanning plane projected through a light transmission aperture formed in the subsystem housing, a light collecting mirror mounted on the optical bench for collecting reflected laser light off a scanned object (e.g. package) and focusing the same to a focal point located on the surface of a stationary planar mirror mounted on the optical bench, and an avalanche-type photodetector mounted on the optical bench for detecting laser light focused onto the stationary planar mirror and producing an electrical signal corresponding thereto, signal processing circuitry for processing the produced electrical signal and generating raw digital range data representative of the distance from the polygonal scanning element to sampled points along the scanned object (as well digital scan data representative of any bar code symbol the scanned surface of the object), a programmed digital image data processor for preprocessing the raw digital range data and removing background information components, and for processing the preprocessed range data so as to extract therefrom information regarding the dimensions (e.g. area, height and vertices) of the scanned object and produce data representative thereof, and a bar code symbol digitizing and decoding circuitry for processing the digital scan data signal and producing symbol character data representative of any bar code symbol located on the scanned surface of the object; 
     FIG. 44C is a schematic representation of the avalanche photodetector employed within the LADAR-based imaging and dimensioning subsystem shown in FIG. 44B; 
     FIG. 44D is a schematic representation illustrating that the information specified in the polar-type coordinate reference subsystem symbolically embedded within the LADAR-based subsystem of FIG. 44B can be converted (or translated) to the Cartesian-type coordinate reference system symbolically embedded within the automated tunnel-type laser scanning package identification and weighing system of FIG. 42; 
     FIG.  44 E 1  is a schematic representation of a second illustrative embodiment of the LADAR-based imaging and dimensioning subsystem of the present invention, having a holographic scanning disc, rotatably mounted on an optical bench within the subsystem housing, for scanning an amplitude modulated laser beam (produced from a laser beam production module) along a single scanning plane (along multiple depths of focus) projected through a light transmission aperture formed in the subsystem housing, a parabolic light collecting mirror mounted beneath the holographic scanning disc for collecting reflected laser light off a scanned object (e.g. package) and focusing the same to an avalanche-type photodetector mounted above the scanning disc, and producing an electrical signal corresponding thereto, signal processing circuitry for processing the produced electrical signal and generating raw digital range data representative of the distance from the polygonal scanning element to sampled points along the scanned object (as well digital scan data representative of any bar code symbol the scanned surface of the object), a programmed digital image data processor for preprocessing the raw digital range data and removing background information components, and for processing the preprocessed range data so as to extract therefrom information regarding the dimensions (e.g. area, height and vertices) of the scanned object and produce data representative thereof, and a bar code symbol digitizing and decoding circuitry for processing the digital scan data signal and producing symbol character data representative of any bar code symbol located on the scanned surface of the object; 
     FIG.  44 E 2  is a side cross-sectional view of the LADAR-based imaging and dimensioning subsystem shown in FIG.  44 E 1 ; 
     FIG.  44 E 3  is a table setting forth the design parameters used to construct the holographic scanning disc employed in the LADAR-based subsystem of the second illustrative embodiment; 
     FIG.  44 E 4  is a schematic representation of the linear scanning pattern produced from the LADAR-based subsystem of FIG.  44 E 1   
     FIG. 44F is a high-level flow chart indicating the major stages of 2-D range data processing method carried out within the LADAR-based subsystem of FIG.  44 E 1 ; 
     FIG. 44G is a schematic representation of the 2-D range data processing method cyclically carried out on upon the computing platform of the LADAR-based imaging and dimensioning subsystem of the present invention; 
     FIG.  44 G 1  is a flow chart of an algorithmic control structure for the computation of local operators in the LADAR-based subsystem of the present invention; 
     FIGS.  44 H 1  through  44 H 5 , taken together, set forth a flow chart describing the steps of the range data processing method carried out in the LADAR-based imaging and dimensioning subsystem of the illustrative embodiment of the present invention; 
     FIG. 44I is a graphical image of a 2-D range data map synthesized from a large number of rows of raw range data captured from the LADAR-based imaging and dimensioning subsystem of the present invention, in accordance with the data capturing operations specified in Step A 1  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG.  44 I 2  is a graphical image of a 2-D range data map after being processed by the data processing operations specified in Step A 2  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG.  44 I 3  is a graphical image of a 2-D range data map after being processed by the data processing operations specified in Step A 3  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG.  44 I 4  is a graphical image of a 2-D range data map synthesized from a large number of rows of background data removed from rows of raw range data by the data processing operations specified in Step A 4  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG.  44 I 5  is a graphical image of a differentiated 2-D range data map from which background data, indicated in FIG.  44 I 4 , is subtracted during being processed by the data processing operations specified in Steps B 1 , B 2  and B 3  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG. 44J is a flow chart describing the process of retrieving rows of range data, already preprocessed using smoothing and edge-detection techniques, and computes the first vertical derivative and stores the results in an image structure for further processing, such as contour tracing, etc.; 
     FIG. 44K is a flow chart describing the steps carried out by the contour tracing program employed in the LADAR-based imaging and dimensioning subsystem of the present invention; 
     FIG. 44L is a flow chart describing the operations carried out during Step B 6  and B 7  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG. 44M is a flow chart describing the operations carried out during Steps B 6  and B 7  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG. 44N is a flow chart describing the operations carried out during Step B 10  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIGS.  44 O 1  through  44 O 4  set forth polygonal contours of the type traced during Step B 9 , having corner points which are reduced using the algorithm set forth in FIG. 44N; 
     FIG. 44P is a schematic representation of the LADAR-based subsystem of the present invention, illustrating the geometrical transformation between the polar coordinate reference system embedded therewithin and the height of a package scanned thereby defined relative to the Cartesian coordinate reference system embedded within the package identification and dimensioning system of the present invention; 
     FIG. 44Q is a flow chart describing the surface computation operations carried out during Step B 13  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIGS.  44 R 1  and  44 R 2  are polygonal contours which illustrative the method of package surface area computation carried out during Step B 13  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     FIG. 45 is a schematic representation of the second simultaneous multiple-package detection and dimensioning subsystem installed on the output side of the tunnel scanning subsystem, showing its various constituent subcomponents; 
     FIG. 45A is a schematic representation of the height profile data analyzer employed in the subsystem of FIG. 45, comprising a data controller, time-stamping module, a height profile data element queue, a height profile data analyzer, and a plurality of moving package tracking queues assigned to different spatial regions above the conveyor belt of the system located on the output side of the tunnel scanning subsystem; 
     FIG. 45B is a schematic block diagram of the laser scanning mechanism employed in the simultaneous multiple-package detection and dimensioning subsystem shown in FIG. 45; 
     FIGS.  46 A 1 ,  46 A 2  and  46 B, taken together, provide a schematic representation of the data element queuing, handling and processing subsystem of the present invention shown in FIGS. 42 and 43; 
     FIGS. 47A and 47B set forth a table of rules used to handle the data elements stored in the scan beam data element (SBDE) queue in the data element queuing, handling and processing subsystem of FIG.  46 A 1 ,  46 A 2  and  46 B; 
     FIG. 48A is a schematic representation of the surface geometry model created for each package surface by the package surface geometry modeling subsystem (i.e. module) deployed with the data element queuing, handling and processing subsystem of FIGS.  46 A 1 ,  46 A 2  and  46 B, illustrating and showing how each surface of each package transported through package dimensioning/measuring subsystem is mathematically represented (i.e. modeled) using at least three position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global , and a normal vector drawn to the package surface indicating the direction of incident light reflection therefrom; 
     FIG. 48B is a table setting forth a preferred procedure for creating a vector-based surface model for each surface of each package transported through the package detection and dimensioning subsystem of the system hereof; 
     FIG. 49 is a table setting forth a preferred procedure for creating a vector-based ray model for laser scanning beams which have been produced by a holographic laser scanning subsystem of the system hereof, that may have collected the scan data associated with a decoded bar code symbol read thereby within the tunnel scanning subsystem; 
     FIG. 50 is a schematic representation of the vector-based 2-D surface geometry model created for each candidate scan beam by the scan surface modeling subsystem (i.e. module) shown in FIG. 46B, and showing how each omni-directional scan pattern produced from a particular polygon-based bottom scanning unit is mathematically represented (i.e. modeled) using four position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global , and a normal vector drawn to the scanning surface indicating the direction of laser scanning rays projected therefrom during scanning operations; 
     FIG. 51 is a schematic representation graphically illustrating how a vector-based model created within a local scanner coordinate reference frame R localscannerj  can be converted into a corresponding vector-based model created within the global scanner coordinate reference frame R global  using homogeneous transformations; 
     FIG. 52 is a schematic representation graphically illustrating how a vector-based package surface model created within the global coordinate reference frame R global  at the “package height/width profiling position” can be converted into a corresponding vector-based package surface model created within the global scanner coordinate reference frame R global  at the “scanning position” within the tunnel using homogeneous transformations, and how the package travel distance (d) between the package height/width profiling and scanning positions is computed using the package velocity (v) and the difference in time indicated by the time stamps placed on the package data element and scan beam data element matched thereto during each scan beam/package surface intersection determination carried out within the data element queuing, handling and processing subsystem of FIGS.  46 A 1 ,  46 A 2  and  46 B; 
     FIGS. 53A and 53B, taken together, provide a procedure for determining whether the scan beam (rays) associated with a particular scan beam data element produced by a holographic scanning subsystem intersects with any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system; 
     FIGS. 54A and 54B, taken together, provide a procedure for determining whether the scanning surface associated with a particular scan beam data element produced by a non-holographic (e.g. polygon-based) bottom-located scanning subsystem intersects with any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system; 
     FIG. 55 is a perspective view of an automated tunnel-type laser scanning package identification and weighing system constructed in accordance with the fourth illustrated embodiment of the present invention, wherein packages, arranged in a singulated configuration, are transported along a high speed conveyor belt, dimensioned, weighed and identified in a fully automated manner without human intervention; 
     FIG. 56 is a block schematic of the system of FIG. 55; 
     FIG. 57 is a block schematic data element computer system management employed in FIG. 55; and 
     FIG. 58 is a schematic representation of an automatic package identification and measurement system of the present invention shown interfaced to a relational database management system (RDBMS) and an Internet information server which are connected to a local information network that is interconnected to the Internet, for the purpose of enabling customers and other authorized personnel to use a WWW-enabled browser program to (1) remotely access (from an Internet server) information about any packages transported through the system, as well as diagnostics regarding the system, and (2) remotely control the various subcomponents of the system in order to reprogram its subsystems, perform service routines, performance checks and the like, as well as carry out other forms of maintenance required to keep the system running optimally, while minimizing downtime or disruption in system operations. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS OF THE PRESENT INVENTION 
     Referring to the figures in the accompanying Drawings, the preferred embodiments of the automated package identification and measurement system of the present invention will be described in great detail, wherein like elements will be indicated using like reference numerals. 
     Automated Tunnel-Type Laser Scanning Package Identification and Measurement System of the First Illustrative Embodiment of the Present Invention 
     In FIG. 1, there is shown an automated tunnel-type laser scanning package identification and measuring (e.g. dimensioning and weighing) system designed to meet the needs of demanding customers, such as the United States Postal Service (USPS), which requires “hands-free” bar code (or code symbol) scanning of at least six-sided packages, wherein the label containing the code symbol to be read could be positioned in any orientation on any one of the six or more sides of the box or container structure. As used hereinafter, the term “hands-free” shall mean scanning of bar codes on boxes or parcels that are travel-ling past the scanners in only one direction on some sort of conveyor system. In this illustrative embodiment, the package should be singulated in a conventional manner. 
     As shown in FIG. 3, the automated tunnel scanning system of the first illustrative embodiment indicated by reference numeral  1  comprises an integration of subsystems, namely: a high-speed package conveyor system  300  having a conveyor belt  300  comprising at least two separated sections  302 A and  302 B, and each having a width of at least 30 inches to support one or more package transport lanes along the conveyor belt; a tunnel scanning subsystem  100  including an arrangement of holographic and non-holographic laser scanning bar code symbol reading subsystems  101  through  117  supported overhead and below the conveyor belt by a support frame  150  so as to produce a truly 3-D omni-directional scanning volume above the conveyor belt, for canning bar codes on packages transported therethrough independent of the package or bar code orientation; a package velocity and length measurement subsystem  400 ; a package-in-the-tunnel indication subsystem  500  realized as a 2-D light sensing structure mounted along the conveyor belt, on the input side of the tunnel, for automatically detecting the presence of each package moving into the scanning tunnel; a package (x-y) dimensioning subsystem  600 , employing the 2-D light sensing structure of subsystem  500 , for producing x-y profile data of detected packages; a package-out-of-the-tunnel indication subsystem  700  realized as an infrared (IR) light sensing object-detecting device mounted along the conveyor belt, on the output side of the tunnel, for automatically detecting the presence of packages moving out of the scanning tunnel; a weighing-in-motion subsystem  900  for weighing packages as they are transported along the conveyor belt; an input/output subsystem  800  for managing the inputs to and output from the system of FIG. 1; and a data management computer  900  with a graphical user interface (GUI)  901 , for realizing a data element queuing, handling and processing subsystem  1000  as shown in FIG. 22, as well as other data and system management functions. 
     Laser Scanning Tunnel Subsystem of First Illustrative Embodiment of the Present Invention 
     As shown in FIGS. 1 through 1E, the tunnel scanning system of the first illustrative embodiment  1  comprises an arrangement of laser scanning subsystems (i.e. scanners) which, by virtue of their placement, relative to the conveyor belt subsystem  300 , essentially form a “tunnel” scanning subsystem over and about the conveyor belt of the conveyor subsystem  300 . In the field of package sortation of any sort, whether it be mail, luggage (as in an airport terminal) or other items or boxes, this type of code symbol scanning system is known as a “tunnel scanning system” by those skilled in the art. 
     The tunnel scanning system of the first illustrative embodiment, shown in great detail in FIGS. 1 through 32B, can be designed and constructed to meet any specific set of customer-defined scanning parameters. For example, in the first illustrative embodiment, the bar code label can be on any one side of a box having six or more sides. The bar code label could be in any orientation. Furthermore, the object bearing the bar code label to be read would be moving past the scanners of the conveyor belt travel-ling at speeds in excess of 600 feet per second. In the illustrative embodiment, the conveyor belts  302 A and  302 B are moving at 520 feet per second but many move faster in other embodiments. 
     The types of codes to be read to include such codes as Code 39, Code 128 and others. The aspect ratio of the bar codes to be read is on the order of 10 mils and up. 
     The tunnel scanning system of the present invention can be used in various types of applications, such as for example, where the bar codes are read to determine (a) identification of incoming packages, (b) identification of outgoing packages, and (c) sortation of outgoing packages. For sortation types of applications, the information derived from the bar code will be used not only to identify the package, but also to direct the package along a particular path using deflectors, routers and other instruments well known in the package and parcel handling art. 
     In the first illustrative embodiment shown in FIG. 1, the volume to be scanned within the tunneling subsystem (e.g. its 3-D scanning volume) is approximately: 1 meter wide (i.e. the width of the conveyor belt); ten feet long; and 1 meter tall (i.e. the height of the tallest possible box going through). The laser scanning pattern produced by the concerted operation of the holographic laser scanning subsystems identified in the drawings, and described above, fills this entire 3-D scanning volume with over 400,000 scan lines per second. The 3-D scanning volume of the tunnel scanning system, measured with respect to the surface of the conveyor belt, begins at the surface of the conveyor belt in order to scan flat items (such as envelopes), and extends up approximately 1 meter (“h) above the surface of the conveyor belt subsystem. 
     As shown in FIGS. 1 through 1C, sixteen holographic laser scanning subsystems  101  through  116  are mounted on a lightweight scanner support framework  304 , at positions specified in Tunnel Scanner Positioning Data Table shown in FIG.  2 C. The terms (e.g. “Top/Front”, Top/Back”, etc.) used in this Table to identify the individual holographic scanning subsystems of the tunnel scanning system hereof are used throughout the drawings, rather than reference numerals. The one fixed-projection scanner subsystem, identified by the label “Bottom” or  117 , is mounted between the gap  305  provided between the first and second conveyor platforms  302 A and  302 B comprising the conveyor subsystem  300  of the tunnel scanning subsystem  100 . 
     The various omni-directional and orthogonal scanning directions provided for within the 3-D scanning volume of the tunnel-scanning system of the present invention are schematically illustrated in FIGS. 5A through 9B. These illustrations indicate how each of the laser scanning subsystems within the tunnel scanning system contribute to produce the truly omni-directional scanning performance attained by the tunnel scanner hereof. 
     Omni-Directional Holographic Laser Scanning Subsystem of the Present Invention 
     As shown in FIGS. 1B and 1C, the eight triple-disc holographic scanners (denoted as Top/Front, Top/Back, Front, Back, Right Side/Front, Right Side/Back, Left Side/Front and Left Side/Back) are mounted about the conveyor belt by way of the scanner support framework, in accordance with the positioning data set forth in the table of FIG.  2 C. Notably, using the eight corner scanners in this system embodiment, the Front and Back Scanners should not be required and thus would be optional to achieve full omni-directional scanning with the 3-D scanning volume of the tunnel scanning subsystem. Each of these eight triple-disc holographic scanning subsystems (denoted as Top/Front, Top/Back, Front, Back, Right Side/Front, Right Side/Back, Left Side/Front and Left Side/Back) is shown in greater detail in FIGS.  4 A 1  through  4 A 10 . 
     As shown in FIGS.  4 A 1  and  4 A 2 , each triple-disc holographic scanning subsystem has three laser scanning platforms installed within a scanner housing  140 . Each laser scanning platform, shown in greater detail in FIG.  4 A 2  produces a 3-D laser scanning volume as shown in FIG.  4 A 8 C, to produce Penta 1 Scanner. Each 3-D scanning volume contains a omni-directional laser scanning pattern having four over-lapping focal zones which are formed by five laser scanning stations indicated as LS 1 , LS 2 , LS 3 , LS 4  and LS 5  in FIG.  4 A 1 , arranged about a sixteen-facet holographic scanning disc  130 . When combining a pair of such scanning platforms, a Penta 2 Scanner is produced that is capable of producing a double-sized scanning volume as shown in FIG.  4 A 8 B. When combining three such scanning platforms, a Penta 3 Scanner is produced that is capable of producing a triple-sized scanning volume as shown in FIG.  4 A 8 A. The scan pattern and scan speeds for such alternative embodiments of this omni-directional scanning subsystem of the present invention is shown in the specification table set forth in FIG.  4 A 8 D. 
     In general, each holographic laser scanning subsystem within these triple-disc scanners can be designed and constructed using the methods detailed in Applicant&#39;s copending application Ser. Nos. 08/949,915 filed Oct. 14, 1997; Ser. No. 08/854,832 filed May 12, 1997; Ser. No. 08/886,806 filed Apr. 22, 1997; Ser. No. 08/726,522 filed Oct. 7, 1996; and Ser. No. 08/573,949 filed Dec. 18, 1995, each incorporated herein by reference. The design parameters for each sixteen facet holographic scanning disc shown in FIG.  44 A 4 , and the supporting subsystem used therewith, are set forth in the Table of FIG.  4 A 5 . The design parameters set forth in the table of FIG.  4 A 5  are defined in detail in the above-referenced U.S. Patent Applications. The scanning pattern projected within the middle (third) focal plane of the holographic scanning subsystem by one of its scanning platforms is shown in FIG.  4 A 9 . The composite scanning pattern projected within the middle (third) focal/scanning plane of the triple-disc holographic scanning subsystem of FIG.  4 A 1  is shown in FIG.  4 A 10 . 
     As shown in the system diagram of FIGS.  4 A 6 A through  4 A 6 C, each holographic laser scanning unit of the present invention  101  through  108  (denoted as Top/Front, Top/Back, Front, Back, Right Side/Front, Right Side/Back, Left Side/Front and Left Side/Back in FIGS. 1 through 1C) comprises a number of system components, many of which are realized on a control board  200 , a plurality (e.g. six) analog signal processing boards  201 A- 201 -F, and six digital signal processing boards  202 A- 202 F. 
     As described in WIPO Patent Application Publication No. WO 98/22945, each holographic laser scanning unit  101  through  108  employed herein cyclically generates from its compact scanner housing  140  shown in FIG.  4 A 1 , a complex three-dimensional laser scanning pattern within a well defined 3-D scanning volume which will be described in greater detail hereinbelow. In the system of the first illustrative embodiment, each such laser scanning pattern is generated by a rotating holographic scanning disc  130 , about which are mounted five (5) independent laser scanning stations, sometime referred to as laser scanning modules by Applicants. In FIG.  4 A 1 , these laser scanning stations are indicated by LS 1 , LS 2 , LS 3 , LS 4  and LS 5 . 
     In FIG.  4 A 2 , one of the laser scanning stations in the holographic scanner is shown in greater detail. For illustration purposes, all subcomponents associated therewith shall be referenced with the character “A”, whereas the subcomponents associated with the other four laser scanning stations shall be referenced using the characters B through E. As illustrated in FIG.  4 A 2 , the beam folding mirror  142 A associated with each laser scanning station, has a substantially planar reflective surface and is tangentially mounted adjacent to the holographic scanning disc  130 . In the illustrative embodiment, beam folding mirror  142 A is supported in this position relative to the housing base (i.e. the optical bench)  143  using support legs  144 A and  145 A and rear support bracket  146 . 
     As shown in FIG.  4 A 2 , the laser beam production module  147  associated with each laser scanning station is mounted on the optical bench (i.e. housing base plate  143 ), immediately beneath its associated beam folding mirror  142 A. Depending on which embodiment of the laser beam production module is employed in the construction of the holographic laser scanner, the position of the laser beam production module may be different. 
     As shown in FIG.  3 A 2 , six laser production modules  142 A through  142 E are mounted on base plate  143 , substantially but not exactly symmetrically about the axis of rotation of the shaft of electric motor  150 . During laser scanning operations, these laser beam production modules produce six independent laser beams which are directed through the edge of the holographic disc  130  at an angle of incidence A i , which, owing to the symmetry of the laser scanning pattern of the illustrative embodiment, is the same for each laser scanning station (i.e. A i =43.0 degrees for all values of i). The incident laser beams produced from the six laser beam production modules  142 A through  142 E extend along the five central reference planes, each extending normal to the plane of base plate  143  and arranged about 72 degrees apart from its adjacent neighboring central planes, as best illustrated in FIG.  4 A 2 . While these central reference planes are not real (i.e. are merely virtual), they are useful i n describing the geometrical structure of each laser scanning station in the holographic laser scanner of the present invention. 
     As shown in FIG.  4 A 2 , the photodetector  152 A (through  152 E) of each laser scanning station is mounted along its central reference plane, above the holographic disc  130  and opposite its associated beam folding mirror  142 A (through  142 E) so that it does not block or otherwise interfere with the returning (i.e. incoming) laser light rays reflecting off light reflective surfaces (e.g. product surfaces, bar code symbols, etc) during laser scanning and light collecting operations. In the illustrative embodiment, the five photodetectors  152 A through  152 E are supported in their respective positions by a photodetector support frame  153  which is stationarily mounted to the optical bench by way of vertically extending support elements  154 A through  154 E. The electrical analog scan data signal produced from each photodetector is processed in a conventional manner by its analog scan data signal processing board  201 A (through  201 E) which is also supported upon the photodetector support frame, as shown. Notably, the height of the photodetector support board, referenced to the base plate (i.e. optical bench), is chosen to be less than the minimum height so that the beam folding mirrors must extend above the holographic disc in order to realize the prespecified laser scanning pattern of the illustrative embodiment. In practice, this height parameter is not selected (i.e. specified) until after the holographic disc has been completely designed according to the design process of the present invention, while satisfying the design constraints imposed on the disc design process. As explained in detail in WIPO Patent Application Publication No. WO 98/22945, the use of a spreadsheet-type computer program to analytically model the geometrical structure of both the laser scanning apparatus and the ray optics of the laser beam scanning process, allows the designer to determine the geometrical parameters associated with the holographic scanning facets on the disc which, given the specified maximum height of the beam folding mirrors Y j , will produce the prespecified laser scanning pattern (including focal plane resolution) while maximizing the use of the available light collecting area on the holographic scanning disc. 
     As best shown in FIG.  4 A 3 , the parabolic light collecting mirror  149 A (through  149 F) associated with each laser scanning station is disposed beneath the holographic scanning disc  130 , along the central reference plane associated with the laser scanning station. While certainly not apparent from this figure, precise placement of the parabolic light collecting element (e.g. mirror)  149 A relative to the holographic facets on the scanning disc  130  is a critical requirement for effective light detection by the photodetector ( 152 A) associated with each laser scanning station. Placement of the photodetector at the focal point of the parabolic light focusing mirror alone is not sufficient for optimal light detection in the light detection subsystem of the present invention. As taught in WIPO Patent Application Publication No. WO 98/22945, careful analysis must be accorded to the light diffraction efficiency of the holographic facets on the scanning disc and to the polarization state(s) of collected an d focused light rays being transmitted therethrough for detection. As will become more apparent hereinafter, the purpose of such light diffraction efficiency analysis ensures the realization of two important conditions, namely: (i) that substantially all of the incoming light rays reflected off an object (e.g. bar code symbol) and passing through the holographic facet (producing the corresponding instant scanning beam) are collected by the parabolic light collecting mirror; and (ii) that all of the light rays collected by the parabolic light collecting mirror are focused through the same holographic facet onto the photodetector associated with the station, with minimal loss associated with light diffraction and refractive scattering within the holographic facet. A detailed procedure is described in WIPO Patent Application Publication No. WO 98/22945 for designing and installing the parabolic light collecting mirror in order to satisfy the critical operating conditions above. 
     As shown in FIGS.  3 A 2  and  3 A 3 , the five digital scan data signal processing boards  202 A through  202 E, are arranged in such a manner to receive and provide for processing the analog scan data signals produced from analog scan data signal processing boards  201 A through  201 E, respectively. As best shown in FIGS.  4 A 2  and  4 A 3 , each digital scan data signal processing board is mounted vertically behind its respective beam folding mirror. A control board (i.e. motherboard)  200  is also mounted upon the base plate  143  for processing signals produced from the digital scan data signal processing boards. A conventional power supply board  155  is also mounted upon the base plate  143 , within one of its extreme corners. The function of the digital scan data signal processing boards, the central processing board, and the power supply board will be described in greater detail in connection with the functional system diagram of FIGS.  4 A 6 A through  4 A 6 C. As shown, electrical cables are used to conduct electrical signals from each analog scan data signal processing board to its associated digital scan data signal processing board, and from each digital scan data signal processing board to the central processing board. Regulated power supply voltages are provided to the central signal processing board  200  by way of an electrical harness (not shown), for distribution to the various electrical and electro-optical devices requiring electrical power within the holographic laser scanner. In a conventional manner, electrical power from a standard 120 Volt, 60 HZ, power supply is provided to the power supply board by way of flexible electrical wiring (not shown). Symbol character data produced from the central processing board  200  is transmitted to the I/O subsystem  800 , over a serial data transmission cable connected to a serial output (i.e. standard RS232) communications jack installed through a wall in the scanner housing  140 . 
     Many of the system components comprising each of the holographic laser scanning units  101  through  116  are realized on control board  200 , the plurality (e.g. five) analog signal processing boards  201 A through  201 E, and the six digital signal processing boards  202 A through  202 E. 
     In the illustrative embodiment shown in FIG.  4 A 6 A, each analog scan data signal processing board  201 A through  201 E has the following components mounted thereon: and photodetector  152 A (through  152 E) (e.g. a silicon photocell) for detection of analog scan data signals as described hereinabove; and analog signal processing circuit  235 A (through  235 E) for processing detected analog scan data signals. 
     In the illustrative embodiment, each photodetector  152 A through  152 E is realized as an optoelectronic device and each analog signal processing circuit  235 A aboard the analog signal processing board ( 201 A through  201 E) is realized as an Application Specific Integrated Circuit (ASIC) chip. These chips are suitably mounted onto a small printed circuit (PC) board, along with electrical connectors which allow for interfacing with other boards within the scanner housing. With all of its components mounted thereon, each PC board is suitably fastened to the photodetector support frame  153 , along its respective central reference frame, as shown in FIG.  4 A 2 . 
     In a conventional manner, the optical scan data signal D 0  focused onto the photodetector  152 A during laser scanning operations is produced by light rays of a particular polarization state (e.g. S polarization state) associated with a diffracted laser beam being scanned across a light reflective surface (e.g. the bars and spaces of a bar code symbol) and scattering thereoff. Typically, the polarization state distribution of the scattered light rays is altered when the scanned surface exhibits diffuse reflective characteristics. Thereafter, a portion of the scattered light rays are reflected along the same outgoing light ray paths toward the holographic facet which produced the scanned laser beam. These reflected light rays are collected by the scanning facet and ultimately focused onto the photodetector of the associated light detection subsystem by its parabolic light reflecting mirror  149 A disposed beneath the scanning disc  130 . The function of each photodetector  152 A is to detect variations in the amplitude (i.e. intensity) of optical scan data signal D 0 , and to produce in response thereto an electrical analog scan data signal D 1  which corresponds to such intensity variations. When a photodetector with suitable light sensitivity characteristics is used, the amplitude variations of electrical analog scan data signal D 1  will linearly correspond to the light reflection characteristics of the scanned surface (e.g. the scanned bar code symbol). The function of the analog signal processing circuitry is to band-pass filter and preamplify the electrical analog scan data signal D 1 , in order to improve the SNR of the output signal. 
     In the illustrative embodiment of FIG.  4 A 1 , each digital scan data signal processing board  202 A through  202 E is constructed in substantially the same manner. On each of these signal processing boards, the following devices are provided: an analog-to-digital (A/D) conversion circuit  238 A through  238 E, as taught in copending U.S. application Ser. Nos. 09/243,078 filed Feb. 2, 1999 and Ser. No. 09/241,930 filed Feb. 2, 1999, realizable as a first application specific integrated circuit (ASIC) chip; a programmable digitizing circuit  239 A through  239 E realized as a second ASIC chip; a start-of-facet-sector pulse (SOFSP) generator  236 A through  236 E realizable as a programmable IC chip, for generating SOFSPs relative to home-offset pulses (HOP) generated by a HOP generation circuit  244  on the control board  200 , shown in FIG.  4 A 6 B, and received by the SOFSP generator; an EPROM  237 A through  237 E for storing parameters and information represented in the tables of FIGS. 10B,  10 D,  10 E 1  and  10 E 2 ; and a programmed decode computer  240 A through  240 E realizable as a microprocessor and associated program and data storage memory and system buses, for carrying out symbol decoding operations and recovery of SOFSPs from the digitizer circuit  239 A in a synchronous, real-time manner as will be described in greater detail hereinafter. In the illustrative embodiment, the ASIC chips, the microprocessor, its associated memory and systems buses are all mounted on a single printed circuit (PC) board, using suitable electrical connectors, in a manner well known in the art. 
     The function of the A/D conversion circuit  238 A is to perform a thresholding function on the second-derivative zero-crossing signal in order to convert the electrical analog scan data signal D 1  into a corresponding digital scan data signal D 2  having first and second (i.e. binary) signal levels which correspond to the bars and spaces of the bar code symbol being scanned. In practice, the digital scan data signal D 2  appears as a pulse-width modulated type signal as the first and second signal levels thereof vary in proportion to the width of bars and spaces in the scanned bar code symbol. 
     The function of the programmable digitizing circuit  239 A of the present invention is two-fold: (1) to convert the digital scan data signal D 2 , associated with each scanned bar code symbol, into a corresponding sequence of digital words (i.e. a sequence of digital count values) D 3  representative of package identification (I.D.) data; and (2) to correlate time-based (or position-based) information about the facet sector on the scanning disc that generated the sequence digital count data (corresponding to a scanline or portion thereof) that was used to read the decoded bar code symbol on the package scanned in the scanning tunnel subsystem  100 . Notably, in the digital word sequence D 3 , each digital word represents the time length duration of first or second signal level in the corresponding digital scan data signal D 2 . Preferably, the digital count values are in a suitable digital format for use in carrying out various symbol decoding operations which, like the scanning pattern and volume of the present invention, will be determined primarily by the particular scanning application at hand. Reference is made to U.S. Pat. No. 5,343,027 to Knowles, incorporated herein by reference, as it provides technical details regarding the design and construction of microelectronic digitizing circuits suitable for use in each holographic laser scanning subsystem  101  through  116  in the system of the present invention. 
     In bar code symbol scanning applications, the each programmed decode computer  240 A through  240 E has two primary functions: (1) to receive each digital word sequence D 3  produced from its respective digitizing circuit  239 A through  239 E, and subject it to one or more bar code symbol decoding algorithms in order to determine which bar code symbol is indicated (i.e. represented) by the digital word sequence D 3 , originally derived from corresponding scan data signal D 1  detected by the photodetector associated with the decode computer; and (2A) to generate a specification for the laser scanning beam (or plane-sector) that was used to collect the scan data underlying the decode bar code symbol, or alternatively, (2B) to generate a specification of the holographic scanning facet sector or segment that produced the collected scan data from which each laser-scanned bar code symbol is read. 
     In accordance with general convention, the first function of the programmed decode computer  240 A hereof is to receive each digital word sequence D 3  produced from the digitizing circuit  239 A, and subject it to one or more pattern recognition algorithms (e.g. character recognition algorithms) in order to determine which pattern is indicated by the digital word sequence D 3 . In bar code symbol reading applications, in which scanned code symbols can be any one of a number of symbologies, a bar code symbol decoding algorithm with auto-discrimination capabilities can be used in a manner known in the art. 
     The second function of the programmed decode processor  240 A through  240 E is best described with reference to FIGS. 11D and 11E. In the illustrative embodiment hereof, each programmed decode computer  240 A through  240 E generates a specification for the laser scanning beam (or plane-sector) in terms of the minimum and maximum facet angles delimited by the facet sector involved in the scanning the decoded bar code symbol. Such minimum and maximum facet angles are indicated in the last column of the table shown in FIG.  11 D. Alternatively, each programmed decode computer  240 A through  240 E could generate a specification of the holographic scanning facet sector or segment that produced the collected scan data from which each laser-scanned bar code symbol is read. In such a case, each programmed decode processor would generate for each decoded bar code symbol, the following items of information: the identification number of the laser scanning subsystem that produced the underlying scan data from which the bar code symbol was read; the identification number of the laser scanning station that produced the underlying scan data from which the bar code symbol was read; the facet number of the scanning facet on the scanning disc that produced the underlying scan data from which the bar code symbol was read; and the facet sector number of the scanning facet on the scanning disc that produced the underlying scan data from which the bar code symbol was read. Such information items could be generated using tables similar to those set forth in FIG. 11D, except that instead of reading out minimum and maximum facet angles (as provided in the rightmost column thereof), the facet sector (or segment) number could be read out, and assembled with the other items of information providing the specification of how the laser scanning beam in issue was generated from the holographic laser scanning subsystem. In either case, such information will enable the data management computer system  900  to compute a vector-based geometrical model of the laser scanning beam used to scan the read bar code symbol represented by the coordinated symbol character data. 
     As will be described in greater detail hereinafter, the geometrical model of the laser beam is produced in real-time aboard the data management computer system  900  using “3-D ray-tracing techniques” which trace the laser scanning beam from (1) its point of original on the holographic scanning disc, (2) to its point of reflection off the corresponding beam folding mirror, and (3) towards the focal point of the laser scanning beam determined by the focal length of the scanning facet involved in the production of the laser scanning beam. From the computed vector-based geometrical model of the laser scanning beam, the location of the decoded bar code symbol (i.e. when it was scanned by the laser scanning beam being geometrically modeled) can be specified (i.e. computed) in real-time relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem. 
     As shown in FIG.  4 A 6 B, the control board  200  comprises a number of components mounted on a small PC board, namely: a programmed microprocessor  242  with a system bus and associated program and data storage memory, for controlling the system operation of the holographic laser scanner and performing other auxiliary functions; first, second, third, forth and fifth serial data channels  243 A through  243 E, for receiving serial data input from the programmable decode computers  240 A through  240 E; an input/output (I/O) interface circuit  248  for interfacing with and transmitting symbol character data and other information to the I/O subsystem  800 , and ultimately to the data management computer system  900 ; home pulse detector  245  realizable as the electronic circuit shown in FIG.  4 A 6 C, for detecting the home pulse generated when the laser beam  250  from VLD  253  (in home pulse marking sensing module  251  shown in FIG.  4 A 6 C) is directed through home-pulse gap  260  (between Facets Nos.  6  and  7 ) and sensed by photodetector  253 ; and a home-offset-pulse (HOP) generator  244  realized as an ASIC chip, for generating a set of five home-offset pulses (HOPs) in response to the detection of each home pulse by circuit  245 . In the illustrative embodiment, each serial data channel  243 A through  243 E is realized as an RS232 port, although it is understood that other structures may be used to realize the function performed thereby. The programmed control computer  242  also produces motor control signals, and laser control signals during system operation. These control signals are received as input by a power supply circuit  252  realized on the power supply PC board. Other input signals to the power supply circuit  252  include a 900 Volt, 60 Hz line voltage signal from a standard power distribution circuit. On the basis of the received input signals, the power supply circuit produces as output, (1) laser source enable signals to drive VLDs  253 A through  253 E, respectively, and (2) a motor enable signal in order to drive the scanning disc motor  150  coupled to holographic scanning disc  130 . 
     Corner-located Orthogonal Laser Scanning Subsystem of the Present Invention 
     Each of the holographic scanners (denoted by R/F Corner # 1 , R/F Corner # 2 , R/B Corner # 1 , R/B Corner # 2 , L/F Corner # 1 , L/F Corner # 2 , L/B Corner # 1  and L/B Corner # 2  in FIGS.  4 A 2  and  4 A 3 ) mounted within the corners of the scanner support framework are triple-disc holographic scanning subsystems designed to produce a 3-D scanning volume having three spatially-separated focal zones, best shown in FIG.  4 B 7 . Within each of these focal zones, horizontal and vertically arranged (i.e. orthogonal) scanning planes are projected within the region defined by solid lines in FIG.  4 B 7 , whereas only horizontal scanning planes are projected within the region defined by dotted lines in FIG.  4 B 7 . Within the solid line defined region, ladder and picket-fence oriented bar code symbols are aggressively read, even if located on front-facing or back-facing surfaces, possibly downwardly directed, as in the case of postal tubs and trays used by the United States Postal Service (USPS. Each of these eight triple-disc holographic scanning subsystems (denoted as R/F Corner # 1 , R/F Corner # 2 , R/B Corner # 1 , R/B Corner # 2 , L/F Corner # 1 , L/F Corner # 2 , L/B Corner # 1 , L/B Corner # 2 ) is shown in greater detail in FIGS.  4 B 1  through  4 B 12 . 
     As shown in FIGS.  4 B 1  and  4 B 2 , each triple-disc holographic scanning subsystem has three laser scanning platforms installed within a scanner housing  140 ′. Each laser scanning platform is similar in design to that shown in FIG.  4 A 2 , and produces a 3-D laser scanning volume as shown in FIG.  4 B 5 C. Each 3-D scanning volume contains an orthogonal-type laser scanning pattern having three non-contiguous (i.e. non-over-lapping focal zones) which are formed by six laser scanning stations that are indicated as LS 1 , LS 2 , LS 3 , LS 4 , LS 5  and LS 6  in FIG.  4 B 1 , in a non-equally spaced apart manner specified in FIG.  4 B 1 A, arranged about a twenty-one facet holographic scanning disc  130 ′. When combining a pair of such laser scanning platforms, an Ortho 2 Scanner is produced that is capable of producing a double-sized scanning volume as shown in FIG.  4 B 5 B. When combining three such laser scanning platforms, an Ortho 3 Scanner is produced that is capable of producing a triple-sized scanning volume as shown in FIG.  4 B 5 A. 
     Notably, laser scanning stations LS 1 , LS 2 , LS 4  and LS 5  indicated in FIG.  4 B 1  produce the horizontally (or near horizontally) oriented groups of laser scanning planes within the scanning volume of each orthogonal scanning subsystem  109  through  116 . Laser scanning stations LS 3  and LS 6  indicated in FIG.  4 B 1  produce the vertically (or near vertically) oriented groups of laser scanning planes within the scanning volume of each orthogonal scanning subsystem  109  through  116 . In order to increase the code element scanning resolution along the horizontal scanning direction of each orthogonal scanning subsystem, the laser beam production modules in laser scanning stations LS 1 , LS 2 , LS 4  and LS 5  employ different optics than laser scanning stations LS 3  and LS 5  to produce smaller spot sizes at each of the three focal zones, along the horizontal scanning direction, as evidenced by the spot size plots as a function of distance, shown in FIGS.  4 B 10  and  4 B 11 . The scan pattern and scan speeds for such alternative embodiments of the orthogonal scanning . subsystem of the present invention is shown in the specification table set forth in FIG.  4 B 5 D. 
     In general, each holographic laser scanning platform within these triple-disc scanners  109  through  116  can be designed and constructed using the methods detailed in applicant&#39;s copending application Ser. Nos. 08/949,915 filed Oct. 14, 1997; Ser. No. 08/854,832 filed May 12, 1997; Ser. No. 08/886,806 filed Apr. 22, 1997; Ser. No. 08/726,522 filed Oct. 7, 1996; and Ser. No. 08/573,949 filed Dec. 18, 1995, each incorporated herein by reference. The design parameters for each twenty-one facet holographic scanning disc shown in FIG.  4 B 2 , and the supporting subsystem used therewith, are set forth in the Table of FIGS.  4 B 3 A and  4 B 3 B. The design parameters set forth in the table of FIGS.  4 B 3 A and  4 B 3 B are defined in detail in the above-referenced U.S. Patent Applications. The laser scanning pattern produced by one of the scanning platforms in the subsystem of FIG.  4 B 1  is graphically depicted in FIG.  4 B 8 . The laser scanning pattern produced by all three of the scanning platforms in the subsystem of FIG.  4 B 1  is graphically depicted in FIG.  4 B 9 . The time-lapsed composite scan coverage pattern produced by the holographic scanning subsystem of FIG.  4 B 1 , over the length of its scanning volume, is graphically depicted in FIG.  4 B 12 . 
     As shown in the system diagram of FIGS.  4 B 4 A through  4 B 4 C, each holographic laser scanning unit of the present invention  108  through  116  (denoted as R/F Corner # 1 , R/F Corner # 2 , R/B Corner # 1 , R/B Corner # 2 , L/F Corner # 1 , L/F Corner # 2 , L/B Corner # 1 , L/B Corner # 2  in FIGS. 1 through 1C) comprises a number of system components, many of which are realized on a control board  200 ′, a plurality (e.g. six) analog signal processing boards  201 A′ through  201 E′, and six digital signal processing boards  202 A′ through  202 E′. 
     As described in WIPO Patent Application Publication No. WO 98/22945, each holographic laser scanning unit  109  through  116  employed herein cyclically generates from its compact scanner housing  140 ′ shown in FIG.  4 B 1 , a complex three-dimensional laser scanning pattern within a well defined 3-D scanning volume which will be described in greater detail hereinbelow. In the system of the first illustrative embodiment, each such laser scanning pattern is generated by a rotating holographic scanning disc  130 ′, about which are mounted six (5) independent laser scanning stations. In FIG.  4 B 1 , these laser scanning stations are indicated by LS 1 , LS 2 , LS 3 , LS 4 , LS 5  and LS 6 . 
     In general, the design and construction of the laser scanning subsystem of FIG.  4 B 1  is similar to that shown in FIGS.  4 A 1  and  4 A 2 , except that the number of scanning stations employed is six rather than five, the angular spacing thereof is not even between each scanning station, as shown in FIG.  4 B 1 A, and the holographic scanning disc of FIG.  4 B 2  has twenty-one scanning facets with different optical characteristics, as revealed in the disc design table set forth in FIGS.  4 B 3 A and  4 B 3 B. 
     As shown in FIGS.  4 B 1  and  4 B 4 A, the six digital scan data signal processing boards  202 A′ through  202 F′, are arranged in such a manner to receive and provide for processing the analog scan data signals produced from analog scan data signal processing boards  201 A through  201 F, respectively. As shown in FIGS.  4 B 1 , each digital scan data signal processing board is mounted vertically behind its respective beam folding mirror. A control board (i.e. motherboard)  200 ′ is also mounted upon the base plate  143 ′ for processing signals produced from the digital scan data signal processing boards. A conventional power supply board  155 ′ is also mounted upon the base plate  143 ′, within one of its extreme corners. The function of the digital scan data signal processing boards, the central processing board, and the power supply board will be described in greater detail in connection with the functional system diagram of FIGS.  4 B 4 A through  4 B 4 C. As shown, electrical cables are used to conduct electrical signals from each analog scan data signal processing board to its associated digital scan data signal processing board, and from each digital scan data signal processing board to the central processing board. Regulated power supply voltages are provided to the central signal processing board  200 ′ by way of an electrical harness (not shown), for distribution to the various electrical and electro-optical devices requiring electrical power within the holographic laser scanner. In a conventional manner, electrical power from a standard 120 Volt, 60 HZ, power supply is provided to the power supply board by way of flexible electrical wiring (not shown). Symbol character data produced from the central processing board  200 ′ is transmitted to the I/O subsystem  800 , over a serial data transmission cable connected to a serial output (i.e. standard RS232) communications jack installed through a wall in the scanner housing  140 ′. 
     Many of the system components comprising each of the holographic laser scanning units  109  through  116  are realized on control board  200 ′, the plurality (e.g. six) analog signal processing boards  201 A through  201 E, and the six digital signal processing boards  202 A′ through  202 F. 
     In the illustrative embodiment shown in FIG.  4 B 4 A, each analog scan data signal processing board  201 A′ through  201 F′ has the following components mounted thereon: and photodetector  152 A′ (through  152 F′) (e.g. a silicon photocell) for detection of analog scan data signals as described hereinabove; and analog signal processing circuit  235 A′ (through  235 F) for processing detected analog scan data signals. 
     In the illustrative embodiment, each photodetector  152 A′ through  152 F′ is realized as an opto-electronic device and each analog signal processing circuit  235 A′ aboard the analog signal processing board ( 201 A′ through  201 F′) is realized as an Application Specific Integrated Circuit (ASIC) chip. These chips are suitably mounted onto a small printed circuit (PC) board, along with electrical connectors which allow for interfacing with other boards within the scanner housing. With all of its components mounted thereon, each PC board is suitably fastened to the photodetector support frame  153 ′, along its respective central reference frame. 
     In a conventional manner, the optical scan data signal Do focused onto the photodetector  152 A′ during laser scanning operations is produced by light rays of a particular polarization state (e.g. S polarization state) associated with a diffracted laser beam being scanned across a light reflective surface (e.g. the bars and spaces of a bar code symbol) and scattering thereoff. Typically, the polarization state distribution of the scattered light rays is altered when the scanned surface exhibits diffuse reflective characteristics. Thereafter, a portion of the scattered light rays are reflected along the same outgoing light ray paths toward the holographic facet which produced the scanned laser beam. These reflected light rays are collected by the scanning facet and ultimately focused onto the photodetector of the associated light detection subsystem by its parabolic light reflecting mirror  149 A′ disposed beneath the scanning disc  130 ′. The function of each photodetector  152 A′ is to detect variations in the amplitude (i.e. intensity) of optical scan data signal D 0 , and to produce in response thereto an electrical analog scan data signal D 1  which corresponds to such intensity variations. When a photodetector with suitable light sensitivity characteristics is used, the amplitude variations of electrical analog scan data signal D 1  will linearly correspond to the light reflection characteristics of the scanned surface (e.g. the scanned bar code symbol). The function of the analog signal processing circuitry is to band-pass filter and preamplify the electrical analog scan data signal D 1 , in order to improve the SNR of the output signal. 
     In the illustrative embodiment of FIG.  4 B 1 , each digital scan data signal processing board  202 A′ through  202 F′ is constructed in substantially the same manner. On each of these signal processing boards, the following devices are provided: an analog-to-digital (A/D) conversion circuit  238 A′ through  238 F′ as taught in copending U.S. application Nos. 09/243,078 filed Feb. 2, 1999 and Ser. No. 09/241,930 filed Feb. 2, 1999, realizable as a first application specific integrated circuit (ASIC) chip; a programmable digitizing circuit  239 A′ through  239 F′ realized as a second ASIC chip; a start-of-facet-sector pulse (SOFSP) generator  236 A′ through  236 F′ realizable as a programmable IC chip, for generating SOFSPs relative to home-offset pulses (HOP) generated by a HOP generation circuit  244 ′ on the control board  200 ′, shown in FIG.  4 B 4 B, and received by the SOFSP generator; an EPROM  237 A′ through  237 F′ for storing parameters and information represented in the tables of FIGS. 10B,  10 D,  10 E 1  and  10 E 2 ; and a programmed decode computer  240 A′ through  240 F′ realizable as a microprocessor and associated program and data storage memory and system buses, for carrying out symbol decoding operations and recovery of SOFSPs from the digitizer circuit  239 A′ in a synchronous, real-time manner as will be described in greater detail hereinafter. In the illustrative embodiment, the ASIC chips, the microprocessor, its associated memory and systems buses are all mounted on a single printed circuit (PC) board, using suitable electrical connectors, in a manner well known in the art. 
     The function of the A/D conversion circuit  238 A′ is to perform a thresholding function on the second-derivative zero-crossing signal in order to convert the electrical analog scan data signal D 1  into a corresponding digital scan data signal D 2  having first and second (i.e. binary) signal levels which correspond to the bars and spaces of the bar code symbol being scanned. In practice, the digital scan data signal D 2  appears as a pulse-width modulated type signal as the first and second signal levels thereof vary in proportion to the width of bars and spaces in the scanned bar code symbol. 
     The function of the programmable digitizing circuit  239 A′ of the present invention is two-fold: (1) to convert the digital scan data signal D 2 , associated with each scanned bar code symbol, into a corresponding sequence of digital words (i.e. a sequence of digital count values) D 3  representative of package identification (I.D.) data; and (2) to correlate time-based (or position-based) information about the facet sector on the scanning disc that generated the sequence digital count data (corresponding to a scanline or portion thereof) that was used to read the decoded bar code symbol on the package scanned in the scanning tunnel subsystem  100 . Notably, in the digital word sequence D 3 , each digital word represents the time length duration of first or second signal level in the corresponding digital scan data signal D 2 . Preferably, the digital count values are in a suitable digital format for use in carrying out various symbol decoding operations which, like the scanning pattern and volume of the present invention, will be determined primarily by the particular scanning application at hand. Reference is made to U.S. Pat. No. 5,343,027 to Knowles, incorporated herein by reference, as it provides technical details regarding the design and construction of microelectronic digitizing circuits suitable for use in each orthogonal laser scanning subsystem  109  through  116  in the system of the present invention. 
     In bar code symbol scanning applications, the each programmed decode computer  240 A′ through  240 F′ has two primary functions: (1) to receive each digital word sequence D 3  produced from its respective digitizing circuit  239 A′ through  239 F′, and subject it to one or more bar code symbol decoding algorithms in order to determine which bar code symbol is indicated (i.e. represented) by the digital word sequence D 3 , originally derived from corresponding scan data signal D 1  detected by the photodetector associated with the decode computer; and (2A) to generate a specification for the laser scanning beam (or plane-sector) that was used to collect the scan data underlying the decode bar code symbol, or alternatively, (2B) to generate a specification of the holographic scanning facet sector or segment that produced the collected scan data from which each laser-scanned bar code symbol is read. 
     In accordance with general convention, the first function of the programmed decode computer  240 A′ hereof is to receive each digital word sequence D 3  produced from the digitizing circuit  239 A′, and subject it to one or more pattern recognition algorithms (e.g. character recognition algorithms) i n order to determine which pattern is indicated by the digital word sequence D 3 . In bar code symbol reading applications, in which scanned code symbols can be any one of a number of symbologies, a bar code symbol decoding algorithm with auto-discrimination capabilities can be used in a manner known in the art. 
     The second function of the programmed decode processor  240 A′ through  240 F′ is best described with reference to FIGS. 11D and 11E. In the illustrative embodiment hereof, each programmed decode computer  240 A through  240 E generates a specification for the laser scanning beam (or plane-sector) in terms of the minimum and maximum facet angles delimited by the facet sector involved in the scanning of the decoded bar code symbol. Such minimum and maximum facet angles are indicated in the last column of the table shown in FIG.  11 D. Alternatively, each programmed decode computer  240 A′ through  240 F′ could generate a specification of the holographic scanning facet sector or segment that produced the collected scan data from which each laser-scanned bar code symbol is read. In such a case, each programmed decode processor would generate for each decoded bar code symbol, the following items of information: the identification number of the laser scanning subsystem that produced the underlying scan data from which the bar code symbol was read; the identification number of the laser scanning station that produced the underlying scan data from which the bar code symbol was read; the facet number of the scanning facet on the scanning disc that produced the underlying scan data from which the bar code symbol was read; and the facet sector number of the scanning facet on the scanning disc that produced the underlying scan data from which the bar code symbol was read. Such information items could be generated using tables similar to those set forth in FIG. 11D, except that instead of reading out minimum and maximum facet angles (as provided in the rightmost column thereof), the facet sector (or segment) number could be read out, and assembled with the other items of information providing the specification of how the laser scanning beam in issue was generated from the holographic laser scanning subsystem. In either case, such information will enable the data management computer system  900  to compute a vector-based geometrical model of the laser scanning beam used to scan the read bar code symbol represented by the coordinated symbol character data. 
     As will be described in greater detail hereinafter, the geometrical model of the laser beam is produced in real-time aboard the data management computer system  900  using “3-D ray-tracing techniques” which trace the laser scanning beam from (1) its point of original on the holographic scanning disc, (2) to its point of reflection off the corresponding beam folding mirror, and (3) towards the focal point of the laser scanning beam determined by the focal length of the scanning facet involved in the production of the laser scanning beam. From the computed vector-based geometrical model of the laser scanning beam, the location of the decoded bar code symbol (i.e. when it was scanned by the laser scanning beam being geometrically modeled) can be specified (i.e. computed) in real-time relative to a local coordinate reference system symbolically embedded within the laser scanning subsystem. 
     As shown in FIG.  4 B 4 B, the control board  200 ′ comprises a number of components mounted on a small PC board, namely: a programmed microprocessor  242 ′ with a system bus and associated program and data storage memory, for controlling the system operation of the holographic laser scanner and performing other auxiliary functions; first, second, third, forth and fifth serial data channels  243 A′ through  243 F′, for receiving serial data input from the programmable decode computers  240 A′ through  240 F′; an input/output (I/O) interface circuit  248 ′ for interfacing with and transmitting symbol character data and other information to the I/O subsystem  800 , and ultimately to the data management computer system  900 ; home pulse detector  245 ′ realizable as the electronic circuit shown in FIG.  4 B 4 C, for detecting the home pulse generated when the laser beam  250 ′ from VLD  253 ′ (in home pulse marking sensing module  251 ′ shown in FIG.  4 B 4 C) is directed through home-pulse gap  260 ′ (between Facets Nos.  4  and  8 ) and sensed by photodetector  253 ′; and a home-offset-pulse (HOP) generator  244 ′ realized as an ASIC chip, for generating a set of five home-offset pulses (HOPs) in response to the detection of each home pulse by circuit  245 ′. In the illustrative embodiment, each serial data channel  243 A′ through  243 F′ is realized as an RS232 port, although it is understood that other structures may be used to realize the function performed thereby. The programmed control computer  242 ′ also produces motor control signals, and laser control signals during system operation. These control signals are received as input by a power supply circuit  252 ′ realized on the power supply PC board. Other input signals to the power supply circuit  252 ′ include a 900 Volt, 60 Hz line voltage signal from a standard power distribution circuit. On the basis of the received input signals, the power supply circuit produces as output, (1) laser source enable signals to drive VLDs  253 A′ through  253 F′, respectively, and (2) a motor enable signal in order to drive the scanning disc motor  150  coupled to holographic scanning disc  130 ′. 
     As shown in FIG.  4 B 13 , when using four orthogonal scanning subsystems of the type shown in FIG.  4 B 1 , alone or in combination with other laser or CCD scanning subsystems (e.g. as shown in FIG.  4 A 1 ), the orthogonal scanning zones produced by each scanning subsystem spatially and orthogonally overlap above and across the width of the conveyor belt, at four regions indicated by OZ 1 , OZ 2 ,  0 Z 3  and  0 Z 4  in FIG.  4 B 13 . Thus, when bar code symbols arranged in either a ladder or picket-fence orientation on the front or rear surface of a package moving along the conveyor belt, and to some degree bar code symbols located on the side surfaces of such packages, will be aggressively scanned by both the horizontally and vertically (i.e. orthogonally) oriented laser scanning planes (or lines) produced at the orthogonal regions of the three focal zones of at least one corner-mounted orthogonal scanning subsystem. Even when bar code symbols are located on the front or back surfaces of package surfaces facing downwardly towards to the conveyor surface, the orthogonal scanning regions of the resulting orthogonal scanning volume will aggressively read the code symbol in a highly reliable manner. 
     As shown in FIG.  4 B 14 , when using eight orthogonal scanning subsystems of the type shown in FIG.  4 B 1 , alone or in combination with other laser or CCD scanning subsystems (e.g. as shown in FIG.  4 A 1 ), the orthogonal scanning zones produced by each scanning subsystem spatially and orthogonally overlap above and across the width of the conveyor belt, at many regions to complex to graphically identify by reference numbers in FIG.  4 B 13 . Thus, when bar code symbols arranged in either a ladder or picket-fence orientation on the front or rear surface of a package moving along the conveyor belt, and to some degree bar code symbols located on the side surfaces of such packages, will be very aggressively scanned by both the horizontally and vertically (i.e. orthogonally) oriented laser scanning planes (or lines) produced at the orthogonal regions of the three focal zones of at least one corner-mounted orthogonal scanning subsystem. Even when bar code symbols are located on the front or back surfaces of package surfaces facing downwardly towards to the conveyor surface, the orthogonal scanning regions of the resulting orthogonal scanning volume will aggressively read the code symbol in a highly reliable manner. 
     The time-lapsed scan coverage pattern shown in FIG.  4 B 12  graphically indicates how many laser scanning lines are projected across the front or rear surface of a package as it moves through an orthogonal scanning system, as shown in either FIG.  4 B 13  or FIG.  4 B 14 . 
     Polygonal-Based Bottom Scanning Subsystem of the Present Invention 
     The bottom-mounted fixed projection scanner (denoted as Bottom) employed in the tunnel scanning system hereof is shown in greater detail in FIGS.  4 C 1  through  4 C 7 . As shown in FIG.  4 C 1 , the bottom-mounted scanner comprises eight fixed-projection laser scanning subsystems  118 , shown in FIG.  4 C 2 , that are mounted along optical bench  119  shown in FIG.  4 C 1 . Each fixed projection scanning subsystem  118  comprises: four stationary mirrors  120 A through  120 D arranged about a central reference plane passing along the longitudinal extent of the optical bench  121  of the subsystem; and eight-sided motor driven polygon scanning element  122  mounted closely to the nested array of mirrors  120 A through  120 D; a light collecting mirror  123  mounted above the nested array along the central reference plane; a laser diode  124  for producing a laser beam which is passed through collecting mirror  123  and strikes the polygon scanning element  122 ; and a photodetector  125 , mounted above the polygon scanning element  122 , for detecting reflected laser light and produce scan data signals indicative of the detected laser light intensity for subsequent signal processing in a manner known in the bar code reading art. 
     As shown in FIG.  4 C 1 , each subsystem  118  is mounted on optical bench  119 , and a housing  126  with light transmission aperture  127 , is mounted to the optical bench  119  in a conventional manner. As shown, a protective, scratch-resistant scanning window pane  128  is mounted over the light transmission aperture  127  to close off the interior of the housing from dust, dirt and other forms of debris. When the bottom scanning unit  117  is assembled, it is then mounted to a pair of support brackets  129  which in turn are mounted to a base support bracket  130  connected to the scanning tunnel framework  304 A, clearly shown in FIG.  1 C. As shown in FIG.  4 C 2 , the scanning unit  117  is mounted relative to the conveyor belt sections  302 A and  302 B so that the scanning window  128  on the bottom scanning unit  117  is disposed at about 28° to the protective conveyor window  306 , disposed over the gap region  305  (e.g. about 5.0 inches wide) formed between the conveyor belt sections  302 A and  302 B. As shown in FIG.  4 C 2 , the bottom scanning unit  117  is mounted about 12.5 inches below the conveyor scanning window  306 . Also, the symbol character data outputs from subsystems  118  are supplied to a digital data multiplexer  130  which transmits the symbol character data to the I/O subsystem  800 , shown in FIG.  3 . 
     The partial scan patterns produced by individual stationary mirrors  120 B,  102 C and  120 A, 120 D, respectively, in each subsystem  118  are shown in FIGS.  4 C 4  and  4 C 5 , respectively. The complete pattern generated by each subsystem  118  is shown in FIG.  4 C 6 . The composite omni-directional scanning pattern generated by the eight subsystems  118  working together in the bottom scanner unit is shown in FIG.  4 C 7 . 
     First Method of Determining Laser Beam Position in Laser Scanning Subsystems Hereof Under Constant Scanning Motor Speed Conditions 
     In FIGS. 10 through 11E, a first method is shown for (i) determining the position of the laser scanning beam produced by either the laser scanning subsystems shown in FIG.  4 A 1  and/or  4 A 2  when scanning motor speed is constant, and (ii) synchronously encoding facet section information with digital count data generated by the digitizer circuit on each decode board of such subsystems. In general, this method involves optically encoding the “home pulse mark/gap” along the edge of the holographic scanning disc, and upon detecting the same, generating home offset pulses (HOPs) which are used to automatically generate the start of each facet pulse (SOFPs), and the SOFPs in turn are used to automatically generate the start-of-facet-sector pulses (SOFSPs) aboard each decode board. The details of this process will be described hereinbelow. 
     Referring now to FIGS. 10 through 11E, it is noted that each home offset pulse produced from HOP generating circuit  244  is provided to the SOFSP generator  236 A through  236 F on the decode processing board. When the HOP pulse is received at the SOFSP generator  236 A through  236 F on a particular decode processing board, the home pulse gap on the scanning disc  130  is starting to pass through the laser beam directed therethrough at the scanning station associated with the decode signal processing board. As shown in FIGS. 10 through 11E, timing information stored in the tables shown in these figures is used by the SOFSP generator  236 A to generate a set of SOFSPs in response to the received HOP pulse during each revolution of the scanning disc. This enables a digital number count (referenced from the HOP) to be generated and correlated along with the digital data counts produced within the digitizer circuit  239 A in a synchronous manner. As shown in FIG. 10A, each SOFSP generator  236 A through  236 B comprises: a clock  260  for producing clock pulses (e.g. having a pulse duration of about 4 microseconds); a SOFP generation module  261  for generating SOFPs using the table of FIG. 10B in accordance with the process depicted in FIG. 10C; a SOFSP generation module  262  for generating SOFSPs using the table of FIG.  10 D and production rules set forth in FIGS.  10 E 1  and  10 E 2 , in accordance with the process depicted in FIG. 10F; and a control module  263  for controlling the SOFP generator  261  and the SOFSP generator  262 , and resetting the clock  260  upon each detection of a new HOP from the HOP generator on the control board  200  associated with the holographic scanning unit. 
     As shown in FIGS.  11 A 1  and  11 A 2 , the digitizer circuit  239 A of the present invention comprises a number of subcomponents. In particular, a scan data input circuit  322  is provided for receiving digital scan data signal D 2 . A clock input  132  is provided from an external fixed frequency source  313 , e.g. a 40 MHz crystal, or another external clock  15  to produce a pulse train. The output of the clock input circuit  312  is provided to the clock divider circuitry  314 . That circuit  314  includes dividers for successively dividing the frequency of the clock pulses by a factor of two to produce a plurality of clock frequencies, as will be described in detail later. This plurality of clock signals is provided to a clock multiplexer  136 . As shown in FIGS.  11 A 1  and  11 A 2 , the 40 MHz clock input signal is also provided directly to the clock multiplexer  316 . The clock multiplexer  136  selects the desired output frequencies for the device based upon control signals received from clock control circuitry in the programmable processor  240 A and in associated circuitry. The output of the clock multiplexer  316  comprises an S clock signal which provides the basic timing for the digitizer circuit  239 A, as well as the input to digital counters. The processing of the input (bar code) scan data D 2  is provided from signal processor  238 A. The scanner input circuit  322  provides output signals which represent the detected bar code signal to be processed and are provided to the transition and sign detecting circuit  324 . That circuit detects the transition from a bar to a space or from a space to a bar from the input signals provided thereto, and also determines whether the symbol occurring before the transition is a bar or a space. Thus, the transition and sign detector  324  provides a signal bearing the “sign: information (referred to as the “SIGN” signal) which is provided to multiplexer  342 , and thus a primary first-in, first-out (FIFO) memory which serves as the input of programmable processor  240 A. The transition and sign circuit  324  also provides a signal to the sequencing means  328  to commence operation of the sequencing circuit  328 . The sequencing circuit  328  sequences the digitizer circuit through a predetermined number of steps which begin at the occurrence of each symbol transition and which will be described in detail later. Sequencing circuit  328  provides a FIFO write signal to the FIFO input of primary FIFO  340  and the auxiliary FIFO  341 , at the proper time to enable it to accept data thereinto. The sequencing circuit  328  provides input signals to digitizing counting circuit  330  so that the starting and stopping of the counters, occurring with the detection of each transition, is properly sequenced. The counting circuit  330  also receives an input signal from the clock multiplexer  316  (S Clock). This signal runs the counters at the selected rate when they are enabled by the sequencing means  328 . The clock multiplexer  316 , the sequencer circuit  328  and the counting circuit  330  each supply signals to the interface circuit  333  which enables it to properly pass the digitized count data to the primary and auxiliary FIFOs  340  and  341 , via multiplexer  342 , as shown in FIGS.  11 A 1 ,  11 A 2  and  11 B. The clock multiplexer  316  is arranged to provide two banks of available frequencies for the device to use, namely, an upper and a lower bank. The selection of frequencies from the upper bank or the lower bank is determined by a frequency bank switching circuit  362 . The frequency bank switching circuit  362  also provides an input to an array reset  38  which provides a signal to reset the clock divider  314  on command. The clock divider circuitry  314  also generates a TEST reset signal by inverting the array reset signal. The TEST reset signal resets the remainder of the circuit  239 A. The command which initiates this reset condition is normally generated by a testing device (not shown) connected to device  239 A and used to test it upon its fabrication. 
     As shown in FIGS.  11 A 1 ,  11 A 2  and  11 B, digital count data or a string of zeros (representative of correlated SOFP data or count values from the HOP) are written into the primary FIFO using multiplexer  342  and write enable signals generated by the sequencing circuit  238 . The SOFP marker (i.e. string of zeros) is written over the data in the primary FIFO  340  whenever the SOFP count data is presented to the digitizer circuit. Also, digital count data or a string of zeros (representative of correlated SOFSP data or SFS count values from the HOP) are written into the auxiliary FIFO  341  using multiplexer  342  and write enable signals generated by the sequencing circuit  238 . The SOFSP marker (i.e. string of zeros) is written over the data in the auxiliary FIFO  341  whenever the SOFP count data is presented to the digitizer circuit. With such a data encoding scheme, the decoder  240 A is allowed to decode process the scan count data i n the FIFOs, as well as determine which facet sector produced the laser scanning beam. The later function is carried out using the tables set forth in FIGS.  11 C 1  through  11 D and the method described in the flow chart of FIG.  11 E. As shown in FIG. 11B, the output of the  240 A is a scan beam data element comprising the package ID data, the scanner number (SN), the laser scanning station number (SSN), facet number (FN) and minimum and maximum facet angles subtending the facet sector involved in generating the laser beam used to read the decoded bar code symbol representative of the package ID data. Additional details concerning the design and construction of digitizer circuit ( 239 A) can be found in Applicant&#39;s U.S. Pat. No. 5,343,027 incorporated herein by reference in its entirety. 
     Second Method of Determining Laser Beam Position in Holographic Laser Scanners Under Constant Scanning Motor Speed Conditions 
     In FIGS. 12A through 13D, an alternative method is shown for (i) determining the position of the laser scanning beam produced by either the laser scanning subsystems shown in FIG.  4 A 1  and/or  4 A 2  when scanning motor speed is constant, and (ii) synchronously encoding facet section information with digital count data generated by the digitizer circuit on each decode board of such subsystems. This method involves optically encoding the start of each facet sector (SFS) mark along the outer edge of the holographic scanning disc  130 , as shown in FIG.  12 A. This optical encoding process can be carried out when mastering the scanning disc using a masking pattern during laser exposure. The home pulse gap sensing module described above can be used to detect the home pulse gap as well as the SFS marks along the edge of the scanning disc. As shown, the home gap or functionally equivalent mark of a predetermined opacity generates a home pulse, whereas the SFS marks generate a series of SOFSPs during each revolution of the scanning disc. The home pulse is detected on the home pulse detection circuit on the control board and is used to generate HOPs as in the case described above. The HOPs are transmitted to each decode board where they are used reference (i.e. count) how many SOFSPs have been counted since the received HOP, and thus determine which facet sector the laser beam is passing through as the scanning disc rotates. Digital counts representative of each SOFSP are synchronously generated by the SOFSP generator aboard each decode board and are loaded into the auxiliary FIFO  341 , while correlated digital count scan data is loaded into both the primary and auxiliary FIFOs in a manner similar to that described above. The decode processor can use the information in tables  13 C 1  and  13 C 2  to determine which SOFSP counts correspond to which minimum and maximum facet angles in accordance with the decode processing method of the present invention described in FIG.  13 D. The advantage of this method is that it is expected to be less sensitive to variations in angular velocity of the scanning disc. 
     Referring now to FIG. 3, the individual scanning subsystems within the system of the first illustrative embodiment are shown interfaced with the data management computer system  900  by way of I/O port subsystem  800  well known in the art. As shown, the data management computer system  900  has a graphical user interface (GUI)  901  supported by a display terminal, an icon-pointing device (i.e. a mouse device), keyboard, printer, and the like. The GUI enables programming of the system, as well as the carrying out of other management and maintenance functions associated with proper operation with the system. Preferably, the data management computer system  900  also includes a network interface card for interfacing with a high-speed Ethernet information network that supports a network protocol such as TCP/IP well known in the art. 
     The above-described methods for determining the position of laser scanning beams in holographic laser scanning systems involve recovering laser position information using a “home-pulse” mark on the holographic disc rotated a constant angular velocity. However, it has been discovered that such techniques work satisfactorily only when the angular velocity of the scanning disc is maintained very close to the designed nominal angular velocity during start-up and steady-state operation. In many applications, it is difficult o r otherwise unfeasible to maintain the angular velocity of the scanning disc constant such modes of operation, even when using speed locking/control techniques known in the electrical motor arts. Thus in many applications there will be a need for a laser beam position determination system and method that works for any scanning disc motor speed as well as under small accelerations (and decelerations) of the scanning disc motor, hereinafter referred to as varying scanning motor speed conditions. 
     Laser Position Determination in Holographic Laser Scanners Under Varying Scanning Motor Speed Conditions 
     In FIGS. 14A through 14D, a novel system and method is illustrated for (i) accurately determining the position of the laser scanning beam produced by either the laser scanning subsystems shown in FIG.  4 A 1  and/or  4 A 2  independent of whether or not the scanning motor speed can be maintained constant, and (ii) synchronously encoding facet section information with digital count data generated by the digitizer circuit on each decode board of such subsystems. In this embodiment of the present invention, a holographic scanning disc having a home pulse mark or gap  260  ( 260 ) as described hereinabove can be used to generate the required laser scanning pattern. Also, as shown in FIG.  4 B 1 , each holographic scanning disc is provided with a home pulse sensing module  251  ( 251 ′) and home pulse detection circuit  245  ( 245 ′) as described in detail hereinabove. For purposes of illustration, this subsystem and method will be described below with reference to the laser scanning subsystem of FIG.  4 A 1 , although the same remarks apply equally to the holographic scanning subsystem of FIG.  4 B 1 , as well as the polygonal scanning subsystem of FIG.  4 C 1 . 
     As illustrated in FIG. 14A, each time the home pulse mark or gap on the scanning disc  130  passes the home pulse sensing module  251 , a home pulse (HP) is automatically generated from the home pulse detection circuit  245 . Each time a home pulse is generated from the home pulse detection circuit  245 , a set of home offset pulses (HOPs) is sequentially produced from HOP generation circuit  244 ′ in accordance with the process depicted in FIG.  14 C. The number of HOPs produced in response to each detected HP is equal to the number of laser scanning stations (i.e. scanning modules), N, arranged about the laser scanning disc. Each generated HOP is provided to the SOFSP generator ( 236 A′ through  236 F′) on the decode processing board ( 202 A′ through  202 F′) associated with the HOP. When the HOP pulse is received at the SOFSP generator on its respective decode signal processing board, the home pulse mark or gap on the scanning disc  130  is then starting to pass through the laser beam directed therethrough at the laser scanning station associated with the decode signal processing board. During each revolution of the scanning disc, the SOFSP generation module  261 ′ within each SOFSP generation circuit  236 A′ through  236 F′ generates a set of start of facet pulses (SOFPs) relative to the HOP, and also a set of start of facet sector pulses (SOFSPs) relative to each SOFSP. This enables a SOFP and a SOFSP (referenced from the HOP) to be generated by each SOFSP generation circuit  236 A′ through  236 F′ and provided to the digitizer circuit  239 A through  239 F so that the SOFP and SOFSP data can be correlated with the digital data counts produced within the digitizer circuits in a synchronous manner. Within the decode processor, SOFP and SOFSP data can be translated into laser beam position data expressed in terms of the minimum and maximum angles that delimit the facet sector producing the scan data from which the bar code symbol was decoded. 
     In the illustrative embodiment, the HOP generation circuit  244 ′ is implemented using an 87C51 microcontroller. The microcontroller uses two inputs: the home-pulse detected signal from the home pulse detection signal  245 ″ connected to an interrupt pin of the 87C51; and a “motor-stable” signal from the scanning motor controller. The microcontroller has as many outputs as there are laser scanning stations (i.e. scanning modules) in each laser scanning subsystem. Each output pin is dedicated to sending HOPs to a particular laser scanning station within the subsystem. 
     In general, each SOFSP generation circuit is realized as a programmed microprocessor. However, for purposes of understanding the SOFSP generation circuit, it will be helpful to schematically represent it as comprising a number of subcomponents, as shown in FIG.  14 B. As shown therein, each SOFSP generator  236 A″ through  236 B″ comprises: a clock  260 ″ for producing clock pulses (e.g. having a pulse duration of about 4 microseconds); a SOFP generation module  261 ″ for generating SOFPs in accordance with the process depicted in FIG. 14D; a SOFSP generation module  262 ″ for generating SOFSPs in accordance with the process depicted in FIG. 14D; and a control module  263 ″ for controlling the SOFP generator  261 ″ and the SOFSP generator  262 ″, and resetting the clock  260 ″ upon each detection of a new HOP from the HOP generator  244 ″ on the control board  200 ″ associated with the holographic scanning unit. 
     In the illustrative embodiment, the SOFP/SOFSP generation circuit  236 A″ (through  236 F″) has been implemented using an programmed 87C52 microcontroller mounted on each decoding board associated with a particular scanning station. The HOP for the corresponding scanning station is received on an interrupt pin of the microcontroller. The microcontroller outputs three signals to the decode processor  240 A (through  240 F): (i) SOFPs; (ii) SOFSPs; and (iii) a signal processor adjustment signal which constitutes a level high (or low) when the facet that passes the scanning station&#39;s laser is a facet on a near (or far) focal plane. 
     The operation of the HOP generation circuit  244 ″ and the SOFSP generation circuit  236 A″ (through  236 F′) will now be described within reference to the flow charts set forth in FIGS. 14C and 14D. In these flow charts described below, the following list of symbols are used: 
     t i =timer value at start of home-pulse for the i th  rotation of the disc; 
     T i =time-period of the (i−l) th  rotation of the disc; 
     x Hj =angular value of the position of the laser of the j th  scanning station (i.e. scanning module) of the system, relative to the previous scanning station (home-pulse laser for scanning station 1); 
     x Fj =angular width of the j th  facet of the disc; 
     x Fjm =angular width of the m th  sector (i.e. segment) of the j th  facet of the disc; 
     t i   Hj =time elapsed between the j th  HOP and the (j−l) th  HOP of the i th  rotation of the disc; 
     t i   Fj =time elapsed between the Start of Facet Pulse (SOFP) of facet j and facet j−l of the i th  rotation of the disc; 
     t i   Fjm =time elapsed between the Start of Facet Segment Pulse (SOFSP) of sector m and sector m−l of facet j of the i th  rotation of the disc; 
     t i   n .=time at which the n th  HOP/SOFP of the i th  rotation of the disc is outputted; and 
     t i   pn =time at which the p th  SOFSP of the n th  facet of the i th  rotation of the disc is outputted. 
     Each time the “start of home-pulse mark” is detected, the home-pulse pickup circuit  251  described hereinabove automatically produces a negative going output pulse which is provided to the HOP generation circuit  244 ″, as shown in FIG.  14 A. The HOP generation circuit  244 ′ uses this negative going output pulse to calculate the times at which the home-pulse mark reaches the different modules (i.e. laser scanning stations) and, in response to such calculated times, to automatically generate and provided HOPs to the SOFSP generation circuit  236 A′ (through  236 F′). The calculation is based on the important assumption that the motor speed for the i th  rotation is very close to the motor speed for the (i−l) th  rotation. 
     As indicated at Block A in FIG. 14C, the process within the SOFSP generation circuit  236 A″ defines N as the number of laser scanning stations (i.e. scanning modules) in the holographic scanner, and x Hj  as the angular offset (i.e. position) of a laser scanning station from the home-pulse sensing module (i.e. pickup)  251 . At Block B in FIG. 14C, the process involves initializing the time period or setting T 0 =0. Then at Block C, the HOP generation circuit determines whether a home pulse (HP) has been detected at its input port. Until an HP is detected, the circuit remains at this control block. When an HP is detected, then at Block D the circuit starts the timer therewithin (i.e. t=t 0 ). Then at Block E, the circuit determines whether another HP has been detected. As shown, the circuit remains at this control block until the next HP is detected. When the HP is detected, then at Block F the circuit samples the timer. The time-period of rotation of the scanning disc is calculated from two consecutive home-pulse detections as follows: 
     T i =t i −t i−l , where T i  is the time-period for the i th  rotation of the disc. Then at Block G, the circuit determines whether the time-period for the i th  rotation is “close” to that for the (i−l) th  rotation. 
     As indicated at Block G, a measure of “closeness” is defined as: |T i −T i−l |&lt;45 uS. If the time measure is not close, i.e. |T i −T i−l |&gt;45 uS, then if the time-period of rotation for the i th  and (i−l) th  rotation does not satisfy, |T i −T i−l |&lt;45 uS, the circuit checks at Block H to determine whether the scanning disc has rotated at least a 100 times (experimental value). If the scanning disc has not rotated at least a 100 times, then the circuit proceeds to Block E and waits for the next home-pulse and carries out the control process over again. Since it is critical to the performance of the scanner that every scan be associated with laser position information, the time-period has to be accurately predicted when for some reason the time-period between two consecutive rotations of the disc differs by more than 45 uS (experimental value). The assumption here is that the scanning motor speed cannot change suddenly between two rotations. 
     If the scanning disc has rotated at least a 100 times (i.e. i&gt;100), then the circuit proceeds to Block I and estimates the time-period of the current rotation T i  by using the time period data for the past n rotations of the disc, given by the following expression:          T   i     =       ∑     k   =     i   -   1   -   n         i   -   1                         a   k     *     T   k                         
     Where the n coefficients a i−l−n  through a i−l  can be calculated beforehand (and offline) as follows: 
     If T i  is the actual time-period of rotation i of the disc, at least squares estimate of the time-period for rotation i+l can be calculated by minimizing the function,        E   =       ∑     k   =     i   -   1   -   n         i   -   1              (       T   k   *     -       ∑     j   =   1     n                       a   j          T     k   -   j     *           )     2                       
     with respect to each a j  (j=1, . . . ,n) 
     The final expressions for the minimized “optimal” values of the coefficients aj are given by:          a   j     =       (                            k                               T   4   *          T     k   -   j     *       )     /     (                                         k                                                        j                                 T     k   -   j     *       )                       
     A good value for n with reasonable computational complexity was found to be 5. As indicated at Block J, the circuit then calculates the “inter-HOPS” t i   Hj  which is the time taken by the home-pulse mark to reach to scanning station j from scanning station j−l. This measure is given by the expression: t i   Hj =x Hj *T i , j=1, . . . ,N 
     Finally, at Block K, the circuit sends (i.e. transmits) HOPs to the SOFSP generation circuit of each laser scaning station (for the ith rotation) at each instant of time given by the expression:            t   i   k     =               j   =   1     k                     t   i   Hj       ,                k   =   1     ,   …              ,                   
     Thereafter, the control process returns to Block E as indicated in FIG.  14 C. If at Block G, the time measure is “close” (i.e. |T i −T i−l |&lt;45 uS), then the circuit proceeds directly to control Block J. 
     As described above, the HOP generation circuit  244 ″ on the control board  200  accurately predicts when the home-pulse mark on the scanning disc arrives at each scanning station and sends out a negative going pulse to each laser scanning station. In contrast, the SOFP generation circuit  236 A″ uses the HOPs to calculate when each facet/facet sector passes the laser module in each laser scanning station. Notably, an important assumption here is that the scanning motor speed does not vary too much between two consecutive rotations of the scanning disc. 
     As indicated at Block A in FIG. 14C, the process within the SOFSP generation circuit  236 A″ defines the following parameters: N as the number of laser scanning stations (i.e. scanning modules) in the holographic scanner; M as the number of sectors (or “Ticks”) on each facet of the scanning disc: x Fj  as the angular width of facet j of the scanning disc; and x Fjm  as the angular width of sector m of facet j of the scanning disc. 
     At Block B in FIG. 14C, the process involves initializing the time period or setting T 0 =0. Then at Block C, the SOFSP generation circuit determines whether a home pulse (HP) has been detected at its input port. Until an HP is detected, the SOFSP generation circuit remains at this control block. When an HP is detected, then at Block D the SOFSP generation circuit starts the timer therewithin (i.e. t=t 0 ). Then at Block E, the SOFSP generation circuit determines whether another HP has been detected. As shown, the SOFSP generation circuit remains at this control block until the next HP is detected. When the HP is detected, then at Block F the SOFSP generation circuit samples the timer contained therewithin. The time-period of rotation of the scanning disc is calculated from two consecutive home-pulse detections as follows: T i =t i −t i−l , where T i  is the time-period for the i th  rotation of the disc. Then at Block G, the SOFSP generation circuit determines whether the time-period for the i th  rotation is “close” to that for the (i−l) th  rotation. 
     As indicated at Block G, a measure of “closeness” is defined as: |T i −T i−l |&lt;45 uS. If the time measure is not close, then the time-period of rotation for the i th  and (i−l) th  rotation does not satisfy, |T i −T i−l |&lt;45 uS, and the SOFSP generation circuit returns to Block E, as indicated in FIG.  14 D and looks for another HOP, without sending any SOFP/SOFSP. 
     If the time-period of rotation for the i th  and (i−l) th  rotation does satisfy, |T i −T i−l |&lt;45 uS, then the SOFSP generation circuit proceeds to Block H where the time between start of facet pulses (SOFSs) for facets j−l and j of the disc for the i th  rotation is calculated using the expression: 
     
       
           t   i   Fj   =x   Fj   *T   i   , j= 1 , . . . ,N   
       
     
     Then at Block I, the SOFSP generation circuit calculates the “inter-HOPs” which are defined as the time between start of sector pulses m−l and m for facet j, corresponding to rotation i of the disc. Such inter-HOPs are calculated by the expression: 
     
       
           t   i   Fjm   =t   i   Fj   /M, m =1 , . . . ,M   
       
     
     At Block J, the SOFP generation circuit sends out (to the decode processor) SOFPs at the times given by the expression:            t   i   n     =               j   =   1     n                     t   i   Fj       ,                n   =   1     ,   …              ,   N                   
     Likewise, the SOFSP generation circuit sends out (to the decode processor) SOFSPs at the times given by the expression:            t   i   n     =               j   =   1     n                               m   =   1     p                     t   i   Fjm       ,                n   =   1     ,   …              ,     N   ;                p   =   1       ,   …              ,   M                   
     Using the transmitted SOFPs/SOFSPs, correlated with bar code scan data at the digitizer circuit  239 A (through  239 F), the decode circuit  240 A ( 240 F) can then specify the laser beam position in terms of the minimum and maximum angle of the scanning facet sector that generated the bar code scan data that has been correlated therewith using the dual-FIFO digitizer circuit  240  of the present invention. Typically, calculations for each SOFP/SOFSP will be performed in a pipelined fashion since the total computation time far exceeds the time between any two SOFSPs. The laser beam position determination subsystem illustrated i n FIGS. 14A through 14D and described hereinabove, has been built and tested in holographic tunnel scanning system employing holographic laser scanners having 5 laser scanning stations, scanning discs with 16 facets and 20 facet sectors/segments, and scanning motor speed variations within the range of between 4800 rpm and 5800 rpm. The system can handle small scanning-motor accelerations (and decelerations). 
     Notably, the above-described subsystem has limitations on the number of sectors (or segments) that each facet can be resolved into along the scanning disc. While a large number of sectors per facet will guarantee more accurate laser beam position information, the subsystem is limited by the computational time required to output each SOFSP. Average computational times for outputting SOFPs is found to be about 20 uS, and about 12 uS for SOFSPs. 
     The Laser-Based Package Velocity and Length Measurement Subsystem of the First Illustrative Embodiment of the Present Invention 
     In FIG. 15, the package velocity and length measurement subsystem  400  is configured in relation to the tunnel conveyor subsystem  500  and package height/width profiling subsystem  600  of the illustrative embodiment. In FIG. 15A, a direct transmit/receive configuration of the dual-laser based package velocity and measurement subsystem  400 ′ is installed at the location of the vertical and horizontal light curtains  601  and  602  employed in the package height/width profiling subsystem  600 . As shown in FIG. 15A, subsystem  400 ′ comprises a pair of laser diodes (D 1  and D 2 )  401 A and  401 B, respectively, spaced apart by about 2 inches and mounted on one side of the conveyor belt; a pair of photo-diodes  402 A and  402 B spaced apart by about 2 inches and mounted on the other side of the conveyor belt, opposite the pair of laser diodes  401 A and  401 B; and electronic circuits, including a programmed microprocessor  403 , for providing drive signals to the laser diodes  401 A and  401 B, and for receiving and processing the electrical data signals P 1  and P 2  produced by the photodiodes  402 A and  402 B so that information representative of the length (L) and velocity (V) of the package  404  moving on the conveyor belt is automatically computed in accordance with the flow chart shown in FIGS.  15 C 1  through  15 C 3 . 
     In FIG. 15B, a retro-reflection configuration of the dual-laser based package velocity and measurement subsystem  400  is shown installed at the location of the vertical and horizontal light curtains  601  and  602  employed in the package height/width profiling subsystem  600 . The dual laser diodes  405 A and  405 B used in the dual-laser based package velocity and length measurement subsystem  400  can be driven using the VLD driver circuitry  406 A and  406 B circuitry shown in FIG.  15 B 1 . In FIG.  15 B 2 , electronic circuitry  407 A and  407 B is shown for conditioning the signals received by the photoreceivers  407 A and  407 B in this subsystem are shown in FIG.  15 B 2 . The velocity (v) and length (L) of the package transported through the package velocity and measurement subsystem  400  can be computed using  409  carrying out the algorithm disclosed in FIGS.  15 C 1  through  15 C 3 . As shown in FIG. 15B, the laser beam transmitted from laser diode  405 A is retro-reflected by retro-reflector  410 A mounted on support structure  411  disposed opposite the support structure  412  supporting laser diodes  405 A and  405 B and photodiodes  408 A and  408 B. As shown in FIG. 15B, the laser beam from laser diode  405 A is reflected off retro-reflector  410 A and is detected by photodiode  408 A, whereas the laser beam from laser diode  405 B is reflected off retro-reflector  410 B and is detected by photodiode  408 B. As when in FIG. 15B, the output signals from photodetectors  408 A and  408 B are provided to photoreceiving circuits  407 A and  408 B respectively, for processing and are then provided to micro-computing system  409  so that the Length (L) and Velocity (V) of the moving packages are computed in accordance with the algorithm described in FIGS.  15 C 1  through  15 C 3 . In the illustrative embodiment shown in FIGS.  15 B and  15 B 1 , laser diode  405 A and photodiode  408 A are packages as a first laser transceiver module indicated at Block  413 , whereas laser diode  408 B and photodiode  408 B are packaged as a second laser transceiver module  414 . As shown in FIG. 15B micro-computing system  409  comprises a microprocessor (CPU)  409 A display device  409 B and keyboard  409 C. 
     The Package Height/Width Profiling Subsystem of the First Illustrative Embodiment of the Present Invention 
     As shown in FIGS. 16 and 16A, the global coordinate reference system R global  is symbolically embedded within the structure of the package height/width profiling subsystem  600  (and also the package-in-tunnel signaling subsystem  500 ). As shown in FIG. 16A, the vertically arranged light transmitting and receiving structures  601 A and  601 B associated with the package height/width profiling subsystem, as well as horizontally arranged light transmitting and receiving structures  602 A and  602 B associated therewith, are arranged in a manner generally known in the package handling art. As shown in FIG. 16A, the vertically arranged light transmitting and receiving structures  601 A and  601 B are controlled by a height control unit  603 , which produces, as output, a signal S H  consisting of time-sampled package height data collected along the vertical extent of the scanning tunnel aperture, similarly, horizontally arranged light transmitting and receiving structures  603  are controlled by a width control unit  604 , which produces, as output, a signal S w  consisting of time-sampled package height data collected along the horizontal extent of the scanning tunnel aperture. The output data streams from height and width control units  603  and  604 , and the package length/velocity measurement subsystem  400 , are provided as input to an H/W data processor  605 , programmed to produce (i) package profile dimension data element (e.g. H, weight, etc. as well as (ii) a package-in-tunnel (PIT) Indication (token) Data Element for each package detected by subsystem  600 . 
     In the illustrative embodiment, package height/width profiling subsystem  600  is realized by integrating (i) the profiler system (Model No. P101-144-200) from KORE, Inc. of Grand Rapids, Mich., and (ii) the package velocity and measurement subsystem  400  described above, and providing programmed H/W data processor  605  in accordance with the principles of the present invention. The primary function of the package height/width profiling subsystem  600  is to obtain x and y coordinates associated with the profile of each package as it passes through the light curtain arranged in the x-y plane of the global coordinate reference system R global . The function of the package velocity and length measurement subsystem  400  is to obtain the z coordinate(s) (i.e. the run-length L) of the package relative to the global reference system, at the time of package height/width profiling (i.e. when the package has past the dual laser beam transceiver of this subsystem). Notably, the package height/width profiling subsystem  600  carries out the function of the package-in-tunnel signaling subsystem  500 . That is, each time a package is detected at the entry side of the scanning tunnel, the subsystem  600 / 500  automatically generates a package-in-tunnel (PIT) data element for transmission to the data element queuing, handling and processing subsystem  1000  to be described in greater detail below. 
     In the tunnel scanning system of the first illustrative embodiment, packages must be transported along the conveyor belt in a singulated manner (i.e. physically arranged so that one package is positioned behind the other package with a space disposed therebetween). In the event that this condition is not satisfied, the package height/width profiling subsystem  600  is designed to automatically detect that packages within the system have not been properly singulated (i.e. are arranged in a side-by-side and/or stacked configuration) and generate a control signal which causes a downstream package deflector to reroute the multiple packages through a package singulator unit and then rerouted through the scanning tunnel system without human intervention. 
     For example, subsystem  600  can simultaneously detect when two boxes  608  and  609  moving along conveyor  300 , pass through non-singulated with a small gap or space  610  between the boxes, as shown in FIGS. 17A through 17C. In this case, the horizontal light curtain T w , R w  of the package dimensioning subsystem  600  will automatically detect the gap  610 . 
     When the two boxes  611  and  612  are close to each other or when one is on top of the other, as shown in FIGS. 18A through 18C, subsystem  600  employs a simultaneous package detection method based on package width (or height) measurements. This method of simultaneous package detection is best described by considering the width measurement taken by the subsystem over time as being expressible as [x 1 , x 2 , . . . x n ]. According to the simultaneous package detection/tracking method hereof, the subsystem  600  employs a novel FIR digital filter system, as illustrated in FIGS. 19,  19 A and  19 B. 
     In general, the FIR digital filter formulation has a transfer function which fits the linear operation of differentiation where d/dt e iwt =iwe iwt . In the frequency domain, this implies that the transfer function is of the form: 
     
       
           H ( w )= iw.   
       
     
     Letting the digital filter be of the form 
     Y a =(N/Z K=−N ) C k x n−k . with coefficients C k =−C k , the transfer function can be expressed as: 
     
       
           H ( w )=[2 c   i  sin  w +2 c   2  sin 2 w + . . . +2 c   N  sin  Nw]i.   
       
     
     A Fourier Series approximation of the function can be expressed as:=          H        (   w   )       =     {               iw           c                          w        &lt;     w   c                      w        &gt;     w   c                                     
     The resulting filter will have a passband of [o,w c ]. This is a low pass (smoothing) differentiator for w c &lt; π . The filter coefficients can be computed using the formula C k =(a k +ib k )/2 where k=0.          Where                   a   k       =       υ                 and                   b   k       =       (     1   /   π     )          I     -   π                       μ        (   w   )          sin                 kwdw                 b   k     =       (     2   /   π     )          I   0   wc        i                 ωsin                 kwdw               C   k     =       (       -   1     /   π     )          (       (     sin                   kw   c        k     )     -     (       ω   c        cos                     kw   c     /   k       )       )                       
     Notably, w c  is a value in the range of [o,π] when w c =π, and also 
     
       
           C   k =(1 /k )(−1) k   
       
     
     Using the above formulation, a digital filter can be designed for the simultaneous package detection method of subsystem  600 . For the 1st derivative, a low pass stop frequency of f c +o (1 is used where w c =2π). This will help filter out the noise during measurement operations in subsystem  600 . For the 2nd derivative, an all pass band (w c =π) is used. To improve the detection performance, in particular to reduce flash-alarm rate, the present invention teaches using a 3rd derivative to sample the 2 nd  derivative zero crossings and thus ensure that false-alarms do not happen due to the lowering of the  1 st derivative threshold in the digital filter design. 
     As illustrated in FIG. 19, the digital filter method of the present invention comprises: (A) computing the 1 st  spatial derivative (or gradient function) of x(n) for all spatial samples n; (B) computing the 2 nd  spatial derivative of x(n) for all samples n; (C) computing the 3 rd  spatial derivative of x(n) for all spatial samples n; (D) determine whether the 1st spatial derivative signal x′(n) is greater than the threshold τ 1 ; (E) using the thresholded  1 st spatial derivative signal x′(n) to sample the 2 nd  spatial derivative signal x″(x); (F) detecting the zero-crossings of x″(n) to produce a zero-crossing signal; (G) sampling the detected zero-crossing signal using the 3 rd  spatial derivative signal x′″(n) to produce a sampled zero-crossing signal; (H) thresholding the sampled zero-crossing signal against the threshold τ 2  to detect sudden changes in the value of x(n); and (I) analyzing the changes in the value of x(n) over a number of time sampling periods in order to determine whether packages are configured side-by-side, stacked or singulated manner. 
     In FIG. 19A, the digital filter method the present invention is represented in a flow chart, indicating the particular operations carried out in a real-time sequential manner. 
     As indicated at Block A in FIG. 19A, a sampled position signal x(n) is obtained where n=0, 1,2, . . . , N−1; the digital filter coefficients c[i] are selected; and thresholds τ 1  and τ 2 are obtained using empirical methods. At Block B in FIG. 19A, the 1 st  spatial derivative of x(n), denoted x′(n), is computed for all samples n. At Block C in FIG. 19A, the 2 nd  spatial derivative of x(n), denoted x″(x), is computed for all samples n. A Block D in FIG. 19A, the 3 rd  spatial derivative of x(n), denoted x′″(x), is computed for all samples n. At Block E in FIG. 19A, the position index n is set to zero. At Block F in FIG. 19A, the filter determines whether the 1st spatial derivative signal x′(n) is greater than the threshold τ 1 , whether sign (x″[x])≠sign (x″[n−1]) and whether x″[n]&gt;τ 2 . If any one of these conditions are not satisfied, then at Block G the position index n is incremented by 1 (i.e. n=n+1) and then, at Block H, a check is made to determine whether. the position index n is less than N. If not, then at Block I, no change is detected. If n&lt;N, then the process flow returns to Block F, as indicated at Block F. If at Block F, all three of the conditions listed therein are satisfied, then at Block J a change is detected at position n across the width of the conveyor belt. 
     Notably, the digital FIR filter system illustrated in FIGS. 19 and 19A is used as a basic filtering module within H/W Data Processor  605  of FIG.  16 A. During the operation of the system of the present invention, the H/W Data Processor  605  carries out the simultaneous package detection process of the present invention to be described hereinbelow with reference to FIGS. 19B and 19C. 
     In general, there are two basic scenarios to consider when carrying out the simultaneous package detection method of the present invention: (1) when one box is disposed beside another, as shown in FIGS. 17A through 17C; and (2) when one box is disposed on top of another as shown in FIGS. 18A through 18C. The cases of more than 2 boxes can be easily extended from these two box scenarios. 
     Considering the side-by-side boxes case, shown in FIGS. 17A through 17C, it is noted that the light transmitting and receiving structures (T w , R w )  602 A and  602 B, respectively, are used to measure the width of the packages when they move through the light curtain structure of FIG. 16A, as it is often referred to by those skilled in the art. In the case of side-by-side boxes, the measurement of package width will change while packages are passing through the light curtain structure. The method of simultaneously detecting packages arranged in a “side-by-side” configuration is illustrated in the flow chart of FIG.  19 B. 
     As indicated at Block A in FIG. 19B, the first step in the method involves obtaining an array of N sampled width measurements W(n) along the total width of the conveyor belt (i.e. edge to edge) as the conveyor belt with packages thereon is transported through the light curtain shown in FIG.  16 A. Collection of the array of width data elements, denoted by W(n) for n=0, 1, 2, . . . , N−1, is achieved using the array of light beam transmitters and receivers  602 A and  602 B, shown in FIG.  16 A. Naturally, the spatial sampling rate (and thus the number and position of the N samples along the conveyor belt) is selected so that enough width measurements are taken and gaps between packages can be detected. 
     As indicated at Block B in FIG. 19B, second step in the method involves providing the array of sampled width data W(n) as input to the digital filter system of FIG. 19 so as to detect sudden changes in width data at one or more positions along the width of the conveyor belt. The first spatial derivative of the discrete set of width samples W(n)is defined as W′(n)=W(n)−W(n−1) where n=1,2, . . . N. The second spatial derivative of the discrete set of height samples W(n)is defined as W″(n)=W′(n)−W′(n−1) where n=1,2, . . . N. The third spatial derivative of the discrete set of width samples W(n)is defined as W′″(n)=W(n)″−W″(n−1) where n=1,2, . . . N. The digital filter system of FIG. 19 differentiates the sudden changes in values of W(n) from noise (e.g. measurement errors and slight irregularities in the box shape). As illustrated at Block F in FIG. 19A, the decision rules for the simultaneous detection method are: 
     (1) determine that the boxes are “side-by-side” if W′(n)&gt;τ 1 , sign(W″[n]) ≠sign(W″[n−1]) and W″(n)&gt;τ 2 , for any n; and 
     (2) otherwise, determine that the boxes are singulated. Notably, sign ( ) denotes the algebraic sign function which is used to find zero crossings in the 2nd spatial derivative signal W″(n). Simulations show that the above decision rules are work well with regard to noise, and always correctly locate abrupt changes in width data, which is necessary to determine that boxes are arranged in a side-by-side configuration. 
     As indicated at Block C in FIG. 19B, the third step of the method involves analyzing the detected changes in the width data array W(n) for n=0, 1, 2, . . . , N−1 for a number of time sampling periods, so as to determine the specific “side-by-side” configuration of packages on the conveyor belt. 
     As indicated at Block D in FIG. 19B, the fourth and last step of the method involves correlating the package dimension data (if collected) with each package in the detected “side-by-side” configuration, and transmitting a special “multiple-in-tunnel” package indicating data element (e.g. MPIT data element) to the data element queuing, handling and processing subsystem  1000  indicates that within subsystem  1000  there is either an irregular-shaped package in the tunnel or multiple side-by-side packages in the tunnel. Subsystem  1000  can then generate a control signal to cause a downstream package router to route such multiple packages through a package singulation unit, and then once again through the scanning tunnel system without human intervention. Considering the “stacked” boxes case, shown in FIGS. 18A through 18C, it is noted that the light transmitting and receiving structures (T w , R w )  601 A and  601 B, respectively, are used to measure the height of the packages when they move through the light curtain structure shown in FIG.  16 A. In the case of stacked boxes, the measurement of the package height will change while packages are passing through the light curtain. The method of simultaneously detecting packages arranged in a “stacked” configuration is illustrated in the flow chart of FIG.  19 C. 
     As indicated at Block A in FIG. 19C, the first step in the method involves obtaining an array of N sampled height measurements W(n) along the total height of the tunnel aperture (i.e. top to bottom) as the conveyor belt with packages thereon is transported through the light curtain structure shown in FIG.  16 A. Collection of the array of height data elements, denoted by H(n) for n=0, 1, 2, . . . , N−1, is achieved using the array of light beam transmitters and receivers  601 A and  601 B, shown in FIG.  16 A. Naturally, the sampling rate (and thus the position of the N samples above the conveyor belt) is selected so that enough height measurements are taken. 
     As indicated at Block Bin FIG. 19C, the second step in the method involves providing the array of sampled height data H(n) as input to the digital filter system of FIG. 19 so as to process the data array(s) and detect sudden changes in height data at one or more positions above the height of the conveyor belt. The first spatial derivative of the discrete set of height samples H(n) is defined as H′(n)=H(n)−H(n−1) where n=1,2, . . . , N. The second spatial derivative of the discrete set of height samples H(n) is defined as H″(n)=H′(n)−H′(n−1) where n=1,2, . . . N. The third spatial derivative of the discrete set of height samples H(n) is defined as H′″(n)=H(n)″−H″(n−1) where n=1,2, . . . N. The digital filter system of FIG. 19 differentiates the sudden changes in values of H(n) from noise (e.g. measurement errors and slight irregularities in the box shape). As illustrated at Block Fin FIG. 19A, the decision rules for the simultaneous detection method operating on sampled height data, are: 
     (1) determine that the boxes are “stacked” if H(n)&gt;τ 1 , sign(H″[n])≠sign(H″[n−1]) and H″(n)&gt;τ 2 , for any n; and 
     (2) otherwise, determine that the boxes are singulated. 
     Notably, sign ( ) denotes the algebraic sign function which is used to find zero crossings in the 2nd spatial derivative signal H″(n). Simulations show that the above decision rules work well with regard to noise, and always correctly locate abrupt changes in height data, which is necessary to determine that boxes are arranged in a stacked configuration. 
     As indicated at Block C in FIG. 19C, the third step of the method involves analyzing the detected changes in the height data array H(n) for n=0, 1, 2, . . . , N−1 for a number of time sampling periods, so as to determine the specific “stacked” configuration of packages on the conveyor belt. 
     As indicated at Block D in FIG. 19C, the fourth and last step of the method involves correlating the package dimension data (if collected) with each package in the detected “side-by-side” configuration, and transmitting corresponding package indicating data elements (e.g. PIT data elements) to the data element queuing, handling and processing subsystem  1000 . As will become apparent hereinafter, these PIT data elements enable detected packages to be tracked within the overall system and eventually linked up with corresponding package identification data acquired by the bar code symbol reading subsystems employed within the Tunnel Scanning System. 
     Using the package detection method described above, any arrangement of non-singulated boxes on the conveyor belt can be automatically detected and successfully tracked. 
     The sampling rate for the above described digital filtering method, denoted by T, can be determined as follows: Let the speed of the box/conveyor be denoted by ν, and the minimum tolerance for package separation be denoted as D. Then considering the necessary data points to perform the second derivative, the following expression must hold true: 
     
       
           T ≠3 D/ν   
       
     
     Using this rule for a 600 ft/min. conveyor belt, if the minimum tolerance is 50 mm (2 in.), then the sampling period is about 5 ms, which corresponds to a sampling frequency of about 200 Hz 
     The In-Motion Package Weighing Subsystem of the First Illustrative Embodiment of the Present Invention 
     As shown in the FIGS. 20A and 20B, the in-motion package weighing subsystem  750  is preferably arranged about the package height/width profiling subsystem  600 . As shown, the in-motion weighing subsystem  750  comprises: a scale platform  751  integrated with the conveyor subsystem  300 , for producing analog or digital weight signals indicative of the weight of a package(s)  754  moving across the scale platform  751 ; a filtering circuit  752  for filtering the analog or digital weight signals in order to remove noise components and artifacts therefrom; and a signal processor  753  for processing the filtered weight signals in order to produce a digital word representative of the measured weight of the package. Notably, the in-motion weighing subsystem of the illustrative embodiment can be used to realize using the 9480 EXPRESSWEIGHT™ In-Motion Variable Box and Package Weighing System from Mettler-Toledo, Inc. of Worthington, Ohio. 
     The Package-in-Tunnel Signaling Subsystem of the First Illustrative Embodiment of the Present Invention 
     The package-in-tunnel indication subsystem  500  can be realized in a variety of ways. One way shown in FIG. 21, is to use a light transmitting/receiving structure as employed in package identification and measuring system  600 , and generating a package-out-of-tunnel (POOT) data element upon detecting the exit of each package from the scanning tunnel. As shown in FIG. 21, the vertically arranged light transmitting and receiving structures  801 A and  801 B, as well as horizontally arranged light transmitting and receiving structures  802 A and  802 B, are arranged in a manner generally known in the package handling art. As shown in FIG. 21, the vertically arranged light transmitting and receiving structures  801 A and  801 B are controlled by a height control unit  803 , which produces, as output, a signal SH consisting of time-sampled package height data collected along the vertical extent of the scanning tunnel aperture, similarly, horizontally arranged light transmitting an d receiving structures  803  are controlled by a width control unit  804 , which produces, as output, a signal S w  consisting of time-sampled package height data collected along the horizontal extent of the scanning tunnel aperture. The output data streams from height and width control units  803  and  804 , and the package length/velocity measurement subsystem  400 , are provided as input to an H/W data processor  805 , programmed to produce a package-out-of-tunnel (POOT) Indication (token) Data Element for each package detected by  800 . In the illustrative embodiment, subsystem  800  is realized by integrating (i) the profiler system (Model No. P101-144-200) from KORE, Inc. of Grand Rapids, Michigan, and providing programmed H/W data processor  805  which includes the digital filter system described in FIGS. 19 through 19C in order to simultaneously detect side-by-side configured packages, stacked packages, as well as singulated packages in the manner described in great detail hereinabove. 
     As shown in FIG. 21, the best location for this subsystem is at the exit plane of the scanning tunnel. The POOT data element is provided to the data element queuing, handling and processing subsystem  1000 , in the manner similar to that of all other data elements generated from the package height/width profiling subsystem  600 , scanning units associated with the tunnel scanning subsystem, and package-in-tunnel indication subsystem  500 . 
     The Data Element Queuing, Handling and Processing Subsystem of the First Illustrative Embodiment of the Present Invention 
     In FIGS.  22 A 1 ,  22 A 2  and  22 B, the structure and function of data element queuing, handling and processing subsystem  1000  is shown in greater detail. As shown in FIGS.  22 A 1  and  22 A 2 , all data elements entering subsystem  1000  are provided to an I/O subsystem  1001 , the output port of which is connected to a data element time-stamping unit  1002  that is controlled by a timing/control unit  1003 . In the illustrative embodiment, there are four possible types of data elements that might be loaded into the system event queue  1004 , realized as a FIFO data structure known in the computing art. As shown in FIGS.  22 A 1  and  22 A 2 , the four possible data element types are: package data elements; scan beam data elements; package-in-tunnel (PIT) data elements; and package out-of-tunnel (POOT) data elements. 
     As shown in FIGS.  22 A 1  and  22 A 2 , the data element queuing, handling and processing subsystem  1000  further comprises a number of other modules, namely: a moving package tracking queue  1005 , realized as a FIFO data structure known in the computing art, for queuing package data elements, package-in-tunnel (PIT) data elements and package out-of-tunnel (POOT) data elements; and a data element analyzer  1006  (e.g. programmed microprocessor and associated memory structures) for reading the different types of data elements from the output of the system event queue  1004  and analyzing and handling the same according to the Data Element Handling Rules set forth in FIGS.  23 A 1  and  23 A 2 . 
     As shown in FIGS.  22 A 1  and  22 A 2 , scan beam data elements generated from “holographic type” laser scanning subsystems must be processed using a system of data processing modules illustrated in FIGS.  22 A 1  and  22 A 2 . As shown in FIGS.  22 A 1  and  22 A 2 , this system of data processing modules comprises a data element combining module  1007 A for combining (i) each scan beam data element generated from “holographic-type” laser scanning subsystems and accessed from the system event queue  1004  with (ii) each and every package data element in the moving package tracking queue  1005 , so as to produce a plurality of combined data element pairs; a package surface geometry modeling module  1008 A for generating a geometrical model for the package represented by the package data element in each combined data element pair produced by the data element combining module  1007 A; a homogeneous transformation (HG) module  1009 A for transforming (i.e. converting) the coordinates of each package surface geometry model produced at the “dimensioning position” in the global coordinate reference frame R global , into package surface geometry model coordinates at the “scanning position” within the scanning tunnel (i.e. displaced a distance z from the package dimensioning position); a scan beam geometry modeling module  1010 A for generating a geometrical model for the laser scanning beam represented by the scan beam data element in each combined data element pair produced by the data element combining module  1007 A; a homogeneous transformation (HG) module  1011 A for transforming (i.e. converting) the coordinates of each scanning beam geometry model referenced to the local frame of reference symbolically embedded within the holographic laser scanning system, into scanning beam geometry model coordinates referenced to the global coordinate reference R global  at the “scanning position” within the scanning tunnel; a scan beam and package surface intersection determination module  1012 A for determining, for each combined data element pair produced from the data element combining module, whether the globally-referenced scan beam model produced by the HG transformation module  1009 A intersects with the globally-referenced package surface model produced by the HG transformation module  1011 A, and if so, then the data output subsystem  1013 A produces, as output, package identification data, package dimension data (e.g. height, width data etc.), and package weight data, for use by auxiliary systems associated with the tunnel scanning system of the present invention. 
     As shown in FIGS.  22 A 1 ,  22 A 2  and  22 B, scan beam data elements generated from “non-holographic type” laser scanning subsystems must be processed using a different system of data processing modules than that shown in FIGS.  22 A 1  and  22 A 2 . As shown in FIG. 22B, this system of data processing modules comprises: a data element combining module  1007 B (similar to module  1007 A) for combining (i) each scan beam data element generated from the “non-holographic-type” bottom-located laser scanning subsystems and accessed from the system event queue  1004  with (ii) each and every package data element in the moving package tracking queue  1005 , so as to produce a plurality of combined data element pairs; a package surface geometry modeling module  1008 B (similar to module  1008 A) for generating a geometrical model for the package represented by the package data element in each combined data element pair produced by the data element combining module  1007 B; a homogeneous transformation (HG) module  1009 B (similar to module  1009 A) for transforming (i.e. converting) the coordinates of each package surface geometry model produced at the “dimensioning position” in the global coordinate reference frame R global , into package surface geometry model coordinates at the “scanning position” within the scanning tunnel (i.e. displaced a distance z from the package dimensioning position); a X-Z scanning surface (geometry) modeling module  1010 B for generating a geometrical model for the laser scanning surface represented by the scan beam data element in each combined data element pair produced by the data element combining module  1007 B; a homogeneous transformation (HG) module  1011 B for transforming (i.e. converting) the coordinates of each x-z scanning surface geometry model referenced to the local frame of reference symbolically embedded within the non-holographic bottom laser scanning subsystem, into scanning beam geometry model coordinates referenced to the global coordinate reference R global  at the “scanning position” within the scanning tunnel; a scan beam and package surface intersection determination module  1012 B for determining, for each combined data element pair produced from the data element combining module, whether the globally-referenced scanning surface model produced by the HG transformation module  1009 B intersects with the globally-referenced package surface model produced by the HG transformation module  1011 B, and if so, then the data output subsystem  1013 B produces, as output, package identification data, package dimension data (e.g. height, width data etc.), and package weight data, for use by auxiliary systems associated with the tunnel scanning system of the present invention. 
     Having described the overall structure and function of the data element queuing, handling and processing subsystem  1000 , it is appropriate at this juncture to now briefly describe the operation thereof with reference to FIGS.  22 A 1 ,  22 A 2  and  22 B. 
     Prior to loading into the system event queue  1004 , each data element is time-stamped (i.e. T j ) by the timing stamping module  1002  driven by a master clock within timing/control unit  103  referenced to the global reference frame R global . All data elements in the system event queue  1004  are handled by a data element analyzer/handler  1006  which is governed by the table of Data Element Handling Rules set forth in FIGS.  23 A 1  and  23 A 2 . In general, subsystem  1000  is best realized by a computing platform having a multi-tasking operating system capable of handling multiple “threads” at the same time. 
     Each package moving through the scanning tunnel will be represented b y a data element (i.e. an object in an object-oriented programming environment e.g. Java programming environment) stored in a moving package tracking queue  1005  operably connected to the data element handler  1006 . Package data elements are placed in the moving package tracking queue  1005  and matched with each scan beam data element accessed from the system event queue  1004  using a data element combining module  1007 A. Scan beam data elements generated from holographic-based scanning units are processed along the scan data processing channel illustrated by blocks  1008 A,  1009 A,  1010 A,  1011 A,  1012 A, and  1013 A set forth in the lower right hand corner of FIGS.  22 A 1  and  22 A 2 , whereas scan beam data elements generated from non-holographic based scanning units (e.g. from the bottom-located polygon scanners in the tunnel) are processed along a different scan data processing channel illustrated by blocks  1008 B,  1009 B,  1010 B,  1011 B,  1012 B, and  1013 B set forth on FIG.  22 B. This is because scan beam data elements generated from holographic-based scanning units have been generated from laser scanning beams (or finite scanning sectors) which can be tracked with scan package identification data by tracking facet sectors on the scanning disc in issue. While a similar technique can be used for polygon-based scanners (e.g. tracking “mirror sectors” instead of HOE-based facet sectors), a different approach has been adopted in the illustrative embodiment. That is, the scanning surface (e.g. 3×5″) of each polygon scanning unit along the bottom scanner is accorded a vector-based surface model, rather than a ray-type model used for package identification data collected using holographic scanning mechanisms. 
     The Package Surface Geometry Modeling Subsystem of the First Illustrative Embodiment of the Present Invention 
     As shown in FIG. 24, a surface geometry model is created for each package surface by the package surface geometry modeling subsystem (i.e. module)  1008 A deployed with the data element queuing, handling and processing subsystem  1000  of FIGS.  22 A 1  and  22 A 2 . In the illustrative embodiment, each surface of each package transported through package dimensioning/measuring subsystem  600  and package velocity/length measurement subsystem  400  is mathematically represented (i.e. modeled) using at least three position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global , and a normal vector to the package surface indicating the direction of incident light reflection therefrom. The table of FIG. 24A describes a preferred procedure for creating a vector-based surface model for each surface of each package transported through the package dimensioning/measuring subsystem  600  and package velocity/length measurement subsystem of the system  400  hereof. 
     The Scan Beam Geometry Modeling Subsystem of the First Illustrative Embodiment of the Present Invention 
     As shown in FIGS.  25 A through  25 A 1 , a vector-based model is created by the scan beam geometry modeling subsystem (i.e. module)  1010 A of FIGS.  22 A and  22 A 2 , for the propagation of the laser scanning beam (ray) emanating from a particular point on the facet, to its point of reflection on the corresponding beam folding mirror, towards to the focal plane determined by the focal length of the facet. The table set forth in FIGS.  25 B 1  through  25 B 3  define the parameters used to construct the diffraction-based geometric optics model of the scanning facet and laser scanning beam shown in FIGS.  25 A and  25 A 1 . Details of this modeling procedure can be found in Applicant&#39;s copending application Ser. No. 08/726,522 filed Oct. 7, 1996; and Ser. No. 08/573,949 filed Dec. 18, 1995. FIG. 26 provides a schematic representation of the laser scanning disc shown in FIGS.  25 A and  25 A 1 , labeled with particular parameters associated with the diffraction-based geometric optics model of FIGS.  25 A and  25 A 1 . 
     In FIG. 27, a preferred procedure is described for creating a vector-based ray model for laser scanning beams which have been produced by a holographic laser scanning subsystem of the system hereof, that may have collected the scan data associated with a decoded bar code symbol read thereby within the tunnel scanning subsystem. 
     The Scan Surface Modeling Subsystem of the First Illustrative Embodiment of the Present Invention 
     FIG. 28 schematically shows how the scan surface modeling subsystem (i.e. module) shown of FIG. 22B can be used to define a vector-based 2-D surface geometry model for each candidate scan beam generated by the polygonal-based bottom scanners in the tunnel scanning system. As shown in FIG. 28, each omni-directional scan pattern produced from a particular polygon-based bottom scanning unit is mathematically represented (i.e. modeled) using four position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global , and a normal vector to the scanning surface indicating the direction of laser scanning rays projected therefrom during scanning operations. 
     The Homogeneous (HG) Transformation Module of the First Illustrative Embodiment of the Present Invention 
     FIG. 29 schematically describes how the homogeneous (HG) transformation module  1009 A of FIGS.  22 A 1  and  22 A 2  uses homogeneous transformations to convert a vector-based model within a local scanner coordinate reference frame R localscannerj  into a corresponding vector-based model created within the global scanner coordinate reference frame R global . This mathematical technique is essential in that it converts locally-referenced coordinates used to represent a laser beam (which scanned a bar code symbol) into globally-referenced coordinates used to represent the same laser scanning beam. 
     FIG. 30 describes how the homogeneous (HG) transformation module  1010 A of FIGS.  22 A 1  and  22 A 2  uses homogeneous transformations to convert a vector-based package surface model specified within the global coordinate reference frame R global  at the “package height/width profiling position”, into a corresponding vector-based package surface model created within the global coordinate reference frame R global  specified at the “scanning position” within the tunnel scanning system. This mathematical technique is essential in that it converts locally-referenced coordinates used to represent a package surface into globally-referenced coordinates used to represent the same package surface. Notably, this method of coordinate conversion involves computing the package travel distance (z=d) between the package height/width profiling and scanning positions using (1) the package or conveyor belt velocity (v) and the difference in time (i.e. ΔT=T 1 −T 2 ) indicated by the time stamps (T 1  and T 2 ) placed on the package data element and scan beam data element, respectively, matched thereto during each scan beam/package surface intersection determination carried out within module  1012 A in the data element queuing, handling and processing subsystem  1000  of FIGS.  22 A 1 ,  22 A 2  and  22 B. Notably, this package displacement distance z=d between the profiling and scanning positions is given by the mathematical expression d=v ΔT. 
     The Scan Beam And Package Surface Intersection Determination Subsystem of the First Illustrative Embodiment of the Present Invention For Use With Scan Beam Data Elements Produced by Holographic Scanning Subsystems 
     FIGS. 31A and 31B, taken together, describes a procedure which is carried out within the scan beam and package surface intersection determination module  1012 A of the illustrative embodiment in order to determine whether (i) the scan beam (rays) associated with a particular scan beam data element produced by a holographic scanning subsystem intersects with (ii) any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system. 
     As indicated at Block A in FIG. 31A, the first step of the procedure involves using the minimum and maximum scan rays models of the laser scan beam to determine the intersection point between the scan ray and a surface on the package (using the vector-based models thereof) referenced to the global coordinate reference frame. As indicated at Block B in FIG. 31A, if an intersection point has been determined at Block A, then confirm that the sign of the normal vector of the surface is opposite the sign of the scan ray direction vector. As indicated at Block C in FIG. 31A, if the sign of the normal vector is opposite the sign of the scan ray direction vector, then determine if the intersection point (found at Block A) falls within the spatial boundaries of the package surface. As indicated at Block D in FIG. 31B, if the intersection point falls within the boundaries of the surface, then output a data element to the output queue in the data output subsystem  1013 A, wherein the data element comprises package identification data and data representative of the dimensions and measurements of the package by the system for use by other subsystems. When a scan beam data element taken from the system event queue  1004  is correlated with a package data element using the above described method, then the subsystem  1000  outputs a data element (in an output data queue  1013 A) containing the package ID data and the package dimensional and measurement data. Such data elements can be displayed graphically, printed out as a list, provided to sorting subsystems, shipping pricing subsystems, routing subsystems and the like. 
     The Scan Surface and Package Surface Intersection Determination Subsystem of the First Illustrative Embodiment of the Present Invention For Use With Scan Beam Data Elements Produced by Non-Holographic Scanning Subsystems 
     FIGS. 32A and 32B, taken together, describes a procedure which can be carried out within the scan surface and package surface intersection determination module  1012 B of FIG. 22B in order to determine whether the scanning surface associated with a particular scan beam data element produced by a non-holographic (e.g. polygon-based) “bottom-located” scanning subsystem spatially intersects with any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system. 
     As indicated at Block A in FIG. 32A, the first step of the procedure involves using the vector-based surface models of the laser scan surfaces of the bottom polygon scanners and side surfaces of the packages so as to determine whether or not there exists a point of intersection between the scanning surface of the polygon-based scanners and any surface of the package. As indicated at Block B in FIG. 32A, if an intersection point exists, then confirm that the sign of the vector model of the scanning surface (i.e. the normal vector) is opposite the sign of the vector model of the package surface. As indicated at Block C in FIG. 32B, if the sign of the normal vector of the scanning surface is opposite the sign of the normal vector to the package surface, then confirm that certain of the points bounded by the scanning surface coincide with points bounded by the surface of the package. As indicated at Block D in FIG. 32B, if sufficient overlap is found to exist between the scanning surface and the package surface, then output a data element to the output queue in the data output subsystem  1013 B, wherein the data element comprises package identification data and data representative of the dimensions and measurements of the package by the system for use by other subsystems. When a scan beam data element taken from the system event queue  1004  is correlated with a package data element using the above described method, then the subsystem  1000  outputs a data element (in an output data queue  1013 B) containing the package ID data and the package dimensional and measurement data. Such data elements can be displayed graphically, printed out as a list, provided to sorting subsystems, shipping pricing subsystems, routing subsystems and the like. 
     Notably, the smaller the facet sectors on the scanning disc, then the better resolution the system hereof will have with regarding to correlating package identification data with package measurement data. As the facet sector gets smaller, the corresponding minimum and maximum facet angles generated from the decoder device hereof will get closer and closer, approaching a single scanning ray in the ideal situation. 
     Automated Tunnel-type Laser Scanning Package Identification and Weighing System Constructed According to a Second Illustrated Embodiment of the Present Invention Package Identification and Measurement 
     Referring now to FIGS. 33 through 34, the “dual-lane” automated tunnel-type laser scanning system of the second illustrated embodiment  2000  will now be described in detail. As in the first illustrative embodiment depicted in FIGS. 1 through 32B, the system of the second illustrative embodiment is designed to identify and measure packages that are singulated along a conveyor subsystem in a conventional manner. 
     Overview of the Tunnel Scanning System of the Second Illustrative Embodiment of the Present Invention 
     As shown in FIGS. 33 and 34, the automated tunnel scanning system of the second illustrative embodiment indicated by reference numeral  2000  comprises an integration of subsystems, namely: a high-speed package conveyor system  2100  having a conveyor belt  2101  having a width of at least 60 inches to support a pair of package transport lanes along the conveyor belt; a first pair of triple-disc holographic laser scanning bar code symbol reading subsystems  2200 A and  2200 B supported overhead above the conveyor belt  2101  by a support frame  2102  so as to produce a 3-D omni-directional scanning volume  2103  thereabove, for scanning bar codes  2104  on packages  2105  transported therethrough; a second pair of triple-disc holographic laser scanning bar code symbol reading subsystems  2200 C and  2200 D supported on opposite sides of the conveyor belt structure as shown in FIG. 33, so as to produce a 3-D omni-directional scanning volume  2103  thereabove, for scanning bar codes  2104  on packages  2105  transported therethrough; a four of triple-disc holographic laser scanning bar code symbol reading subsystems  2200 E through  2200 H mounted in the four corners of the tunnel system, as shown in FIG. 33A, for scanning bar codes  2104  on front and back surfaces of packages  2105  (e.g. USPS tubs and trays) transported therethrough; a package-in-the-tunnel indication subsystem  2300  realized as a pair of IR-based package detectors  2301 A and  2301 B directed over the first and second conveyor lanes (CL 1  and CL 2 )  2102 A and  2102 B of the conveyor belt, respectively, for automatically detecting the presence of packages  2205  moving within lanes of the conveyor belt and into the scanning tunnel; a package-out-of-the-tunnel indication subsystem  2400  realized as a pair of IR-based package detectors  2401 A and  2401 B directed over the first and second conveyor lanes (CL 1  and CL 2 )  2102 A and  2102 B of the conveyor belt, respectively, for automatically detecting the presence of packages moving within lanes of the conveyor belt and out of the scanning tunnel; a weighing-in-motion subsystem  2500  for weighing packages as they are transported along the conveyor belt  2101 ; a package/belt velocity measurement subsystem  2600  realized using a roller wheel  2601  engaged against the undersurface of the conveyor belt  2101 , an optical shaft incremental encoder  2602  connected to the axle of the roller wheel  2601  and producing an electrical pulse output stream per revolution of the roller wheel, and a programmed microprocessor  2603  for processing the output pulse stream and producing digital data representative of the velocity of the conveyor belt (and thus package transported thereby) at any instant in time; an input/output subsystem  2700  for managing the data inputs to and data outputs from the system of FIG. 33; and a data management computer  2800 , with a graphical user interface (GUI)  2701 , for realizing a data element queuing, handling and processing subsystem  2900  as shown in FIG. 41, as well as other data and system management functions. 
     The High-Speed Conveyor Belt Subsystem of the Second Illustrative Embodiment 
     As shown in FIGS. 33, the high-speed conveyor belt subsystem  2100  of the illustrative embodiment comprises: a plurality of rollers  2102  spaced apart and supported by support frame structure (not shown in FIG.  33 ); a belt structure  2101 , extending between and supported by a belt support structure  2103 , and having a width of at least  60  inches to provide a pair of package transport lanes CL 1  and CL 2  along the conveyor belt subsystem; a drive motor  2104  for imparting torque to the rollers; and a belt velocity controller  2106  for controlling the velocity of the belt and thus packages during system operation. 
     Triple-disc Holographic Laser Scanning Bar Code Symbol Reading Subsystems of the Present Invention 
     As shown in FIG. 33, triple-disc holographic laser scanning bar code symbol reading subsystem  2200 A and  2200 B are supported overhead above the conveyor belt  2101  by a support frame  2202 . Triple-disc holographic laser scanning bar code symbol reading subsystem  2200 C and  2200 D are supported about the sides of the above the conveyor belt  2101  by support frame  2202 , as well. Triple-disc holographic laser scanning bar code symbol reading subsystem  2200 E through  2200 G are supported in the four corners of the tunnel formed by subsystems  2200 A through  2200 D, as shown in FIG. 33A, also by way of support frame  2202 , some of whose structure has not been shown for purposes of illustration in FIG.  33 . Each triple-disc scanner  2200 A through  2200 D can be the same scanner shown in FIGS.  4 A 1  through  4 A 10 . Each triple-disc scanner  2200 E through  2200 G can be the same scanner shown in FIGS.  4 B 4  through  4 B 12 . 
     During system operation, each triple-disc holographic laser scanning subsystem  2200 A through  2200 D produces a 3-D omni-directional scanning volume  2203  having four focal planes for omni-directional scanning of bar codes on package transported therethrough. The omni-directional laser scanning pattern projected from each scanning disc, within a particular focal plane of the scanning volume, is schematically depicted in FIGS.  4 A 8 A and  4 A 10 . During system operation, each triple-disc holographic laser scanning subsystem  2200 E through  2200 G produces a 3-D scanning volume having three spatially-separated focal zones, as shown in FIGS.  4 B 7  through  4 B 9 , for providing orthogonal (both horizontal and vertical) laser scanning patterns over regions indicated by solid lines (i.e. H&amp;V) and only horizontal laser scanning patterns over the regions indicated by dotted lines (HSR). 
     Package-In-The-Tunnel Indication Subsystem of the Second Illustrative Embodiment of the Present Invention 
     The package-in-the-tunnel indication subsystem  2300  depicted in FIGS. 33 and 34 are realized as a pair of IR-based package detectors  2301 A and  2301 B which are mounted on the edges of the first and second conveyor lanes (CL 1  and CL 2 )  2102 A and  2102 B of the conveyor belt, respectively. Each IR-based package detector  2301 A and  2301 B comprises an infared (IR) transmitter  2302  in synchronous operation with an IR receiver  2303 , as taught in U.S. Pat. No. 5,789,730 to Rockstein, et al., incorporated herein by reference. The function of each synchronous IR transmitter and receiver  2302  and  2303  is to automatically detect the presence of a package (i.e. object) moving into the scanning tunnel along the conveyor belt lane assigned thereto. Notably, in the illustrative embodiment, where there are dual package conveyor lanes, the IR range of each IR-based package detector is adjusted so that it extends only half the width of the conveyor belt. In alternative single-lane systems, only a single IR-based package detector is required to construct the package-in-the-tunnel indication subsystem  2300 , and in such embodiments, the range of the IR-based package detector will extend across the entire length of the conveyor belt. 
     Package-out-the-tunnel Indication Subsystem of the Second Illustrative Embodiment of the Present Invention 
     The package-out-of-the-tunnel indication subsystem  2400  depicted in FIGS. 33 and 34 are also realized as a pair of IR-based package detectors  2401 A and  2401 B which are mounted on the edges of the first and second conveyor lanes (CL 1  and CL 2 )  2102 A and  2102 B of the conveyor belt, respectively. Each IR-based package detector  2401 A and  2401 B comprises an infrared (IR) transmitter  2402  in synchronous operation with an IR receiver  2403 , as taught in U.S. Pat. No. 5,789,730, supra, incorporated herein by reference. The function of each synchronous IR transmitter and receiver  2402  and  2403  is to automatically detect the presence of a package (i.e. object) moving out of the scanning tunnel along the conveyor belt lane assigned thereto. Notably, in the illustrative embodiment, where there are dual package conveyor lanes, the IR range of each IR-based package detector  2401 A and  2401 B is adjusted so that it extends only half the width of the conveyor belt. In alternative single-lane systems, only a single IR-based package detector is required to construct the package-out-of-the-tunnel indication subsystem  2400 , and in such embodiments, the range of the IR-based package detector will extend across the entire length of the conveyor belt. 
     Package/Belt Velocity Measurement Subsystem of the Second Illustrative Embodiment of the Present Invention 
     As illustrated in FIG. 33, the package/belt velocity measurement subsystem  2600  of the illustrative embodiment is realized engaging a roller wheel  2601  (with a one linear foot circumference) against the undersurface of the conveyor belt  2101  and connecting a Model RG/RJ Optical Shaft Incremental encoder  2602  from PhotoCraft, Inc. of Elburn, Illinois, to the axle of the roller wheel  2601 . The function of the shaft encoder  2602  is to automatically generate a predetermined number of electrical pulses for each revolution of the roller wheel  2601  in order to indicate that the belt  2101  has undergone one linear foot of travel. These electrical pulses are provided to the high-speed input port of a programmed microprocessor  2603  which count the electrical pulses and generate a digital data element representative of the physical displacement of the conveyor belt, z=A. By timing the displacement of each linear foot of conveyor belt travel, the programmed microprocessor  2603  can calculate the instantaneous velocity of the conveyor belt and produce a digital data element representative thereof for use by the data element queuing, handling and processing subsystem  2800 . In the illustrative embodiment, the programmed microprocessor  2603  also carries out the computational process depicted in the flow chart set forth in FIGS. 40A through 40C in order to compute the instantaneous velocity of the conveyor belt of the system of the second illustrative embodiment of the present invention. 
     Weighing-In-motion Subsystem of the Second Illustrative Embodiment of the Present Invention 
     As shown in the FIG. 33, the in-motion package weighing subsystem  2500  is preferably arranged about the package in-the-tunnel detection subsystem  2400 . As shown, the in-motion weighing subsystem  2500  comprises: a pair of scale platforms  2501 A and  2501 B mounted along conveyor lanes CL 1  and CL 2 , respectively, and each producing analog or digital weight signals indicative of the weight of a package(s)  2205  moving across the scale platforms  2501 A and  2501 B; a filtering circuit  2502  for filtering the analog or digital weight signals in order to remove noise components and artifacts therefrom; and a signal processor  2503  for processing the filtered weight signals in order to produce a digital data element representative of the measured weight of the package, for provision to the data element queuing, handling and processing subsystem  2800 , via the I/O subsystem  2700 . Notably, the in-motion weighing subsystem  2700  of the illustrative embodiment can be realized using the EXPRESSWEIGHT™ Model 9480 In-Motion Variable Box and Package Weighing System from Mettler-Toledo, Inc. of Worthington, Ohio. 
     Input and Output Subsystem of the Second Illustrative Embodiment of the Present Invention 
     In the second illustrative embodiment shown in FIG. 33, the function of the input/output (I/O) subsystem  2700  is to manage the data inputs to and the data outputs from the data management computer system  2800 . In the illustrative embodiment, I/O subsystem  2700  can be realized using one or more rackmounted I/O adapter boxes, such as the RocketPort Series RM 16 -RJ 45  multiport serial controller having sixteen I/O ports, sold by the Comtrol Corporation, of Saint Paul, Minn. 
     Data Element Queuing. Handling And Processing Subsystem of the Second Illustrative Embodiment of the Present Invention 
     As illustrated in FIG. 34, data management computer  2800  is used to carry out the data element queuing, handling and processing subsystem  2900  in the second illustrative embodiment of the system of the invention. In FIG. 41, the structure and function of data element queuing, handling and processing subsystem  2900  is shown in greater detail. 
     As shown in FIG. 41, all data elements entering subsystem  2900  are provided to an I/O module  2901  having a plurality of input ports, and an output port which is connected to a data element time-stamping unit  2902  that is controlled by a timing/control unit  2903 . In the illustrative embodiment, there are four (4) general types of data elements that might be loaded into the system event queue  2904 , realized as a FIFO data structure known in the computing arts: (1) scan beam data elements; (2) package (weight) data elements; (3) package-in-tunnel (PIT) data elements; (4) package out-of-tunnel (POOT) data elements. 
     As shown in FIG. 36, the data element queuing, handling and processing subsystem  2900  further comprises a number of other modules, namely: a moving package tracking queue  2905  realized as a FIFO data structure known in the computing art, for queuing package (weight) data elements, package-in-tunnel (PIT) data elements, and package out-of-tunnel (POOT) data elements; and a data element analyzer  2906  (e.g. programmed microprocessor and associated memory structures) for reading the different types of data elements from the output of the system event queue  2904  and analyzing and handling the same according to the Data Element Handling Rules set forth in FIGS. 37A and 37B. 
     As shown in FIG. 36, scan beam data elements generated from the holographic laser scanning subsystems  2200 A and  2200 B are processed using a number of data processing modules, namely: a data element combining module  2907  for combining (i) each scan beam data element generated from holographic laser scanning subsystems  2200 A and  2200 B and accessed from the system event queue  2904  with (ii) each and every package data element in the moving package tracking queue  2905  so as to produce a plurality of combined data element pairs; a package location region (geometrical) modeling module  2908  for generating a vector-based (geometrical) model for the package location region indicated by the package data element in each combined data element pair produced by the data element combining module  2907 ; a scan beam geometry modeling module  2909  for generating a geometrical model for the laser scanning beam indicated by the scan beam data element in each combined data element pair produced by the data element combining module  2909 ; a homogeneous transformation (HG) module  2910  for transforming (i.e. converting) the coordinates of each scanning beam geometry model referenced to the local frame of reference (symbolically embedded within the holographic laser scanning system) into scanning beam geometry model coordinates referenced to the global coordinate reference R global  at the “scanning position” within the scanning tunnel; a scan beam and package location region intersection determination module  2911  for determining, for each combined data element pair produced from the data element combining module, whether the globally-referenced scan beam model produced by the HG transformation module  2910  intersects with the globally-referenced package location region model produced by the package location region modeling module  2908 , and if so, then the data output subsystem  2912  produces, as output, package identification data and package weight data for use by auxiliary systems associated with the tunnel scanning system of the second illustrative embodiment of the present invention. 
     Having described the overall structure and function of the data element queuing, handling and processing subsystem  2910  it is appropriate at this juncture to now briefly describe the operation thereof with reference to FIG.  36 . 
     Prior to loading into the system event queue  2904  each data element is time-stamped (i.e. T j ) by the time-stamping module  2902  driven by a master clock within timing/control unit  2903  referenced to the global reference frame R global . All data elements in the system event queue  2904  are handled by a data element analyzer/handler  2906  whose operation is governed by the Data Element Handling Rules set forth in the table of FIGS. 37A and 37B. In general, the data element queuing, handling and processing subsystem  2900  is best realized by an computing platform having a multi-tasking operating system (e.g. UNIX) capable of handling multiple “threads” at the same time. 
     Each package moving through the scanning tunnel shown in FIG. 33 will be represented by a data element (i.e. an object in an object-oriented programming environment e.g. Java programming environment) stored in the moving package tracking queue  2905 . Package data elements are placed in the moving package tracking queue  2905  and matched with each scan beam data element accessed from the system event queue  2904  using the data element combining module  2906 . Scan beam data elements generated from holographic-based scanning units  2200 A and  2200 B are processed along the scan data processing channel illustrated by blocks  2908 ,  2909 ,  2910  and  2911  set forth in FIG.  36 . 
     The Package Location Region Modeling Subsystem of the Present Invention 
     As shown in FIG. 38, for each package scanned within the tunnel scanning subsystem, a vector-based model of the package location region is created by the package location region modeling subsystem (i.e. module)  2920  deployed with the data element queuing, handling and processing subsystem  2900  of FIG.  36 . Notably, in the illustrative embodiment of FIG. 33, the “package location region” at the point of scanning within the tunnel is the subject matter of the modeling subsystem  2908 , rather than the geometry of the package itself as was the case in the system of the first illustrative embodiment shown in FIG. 1 through 32B. This is because the dimensions of the package are not determined in this illustrative embodiment, as they were in the first illustrative embodiment of the system of the present invention shown in FIG.  33 . In the second illustrative embodiment, each package location region  2920  is mathematically represented (i.e. modeled) using a set of vectors (referenced to x=0, y=0, z=0) in the global reference frame R global ,. The flow chart of FIGS. 39A and 39B describes a preferred modeling procedure for creating a vector-based model of the package location region at the point of package scanning within the tunnel scanning subsystem of FIG.  33 . 
     As indicated at Block A in FIG. 39A, the first step in the modeling procedure involves determining whether the detected package is located in the first conveyor lane (CL 1 ) or the second conveyor lane (CL 2 ). As indicated at Block B in FIG. 39A, the second step uses (i) the time stamp (Tj) placed on the package data element associated with the detected package, and (ii) the time stamp (Tj+k) placed on the scan beam data element matched to the package data element by the data element combining module  2907 . 
     As indicated at Block Bin FIG. 39A, the above-identified time stamps (Tj) and (Tj+k) are used to compute the distance “d” traveled by the package using the following formula: d=ΔT V, where ΔT=(Tj+k)−(Tj), and v=package velocity determined by the package/belt velocity measurement subsystem  2600 . As indicated at Block C in FIG. 39A, if the detected package resides in the first conveyor lane (CL 1 ), then the subsystem assigns thereto a “package location region” model specified by the vector model: 0≦x≦W/2; 0&lt;y; d−Δd≦z≦d+Δd in the global reference system, wherein Δd is the prespecified focal zone depth associated with the laser scanning beam scanning the package at its scanning position at time (Tj+k). 
     As indicated at Block D in FIG. 39B, if the detected package resides in the second conveyor lane (CL 2 ), then the subsystem assigns thereto a package location region model specified by the vector model: W/2≦x≦W; 0≦y; d−Δd≦z≦d+Δd in the global reference system, wherein Δd is the prespecified focal zone depth associated with the laser beam scanning the package at its scanning position at time (Tj+k). 
     The Scan Beam Geometry Modeling Subsystem of the Second Illustrative Embodiment of the Present Invention 
     In the tunnel scanning system of FIG. 33, the scan beam geometry modeling subsystem (i.e. module) depicted in FIGS. 25A through 26 is employed in the subsystem  2909  shown in FIG.  36 . Thus, the function of the scan beam geometry modeling subsystem (i.e. module)  2909  of FIG. 36 is to create a vector-based model for the propagation of the laser scanning beam (ray) (i) emanating from a particular point on the facet, (ii) to its point of reflection on the corresponding beam folding mirror, and (iii) towards to the focal plane determined by the focal length of the facet. This modeling method is similar to the method illustrated in FIGS.  25 B 1  through  26  and described hereinabove, and therefore will not be repeated to avoid obfuscation of the present invention. 
     The Homogeneous (HG) Transformation Module of the Present Invention 
     FIG. 40 schematically describes how the homogeneous (HG) transformation module  2910  of FIG. 36 uses homogeneous transformations to convert a vector-based “scanning beam” model referenced to a local scanner coordinate reference frame R localscannerj  into a corresponding vector-based “scanning beam” model referenced to the global scanner coordinate reference frame R global  symbolically embedded within the system of FIG.  33 . This mathematical technique is essential in that it converts locally-referenced coordinates used to represent the laser beam (which scanned a bar code symbol) into globally-referenced coordinates used to represent the same laser scanning beam. Notably, this method of coordinate conversion involves computing the package travel distance (z=d) between (i) the package detection position at which time stamp (Tj) is applied to the PIT data element, and (ii) the package scanning position at which time stamp (Tj+k) is applied to the scan beam data element. In the illustrative embodiment, this computation involves using (i) the package or conveyor belt velocity (v), and (ii) the difference in time (i.e. ΔT=(Tj+k)−(Tj)) indicated by the time stamps (Tj+k) and (Tj) placed on the scan beam data element and package data element, respectively, matched thereto during each scan beam/package location region intersection determination carried out within module  2911 . Notably, this package displacement distance z=d, defined between the package detection and scanning positions, is given by the mathematical expression d=v ΔT. 
     The Scan Beam and Package-Scanning Region Intersection Determination Subsystem of the Second Illustrative Embodiment of the Present Invention for Use with Scan Beam Data Elements Produced by Holographic Scanning Subsystems 
     The procedure carried out within the scan beam and package location region intersection determination module  2911  of FIG. 36 is shown in FIG.  41 . In general, the function of this computational module is to determine whether (i) the scan beam (rays) associated with a particular scan beam data element produced by a holographic scanning subsystem intersects with (ii) the package location region that has been modeled at a particular scanning position (i.e. specified by laser beam position information associated with the corresponding scan beam data element). If so, the module  2910  correlates the particular scan beam data element (i.e. package identification data element) with the package measurement data element corresponding to the modeled package location position. 
     As indicated at Block A in FIG. 41, the first step of the procedure involves using the minimum and maximum scan rays models of the laser scan beam (i.e. specified by the minimum and maximum facet scan angles) to determine the zone of coordinates about and within the focal planes of such scan rays models, expressed as: x min ±Δx;y min ±Δy;z min ±Δz; and x max ±Δx;y max ±Δy;z max ±Δz. 
     As indicated at Block B in FIG. 41 the next step of the method involves determining whether or not the zone of coordinates about and within the focal planes of the minimum and maximum scan rays fall within the spatial boundaries of the computed package location region within either the first or second conveyor lane of the system. If the scan rays fall within the zone of coordinates specified at Block A, then, at Block C in FIG. 41, the method involves outputting a data element in the output queue comprising the package identification data (and weight measurement data if taken) for use by other auxiliary subsystems operably connected to the system. In general, such data elements can be displayed graphically, printed out as a list, provided to sorting subsystems, shipping pricing subsystems, routing subsystems and the like. If the scan rays do not fall within the zone of coordinates specified at Block A then, the method involves not outputting any data element in the output queue. 
     Automated Tunnel-type Laser Scanning Package Identification and Weighing System Constructed According to a Third Illustrated Embodiment of the Present Invention: 
     Referring now to FIGS. 42 through 54B the automated laser scanning package identification and measurement system of the third illustrated embodiment  3000  will now be described in detail. In contrast with the capabilities of the systems of the first and second illustrative embodiments detailed above, the system of the third embodiment is capable of detecting, measuring, identifying and tracking multiple packages along the conveyor belt, regardless of their orientation or arrangement (e.g. stacked side-by-side and/or overlapping arrangements). As such, this novel system design, by incorporating many of the functionalities of the systems of the first and second illustrative embodiments, while providing several additional functionalities, enables simultaneous measurement and identification of non-singulated packages during transport along a high-speed conveyor subsystem so that auxiliary subsystems, operably connected to the tunnel-based system, can determine its safety and suitability for transport to its place of destination, and/or along its planned shipment route, with no human intervention. 
     Overview of the Tunnel Scanning System of the Third Illustrative Embodiment of the Present Invention 
     As shown in FIGS. 42 and 43, the automated simultaneous package detecting, dimensioning and identifying system of the third illustrative embodiment is indicated by reference numeral  3000  and comprises an integration of subsystems, namely: a high-speed package conveyor system  3100  having a conveyor belt  3101  having a width of at least  30  inches to support one or more package transport lanes along the conveyor belt; a tunnel or similar arrangement of bar code symbol readers  3200  including, in the illustrative embodiment, holographic and non-holographic (e.g. polygonal) laser scanning bar code symbol reading subsystems  3201 A through  3201 R supported overhead, alongside, and below the conveyor belt  3101  by a support frame  3202 , for generating a 3-D “six-axis” type omni-directional scanning volume  3203  thereabove, as depicted in FIGS. 5A through 9B, for scanning bar codes  3205  on packages  3204  transported therethrough; a first simultaneous multiple-package detection and dimensioning subsystem  3300  arranged on the input side of the tunnel scanning subsystem  3200 ; a second simultaneous multiple-package detection and dimensioning subsystem  3500  arranged on the output side of the tunnel scanning subsystem  3200 , and including, in the illustrative embodiment, (i) a LADAR-based imaging and dimensioning subsystem  3301 B for scanning packages and generating information representative of package dimensions (e.g. surface area, height and vertices) and optionally bar code symbols on the scanned surfaces thereof, (ii) a laser-based package-in-the tunnel (PIT) detection subsystem  3350  for simultaneously detecting multiple packages entering the scanning tunnel, generating a data element (i.e. data object) indicative of each such detected package and linking associated dimensional data (generated b y subsystem  3500 ) thereto, and linking the PIT data element and associated dimensional data element thereto, with a time stamp Ti generated at the time the package was detected by the PIT detection subsystem  3350 a weighing-in-motion subsystem  3700 , installed beneath the first simultaneous multiple-package detection and dimensioning subsystem  3500 , along the conveyor belt structure, for weighing packages as they are transported therealong; a package/belt velocity measurement subsystem  3800  realized using a roller wheel  3801  engaged against the undersurface of the conveyor belt  3101 , an optical shaft incremental encoder  3802  connected to the axle of the roller wheel  380   1  and producing an electrical pulse output stream per revolution of the roller wheel, and a programmed microprocessor  3803  for processing the output pulse stream and producing digital data representative of the velocity of the conveyor belt (and thus package transported thereby) at any instant in time; an input/output subsystem  3900  for managing the data inputs to and data outputs from the system of FIG. 33; and a data management computer  3925 , with a graphical user interface (GUI)  3926 , for realizing a data element queuing, handling and processing subsystem  3950  as shown in FIGS. 44 and 44A, as well as other data and system management functions. 
     The High-Speed Conveyor Belt Subsystem of the Third Illustrative Embodiment 
     As shown in FIG. 42, the high-speed conveyor belt subsystem  3100  of the third illustrative embodiment comprises: a plurality of rollers  3102  spaced apart and supported by support frame structure (not shown in FIG.  33 ); a belt structure  3101 , extending between and supported by a belt support structure  3103 , and having a width of at least  30  inches to provide one or more package transport lanes along the conveyor belt subsystem; a drive motor  3104  for imparting torque to the rollers; and a belt velocity controller  3105  for controlling the velocity of the belt and thus packages during system operation. 
     First Simultaneous Multiple-Package Detection and Dimensioning Subsystem of the Third Illustrative Embodiment of the Present Invention 
     As shown in FIG. 44, the first simultaneous multiple-package detection and dimensioning subsystem  3300  of the illustrative embodiment is arranged on the input side of the tunnel scanning subsystem  3200 , and comprises: a LADAR-based imaging and dimensioning unit  3301 , mounted above the conveyor belt as shown in FIG. 44, and adapted for scanning the upwardly-facing surfaces of packages moving along the conveyor belt using an amplitude modulated (AM) laser beam, and generating package dimension (PD) data element representative of dimensions (e.g. surface area, height and vertices) of the scanned package, and optionally bar code symbols on the scanned surfaces thereof; a laser-based package-in-the tunnel (PIT) detection subsystem  3350  for simultaneously detecting multiple packages entering the scanning tunnel, and generating a data element (i.e. data object) indicative of each such detected package; a timing-stamping unit  3304 , controlled by the master clock  3400  in FIG. 43, for generating time stamps T 7  to be attached to PD data elements and PIT data elements; a plurality of moving package tracking queues (FIFOs)  3305 A through  3305 D, each corresponding to different spatial regions above the conveyor belt and adapted for buffering “data objects” representative of detected packages and their various attributes, in an object-oriented programming environment (e.g. a Java programming environment); a data element controller (e.g. realized by a programmed microprocessor)  3306  for receiving PIT and PD data elements from subsystem  3301  or subsystem  3200  respectively, time-stamping PD data elements at the instant when the corresponding package is detected by the PIT detection subsystem  3350  writing the same to the input port of one of the moving package tracking queues  3305 A through  3305 D, and removing one or more data objects (representative of detected/tracked packages) from the output ports of one or more moving package tracking queues  3305 A through  3305 D and writing the same to the input port of the I/O unit  3951 A shown in FIG.  46 . Collectively, subcomponents  3302  through  3306  form the height profile data processor  3307  of the first simultaneous multiple-package detection and dimensioning subsystem  3300 . 
     As shown in FIG. 44A, the LADAR-based imaging and dimensioning subsystem  3301  comprises: at least one visible laser diode VLD  3340  for producing a low power visible laser beam  3341 ; an amplitude modulation (AM) circuit  3342  for modulating the amplitude of the visible laser beam produced from the VLD at a frequency f 0  (e.g. 75 Mhz) with up to 7.5 milliwatts of optical power; an opto-mechanical (e.g. polygonal-reflective or holographic-diffractive) scanning mechanism, an electro-optical scanning mechanism or an acousto-optical scanning mechanism  3343  for sweeping the modulated laser beam across a conveyor belt or like transport structure; a start-of-scan (SOS) pulse generating circuit  3352  including photodetector  3353  disposed inside the system housing, at the corner of the window, automatically generates a “start-of-scan” pulse each time the laser beam passes past this photodetector  3352 ; an optical detector (e.g. an avalanche-type photodetector)  3344 , a part of a larger photodetection module  3344 A, for converting received optical signal  3341 ′ into an electrical signal  3341 ″; an amplifier and filter circuit  3345  for isolating the f 0  signal component and amplifying it; a limiting amplifier  3345 A for maintaining a stable signal level; a phase detector  3346  for mixing the reference signal component f 0  from the AM circuit  3342  and the received signal component f 0  reflected from the packages and producing a resulting signal which is equal to a DC voltage proportional to the Cosine of the phase difference between the reference and the reflected f 0  signals; an amplifier circuit  3346 A for amplifying the phase difference signal; a received signal strength indicator (RSSI)  3354  for producing a voltage proportional to a LOG of the signal reflected from the package (i.e. target) which can be used to provide additional information; a reflectance level threshold analog multiplexer  3355  for rejecting information from the weak signals; a 12 bit A/D converter  3348  for converting the DC voltage signal from the RSSI circuit  3354  into a linear array of M raw range data elements {R n,i }, taken along m=M (e.g. M=256) equally spaced sampling positions (i.e. locations) along the width of the conveyor belt, where each range data element R n,i  provides a measure of the distance from the VLD  3340  to a point on the surface of the scanned package moving therealong; a high performance range/image data microcomputer  3356  with program memory, and data storage memory for buffering arrays of range data, and derivatives thereof, during the 2-D image data processing methods of the present invention; an A/D conversion circuit  3357  for converting analog scan data signals into lines of digital scan data samples; scan line data buffer array  3358  for buffering lines of digital scan data samples; and a programmed 2-D image data processor/decoder (e.g. microcomputer)  3359  for decode processing the bar code symbol represented in the structure of digital image in the scan line data buffer array, and producing symbol character data representative of the bar code symbol. 
     As shown in FIG. 44B, the LADAR-based imaging and dimensioning subsystem of the first illustrative embodiment  3301 A comprises: an optical bench  3360  for supporting optical and electro-optical components of the subsystem; a system housing  3361  having a light transmission aperture  3361 A for enclosing the optical bench and components mounted thereon in a shock-resistant manner; an eight-sided polygonal scanning element  3343 B, rotatably supported on the shaft of an electrical motor  3343 C mounted on the optical bench  3360 , as shown, for scanning the amplitude modulated laser beam  3341  produced by the VLD  3340 , along a single scanning plane projected through the light transmission aperture  3361  formed in the subsystem housing; a light collecting mirror  3362  mounted on the optical bench for collecting reflected laser light off a scanned object (e.g. package)  3364  and focusing the same to a focal point  3365 A on the surface of a stationary planar mirror  3365  mounted o n the optical bench; a small beam directing mirror  3366  mounted on the center of the light collecting mirror  3362  for directing the laser beam from the VLD  3340  to the rotating polygonal scanning element  3343 B and out the light transmission aperture  3361 A towards the package. The ambient light is filtered by a “front window” over the light transmission aperture  3361 A. The avalanche-type photodetector (APD)  3344  detects reflected laser light returning onto the surface of the rotating polygon  3343 B collected by the light collecting mirror  3362  and focused onto the stationary planar mirror  3365  The APD  3344 , with APD module  3344 A, converts light into electrical current signal having a frequency of 75 MHz signal and a phase delayed in relation to the reference signal. LOG amplifier  3345  amplifies the signal significantly and at the same time keep it within certain amplitude range. The limiting amplifiers  3345  and  3346 A ensure that a signal of the same amplitude is produced at the output of each stage regardless of how weak or how strong the reflected light signal is upon striking the APD  3344 . This automatic control feature allows the LADAR-based system to “scan” surfaces of different light reflectance at different distances. Also, the LOG amplifier  3345  enables the subsystem to measure an absolute value of the amplitude of the received laser signal. This gives information about any pattern of different reflectance on the “target” (the labels, large letters, pictures, etc.). In addition, the LOG amplifier  3345  enables setting a “threshold” for a signal level so that very weak or very strong reflections are attenuated. 
     All incoming laser return signals are processed in a synchronized manner using the SOS pulse produced by SOS pulse generating circuit  3353  and associated photodetector  3353 A so as to produce lines of digital range data representative of the distance from the polygonal scanning element to sampled points along the scanned object  3364 . As will be described in greater detail hereinafter, the programmed 2-D digital image data processing computer  3356 , realizable as a serial or parallel computing machine, preprocesses each row of raw range data collected during each scan of the amplitude-modulated laser beam, removes background information components, stores the object related data in an image buffer within image processing computer  3356 , and extracts therefrom information regarding the dimensions (e.g. area, height and vertices) of the object (e.g. package), after performing the necessary geometrical transformations. In connection therewith, it is noted at this juncture that while the collection and processing of raw “range” data is carried out with respect to the polar coordinate reference system R LADAR , symbolically embedded within the LADAR-based imaging and profiling subsystem, geometric transformations, schematically depicted in FIG. 44D, are used to translate (i.e. convert) such information to the global coordinate reference system R global  symbolically embedded within the package identification and measuring system, as illustrated in FIG.  42 . 
     Simultaneously, the analog electrical signal input to the logarithmic amplifier  3345  is also processed along a separate data processing channel, as shown in FIG. 44A, in order to recover amplitude modulation information from received lines of scan image data, for subsequent buffering in the 2-D image array  3358  and decoded-processing by 2-D image data processor-decoder  3359 . The output from the 2-D image data processor/decoder  3359  is symbol character data representative of the bar code symbol embodied within the structure of the received scan data image. 
     The signal and data processing circuitry employed in the subsystem  3301  can be realized on one or more PC boards  3368 . Various types of I/O interfaces  3369  can be used to interface the subsystem  3301  to I/O subsystem  3900 , as well as other devices with which it may be used in any particular application under consideration. 
     As shown in FIGS.  44 E 1  and E 2 , the LADAR-based imaging and dimensioning subsystem of the second illustrative embodiment  3301 B is realized as a holographic-type laser scanning system, as taught generally in Applicants&#39; U.S. Pat. Nos. 6,158,659; 6,085,978; 5,984,185; 6,073,846; and U.S. application No. 08/573,949 filed Dec. 18, 1995, abandoned, each incorporated herein by reference. As shown in FIGS.  44 E 1  and E 2 , the VLD  3340  can be realized as a laser beam production module having a multi-function-HOE (i.e. plate) embedded therewithin as taught in Applicants&#39; U.S. Pat. Nos. 6,158,659; 6,085,978; 5,984,185; 6,073,846; and U.S. application No. 08/573,949 filed Dec. 18, 1995, abandoned, supra. The function of this laser beam production module is to produce a focused amplitude-modulated (AM) laser beam. As shown in FIGS.  44 E 1  and E 2 , the laser beam scanning mechanism  3341  of FIG. 3341 is realized as a holographic laser scanning disc  3370  rotatably mounted on the shaft of an electric motor  3371  mounted on the optical bench  3372  within the subsystem housing  3373 . As shown in FIG.  44 E 3 , the holographic scanning disc of the first illustrative embodiment has eighteen facets with six different focal distances, namely:  36 ″,  41 ″,  46 ″,  52 ″,  58 ″ and  64 ″. These facets generate laser beams that focus with six different focal planes, where each focal plane is repeated three times per revolution of the scanning disc. The design parameters for each facet on the holographic scanning disc of FIG.  44 E 3  are set forth in the Table of FIG.  44 E 4 . The design parameters set forth in the table of FIG.  44 E 3  are defined in detail in the above-referenced US Patent Applications. During operation, the resulting scanning pattern generated by this subsystem has the form of a single straight plane or line (hereinafter referred to as a “linear-type” laser scanning pattern) having six focal regions which, as shown in FIG.  44 E 5 , may spatially overlap. In the first illustrative embodiment, the length of each scan line at each of the six focal planes is 22.35″. Notably, all scan lines leave (i.e. diffract from) the scanning disc at the same elevation angle. 
     As shown in FIGS.  44 E 1  and  44 E 2 , a post-disk beam folding mirror  3374  is mounted above the scanning disc  3370 , at a tilt angle which causes the reflected laser beam to travel above scanning disk, parallel to the disk surface, and exit through the light transmission window  3373 A at the opposite end of the subsystem scanner housing. This arrangement allows for a more compact scanner design and increases the optical path length inside the scanner box. In turn, this reduces the optical throw of the scanner (i.e. the minimum distance from the scanner window at which the scanner can read). By selecting the proper angle of diffraction off the scanning disc, it is possible, with this holographic laser scanner design, to minimize, and virtually eliminate, scan line bow so that the scan lines are all essentially straight lines. This has a number of important advantages in a variety of bar code scanning applications (e.g. when reading high density bar codes with high aspect ratios, when reading bar codes with relatively larger errors in orientation, and when reading bar code symbols at greater label velocities). 
     Alternatively, a second beam folding mirror (not shown) can be mounted within the scanner housing, just prior to the scanner window  3373 A, in order to direct the AM laser beam out a new window formed on the top surface of the scanner, rather than on the side surface thereof, as shown in FIG.  44 E 2 . This modification to the scanner design would allow the AM laser beam to exit the scanner housing perpendicular to the scanning disk, rather than parallel thereto. This modification would minimize the distance that the scanner extends out into the area next to a conveyor system, or it could reduce the required overhead space in an overhead scanning application. Other beam folding options are also envisioned. 
     As shown in FIG.  44 E 2 , the LADAR-based subsystem  330   1 B also includes a parabolic light collecting mirror  3375  mounted beneath the scanning disc, upon the optical bench  3372 . The function of the light collection mirror  3375  is to (1) collect laser light that reflects off the scanned package  3364  and transmitted back through the scanning facet that generated the respective laser beam, and (2) focus the same to a focal point  3376  on a photodetector  3344  mounted on bracket  3377 , above the scanning disc and light collection mirror  3375  as shown in FIG.  44 E 2 . Preferably, bracket  3377  can be used to support post disc beam folding mirror  3374 , as well. Also, photodetector  3344  can be realized as an avalanche-type photodetector as described above and shown in greater detail in FIG.  44 C. The function of photodetector  3344  is to detect collected laser (return) light focused to focal point  3376 , and produce an electrical signal corresponding thereto. The signal and data processing shown in FIG. 44A can be realized on one or more PC boards  3378  and can be provided with the necessary I/O interfaces required in any particular application. 
     The holographic LADAR-based subsystem  3301 B operates in a manner similar to subsystem  3301 A, described above, For each sweep of the AM laser beam, raw digital range data is generated and processed to produce package dimension type data described above. Also, the programmed digital image data processor  3359 , or an analog equivalent of the general type described hereinabove in connection with the other system embodiments hereof, the analog signal from photodetector  3344  to produce symbol character data representative of bar code symbols on the scanned packages. 
     Notably, the holographic LADAR-based imaging and dimensioning systems  3301 B described above, without modification, can also function as compact single-line, laser scanner having very large depth of field, reduced optical throw, and laser scan lines with minimum curvature (i.e. minimum bow). The single line scanner uses a holographic disk to create a sequence of scan lines that all leave the disk at the same diffraction angle but have different focal lengths. In the first embodiment of this scanner described above, the resulting linear scan pattern has six focal planes, providing a very large depth of field for high density bar codes. As mentioned above, six different holographic facets for the six focal planes are spatially repeated three times around the disk for a total of eighteen facets on the scanning disk. This replication of the basic scan pattern results in a high speed scanner. 
     In a second embodiment of this holographic laser scanner, the scanning disc could be provided with four different holographic facets, spatially repeated around the disc five times for a total of twenty facets on the scanning disc. This would result in a linear scanning pattern having four focal planes, providing greater scan speed for lower density bar code symbols. In some alternative embodiments, it may be desirable to provide some rastering of the linear scan pattern. 
     The LADAR-based imaging and dimensioning devices  3501 A and  3501 B described above have numerous applications outside of automatic package identifications and measurement, described hereinabove. In general, each of these ultra-compact devices of the present invention has the following capacities: measuring box size and shape to a tolerance of +/−2 to 3 mm, at 800 scans per second; locate positions of labels on transported boxes; operating from the top of a conveyor belt avoiding the need to make a break therein; identify material present or not present in tilt trays, slots, etc.; confirming the shapes and sizes of objects in tunnel applications (e.g. also solves supermarket check out problem); counting people, animals, and other moving items moving through a portal; measuring shape and size of items; as well as measuring (or profiling) virtually anything in the three dimension space to a tolerance of about 2 mm or so, and generate an accurate coordinate map therefrom. 
     Two-Dimensional Range Data Processing Method of Present Invention 
     The function of the 2-D range data map processor  3356  depicted in FIG. 44A is to process rows of raw range data captured by the LADAR-based imaging and dimensioning subsystem so that package dimension (PD) data is extracted therefrom and data representative of the package dimension data is produced for use by other subsystems in the package identification and measuring system. In accordance with the principles of the present invention, this functionality is realized using a novel 2-D range data processing method. As shown in FIG. 44F, this method employs three stags of preprocessing operations on the captured rows of range data, indicated as (1) “Smoothing”, (2) “Edge-detection”, and (3) “Background Discrimination”. Thereafter, the method employs one stage of “Data Extraction” operations for extracting package dimension data therefrom. As will be described in greater detail hereinafter, the data extraction stage employs (i) 2-D image contour tracing techniques to locate range data indices spatially corresponding to the corner points associated with the scanned object (e.g. package), and (ii) geometric transformations to compute the height, vertices and surface area of the scanned package. 
     As shown in FIG. 44G, the steps involved in carrying out the preprocessing stages of data processing are indicated as Steps A 1  through A 5 , described in Blocks A through E in FIGS.  44 H 1  through  44 H 2 , whereas the steps involved in carrying out the data extraction stage are indicated as Steps B 1  through B 14 , described in Blocks F through S in FIGS.  44 H 2  through  44 H 5 . 
     As indicated at Block A in FIG.  44 H 1 , Step A 1  involves capturing lines (rows) of digitized “range data” produced by the laser scanning/ranging unit, during each sweep of the amplitude modulated laser beam across the width of the conveyor belt. Each row of raw range data has a predetermined number of range value samples (e.g. M=256) taken during each scan across the conveyor belt. Each such range data sample represents the magnitude of the position vector pointing to the corresponding sample point on the scanned package, referenced with respect to a polar-type coordinate system symbolically embedded within the LADAR-based imaging and dimensioning subsystem. As indicated at Block A, Step A 1  also involves loading a predetermined number of rows of raw range data samples into a FIFO-type Preprocessing Data Buffer (e.g. M=9) for buffering 9 rows of range data at any instant of time. 
     FIG. 44I sets forth a graphical image of a 2-D range data map synthesized from a large number of rows of raw range data captured from the LADAR-based imaging and dimensioning subsystem of the present invention, in accordance with the data capturing operations specified in Step Al of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 . 
     As schematically illustrated in block form in FIG. 44G, “CONTROL STRUCTURES” are required and used by the LADAR-based subsystem of the present invention. General control structures as “divide and conquer,” backtracking, dynamic programming etc. support the implementation of the specific algorithms used in the LADAR-based subsystem hereof. These control structures consist of sequences or loops connecting abstract program modules. Window functions or operator kernels employed herein have to be embedded into a general control structure (pixel program loop), organizing the move of placed windows F(p) into all (non-border) point positions p of a given image according to a selected scan order, ensuring that the entire image domain is processed. Allowing small modifications, such a pixel program loop can be used for different local operators. For example, logically structured operators are characterized by data-dependent and/or location-dependent decisions. These decisions take place within the pixel program loop, and do not influence the general control structure of the program. 
     The use of predefined control structures allows often to describe the operators by giving only the operator kernel, which plays the role of a subroutine called at each pixel program loop. In general, the control structure of window operators allows the selection between different square windows of n×n pixel s (odd n), and between parallel or sequential processing. Special inputs made by the user at the beginning of the control structure, i.e. at program start, specify these selections. 
     With the input of a special parameter (PARSEQ=0 or =1) the user chooses parallel or sequential processing. If only parallel processing has to be implemented, then some program lines of the control structure can be eliminated. These rows have the label ⊕ in the following control structures. 
     The structure requires the following data arrays: 
     Ind(1 . . . n): This array contains the indices of indirect row addressing. for example, the initial values are given by DATA ind (1, 2, 3, 4, 5), if n=5. 
     Xind(1 . . . a ), and these values are used as arguments of the operator kernel (cp. FIG.  3 . 5 ). For example, if n=5 then the following arrays are used: 
     DATA xind(1, 1, 0, −1, −1 −1, 0, 1, 2, 2, 2, 1, 0, −1, −2, −2,−2, −2, −2, −1, 0, 1, 2, 2, 0); 
     DATA yind(0, 1, 1, 1, 0, −1, −1, −1, 0, 1, 2, 2, 2, 2, 2, 1, 0, −1, −2, −2, −2, −2, −2, −1, 0) 
     The control structure uses the following parameters and image files: The window size n is assumed to be odd. The value k::=(n−1)/2 follows after initializing n. 
     ⊕ The parameter PARSEQ is specified for selecting parallel (PARSEQ=0) or sequential (PARSEQ=1) processing. For label ⊕, see above. The original image f (or several input images in certain cases) and the resultant image h (in file OUT) have to be allocated as image files 
     Processing follows the scheme as given in FIG.  44 G 1 . Afterwards all open image files must be closed. Many of the operator kernels can be inserted at the location “processing of picture window . . . ” of this control structure in FIG.  44 G 1 . If so then this control structure is mentioned in the operator pseudo-program at beginning of point (4). In this way repeated listings of identical control structures are avoided. 
     While the control structure includes row-wise buffering, operations which are necessary for opening or allocating an image file, acquiring an image (e.g. 2-D range map) via the LADAR-based scanning mechanism described above, are not contained in this control structure. Details on “general control structures” are provided in the textbook “HANDBOOK OF IMAGE PROCESSING OPERATORS” (1996) by R. Kletpe and P. Zamperoni, published by John Wiley and Sons, incorporated herein by reference. 
     As indicated at Block B in FIG.  44 H 1 , Step A 2  involves using, at each processing cycle and synchronized with the capture of each new row of raw range data, a 2-D (9×9) window function embedded into a general control structure (e.g. pixel program loop), to “smooth” each line (or row) of raw range data buffered in the M=9 FIFO Data Buffer using Dilution and Erosion (D/E) processes based on non-linear type min./max methods well known in the image processing art. The output from this non-linear operation is a single row of smooth range data of length M=256 which is input to a three row FIFO buffer, as shown in FIG.  44 G. Details on the operation of the D/E algorithm are provided in the textbook “HANDBOOK OF IMAGE PROCESSING OPERATORS” (1996) by R. Kletpe and P. Zamperoni, published by John Wiley and Sons, supra. 
     FIG.  44 I 2  sets forth a graphical image of a 2-D range data map after being processed by the data processing operations specified in Step A 2  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 . 
     As indicated at Block C in FIG.  44 H 1 , Step A 3  involves using, at each processing cycle, a 2-D (3×3) convolution kernel based on the Sobel operato, and embedded into a general control structure (e.g. pixel program loop), to edge-detect each buffered row of smoothed range data of length M=256 which is input to a first one row (N=1) FIFO buffer as shown in FIG.  44 G. The output row of “edge-detected” range data represents the first spatial derivative of the buffered rows of range data along the n direction of the N=9 FIFO (corresponding to the first spatial derivative of the range data captured along the y direction of the conveyor belt). Details on the operation of the D/E algorithm are provided in the textbook “HANDBOOK OF IMAGE PROCESSING OPERATORS” (1996) by R. Kletpe and P. Zamperoni, supra. 
     FIG.  44 I 3  sets forth a graphical image of a 2-D range data map after being processed by the data processing operations specified in Step A 3  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     As indicated at Block D in FIG.  44 H 2 , Step A 4  involves using, at each processing cycle, a 7-tap FIR-type digital filter (H 1 ) to compute the first spatial derivative of the buffered row of edge-detected range data along the m direction of the N=9 FIFO (corresponding to the first spatial derivative of the range data captured along the x direction of the conveyor belt). The output of this operation is stored in a second one row (N=1) FIFO, as shown in FIG.  44 G. 
     FIG.  44 I 4  sets forth a graphical image of a 2-D range data map synthesized from a large number of rows of background data removed from rows of raw range data by the data processing operations specified in Step A 4  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 ; 
     As indicated at Block E in FIG.  44 H 2 , Step A 5  involves analyzing, at each processing cycle, the edge-detected derivative stored in the second one row FIFO in order to (1) find the maximum value thereof, and then (2) compare the maximum derivative value to a predetermined threshold value. If any of the maximum first derivative values is larger than the predetermined threshold value, then the unloaded row of smoothed range data (from output port of the three row FIFO) is labeled as containing object data, and is loaded into the input port of the FIFO-type Object-related Data Buffer (ODB), also referred to as the “f” Buffer, for future use. Otherwise, the unloaded row of smoothed range data from the three row FIFO is labeled as containing background data and is loaded into the input port of the FIFO-type Background Data Buffer (BDB), and possibly also the ODB, for future use. This concludes the preprocessing operations performed on the input stream of range data from the conveyor belt. The subsequent steps form part of the Dimension Extraction stage of the image data processing method of the present invention. 
     As indicated at Blocks F through H in FIGS.  44 H 2  and  44 H 3 , Steps B 1  through B 3  involves processing rows of smoothed range data in order to derive a 2-D first spatial derivative of the range data map so that 2-D contour tracing can be reliably performed on this spatial derivative data, and the indices m and n associated with corner points of the scanned package found. These data processing operations are further described in the algorithm set forth in FIG.  44 J. 
     As indicated at Block Fin FIG.  44 H 2 , Step B 1  involves computing, at each processing cycle and for each column position in the rows of background data in the BDB (referenced by index m), the “median value” based on the current rows of background data buffered therein. This computational operation is indicated in the first line of Block B in FIG.  44 J. 
     As indicated at Block G in FIG.  44 H 2  Step B 2  involves subtracting, at each processing cycle and for each row of object-related data in the ODB, the precomputed median value (BG) from the corresponding range value (f=X), so as to produce a difference value (X-BG) for each of the 256 column positions in corresponding row of object-related data being buffered in the ODB (also indicated as the “f buffer”), thereby producing a vertical first discrete derivative thereof (having a column length M=256). This computational operation is indicated in the second line of Block B in FIG.  44 J. 
     As indicated at Block H in FIG.  44 H 3 , Step B 3  involves smoothing, at each processing cycle, the computed vertical first discrete derivative. This can be achieved by convolving the same with a 5-tap FIR smoothing filter and truncating the resultant row of smoothed discrete derivative data to length M=256. Thereafter, the row of smoothed discrete derivative data is loaded into the “diff” (i.e. derivative) data buffer having m=256 columns and n=10,000 or more rows (as required by the collected range data map). The output row of discrete derivative data contains object-related data only, and most background noise will be eliminated. This computational operation is indicated at Block C in FIG.  44 J. As shown therein, this operation is repeated for each row of smoothed range data until the condition set forth in Block D in FIG. 44J is satisfied. When this condition is satisfied, then the control structure underlying the data processing method hereof invokes the contour tracing algorithm set forth in FIG. 44K, and described in greater detail hereinbelow. 
     FIG.  44 I 5  is a graphical image of a differentiated 2-D range data map from which background data, indicated in FIG.  44 I 4 , is subtracted during being processed by the data processing operations specified in Steps B 1 , B 2  and B 3  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 . 
     As indicated at Block I in FIG.  44 H 3 , Step B 4  involves performing, at each processing cycle, a 2-D image-based contour tracing operation on the discrete derivative data currently buffered in the diff data buffer in order to produce an array of m,n contour points in M-N Space (and corresponding to x,y contour points in X-Y Cartesian Space). The contour tracing algorithm set forth in FIG. 44K can be used to carry out this step of the data processing method hereof. The array of contour points m,n produced by the algorithm will correspond to the sides of the polygonal object embodied in the rows of object data currently buffered within the Object Data Buffer, and the output data set produced from this step of the method contains extraneous corner points which need to be removed from the produced array of contour points. 
     The program set forth in FIG. 44K traces contours of objects in a bilevel image. It stores the encoded contours (Freeman code) into a file. This program could also be extended to an image-to-image transformation, e.g. by computing geometrical features (convex hull, diameter etc.) for these contours and by visualizing these features. These possible extensions are not introduced here, because this would require the development of a composite program taking account of too many different geometrical features. 
     The program of FIG. 44K performs a complete object search in the input image (i.e. the diff. Of the 2-D range map). If there are several objects (i.e. 8-components), then the program finds all of them, and it computes the contour codes of all objects. The input image can also be a gray value image, as would the case in many package scanning environments. In this case, a global threshold discriminates between object points (gray value higher than the threshold) and background points (gray value lower or equal than the threshold.). The resultant file of encoded contours allows an error-free reconstruction of the bilevel input image. 
     The contour encoding algorithm is a fundamental procedure. It is often used in the context of shape analysis, of geometrical feature extraction of data-reducing image code generation, or of geometrical transformations of bilevel images. Contour codes have the advantage that geometrical features of the object can be computed by means of numerical manipulations of the contour code chain, sometimes just based on simple syntax rules. Algorithms on contour code chains are very time-efficient in general, and they do not need access to the image data. A contour code chain allows an exact reconstruction of the object. 
     The whole process of contour code determination consists of two phases: object finding, and contour tracing. The first phase searches the image line-by-line until a reliable initial point of the next object is found. The second phase traces the contour of this object, and stores the resultant code sequence into a file. Both phases alternate during the whole process until all objects are encoded. 
     Details on the operation of the contour tracing algorithm, set forth in FIG. 44K, provided in the textbook “HANDBOOK OF IMAGE PROCESSING OPERATORS” (1996) by R. Kletpe and P. Zamperoni, published by John Wiley and Sons, incorporated herein by reference. 
     As indicated at Blocks J through M in FIGS.  44 H 3  through  44 H 4 , Steps B 5  through B 8  involves processing the m and n indices associated with the traced contours generated in Step B 4 , so as to find the m and n indices of those corner points which qualify as “break points” and thus possibly corresponding to the corners of the scanned package. 
     As indicated at Block J in FIG.  44 H 3 , Step B 5  involves storing, at each processing cycle, the m,n indices (associated with the corner points of the traced contours) in the x-boundary and y-boundary buffers, respectively. Notably, the length of the X-boundary buffer is M=256, and the length of the y-boundary buffer is also M=256. This computational operation is indicated at Block A in FIG.  44 L. 
     As indicated at Block K in FIG.  44 H 3 , Step B 6  involves detecting, at each processing cycle, the m indices associated with “corner points” in the traced contours. This step can be achieved by convolving the current discrete data set stored in the x-boundary buffer (of length M=256) with the 11-tap FHR filter (i.e. low-pass  1 st differentiator) and storing the resultant discrete min dice data set in the x-temp-array. This computational operation is indicated at Block B in FIG.  44 L. 
     FIG. 44L is a flow chart describing the operations carried out during Step B 6  and B 7  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 . 
     As indicated at Block L in FIG.  44 H 4 , Step B 7  involves detecting, at each processing cycle, the n indices associated with the “corner points” in the traced contours. This step can be achieved by convolving the discrete data set stored i n the y-boundary buffer (of length N) with the an 11-tap FIR digital filter (i.e. low-pass 1st differentiator) and then storing the resultant discrete min dice data set in the y-temp-array. This computational operation is indicated at Block B in FIG.  44 M. 
     FIG. 44M is a flow chart describing the operations carried out during Steps B 6  and B 7  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 . 
     As indicated at Block M in FIG.  44 H 4 , Step B 8  involves finding, at each processing cycle, the “break points” among the detected corner indices stored in the x-temp-array and y-temp-arrays, and buffering the m and n indices associated with these break points in the breaks buffer. In essence, the algorithm set forth in FIG. 44M first determines which m indices in the x_temp_array undergoes a “first derivative” zero-crossing, and then determines which n indices in the y-temp-array undergoes a “first derivative” zero-crossing. Any point along the traced contour having an m or n index (i.e. coordinate) with a zero value, indicating a range peak at the corresponding indices, is deemed to be a “break” point along the traced contour. A break point can be thought of as a location where the traced contour experiences a spatial discontinuity, corresponding to a possible corner point associated with the scanned package. 
     As indicated at Block N in FIG.  44 H 4 , Step B 9  involves performing, at each processing cycle, linear curve fitting between every two consecutive break points stored in the breaks buffer, in order to produce a single line representation thereof. Each line constitutes a side of a polygon representation of the object embodied within the structure of the range data map buffered in the ODB (i.e. “f data buffer”). For every two consecutive sides of the polygon representation, the intersection point is determined, and deemed a corner vertex of the polygon. 
     FIGS.  44 O 1  through  44 O 4  set forth polygonal contours of the type traced during Step B 9 , having corner points which are reduced using the algorithm set forth in FIG.  44 N. 
     As indicated at Block O in FIG.  44 H 4 , Step B 10  involves at each processing cycle, reducing the corner vertices once all corner coordinates (vertices) have been obtained. This step can be carried out using the Sharp/Dull Angle Elimination algorithm and close corner elimination operators, set forth in FIG.  44 N. Typically, the final result is a set of m and n indices corresponding to the x and y coordinates associated with the four corners coordinates of a cubic box, which set is thereafter stored in a corner coordinate (or indice) array. 
     FIG. 44N is a flow chart describing the operations carried out during Step B 10  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 . This algorithm eliminate wrong corners produced by the LADAR-based subsystem hereof. Vertex deletion is done is 2 stages where vertexes with too sharp an angle are deleted in the first. The following, second, stage deletes dull vertexes. 
     FIG.  44 D 1  is an example of an output representing a rectangle with three erroneous corners caused by noise. The goal of the algorithm is to combine lines ‘2’, ‘3’, ‘4’, and ‘5’ into a single line, therefore vertexes ‘c’, ‘d’, and ‘e’ have to be eliminated. The first stage searches vertexes ‘a’ to ‘g and eliminates any sharp ones. Vertex ‘d’ is deleted in the first round and the polygon would look like the one in FIG.  44 O 2 . A second round turns out no sharp angles and stage  1  is completed. 
     The second stage of the algorithm again searches vertexes ‘a’ to ‘g’ and eliminates any dull ones. First, vertex ‘c’ is deleted, then ‘e’. The polygon transformed from FIG.  44 O 2  to FIG.  44 O 3  then to FIG.  44 O 44 . A second round in stage  2  also turns out nothing and the algorithm yields the polygon in FIG.  44 O 4 . 
     As indicated at Block P in FIG.  44 H 5 , Step B 11  involves computing the average range value of the contour points currently buffered in the ODB so as to provide an average height value for the box, and then, for each corner point in the corner coordinate array, use the computed average range value to compute the z coordinate corresponding thereto, and referenced with respect to the global coordinate frame of reference. 
     Having determined the (m,n) indices corresponding to the corner points of the scanned package, and the average height of the scanned package, the data processing method hereof then proceeds to compute corresponding x and y coordinates for each such set of corner indices using geometric transformations. As shown in FIG. 44P, these geometric transformation can be schematically represented in the “polar-coordinate” based geometrical representation of the LADAR-based imaging and dimensioning subsystem of the present invention. 
     In particular, as indicated at Block Q in FIG.  44 H 5 , Step B 12  involves computing the x and y coordinates associated with each corner point currently buffered in the corner coordinate array and specified by indices m and n. Coordinates x and y are referenced with respect to the global coordinate frame. Mathematical expressions for computing these parameters, within geometric transformations implicitly embodied therewithin, can be derived using the geometrical model set forth in FIG.  44 D. 
     According to the geometrical model shown in FIG. 44D, every point scanned by the AM laser beam of the LADAR-based subsystem hereof can be specified a position vector defined within a polar coordinate system embodied therewithin, as shown. Each position vector can be represented by (R, α), where R is the magnitude of the distance from the light source/scanner (e.g. polygonal or holographic scanning element) to the point on the scanned object, and α is the angle of the position vector emanating from the start of scan point, as reference in FIG. 44D, and where the SOS pulse photodetector  3352 A in FIG. 44A is located. The value R is obtained through the phase detection output from A/D conversion circuit  3348 . The value α is obtained from the sampling set up, using the SOS pulse generator  3352 , shown in FIG.  44 A. For example, if a total of M points were sampled at a constant interval from the start of scanning line to the stop scanning line, as shown in FIG. 44D, and the point in question in the mth sampling, then α=m/M. 
     In view of the fact that the polar-coordinate based LADAR unit hereof  3501  and  3502  produces accurately measured values for parameters (R, α, m), the data processing method hereof must employ a geometric transformation between (R, α, m) and (H, x, y), Cartesian coordinate parameters referenced relative to the global coordinate reference employed by the greater system for package data tracking operations and the like. A suitable geometrical transformation for (R, α, m) - - - (H, x, y) is set forth below. 
     The first parameter in (H, x, y), namely “H”, the height of the scanned object (e.g. package), can be computed using the formula: 
     
       
           H=D−R  Sin(π/2−θ/2+α) 
       
     
     The second parameter in (H, x, y),namely, “x”, the position of the sampling point with respect to the edge of the conveyor belt can then be computed using the formula: 
     
       
           x=w /2 −R  Cos(π/2−θ/2+α) 
       
     
     assuming the LADAR-based unit is mounted at the center of the conveyor belt (i.e. at w/2). 
     Finally, the third parameter in (H, x, y), namely “y”, the coordinate along the belt&#39;s travel-ling direction, can be computed using the following formula: 
     
       
         
           y=m.v 
         
       
     
     where ν is the velocity from the tachometer ( 3803 ). 
     As indicated at Block R in FIG.  44 H 5 , Step B 13  involves computing the surface area of the object represented by the contours currently represented in the contour buffer, using the m,n coordinates associated with the corner vertices m and n currently buffered in the corner coordinate array. 
     The algorithm set forth in FIG. 44Q sets forth surface computation operations which can be carried out during Step B 13  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 . FIGS.  44 R 1  and  44 R 2  set forth polygonal contours which illustrative the method of package surface area computation carried out during Step B 13  of the flow chart set forth in FIGS.  44 H 1  through  44 H 5 .                    
     The algorithm shown in FIG. 44Q computes the area of the polygon-shaped package by summing the areas of the triangles that made up the polygon. For example, the polygon shown in FIG.  44 R 1  is made up of 5 triangles. The area 012, 023, 034, and 056 are positive and is negative for 045. In order to determine the polarity of the triangle (OAB)&#39;s area, angles of the 2 vectors OA and OB need to be computed. If the angle of OB is bigger than OA, the area is positive, otherwise negative. The package&#39;s area will be the absolute value of the above sum. 
     As indicated at Block S in FIG.  44 H 5 , Step B 14  involves outputting, for the geometrically represented object (which has been scanned and data-sampled), the computed surface area, height, and corner x,y coordinates thereof, referenced with respect to the global coordinate reference frame. 
     In summary, the LADAR-based imaging and profiling subsystem of the present invention is capable of performing two distinct functions: by analyzing the phase difference between the transmitted AM laser beam, and the received (i.e. return) AM laser bean, the subsystem can geometrically profile virtually any object that is passed; also, by analyzing the magnitude of the return AM laser beam, the subsystem can generate a video image of the object (e.g. box or package or whatever) that is moved across the transmitted AM laser beam. 
     In alternative embodiments, it would be desirable to use blue VLDs with a characteristic wavelength of about 405 nm (now commercially available from Nichia, of Japan in order to generate the AM laser beam having a high resolution and long DOF. This would enable the LADAR-based imaging and profiling subsystem hereof to capture fairly high resolution images of scanned objects and thus read  1 D and  2 D bar code symbols embodied in the structure thereof, and thus be successfully decoded. Also, by providing mechanisms for causing the AM laser beam to be locally “dithered” about a reference direction, it should be possible to produce high density raster scanning patterns for read labels bearing text and the like using OCR techniques, well known in the art. Furthermore, the LADAR-based imaging and profiling subsystem of the present invention can b e used in systems, wherein the AM laser beam produced therefrom is used to locate the label (e.g. text or bar code symbol label), while a high speed rastered laser beam is steered to the located label and aggressively scanned therewith in order to read the label. 
     Second Simultaneous Multiple-Package Detection and Dimensioning Subsystem of the Third Illustrative Embodiment of the Present Invention 
     As shown in FIG. 45, the second simultaneous multiple-package detection and dimensioning subsystem  3500  of the illustrative embodiment is arranged on the output side of the tunnel scanning subsystem  3200 , and comprises the same subcomponents contained in the first simultaneous multiple-package detection and dimensioning subsystem  3300 . The only major difference is function: the function of subsystem  3500  is to simultaneously detect one or more packages exiting the scanning tunnel  3200 , and generate for each such package, package dimension (PD) data and a package-out-of-tunnel (POOT) data element therefor when the POOT detection subsystem  3550 , including laser light curtain or like device, detects the package downstream. The PD and POOT data elements produced from subsystem  3500  are processed in a manner similar to the PD and PIT data elements produced by subsystem  3300 . 
     Weighing-In-Motion Subsystem of the Third Illustrative Embodiment of the Present Invention 
     As shown in the FIGS. 42 and 43, the in-motion package weighing subsystem  3700  is preferably arranged about the first multiple package detection and dimensioning subsystem  3300 . As in the first and second illustrative system embodiments, the in-motion weighing subsystem  3700  comprises: a scale platform integrated with the conveyor belt  3101 , for producing analog or digital weight signals indicative of the weight of a package(s)  3204  moving across the scale platform; a filtering circuit for filtering the analog or digital weight signals in order to remove noise components and artifacts therefrom; and a signal processor for processing the filtered weight signals in order to produce a digital word representative of the measured weight of the package. Notably, the in-motion weighing subsystem of the illustrative embodiment can be used to realize using the 9480 EXPRESSWEIGHT™ In-Motion Variable Box and Package Weighing System from Mettler-Toledo, Inc. of Worthington, Ohio. 
     Package/Belt Velocity Measurement Subsystem of the Third Illustrative Embodiment of the Present Invention 
     In the third illustrative system embodiment shown in FIGS. 42 and 43, the package/belt velocity measurement subsystem  3800  is realized as a number of subcomponents, namely: a roller wheel  3801  engaged against the undersurface of the conveyor belt  3101 ; an optical shaft incremental encoder  3802  connected to the axle of the roller wheel  3801  and producing an electrical pulse output stream per revolution of the roller wheel; and a programmed microprocessor  3803  for processing the output pulse stream and producing digital data representative of the velocity of the conveyor belt (and thus package transported thereby) at any instant in time. As shown in FIG. 42, the digital velocity information is provided to an assigned data input port provided by the I/O subsystem  3900 . 
     Input/Output Subsystem of the Third Illustrative Embodiment of the Present Invention 
     In the system shown in FIGS. 42 and 43, the function of the input/output subsystem  3900  is to manage the data inputs to and the data outputs from the data management computer system  3950 . In the illustrative embodiment, I/O subsystem  3900  or can be realized using one or more rack-mounted I/O adapter boxes, such as the RocketPort Series RM16-RJ45 multiport serial controller having sixteen or thirty-two I/O ports, sold by the Comtrol Corporation, of Saint Paul, Minn. 
     Data Management Computer of the Third Illustrative Embodiment of the Present Invention 
     In the system shown in FIGS. 42 and 43, the function of the data management computer  3925 , with a graphical user interface (GUI)  3926 , is to provide a powerful computing platform for realizing the data element queuing, handling and processing subsystem  3950  in a real-time manner, in addition to carrying out other data and system management functions. In general, subsystem  3950  is best realized by an computing platform having a multi-tasking operating system capable of handling multiple “threads” at the same time. 
     The Data Element Queuing. Handling and Processing Subsystem of the Third Illustrative Embodiment of the Present Invention 
     In FIGS. 44 and 44A, the structure and function of data element queuing, handling and processing subsystem  3950  is shown in greater detail. As shown in FIGS.  46 A 1  and  46 A 2 , all time-stamped data objects, including PIT, POOT and package data elements associated therewith, are transferred from the moving package tracking queues  3305 A through  3305 D in subsystem  3300  and the moving package tracking queues  3505 A through  3505 D in subsystem  3500 , to a first I/O unit  395 A provided in subsystem  3950 . Also, all scan beam data elements (SBDEs) and belt/package velocity measurements are provided to a second I/O unit  3951 B, as shown in FIGS.  46 A 1  and  46 A 2 . 
     As shown in FIGS.  46 A 1  and  46 A 2 , each data object entering the subsystem  3950  though I/O unit  3951 A is directly loaded into the system event queue  3956  under the control of data controller  3952  without performing any form of time-stamping operation, as these data elements already carry time-stamps placed thereon when generated in the package detection and dimensioning subsystems  3300  and  3500 . In the illustrative embodiment, the data controller  3952  is realized as a programmed microprocessor and associated memory structures, whereas the system event queue  3956  is realized as a FIFO data structure known in the computing art. Preferably, data objects obtained from the I/O unit  3951 A having earlier time-stamps are loaded into the system event queue  3956  before data objects having more recent time-stamps. All incoming scan beam data elements and velocity measurements passing through I/O unit  3951 C are time-stamped by the data controller  3952  using time-stamping unit  3953  (referenced to the master clock  3400  shown in FIG.  43 ), and then loaded into the system event queue  3956  under the control of the data controller  3952 , as shown in FIGS.  46 A 1  and  46 A 2 . 
     In the data element queuing, handling and processing subsystem  3950 , the function of the data element analyzer/handler  3955  is to read the data elements (including data objects) from the output port of the system event queue  3956 , and analyze and handle the same according to the Data Element Handling Rules set forth in FIGS. 47A and 47B. 
     As shown in FIGS.  46 A 1  and  46 A 2 , scan beam data elements generated from “holographic type” laser scanning subsystems in the scanning tunnel must be processed using a system of data processing modules illustrated in FIGS.  46 A 1  and  46 A 2 . As shown in FIGS.  46 A 1  and  46 A 2 , this system of data processing modules comprises a data element combining module  3557 A for combining (i) each scan beam data element generated from “holographic-type” laser scanning subsystems and accessed from the system event queue  3956  with (ii) each and every data object (i.e. package data element) in the moving package tracking queues  3954 A through  3954 D, so as to produce a plurality of combined data element pairs; a package surface geometry modeling module  3958 A for generating a geometrical model for the package represented by the package data element in each combined data element pair produced by the data element combining module  3957 A; a homogeneous transformation (HG) module  3959 A for transforming (i.e. converting) the coordinates of each package surface geometry model produced at the “dimensioning position” in the global coordinate reference frame R global , into package surface geometry model coordinates at t he “scanning position” within the scanning tunnel (i.e. displaced a distance “z” from the package dimensioning position); a scan beam geometry modeling module  3960 A for generating a geometrical model for the laser scanning beam represented by the scan beam data element in each combined data element pair produced by the data element combining module  3957 A; a homogeneous transformation (HG) module  3961 A for transforming (i.e. converting) the coordinates of each scanning beam geometry model referenced to the local frame of reference symbolically embedded within the holographic laser scanning system, into scanning beam geometry model coordinates referenced to the global coordinate reference R global  at the “scanning position” within the scanning tunnel; a scan beam and package surface intersection determination module  3962 A for determining, for each combined data element pair produced from the data element combining module, whether the globally-referenced scan beam model produced by the HG transformation module  3961 A intersects with the globally-referenced package surface model produced by the HG transformation module  3959 A and if so, then the data output subsystem  3963 A produces, as output, package identification data, package dimension data (e.g. height, length, width data etc.), and package weight data, for use by auxiliary systems associated with the tunnel scanning system of the present invention. 
     As shown in FIGS. 45 and 45A, scan beam data elements generated from “non-holographic type” laser scanning subsystems must be processed using a different system of data processing modules than that shown in FIG.  46 . As shown in FIG. 46A, this system of data processing modules comprises: a data element combining module  3957 B (similar to module  3957 A) for combining (i) each scan beam data element generated from the “non-holographic-type” bottom-located laser scanning subsystems and accessed from the system event queue  3956  with (ii) each and every package data element in each of the moving package tracking queues  3954 A through  3954 D so as to produce a plurality of combined data element pairs; a package surface geometry modeling module  3958 B (similar to module  3958 A) for generating a geometrical model for the package represented by the package data object in each combined data element pair produced by the data element combining module  39657 B; a homogeneous transformation (HG) module  3959 B (similar to module  3959 A) for transforming (i.e. converting) the coordinates of each package surface geometry model produced at the “dimensioning position” in the global coordinate reference frame R global , into package surface geometry model coordinates at the “scanning position” within the scanning tunnel (i.e. displaced a distance z from the package dimensioning position); a X-Z scanning surface (geometry) modeling module  3960 B for generating a geometrical model for the laser scanning surface represented by the scan beam data element in each combined data element pair produced by the data element combining module  3957 B; a homogeneous transformation (HG) module  3961 B for transforming (i.e. converting) the coordinates of each X-Z scanning surface geometry model referenced to the local frame of reference symbolically embedded within the non-holographic bottom laser scanning subsystem, into scanning beam geometry model coordinates referenced to the global coordinate reference R global  at the “scanning position” within the scanning tunnel; a scan beam and package surface intersection determination module  3962 B for determining, for each combined data element pair produced from the data element combining module  3957 B, whether the globally-referenced scanning surface model produced by the HG transformation module  3960 B intersects with the globally-referenced package surface model produced by the HG transformation module  3959 B, and if so, then the data output subsystem  3963 B produces, as output, package identification data, package dimension data (e.g. height, width data etc.), and package weight data, for use by auxiliary systems associated with the tunnel scanning system of the present invention. 
     Having described the overall structure and function of the data element queuing, handling and processing subsystem  3950 , it is appropriate at this juncture to now briefly describe the operation thereof with reference to FIGS. 45 and 45A. 
     Prior to loading into the system event queue  3956 , each scan beam data element (SBDE) and each belt/package velocity measurement (v) is time-stamped (i.e. T j ) by timing stamping unit  3953  which is driven by a clock therewithin referenced to the master clock  3400  in FIG.  43 . All data elements in the system event queue  3956  and moving package tracking queues  3954 A through  3954 D are handled by the data element analyzer/handler  3955  which is governed by the table of Data Element Handling Rules set forth in FIGS. 47A and 47B. In general, data element queuing, handling and processing subsystem  3950  is best realized by a computing platform having a multi-tasking operating system capable of handling multiple “threads” at the same time. 
     Package data objects removed from system event queue  3956  by data element analyzer/handler  3955  are placed into the appropriate moving package tracking queues  3954 A through  3954 D based on an analysis of the package dimension data elements associated with removed package data objects. As in the case of the multiple package detection and dimensioning subsystem  3300 , each package moving through the scanning tunnel is represented by an “object” in an object-oriented programming environment (e.g. Java programming environment) stored in a moving package tracking queue  3954 A through  3954 D operably connected to the data element analyzer/handler  3955 . Package data objects placed in the appropriate moving package tracking queues  3954 A through  3954 D, are removed therefrom by the data element analyzer-handler  3955  in accordance with the data element handling rules set forth in the table of FIGS. 47A and 47B. 
     Scan beam data elements generated from holographic-based scanning units are processed along the scan data processing channel illustrated by blocks  3960 A,  3961 A and  3962 A set forth in the lower right hand corner of FIG.  46 A 1  and  46 A 2 , whereas scan beam data elements generated from non-holographic based scanning units (e.g. from the bottom-located polygon scanners in the tunnel) are processed along a different scan data processing channel illustrated by blocks  3960 B,  3961 B and  3962 B set forth in FIG.  46 B. This bifurcation of data element processing is required because scan beam data elements generated from holographic-based scanning units are generated from laser scanning beams (or finite scanning sectors) which can be tracked with scan package identification data using the facet sectors on the scanning disc in issue. While a similar technique can be used for polygon-based scanners (e.g. tracking “mirror sectors” of HOE-based facet sectors), a different approach has been adopted in the illustrative embodiment. That is, the scanning surface (e.g. 3×5″) of each polygon scanning unit along the bottom scanner is accorded a vector-based surface model, rather than ray-type model used for package identification data collected using holographic scanning mechanisms. 
     The Package Surface Geometry Modeling Subsystem of the Third Illustrative Embodiment of the Present Invention 
     As shown in FIG. 48A, a surface geometry model is created for each package surface by the package surface geometry modeling subsystem (i.e. module)  3958 A deployed with the data element queuing, handling a n d processing subsystem  3950  of FIGS.  46 A 1  and  46 A 2 . In the illustrative embodiment, each surface of each package transported through multiple package detecting and dimensioning subsystem  3300  is mathematically represented (i.e. modeled) using at least three position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global , and a normal vector to the package surface indicating the direction of incident light reflection therefrom. The table of FIG. 46B describes a preferred procedure for creating a vector-based surface model for each surface of each package transported through the multiple package detecting and dimensioning subsystem  3300  in the system  3000  hereof. 
     The Scan Beam Geometry Modeling Subsystem of the Third Illustrative Embodiment of the Present Invention 
     As described in FIG. 49, a vector-based model is created by the scan beam geometry modeling subsystem (i.e. module)  3960 A of FIGS.  46 A 1  and  46 A 2 , which is similar to structure and function as scan beam geometry modeling subsystem  1010 A shown in FIGS.  22 A 1  and  22 A 2 . The function of this subsystem is to geometrically model the propagation of the laser scanning beam (ray) emanating from a particular point on the facet, to its point of reflection on the corresponding beam folding mirror, towards to the focal plane determined by the focal length of the facet. Details of this modeling procedure can be found in Applicant&#39;s copending application Ser. No. 08/726,522 filed Oct. 7, 1996; and Ser. No. 08/573,949 filed Dec. 18, 1995. 
     The Scan Surface Modeling Subsystem of the Third Illustrative Embodiment of the Present Invention 
     FIG. 50 schematically shows how the scan surface modeling subsystem (i.e. module) shown of FIG. 5146A can be used to define a vector-based 2-D surface geometry model for each candidate scan beam generated by the polygonal-based bottom scanners in the tunnel scanning system. As shown in FIG. 49, each omni-directional scan pattern produced from a particular polygon-based bottom scanning unit is mathematically represented (i.e. modeled) using four position vectors (referenced to x=0, y=0, z=0) in the global reference frame R global  and a normal vector to the scanning surface indicating the direction of laser scanning rays projected therefrom during scanning operations. This modeling subsystem is substantially the same as subsystem  1010 B shown in FIG.  22 B. 
     The Homogeneous (HG) Transformation Modules of the Third Illustrative Embodiment of the Present Invention 
     FIG. 51 schematically describes how the homogeneous (HG) transformation module  3961 A of FIGS.  46 A 1  and  46 A 2  uses homogeneous transformations to convert a vector-based model within a local scanner coordinate reference frame R localscannerj  into a corresponding vector-based model created within the global scanner coordinate reference frame R global . This mathematical technique is essential in that it converts locally-referenced coordinates used to represent a laser beam (which scanned a bar code symbol) into globally-referenced coordinates used to represent the same laser scanning beam. Module  3961 A is similar to module  1010 A in FIGS.  22 A 1  and  22 A 2 . 
     FIG. 52 illustrates how HG transformation module  3959 A is used to convert a vector-based package surface model specified within the global coordinate reference frame R global  at the “package height/width profiling position”, into a corresponding vector-based package surface model created within the global coordinate reference frame R global  specified at the “scanning position” within the tunnel scanning system. This mathematical technique is essential in that it converts locally-referenced coordinates used to represent a package surface into globally-referenced coordinates used to represent the same package surface. Notably, this method of coordinate conversion, similar to that disclosed in FIG. 30, involves computing the package travel distance (z=d) between the package height/width profiling and scanning positions using (1) the package or conveyor belt velocity (v) and the difference in time (i.e. ΔT=T 1 −T 2 ) indicated by the time stamps (T 1  and T 2 ) placed on the package data element and scan beam data element, respectively, matched thereto during each scan beam/package surface intersection determination carried out within module  3962 A in the data element queuing, handling and processing subsystem  3000 . Notably, this package displacement distance z=d between the profiling and scanning positions is given by the mathematical expression d=v ΔT. 
     The Scan Beam and Package Surface Intersection Determination Subsystem of the Third Illustrative Embodiment of the Present Invention for Use with Scan Beam Data Elements Produced by Holographic Scanning Subsystems 
     FIGS. 53A and 53B, taken together, describes a procedure which is carried out within the scan beam and package surface intersection determination module  3962 A of the illustrative embodiment in order to determine whether (i) the scan beam (rays) associated with a particular scan beam data element produced by a holographic scanning subsystem intersects with (ii) any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system. 
     As indicated at Block A in FIG. 53A, the first step of the procedure involves using the minimum and maximum scan rays models of the laser scan beam to determine the intersection point between the scan ray and a surface on the package (using the vector-based models thereof) referenced to the global coordinate reference frame. As indicated at Block B in FIG. 53A, if a n intersection point has been determined at Block A, then confirm that the sign of the normal vector of the surface is opposite the sign of the scan ray direction vector. As indicated at Block C in FIG. 53A, if the sign of the normal vector is opposite the sign of the scan ray direction vector, then determine if the intersection point (found at Block A) falls within the spatial boundaries of the package surface. As indicated at Block D in FIG. 53B, if the intersection point falls within the boundaries of the surface, then output a data element to the output queue in the data output subsystem  3963 A, wherein the data element comprises package identification data and data representative of the dimensions and measurements of the package by the system for use by other subsystems. When a scan beam data element taken from the scan beam data element queue  3956  is correlated with a package data element (i.e. object) using the above described method, then the subsystem  3963 A outputs a data element (in an output data queue) containing the package ID data and the package dimensional and measurement data. Such data elements can be displayed graphically, printed out as a list, provided to sorting subsystems, shipping pricing subsystems, routing subsystems and the like. 
     The Scan Surface and Package Surface Intersection Determination Subsystem of the Third Illustrative Embodiment of the Present Invention for Use with Scan Beam Data Elements Produced by Non-Holographic Scanning Subsystems 
     FIGS. 54A and 54B, taken together, describes a procedure which can be carried out within the scan surface and package surface intersection determination module  3962 B of FIGS.  46 A 1  and  46 A 2  in order to determine whether the scanning surface associated with a particular scan beam data element produced by a non-holographic (e.g. polygon-based) “bottom-located” scanning subsystem spatially intersects with any surface on the package that has been scanned at a particular scanning position, and thus whether to correlate a particular package identification data element with particular package measurement data element acquired by the system. 
     As indicated at Block A in FIG. 54A, the first step of the procedure involves using the vector-based surface models of the laser scan surfaces of the bottom polygon scanners and side surfaces of the packages so as to determine whether or not there exists a point of intersection between the scanning surface of the polygon-based scanners and any surface of the package. As indicated at Block B in FIG. 54A, if an intersection point exists, then confirm that the sign of the vector model of the scanning surface (i.e. the normal vector) is opposite the sign of the vector model of the package surface. As indicated at Block C in FIG. 54B, if the sign of the normal vector of the scanning surface is opposite the sign of the normal vector to the package surface, then confirm that certain of the points bounded by the scanning surface coincide with points bounded by the surface of the package. As indicated at Block D in FIG. 54B, if sufficient overlap is found to exist between the scanning surface and the package surface, then output a data element to the output queue in the data output subsystem  3963 B, wherein the data element comprises package identification data and data representative of the dimensions and measurements of the package by the system for use by other subsystems. When a scan beam data element taken from the system event queue  3956  is correlated with a package data element using the above described method, then the subsystem  3963 B outputs a data element (in an output data queue) containing the package ID data and the package dimensional and measurement data. Such data elements can be displayed graphically, printed out as a list, provided to sorting subsystems, shipping pricing subsystems, routing subsystems and the like. 
     Notably, the smaller the facet sectors on the scanning disc, then the better resolution the system hereof will have with regarding to correlating package identification data with package measurement data. As the facet sector gets small, the corresponding minimum and maximum facet angles generated from the decoder device hereof will get closer and closer, approaching a single scanning ray in the ideal situation. 
     Automated Tunnel-Type Laser Scanning Package Identification and Weighing System Constructed According to a Fourth Illustrated Embodiment of the Present Invention: 
     Referring now to FIG. 55, the automated laser scanning package identification and measurement system of the third illustrated embodiment  5000  will now be described in detail. Like the systems of the first and second illustrative embodiments detailed above, system  5000  is capable of detecting, measuring, identifying and tracking singulated packages along the conveyor belt. 
     As shown in FIG. 55, automated tunnel-type laser scanning package identification and weighing system  5000  comprises: the automated simultaneous package detecting, dimensioning and identifying system of the third illustrative embodiment is indicated by reference numeral  5000  and comprises an integration of subsystems, namely: a high-speed package conveyor system  3100  having a conveyor belt  3101  having a width of at least 30 inches to support one or more package transport lanes along the conveyor belt; a tunnel or similar arrangement of 1-D and 2-D bar code symbol readers including, in the illustrative embodiment, 1-D holographic laser scanning bar code symbol reading subsystem  2200 A,  2200 B, and 2-D laser scanning bar code symbol reading subsystem  5200  supported overhead the conveyor belt  3101  by a support frame  3202 , for generating a 3-D omni-directional scanning volume  3203  thereabove, as depicted in FIG. 55, for scanning 1-D and 2-D bar codes  3205  on packages  3204  transported therethrough; a LADAR-based imaging and dimensioning subsystem  3501 A ( 3501 B) for generating an amplitude modulated laser beam  3302  that is repeatedly scanned across the width-wise dimension of the scanning tunnel at a stationary point of rotation above the conveyor belt, and producing data representative of the height, area and corner coordinates (vertices) of packages entering the scanning tunnel; a package-in-the-tunnel detection subsystem  5400  for detecting each package entering the scanning tunnel and generating a PIT data element (i.e. data object) indicative thereof; a weighing-in-motion subsystem  2500 , installed along the conveyor belt structure beyond the tunnel scanning subsystem for weighing packages as they are transported therealong; a package-out-of-the-tunnel (POOT) detection subsystem  5400  for detecting each package exiting the scanning tunnel and generating a POOT data element (i.e. data object) indicative thereof; a weighing-in-motion subsystem  2500 , installed along the conveyor belt structure beyond the tunnel scanning subsystem for weighing packages as they are transported therealong; a package/belt velocity measurement subsystem  3800  realized using a roller wheel  3801  engaged against the undersurface of the conveyor belt  3101 , an optical shaft incremental encoder  3802  connected to the axle of the roller wheel  3801  and producing an electrical pulse output stream per revolution of the roller wheel, and a programmed microprocessor  3803  for processing the output pulse stream and producing digital data representative of the velocity of the conveyor belt (and thus package transported thereby) at any instant in time; an input/output subsystem  2700  for managing the data inputs to and data outputs from the system; and a data management computer  2800 , with a graphical user interface (GUI)  3926 , for realizing a data element queuing, handling and processing subsystem  3950  as shown in FIGS. 44 and 44A, as well as other data and system management functions. 
     Applications of the System of the Present Invention 
     In general, the package identification and measuring systems of the present invention can be installed in package routing hubs, shipping terminals, airports, factories, and the like. There of course will be numerous other applications for such systems as new situations arise, and the capabilities of such systems become widely known to the general public. 
     As shown in FIG. 58, the system of the present invention ( 1 ,  2000 , or  3000 ) described above can be connected to an information network  4000  supporting TCP/IP or other network protocol. As shown, the network includes at least one relational database management computer system (RDBMS)  4001  designed to receive information collected from each and every package identified, dimensioned and measured while passing through the scanning tunnel subsystem of the system. Notably, a package router  4005  is shown installed downstream from the system in order to route packages in an automated manner using control signals generated by the subsystem  900  in the system. It is understood that many systems  1 ,  2000  or  3000  could be assembled in various types of package routing networks in order to achieve a particular set of functions relating to automatic identification, routing, and sorting operations. 
     As shown in FIG. 58, the RDBMS 4001 is connected to a Java/Jinni-enabled Internet (i.e. http) server  4002  by way of an information network supporting TCP/IP in a manner well known in the art. The HTTP server  4002 , realized using a SUN® workstation supporting Java and Jini server components by Sun 35 Microsystems, Inc. of Palo Alto, Calif., is accessible by any Java/Jini-enabled client machine  4003  equipped with a Java/Jini-enabled (http) browser program known in the art. Any client machine  4003  can be RF linked to Internet infrastructure  4004 , connected thereto by a POTs line, ISDN line, DSL line, T 1  line or any other means available presently or in the future. Typically, computer system  900 , RDBMS 4001, and Internet server  4002  are located in close physical proximity with the automated package identification and measuring system  1 ,  2000  and  3000 , and if no in close physical proximity, then reasonably close thereto in comparison to the distance of a remote client machine  4003  used to remote control and manage the system when required by trained service technicians. 
     In this illustrative embodiment, the data element management computer subsystem  900  within the system  1 ,  2000  or  3000  is also realized using a SUN® workstation running the SOLARIS version of Unix and supporting Java and Jini server components by Sun Microsystems, Inc. Each node in the network, including subsystem  900 , and Internet server  4002 , has an assigned static IP address on the Internet, and is provided with its own Jini™ interface for the purpose of enabling customers a nd other authorized personnel to use a Jini/Java-enabled client machine  4001  located anywhere around the globe so as to: (1) remotely access (from Internet server  4002 ) information about any packages transported through the system, as well as diagnostics regarding the system; and (2) remotely control the various subcomponents of the system in order to reprogram its subsystems, perform service routines, performance checks and the like, as well as carry out other forms of maintenance required to keep the system running optimally, while minimizing down-time or disruption in system operations. 
     While the above-described system employs Jini/Java-enabled remote control technology, it is understood that other forms of remote control technology, known in the computing arts, can be used to implement the remote-controlled diagnostics, management and servicing method of the present invention. 
     Modifications of the Illustrative Embodiments 
     While the package conveyor subsystems employed in the illustrative embodiments have utilized belt or roller structure to transport package, it is understood that this subsystem can be realized in many ways, for example: using trains running on tracks passing through the laser scanning tunnel; mobile transport units running through the scanning tunnel installed in a factory environment; robotically-controlled platforms or carriages supporting packages, parcels or other bar coded objects, moving through a laser scanning tunnel subsystem. 
     In the preferred embodiments of the present invention described above, holographic laser scanning subsystems have been used to generated robust 3-D omni-directional scanning volumes employed in such systems. As such, the laser beam position tracking techniques disclosed herein have been applied to the holographic scanning disc used in such systems to produce facet and facet sector information generated and correlated with each and every line of scan data generated within each holographic scanning subsystem. It is understood, however, when using polygonal type scanning systems, the laser beam position tracking techniques taught herein can be directly applied to the rotating polygon, and in such cases, polygon mirror and mirror sector information would be automatically generated and correlated with each and every line of scan data generated within each polygonal-type laser scanning subsystem of the present invention. 
     While the various embodiments of the package identification and measuring system hereof have been described in connection with linear (1-D) and 2-D code symbol scanning applications, it should be clear, however, that the system and methods of the present invention are equally suited for scanning alphanumeric characters (e.g. textual information) in optical character recognition (OCR) applications, as well as scanning graphical images in graphical scanning arts. All that will be required is to provide image data storage buffers in each of the scanning units so that images of bar code symbols can be reconstructed during scanning operations, and then character recognition techniques, such as taught in U.S. Pat. No. 5,727,081 to Burges, et al, incorporated herein by reference. 
     Advantages and other Features of the System of the Present Invention 
     Through proper programming, the automated package identification a n d measuring systems of the illustrative embodiments described hereinabove can read virtually any bar code symbology imaginable (e.g. Interleaved two of five, Code 128 and Code three of nine) and formats so as to sort and identify packages at various package rates required by USPS or other end-users. The systems of the illustrative embodiments can read the ZIP Code (six digits), Package Identification Code (PIC) (sixteen characters) 1  and Tray bar code (ten digits) symbols. 
     The tunnel scanning systems hereof can be configured so that all of the products passing through the “tunnel” shall be scanned and read for the valid USPS bar coded symbols regardless of the position of the bar code symbol on the surface of the product. This also includes the bottom surface of the product. 
     The tunnel scanning system hereof can be provided with additional equipment including, for example, tachometers, dimensioning units, support structures, special power units (if required), air compressors and any other support equipment required by an application at hand. 
     Preferably, the tunnel scanning systems of the illustrative embodiments are constructed using standard interfaces such that scanners, decoders, concentrator, etc. are interchangeable. 
     The tunnel scanning systems hereof can read bar coded symbols through the entire population of tray and tub label holders in use by the USPS, and other package or parcel carriers. In addition, the tunnel scanning systems can read bar code symbols on the package products when the bar code symbol label is placed under diaphanous materials. 
     There will be more than one bar code symbol on many of the packages found in the tunnel system hereof. Some of these symbols will not be valid USPS symbols. If there are multiple symbols on a package, the scanner logic will automatically identify and process only the USPS valid symbols. 
     The tunnel scanning systems of the illustrative embodiments can process all types of products (e.g. trays and tubs having extremely large variance in surface types, colors, and plastics (e.g. Tyvek material, canvass, cardboard, polywrap, Styrofoam, rubber, dark packages). Some of these product types include: softpack-pillows, bags; packages having non-flat bottoms, such as flats, trays, and tubs with and without bands; cartons; rugs; duffel bags (without strings or metal clips); tires; wooden containers; and sacks. 
     It is understood that the laser scanning systems, modules, engines an d subsystems of the illustrative embodiments may be modified in a variety of ways which will become readily apparent to those skilled in the art, and having the benefit of the novel teachings disclosed herein. All such modifications and variations of the illustrative embodiments thereof shall be deemed to be within the scope and spirit of the present invention as defined by the Claims to Invention appended hereto.