Abstract:
Improved versatility, reliability and performance for field-deployable spatial positioning or measurement systems that use rotating laser fans or beams. Teachings include [1] A system integrated field-deployable length standard uses a reelable tape with positional indents; [2] the use of labyrinth seals at interface volumes between rotating laser heads and transmitter assemblies to prevent ingress of contaminants and allow for elimination of the use of rotary seals; [3] new dynamic leveling techniques to plumb positional laser transmitter systems; [4] strobe beam configurations for improved near/far performance; and [5] a vertical mode sensing scheme that allows switching to measuring tall structures when needed.

Description:
[0001]    This application claims the priority of U.S. Provisional Application Serial No. 60/188,367, filed Mar. 10, 2000. 
     
    
     
         [0002]    This invention relates to field-deployable spatial positioning or measurement systems. Specifically, this invention uses novel system hardware, calibration methods, and transmission/detection modes to provide increased ease-of-use, better reliability and system longevity, easier calibration methods, wider usable range and versatility for spatial positioning systems to provide high resolution, reproducible and accurate spatial or position measurements in two or three dimensions. This allows enhanced accuracy and utility for use in surveying, construction and manufacturing layout, and spatial data generation for design or vehicular systems, or vector and tensor mapping such as accumulating data relating to temperature, wind shear, electric fields, radiation flux, etc.  
           [0003]    Present uses for field-deployable spatial positioning systems include construction layout, where is setting reference points or setting control lines, asymptotes and similar geometric boundaries or guide lines; or laying out parallel or perpendicular lines; measuring linear distances between points; and navigating to specific points entered by a user; or establishing working planes. This would include generation of level or sloped plane references for earthwork and site preparation; generation of vertical (plumb) plane references for tilt-up wall placement; and XY (2-D) or XYZ (3-D) coordinate measurement for positioning concrete forms, footers, and anchor bolts.  
           [0004]    Additional uses for field-deployable spatial positioning systems include machine control or robotic applications, and transfer of measurement or spatial positioning data to and from CAD systems or databases.  
           [0005]    Prior art field-deployable spatial positioning and measurement systems include those described in U.S. Pat. Nos. 4,874,238; 5,100,229; 5,110,202; 5,579,102; 5,461,473; 5,294,970; and 5,247,487, all of which are hereby incorporated by reference in their entirety. Spatial positioning systems described in these patent references usually comprise a single “laser transmitter” and a single “laser receiver”. The transmitter is placed at a fixed location, and serves as a measurement reference or beacon for the receiver. The handheld receiver is carried by the user, and displays in real-time the location of the receiver relative to the transmitter. Because of mathematical constraints, such a single-transmitter system is only capable of measuring the horizontal (azimuth) and vertical (elevation) angular location of the receiver; that is, no direct measurement of the range from the transmitter to receiver is possible. A more advanced system consists of two or more transmitters and a single receiver. The transmitters are again placed at fixed locations, and serve the same purpose as before. The receiver calculates its azimuth and elevation location relative to each transmitter. If the transmitters are at known locations, the receiver can then calculate its position in 3-D space using known methods and algorithms, e.g., see U.S. Pat. No. 5,100,229 as cited above. In either the single or multi-transmitter systems, multiple receivers may be used simultaneously with the same transmitter(s). This is possible since the transmitters only serve as a reference or beacon, in the same way that GPS satellites serve as a reference for many users. Calculations to determine the location of a given receiver take place in that receiver, not the transmitter(s).  
           [0006]    As will be described more fully below, the primary components of a transmitter can include the following: a rotary laser head containing two laser assemblies; a spindle assembly, including a motor and encoder, for spinning the rotary laser head; an optical strobe assembly, which functions as an azimuth reference to establish a “zero” angle for the azimuth angle; a gimbal assembly, including level sensors and motors, for leveling the rotary laser head; and control electronics needed to perform various functions, including sensing, balancing, monitoring, position determination, user interfacing, and data output. The rotary laser head contains two laser assemblies that produce two fanned infrared laser beams perpendicular to the spin axis of the head, as described in the above-reference U.S. patents. The radial axes of the fan beams can be chosen to be separated by approximately 90 degrees (or other angle) around the head. The fan beams are rotated approximately 30 degrees in opposite directions about their respective radial axes.  
           [0007]    The rotating laser head is attached to the top end of a shaft through the spindle assembly. The lower end of the shaft is attached to a motor and rotary encoder. The motor spins the shaft, and thus the head, at a known constant speed. The rotary encoder is used to sense the rotation speed of the shaft, and provides feedback to the motor drive circuit in the control electronics.  
           [0008]    As is described in the above-reference U.S. patents, an optical strobe assembly can be used to synchronize, or set a rotation datum for, the azimuthal angle swept by the fanned beams. This can be implemented as a ring of outward-facing IREDs (infrared emitting diodes) located just below the rotating laser head. The strobe is stationary, and mounted to the outside of the spindle assembly. Using feedback from the rotary encoder on the shaft, the control electronics causes the strobe to emit a very short flash of infrared light once per revolution of the head, or any other set interval. This flash is detected by the mobile receiver, and used as a zero azimuth angle reference.  
           [0009]    The gimbal assembly is attached to the outside of the spindle assembly, and connects it to the outer housing of the transmitter. The purpose of the gimbal assembly is to allow a tilt (in two axes) in a known manner of the rotary head spin axis relative to the outer housing. In most applications it is desirable, for reasons to be explained below, to plumb the spin axis of the head with respect to gravity (or to some other desired axis). If this is done, the radial axes of the fan lasers, which are perpendicular to the spin axis, will sweep through a plane that is level with respect to gravity. In order to plumb the spin axis, the control electronics reads the output of the level sensors, which are attached to the outside of the spindle assembly, and drives the motors of the gimbal assembly until the sensor outputs indicate that the spin axis is plumb. Well known electrolytic vials can be used as monitors in assisting this feedback function.  
           [0010]    Control electronics govern the overall operation of the laser transmitter. As mentioned above, it controls the rotation speed of the head by using the rotary encoder output as feedback, triggers the optical strobe once per revolution of the head, and plumbs the spin axis by moving the gimbal assembly based on feedback from the level sensors.  
           [0011]    The primary components of the receiver generally include the following: a detector such as a (photodiode) assembly for sensing the optical strobe and fan lasers from the transmitter(s); timing electronics for measuring the time between received pulses; and some processor, such as a microprocessor, for calculating the location of the receiver; a user interface, such as a display and keypad. The detector or photodiode assembly produces an electrical output in response to the optical strobe signal from the transmitter(s). It also produces an output pulse whenever it is crossed by one of the rotating fan beams from a transmitter. For example, when the detector is in the vicinity of a single transmitter, the output for one complete rotation of the transmitter head can include times T 1 , T 2 , and Trev measured by timing electronics, where T 1  is the time between a (received) strobe light pulse and a first fanned laser beam; T 2  is the time between a strobe light pulse and a second fanned laser beam; and Trev is the time between strobe pulses. The microprocessor calculates the angular location of the receiver relative to the transmitter by using the output of the timing electronics. Since the strobe is omnidirectional, the absolute time at which the strobe pulse is received is independent of the position of the receiver. The two fan beams projected from the transmitter are tipped 30 degrees in opposite directions about their radial axes, which are separated by 90 degrees about the rotating laser head. Therefore the elevation (vertical) angle of the receiver relative to the transmitter will be a function of the time between the received laser pulses, and the azimuth (horizontal) angle will be a function of the average time from the strobe to the two laser pulses, as given, for example, in U.S. Pat. No. 5,110,202 cited above. If the speed of rotation of the transmitter head is very steady, the angular position of the receiver may be calculated as:  
               azimuth                 angle     =     360   *       (     T1   +   T2     )     /     (     2   *   Trev     )                 Eqn  1                 elevation                 angle     =           360   *       (     T2   -   T1     )     /   Trev       -   90     2     *     cot        (   30   )                 Eqn  2                               
 
           [0012]    The result of these calculations is output in various formats on the display, depending on the particular application. The keypad allows the user to control the operating mode.  
           [0013]    One aspect of such a spatial positioning system is the use of a length standard to set a scale for the spatial positioning system, because the above scheme often measures the azimuthal and elevation angles only, depending on the number of transmitters and the system functions selected. With a single detector and transmitter, for example, the distance between the two is unknown. One method of estimating the distance is to perform a “stadia measurement”, which is a common technique in surveying. This measurement can be performed with two detectors (such as photodiodes) mounted to a straight rod a known distance apart (e.g., 2 meters). Both detectors would be connected to the same receiver, which would then simultaneously calculate the angular position of each detector relative to the transmitter. Since the distance between the detectors is known, the receiver can make a relatively crude estimate of the distance from the rod to the transmitter. This method is suitable if highly accurate measurements are not required, but suffers from parallax type error, especially over long ranges in the field of measurement.  
           [0014]    If more accuracy is required, a multi-transmitter system may be used. This system is capable of calculating accurate 2-dimensional or 3-dimensional positions of a single-detector receiver. The basic measurement is the same as in the single-transmitter system; that is, the receiver calculates its angular location relative to each transmitter. Mathematically, the location of the receiver relative to a given transmitter is somewhere along a vector that starts at the transmitter and passes through the receiver. If the transmitters are at known locations, then solving for the intersection of the vectors extending from each transmitter to the receiver will give coordinates of the receiver. More precisely, the coordinates found are at the center of the detector or photodiode.  
           [0015]    However, for systems using only one transmitter, or for systems using multiple transmitters where increased accuracy and resolution is desired, a scaling reference is needed. One usually introduces a linear scale or distance reference into a known setup procedure for this purpose. Since the basic measurements made are all angular, and the transmitters and setup points are at arbitrary locations, inherent scale in the system can be obtained by several means. For example, a scale bar or tape measure can be used. When, for example, the user measures a point at each end of an object that is exactly one meter long, and the receiver is told that the distance between these points is one meter; then the receiver can adjust the scale of the relative coordinate system to give measurements in meaningful units such as meters, inches, feet, etc. The measurement of this scale reference object must be done very accurately, since the operating distance multiplies any error in the scale reference. That is, if a 1 mm error is made in measuring a 1 m scale reference, then the absolute position error at a distance of 50 m is 50 mm. Therefore it is desirable to use long scale references, such as a 10 meter scale reference.  
           [0016]    A second aspect for such a spatial positioning system, particularly if it is to be field-deployable, is that contaminants are kept out of certain critical areas containing vital components like the spindle shaft and required shaft bearings.  
           [0017]    A third aspect for the spatial positioning system is the desirability of a leveled transmitter, to enhance the accuracy of the measurements that are made. With the automatic leveling described above, there is still a need for frequent and continued calibration of such leveling in the transmitter units. This calibration is vital for accuracy and usability. From the outset, initial manufacturing tolerances must be set before new transmitters are sold. Transmitters that are dropped, or subject to excessive mechanical vibration should preferably be re-calibrated, and six month periodic calibration are usually recommended and expected. Calibrations are also often required after removal and replacement of mechanical components such as the rotating laser head or spindle assembly. Finally, preparation and certification of a used transmitter for sale would require close calibration of the auto-leveling system.  
           [0018]    A fourth aspect of such a spatial positioning system is that the output light or energy from the strobes used to synchronize the azimuthal fan sweep should preferably cover the field of measurement and be of sufficient strength to be detected without ambiguity and with a high enough signal to noise ratio in the control or sensing electronics.  
           [0019]    A fifth aspect of such a spatial positioning system is that fiduciary volume over which the transmitter-receiver combination can function should preferably cover the desired field of measurement, such as when doing spatial positioning of tall or high structures.  
           [0020]    In the prior art, there are problems associated with each of these requirements.  
           [0021]    The first aspect of setting a scale is made difficult by having to measure a ruler, tape, or other reference in the field. Accuracy can suffer, as noted above, due to measurement errors. Reproducibility can suffer from using different length standards, or using the same standard, but with slightly different deployment, such as when a tape measure is not pulled to the same tightness from measurement to measurement.  
           [0022]    The second aspect for keeping contaminants out of selected areas or away from critical components in the transmitter has not been adequately addressed. Typically one uses rotary seals, which introduce friction associated with spinning the rotating laser head. This added friction can reduce battery life in the transmitter. Rotary seals also introduce vibrations and shaft wobble, that, while subtle, can affect accuracy and reproducibility for coordinate measurements, especially over a large field of measurement. Degradation of such rotary seals can reduce system longevity and can send bits of elastomer or other debris into the protected areas, and can release trapped dirt as well.  
           [0023]    The third aspect for a calibration of the automatic leveling in a transmitter is quite onerous, and requires use of known elaborate procedures using measurement stands, sensors, and the like. Such present calibrations are very time consuming, and require the laser output to be painstakingly and manually compared to benchmarks and references in a setup stand. This can take hours per unit, and drives up costs. Careful work is required, and setup errors are not well tolerated, resulting in overall calibration errors.  
           [0024]    The fourth aspect for strobe or synchronization distribution suffers from severe tradeoffs in usable range and signal strength. Light emitting devices that have narrow solid-angle output distributions that are suitable for long distance “reaching” of the strobe beam to far locations in the field of measurement are inadequate for measurements close to the transmitter, especially down low or up high. Conversely, light emitting devices that have wide solid-angle output distributions that are suitable for good wide coverage of measurement very close to the transmitter are inadequate for measurements far from the transmitter, because their output intensity drops rapidly as a function of distance from the strobe.  
           [0025]    The fifth aspect of keeping a large usable range for vertical types of measurements cannot be addressed with present fanned beam transmitters because the divergence or extent of the fan beams used are not sufficient to cover the entire field of measurement, and can suffer from “fringe” effects where the crispness or quality of the beam fans degrades at large divergence angles. When the usable range of measurement over the field of measurement suffers because the working space or fiduciary volume subtended by the capabilities of spatial positioning system operation is limited, such as when working in the vertically extended environments, the system cannot be used. Such conditions come up often, such as when tilting pre-fabricated walls to a vertical position. Conventional spatial positioning systems cannot span the necessary vertical fiduciary volume over which accurate measurements must be made, unless a transmitter dedicated to laser sweeps in a vertical plane is used.  
           [0026]    It is therefore an object of this invention to provide a field-deployable length standard that is built into the spatial positioning system receiver, with capability to reproduce faithfully the force loading of the standard for greater accuracy. It is also an object to provide protection against contaminant entry without the use of rotary seals or other conventional means used in the spatial positioning system field that have not met with great success without the drawbacks mentioned. It is a further object of this invention to provide a method of calibration the leveling of a transmitter which is easy to implement, accurate, and tolerant of setup errors. It is yet a further object of this invention to provide a scheme for synchronization strobe beam distribution which maximizes usable range for both near and far measurements with respect to the transmitter. It is another object of this invention to provide a way to use the same transmitter for vertical types of measurements, while allowing use of the same control electronics and calibration procedures as cited in the third requirement above. Other objects will become apparent upon reading of the specification.  
         SUMMARY OF THE INVENTION  
         [0027]    One general embodiment disclosed includes a transmitter and spatial positioning receiver for a spatial positioning system. The system comprises a stationary portion and a rotating laser head in proximity to the stationary portion, the rotating laser head further comprising a first light emitting device emitting a divergent rotating light fan onto a field of measurement. The system also comprises a synchronization strobe providing a synchronization strobe beam for communicating with the spatial positioning receiver operating in the field of measurement, and a detector in the spatial positioning receiver to detect the divergent rotating light fan and also the synchronization strobe beam. Additionally, there is also a processor to determine at least one spatial coordinate of the detector in the spatial positioning receiver based on a time of receipt of the divergent rotating light fan and the synchronization strobe beam. The transmitter and spatial positioning receiver also comprise a field-deployable length standard for use with the spatial positioning receiver for spatial position-marking, setting, calibrating or referencing in the spatial positioning system. This field-deployable length standard comprises a reelable tape comprising at least one markable position. The reelable tape and the markable position are each so positioned and oriented with respect to the spatial positioning receiver such that when the spatial positioning receiver is posed to a second location upon unreeling the reelable tape and using the markable position, a detector in the spatial positioning receiver is a known distance from a first location of the detector in the spatial positioning receiver prior to unreeling the reelable tape. Additionally, the transmitter is so constructed so that the stationary portion and the rotating laser head are each individually positioned, shaped, and oriented such that there is defined an interface volume therebetween. The transmitter then further comprises a labyrinth seal, so sized, positioned and oriented so as to restrict the motion of contaminants through the interface volume between the rotating laser head and the stationary portion of the transmitter. Additionally, there is found a strobe set to provide a spatial positioning transmitter synchronization strobe beam to improve energy distribution and operating range when communicating with the spatial positioning receiver operating in the field of measurement. The strobe set further comprises a first strobe having an output distribution of a first value for half power beam angular width, oriented to provide output onto the field of measurement. A second strobe is provided having an output distribution of a second value for half power beam width higher than the first value for half power beam angular width, oriented to provide output onto the field of measurement. The first and second strobes are further positioned and oriented such that the operating range of the spatial positioning receiver is increased with respect to the first and second strobes both having either the first value or the second value for half power beam angular width. The transmitter can also comprise a sensor to sense when the transmitter is oriented so as to sweep the divergent rotating light fan in a substantially vertical plane, with the sensor communicating the sense to the processor for a vertical coordinate determination.  
           [0028]    Other embodiments of the inventions described herein will be described below, and individually, some embodiments have only some of the elements thus far cited. For example, we disclose a field-deployable length standard for use with a spatial positioning receiver for spatial position-marking, setting, calibrating or referencing in a spatial positioning system, the field-deployable length standard comprising a reelable tape comprising at least one markable position. The reelable tape and the markable position are each so positioned and oriented with respect to the spatial positioning receiver such that when the spatial positioning receiver is posed to a second location upon unreeling the reelable tape and using the markable position, a detector in the spatial positioning receiver is a known distance from a first location of the detector in the spatial positioning receiver prior to unreeling the reelable tape. Additionally, the markable position can comprise a detent operative upon the reelable tape. Alternatively, the field deployable length standard can comprise a reelable tape reeled upon a reel assembly in mechanical communication with a housing. This reel assembly can optionally be under a spring bias with respect to the housing so as to allow movement of the reel assembly with respect to the housing. The spring bias can optionally allow for a desired force loading along the reelable tape. The housing can also comprise an aperture so shaped, sized, positioned, and oriented so as to allow a viewing of the movement of the reel assembly, with the viewing operative to allow a calibration of the force loading along the reelable tape. Alternatively, the aperture can comprise a lens so shaped, sized, positioned and oriented so as to allow viewing of the movement of the reel assembly, with the viewing through the lens operative to allow a similar calibration of the force loading along said reelable tape.  
           [0029]    Another embodiment can comprise a field-deployable length standard for use with a spatial positioning receiver for spatial position-marking, setting, calibrating or referencing in a spatial positioning system, with the field-deployable length standard comprising a reelable tape in mechanical communication with the spatial positioning receiver. The reelable tape comprises a first markable position, and a second markable position a known path length along the reelable tape from the first markable position when the reelable tape is unreeled. The first and second markable positions can be so positioned and oriented with respect to the spatial positioning receiver when the reelable tape is unreeled such that when the spatial positioning receiver is posed to a first location upon unreeling the reelable tape and using the first markable position, a detector in the spatial positioning receiver is a known distance with respect to the detector when the spatial positioning receiver is posed to a second location upon unreeling the reelable tape and using the second markable position of the reelable tape. In turn, any of the first and second markable positions can comprise a detent operative upon the reelable tape. Optionally, the reelable tape for this embodiment can be reeled upon a reel assembly in mechanical communication with a housing. Additionally, the reel assembly can be under an optional spring bias with respect to the housing so as to allow movement of the reel assembly with respect to the housing. Optionally, this spring bias can allow for a desired force loading along the reelable tape. And, as before, the housing can comprise an aperture so shaped, sized, positioned, and oriented so as to allow a viewing of the movement of the reel assembly, with the viewing operative to allow a calibration of the force loading along the reelable tape. Again, the aperture can optionally comprise a lens so shaped, sized, positioned and oriented so as to allow the viewing of the movement of the reel assembly, with the viewing again operative to allow a calibration of the force loading along the reelable tape.  
           [0030]    Further embodiments include a transmitter for a spatial positioning system, with the transmitter having a stationary portion and a rotating laser head in proximity to the stationary portion, the stationary portion and the rotating laser head each individually positioned, shaped, and oriented such that there is defined an interface volume therebetween. The transmitter further comprises a labyrinth seal, so sized, positioned and oriented so as to restrict the motion of contaminants through the interface volume between the rotating laser head and the stationary portion of the transmitter. The labyrinth seal can optionally be so formed that a necessary path for any contaminants is serpentine, or, in the alternative, substantially straight. Optionally, the stationary portion and the rotating laser head can each be individually positioned, shaped, and oriented such that the labryrinth seal is formed by at least a portion of either or both of the stationary portion and the rotating laser head, with the labyrinth seal operative in the interface volume. Alternatively, the stationary portion and the rotating laser head can comprise a rotary transformer positioned proximate the interface volume where the rotary transformer is positioned, shaped, and oriented such that the labryrinth seal is formed by at least a portion of the rotary transformer, with the labyrinth seal again operative in the interface volume.  
           [0031]    Also disclosed is a method for dynamic leveling of a rotating body to bring a rotational axis of the rotating body into better alignment with a desired axis. This is useful for maintaining functionality and accuracy of the rotating elements used in the systems described. The method comprises:  
           [0032]    [a] Aligning an operating axis of an autocollimator to the desired axis, with the autocollimator designed to output a light ray along the operating axis, and the desired axis as a result of the aligning, and to monitor any reflected light rays from the light ray with respect to the desired axis;  
           [0033]    [b] affixing a mirror to the rotating body;  
           [0034]    [c] orienting the rotating body to within the field of view of the autocollimator;  
           [0035]    [d] noting the position of the reflected light rays monitored by the autocollimator, whereby a circular arc is formed by the reflected light rays;  
           [0036]    [e] determining the direction and magnitude of a deviation of a geometric center of the circular arc from the operating axis of the autocollimator;  
           [0037]    [f] changing the orientation of the rotating body in such a manner so as to bring the rotational axis into better alignment with the operating axis of the autocollimator, whereby the rotational axis will be put into better alignment with the desired axis.  
           [0038]    If desired, the desired axis can be a downward gravitational vector. As comtemplated here, one can certainly make the rotating body be a rotating laser head in a spatial positioning system. Optionally, too, the mirror can be affixed to the rotating laser head in such a manner that a normal axis of the mirror is substantially parallel with the desired axis. Alternatively, the mirror can be affixed to the rotating laser head in such a manner that a normal axis of the mirror is within 90 degrees of the desired axis.  
           [0039]    There is also disclosed a method for forming a spatial positioning transmitter synchronization strobe beam to improve energy distribution and operating range when communicating with a spatial positioning receiver operating in a field of measurement, the method comprising:  
           [0040]    [a] arraying a first strobe having an output distribution of a first value for half power beam angular width onto the field of measurement;  
           [0041]    [b] arraying a second strobe having an output distribution of a second value for half power beam width higher than the first value for half power beam angular width, onto the field of measurement;  
           [0042]    [c] the first and second strobes further positioned and oriented such that the operating range of the spatial positioning receiver is increased with respect to the first and second strobes both having either the first value or the second value for half power beam angular width.  
           [0043]    Optionally, the first value for half power angular beam width can be less than 15 degrees, and/or the second value for half power angular beam width can be more than 20 degrees. Also, a plurality of first strobes can be arrayed about a single second strobe, for output of the beam onto the field of measurement. Such a plurality can also be numerically three, as opposed to two or four. In another embodiment, the plurality of first strobes and a plurality of second strobes can be optionally arrayed in such a manner and orientation that each strobe of such first and second strobes is aimed at a distinct direction onto the field of measurement.  
           [0044]    In the same vein, one can also optionally select a strobe set to provide a spatial positioning transmitter synchronization strobe beam to improve energy distribution and operating range when communicating with a spatial positioning receiver operating in a field of measurement, with the strobe set comprising a first strobe having an output distribution of a first value for half power beam angular width, oriented to provide output onto the field of measurement; a second strobe having an output distribution of a second value for half power beam width higher than the first value for half power beam angular width, oriented to provide output onto the field of measurement; with the first and second strobes further positioned and oriented such that the operating range of the spatial positioning receiver is increased with respect to the first and second strobes both having either the first value or the second value for half power beam angular width, which achieves one of many objectives sought in the instant teachings. Using this prescription, the first value for half power angular beam width can again be less than 15 degrees, and the second value for half power angular beam width can also be more than 20 degrees. Another embodiment allows that a plurality of first strobes are arrayed about a single second strobe, for output of the beam onto the field of measurement; optionally the plurality can be numerically three. Optionally, the plurality of first strobes and a plurality of second strobes are arrayed in such a manner and orientation that each strobe of such first and second strobes is aimed at a distinct direction onto the field of measurement.  
           [0045]    Another embodiment of the instant teachings yields a transmitter and spatial positioning receiver for a spatial positioning system, with the system capable of switching to a vertical mode. That system comprises a stationary portion and a rotating laser head in proximity to the stationary portion, with the rotating laser head further comprising a first light emitting device emitting a divergent rotating light fan onto a field of measurement; a synchronization strobe providing a synchronization strobe beam for communicating with the spatial positioning receiver operating in the field of measurement; a detector in the spatial positioning receiver to detect the divergent rotating light fan and also the synchronization strobe beam; and a processor to determine at least one spatial coordinate of the detector in the spatial positioning receiver based on a time of receipt of the divergent rotating light fan and the synchronization strobe beam. The transmitter and spatial positioning receiver also comprise a sensor to sense when the transmitter is oriented so as to sweep the divergent rotating light fan in a substantially vertical plane, the sensor communicating this directionality or sense to the processor for a vertical coordinate determination.  
           [0046]    Another embodiment includes various elements, such as a field-deployable spatial positioning transmitter and receiver for spatial position-marking, setting, calibrating or referencing, where the field-deployable spatial positioning transmitter and receiver comprise a transmitter kit comprising a rotating laser head emitting an angled fan of light, where angled can mean that the fan is neither orthogonal nor parallel to the plane through which the head rotates, and a strobe emitter that emits a light pulse in predetermined or programmed relation to the position of the laser head; a processor in data communication with a receiver; with the receiver adapted to be moved about a field of measurement and determine, in conjunction with the processor, distance and orientation. The receiver comprises a light detector, and the receiver determines distance and orientation to the transmitter based on the timing of detections of light from the fan of light and from the strobe. The receiver can optionally further comprise a field-deployable length standard. Such a standard can comprise a reelable tape that in turn comprises at least one markable position and a reel attached to or incorporated within a housing for the receiver, the reelable tape and the markable position each so positioned and oriented with respect to the receiver such that when the receiver is posed at a first location and then, upon unreeling the reelable tape and using the markable position, a second location, the processor makes its calculations using light detections at the first location and second location, and a known distance provided by the reelable tape. The processor can optionally be attached to or incorporated within the receiver housing. Alternatively, the rotating laser head and strobe emitter can be incorporated into or attached to a common transmitter housing.  
           [0047]    General embodiments include a transmitter for a spatial positioning system comprising a transmitter having a portion adapted to be stationary during operation and a rotating laser head mounted on the stationary portion; and a labyrinth seal between the rotating laser head and the stationary portion effective to restrict the motion of contaminants between the rotating laser head and the stationary portion.  
           [0048]    The dynamic leveling teachings also include a method for dynamic leveling of a rotating body to bring a rotational axis of the rotating body into better alignment with a desired axis, the method comprising:  
           [0049]    aligning an operating axis of an autocollimator to the desired axis by outputting a light ray along the operating axis, and monitoring any reflected light rays from the light ray to identify any deflection from the desired axis;  
           [0050]    orienting the rotating body, the rotating body having an affixed mirror, to within the operating axis of the autocollimator;  
           [0051]    noting the position of the reflected light rays monitored by the autocollimator, whereby a point or circular arc is formed by the reflected light rays;  
           [0052]    determining the direction and magnitude of a deviation of a geometric center of the point or circular arc from the operating axis of the autocollimator; and  
           [0053]    changing the orientation of the rotating body to bring its rotational axis into better alignment with the operating axis of the autocollimator, whereby the rotational axis is put into better alignment with the desired axis.  
           [0054]    Another embodiment includes method for forming a spatial positioning transmitter synchronization strobe beam to improve energy distribution and operating range when communicating with a spatial positioning receiver operating in a field of measurement, the method comprising:  
           [0055]    operating a rotating a laser head emitting an angled fan of light  
           [0056]    periodically operating, in connection with defined rotations of the laser head, a first strobe having an output distribution of a first value for half power beam angular width onto the field of measurement; and  
           [0057]    periodically operating, in connection with defined rotations of the laser head, a second strobe having an output distribution of a second value for half power beam width higher than the first value for half power beam angular width, onto the field of measurement.  
           [0058]    In kit form, another possible embodiment includes a spatial positioning system, with the system capable of switching between a horizontal and a vertical mode. This system comprises a transmitter kit that further comprises a rotating laser head emitting an angled fan of light; a transmitter processor and a strobe emitter that emits a light pulse in predetermined or programmed relation to the position of the laser head; and a sensor to sense when a housing containing the rotating laser head is oriented so as to sweep in a substantially vertical plane and communicate this information to the transmitter processor; a receiver kit that in turn further comprises a receiver processor, which can be the same as the transmitter processor, in data communication with a receiver, and the receiver adapted to be moved about a field of operation and determine, in conjunction with the receiver processor, distance and orientation, the receiver comprising a light detector, the receiver determining distance and orientation to the transmitter based on the timing of detections of light from the fan of light and from the strobe, wherein the transmitter processor signals the receiver processor of the orientation or modulates the transmitter kit light emissions or rotation in a manner detectable by the receiver kit.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0059]    [0059]FIG. 1 shows a cross sectional schematic view of a transmitter according to the invention.  
         [0060]    [0060]FIG. 2 shows a cross sectional schematic view of a receiver according to the invention.  
         [0061]    [0061]FIG. 3 shows a schematic block diagram of possible controls for the receiver according to the invention.  
         [0062]    [0062]FIG. 4 shows a schematic block diagram of possible controls for the transmitter according to the invention.  
         [0063]    [0063]FIG. 5 shows an oblique exploded view of a possible stadia mount assembly which is part of a field-deployable length standard for the receiver according to the invention.  
         [0064]    [0064]FIG. 6 shows an oblique exploded view of a possible spring assembly which is part of a field-deployable length standard for the receiver according to the invention.  
         [0065]    [0065]FIG. 7 shows a portion of the cross-sectional view of FIG. 1, showing use of a labyrinth seal.  
         [0066]    [0066]FIG. 8 shows a closer cross-sectional view of FIG. 7, showing use of a labyrinth seal.  
         [0067]    [0067]FIG. 9 shows the left side portion of the cross-sectional view of FIG. 8, showing use of a labyrinth seal and a rotary transformer.  
         [0068]    [0068]FIG. 10 shows a close view of the left side portion of the cross-sectional view of FIG. 9, but with non-serpentine labyrinth seals.  
         [0069]    [0069]FIG. 11 shows an end-on surface view of the labyrinth seal shown in FIG. 7, in a plane perpendicular to spindle shaft SFT.  
         [0070]    [0070]FIG. 12 shows conventional leveling of the operating axis of an autocollimator.  
         [0071]    [0071]FIG. 13 shows a transmitter calibration technique for the present invention using a mirror affixed to the rotating laser head RH.  
         [0072]    [0072]FIG. 14 shows a reticle inside the autocollimator of FIG. 12, illustrating the calibration technique of the present invention.  
         [0073]    [0073]FIG. 15 shows a transmitter calibration technique similar to that shown in FIG. 13, but for a transmitter in vertical mode.  
         [0074]    [0074]FIG. 16 shows a prior art configuration of strobe light emitting devices for azimuth synchronization.  
         [0075]    [0075]FIG. 17 shows a longer range prior art configuration of strobe light emitting devices for azimuth synchronization.  
         [0076]    [0076]FIG. 18 shows a configuration of strobe light emitting devices for azimuth synchronization according to the present invention.  
         [0077]    [0077]FIG. 19 shows a unfolded 360 degree view of the strobe light emitting devices arrayed about a transmitter according to the present invention.  
         [0078]    [0078]FIG. 20 shows the detector end of a receiver according to the present invention.  
         [0079]    [0079]FIG. 21 shows the detector end of a receiver according to the present invention, when used with a transmitter in a vertical mode. 
     
    
     DEFINITIONS  
       [0080]    The following definitions shall be employed throughout:  
         [0081]    Autocollimator shall include any optical instrument or technique that provides equivalent information to that given by a conventional autocollimator as known in the field of metrology, such as where a device uses a single lens to collimate diverging light from a slit, and then focuses the light on a exit slit after it has passed through a prism to a mirror and been reflected back through the prism. For this definition, any other device or thing, such as the interior of a 55 gallon drum, could be used as a projection surface for a light ray emitted by a plumbed device, such as an autocollimator. The term autocollimator automatically includes any and all such supplementary devices.  
         [0082]    Azimuthal angle or azimuth shall be consistent with its definition in the field of surveying and shall refer to what is known mathematically as the polar angle θ in spherical polar coordinates (r, θ, φ). The azimuthal angle shall be the angle formed in the horizontal plane between the horizontal projection (or component of) a spatial vector to a spatial position, and an azimuthal reference vector. Corresponding rotations representing changes in the azimuthal angle shall occur through rotations about a vertical axis. (See elevation angle).  
         [0083]    Circular arc(s) shall include complete circles as well as subset segments or arcs of any angular extent.  
         [0084]    Contaminant shall include any material, material body, particle, gas, fluid, or compound deemed undesirable and for which restriction of movement is sought to prevent deleterious effect(s) on selected components.  
         [0085]    Coordinate(s) shall not be limited to whatever spatial coordinate system(s) is/are  3 used herein (e.g., spherical polar (r, θ, φ)), and shall be equivalent to and convertable to other coordinate systems, such as circular cylindrical (r, θ, z), rectangular cartesian (x, y, z), elliptic cylindrical, parabolic cylindrical, bipolar, prolate spheroidal, oblate sphereoidal, parabolic, toroidal, bispherical or other accepted coordinate systems, with or without added scaling factors or metrics used to tailor output information to a user&#39;s needs, e.g., aerodynamic studies over specific air foils, etc.  
         [0086]    Detector shall include any device or devices that receive spatial position-specific information from a transmitter, whether from a light emitting device inside a rotating laser head, or a synchronization (strobe) pulse.  
         [0087]    Elevation angle or elevation shall be consistent with its definition in the field of surveying and shall refer to what is known mathematically as the azimuthal angle φ in spherical polar coordinates (r, θ, φ), and not to be confused with the azimuthal angle from the field of surveying in the definition above. The elevation angle shall be the angle formed in the vertical plane between the vertical projection (or component of) a spatial vector to a spatial position, and a zero degree elevation reference vector determined by gravity. Corresponding rotations representing changes in the elevation angle shall occur through rotations about a horizontal axis. (See azimuthal angle).  
         [0088]    Fan shall include divergent light or laser beams such as those described in U.S. Pat. Nos. 4,874,238 and 5,100,229.  
         [0089]    Half power beam angular width (HPBW) shall be used here, including in the appended claims, as a mere illustration of one of many ways to characterize energy distribution as a function of solid angle (or other spatial parameters) from a strobe or light emitting device, and shall not be taken to be limiting as to other characterizations and distribution functions that can be used.  
         [0090]    Labyrinth seal(s) shall include non-contact seals that serve to restrict motion of fluids and/or contaminants such as particulates by the use of surfaces in close proximity; such non-contact seals shall include—but not be restricted to—conventional labyrinth seals where motion through an interface volume takes a serpentine, curved, or labyrinthine path.  
         [0091]    Laser shall include any active device that uses charged species to convert input energy into a narrow intense beam of phase-coherent light using stimulated emission, such as conventional laser diodes and VCSEL&#39;s (vertical cavity surface emitting lasers), and shall also be broadened in meaning to also include any light emitting device—regardless of any physical, chemical, or electronic light generating mechanisms used therein (such as conventional light emitting diodes or LED&#39;s)—that possesses the requisite coherence, divergence, isotropic uniformity, electromagnetic frequency distribution and capability of modulation to serve the purposes of this invention.  
         [0092]    Light shall include electromagnetic radiation of any frequency, such as radio waves; microwave emissions; infrared, visible, and ultraviolet light; and modulated soft and hard x-rays, and gamma emission, such as might be used for space applications where a light emitting device that does not require input power may be required.  
         [0093]    Light emitting device shall include a strobe as defined below, and any other device that emits electromagnetic waves of any frequency in any manner. This shall include, for example, photoflash units, laser emitting diodes and lamps, with or without mechanical or other means, such as shutters or switchable optical filters, for modulating a time profile of emission.  
         [0094]    Markable position shall refer to any means by which a location on a tape can be used to position a detector for position marking or setting, or spatial data accumulation, including the use of physical detents, indexing, alignment marks or tabs, bosses, holes, hubs, or the use of magnetic or other distinguishing materials on or about the tape surface.  
         [0095]    Necessary path shall denote the path that a contaminant must take in traversing a route, path or interface volume.  
         [0096]    Pose shall refer to spatial translations, rotations, orientations and manipulations (e.g., unfolding or unreeling) to effect a desired result.  
         [0097]    Positioning shall include position measurement in a field of measurement; data acquisition of position information, including map generation, establishing lines, curves, and planes; setting points; and determining or tracking the position of any moveable object, whether by explicit determination of position as a function of time or other parameter, or by providing simple increments or differentials to provide a similar result.  
         [0098]    Processor shall include not only all processors, such as CPU&#39;s (Central Processing Units), but also any intelligent device that performs the functions given, such as analog electrical circuits that perform the same functions. In the appended claims, the word processor can include any processor in the receiver and/or any processor in the transmitter.  
         [0099]    Receiver shall include any device that receives and processes spatial position-specific information from a transmitter.  
         [0100]    Reelable shall include the term foldable, and shall also include any other qualities of a material body (e.g., tape) that allow it to serve as a field-deployable length standard capable of being stowed or made more compact for storage, carrying, or additional deployment. The terms unreeling and unreeled shall be interpreted in a similarly broad manner.  
         [0101]    Rotating laser head shall not require the use of a laser, and shall refer to any rotating body or rotor that serves to pan, scan, disseminate, array, divide, disperse, scatter, broadcast or distribute the output radiation of any light emitting device used for the purposes of this invention.  
         [0102]    Serpentine shall include any labyrinthine or curved path that involves angular deviation or turning along that path, including a necessary path, where the path length is longer than a straight path.  
         [0103]    Spring bias shall include any biasing mechanism, whether mechanical, electrical, electromechanical, or of any other type, which provides a force as a function of deviation from an equilibrium position.  
         [0104]    Strobe shall include any and all light emitting devices that are used as a synchronization method serving the purposes of this invention, such as establishing datum lines or vectors, facilitate transmitter-receiver communications, or interfacing with peripheral devices used in conjunction with this invention.  
         [0105]    Tape shall include strings, cables, wires, polymer extrusions, strands, threads, ropes, filaments or any medium or material body that is capable of being posed linearly or in any other manner (e.g., arcuate) to serve the spatial position-marking, setting, calibrating or referencing purposes of this invention.  
         [0106]    Transmitter shall include any device that broadcasts spatial position-specific information to a receiver.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0107]    Referring to FIG. 1 a cross sectional schematic view of a transmitter according to the invention is shown. Transmitter base B is bolted to an upper housing UH which together enclose and support many active components, including a rotating laser head RH as shown. Inside rotating laser head RH there are installed one or more laser diodes LD or any other light emitting devices for generating a fanned laser beam FLB as shown and discussed above. To condition the output of laser diode(s) LD, a number of elements are used in a known manner, including passing the resultant light through a collimation lens CL, rod lens RL, and passage through a hermetically sealed exit window EW as shown.  
         [0108]    The entire rotating laser head RH is supported and rotated at a constant known angular speed via spindle shaft SFT. Spindle shaft SFT is driven in a precise manner by a known encoder motor EM, which resides inside spindle assembly SP, and is bearingly supported inside the spindle assembly SP using shaft bearings SB. Set inside spindle assembly SP is at least one, but preferably a plurality (for better distribution and reliability) of strobes S used for azimuth synchronization as discussed above. Transmitter base B includes a battery set BAT and a plumb-down laser assembly and associated exit window EWP which are used in a known manner to set the transmitter at a known spot or location on the site or field of measurement. Transmitter base B also includes handle HAN, keypad KEY, and control electronics CET.  
         [0109]    The spindle assembly SP assembly as a whole is moveable on base (B)-mounted gimbal pivots GP, with only one such gimbal pivot shown, so as to provide two tiltable degrees of freedom for leveling purposes. As is known in the art, each such gimbal pivot GP also has provision for tilting the spindle assembly SP using a gimbal motor assembly GMA, with only one such motor shown. Feedback is provided in a known manner by three single axis level sensors SALS (one shown), which serve to report to the control electronics CE the angular position or tilt of the spindle assembly SP and associated rotating laser head RH. Such single axis level sensors SALS can be fabricated using known electrolytic vials which are themselves calibrated independently prior to manufacture.  
         [0110]    Encoder motor EM has a known rotary encoder, such as a disc with holes and an optical monitor device (not shown) to generate pulses so the control electronics CE can regulate the motor speed, and in turn, regulate the azimuthal angular rotation rate of the fanned laser beam(s) that are relied upon to generate positioning information.  
         [0111]    At the point where the rotating laser head RH and the spindle assembly SP are almost touching, there is provided a rotary transformer RT, which provides power to the rotating laser head RH in a known manner using common inductively methods, such as used in a four-head consumer VCR. Just outboard of the rotary transformer RT as shown is a labyrinth seal LS, which will be discussed in detail below.  
         [0112]    Now referring to FIG. 2, a cross sectional schematic view of a receiver according to the invention is shown. As envisioned in the discussion above, the receiver shown comprises a detector DET, which incorporates a known photosensitive device, such as an eight-sided device that has eight photocells wired in parallel so that receipt of a laser fan beam or strobe emission by the transmitter of FIG. 1 can be recorded over a wide possible range of entry angles from the field of measurement. Detector DET can comprises separate detectors tailored for optimal reception of laser fan beam(s) and strobe emissions. For example, a detector designed for optimal detection of a strobe emission could have a larger collection aperture to allow better signal to noise ratios, especially since the strobe emission falls as inverse square of the distance, while the laser fan beam(s) fall of as the inverse of the distance, as is known in the art. The receiver as shown also includes an LCD (liquid crystal display) LED module, a circuit board CB for receiver electronics, and one or more connectors (shown, CONN) for known use with a detector wand, including such a wand comprising two detectors a known distance apart, akin to the “stadia” measurement mentioned above. The receiver can also comprise a user keypad KR, and the housing HR of the receiver as shown can also accommodate a battery set BATR and include mounting provisions (not shown) for the field-deployable length standard discussed in the figures below.  
         [0113]    Now referring to FIG. 3, a schematic block diagram of possible controls for the receiver according to the invention is shown. Many possible schemes can be used to control the receiver, but generally, as known in the art, and discussed in the above-referenced U.S. patents, the signal path can start as shown with a DETECTOR ASSEMBLY where the light pulses are encoded or converted to electrical or electro-optic pulses which are conditioned by the AMPLIFIER ELECTRONICS for use by TIMING ELECTRONICS which interpret the temporal spacing of the pulses as alluded to above. CALCULATION ELECTRONICS then use this information to generate coordinates as needed. User interfacing with this information is achieved via a DISPLAY AND KEYPAD as shown. Processors, including microprocessors with on board memory, cache, and BIOS (basic input/output system) can accomplish this function according to software executable instructions as known in the art.  
         [0114]    Now referring to FIG. 4, a schematic block diagram of possible controls for the transmitter according to the invention is shown. TRANSMITTER CONTROL ELECTRONICS as shown provide functionality to perform transmitter functions, including a MOTOR DRIVE input to the ROTOR MOTOR which drives the rotating laser head RH as previously shown (ROTARY HEAD ASSEMBLY, INCLUDING LASERS) which in turn, via the ROTARY ENCODER gives SPEED FEEDBACK to the TRANSMITTER CONTROL ELECTRONICS. TRANSMITTER CONTROL ELECTRONICS, comprising one or more processors, provides selective energizing of one or light emitting devices, shown here as STROBE ASSEMBLY. TRANSMITTER CONTROL ELECTRONICS also function to provide a GIMBAL MOTOR DRIVE to he GIMBAL MOTORS as shown, which in turn mechanically influence the GIMBAL ASSEMBLY, causing three LEVEL SENSORS to alter their LEVEL FEEDBACK in a known manner as shown. This information is used in a known feedback loop to control the tilt or leveling of the rotating laser head RH.  
         [0115]    The scale reference mentioned above is provided for by use of a field-deployable length standard, such as a “setup cable” or similar material body which will be discussed here. The setup cable is a retractable cable that is integrated into a stadia pole receiver mount or similar assembly. In one embodiment, the user to attaches the end of the cable to a fixed object, pulls the cable out several inches to a first detent, applies tension, and takes a measurement. Then the user releases the cable lock and backs up with the receiver until the cable reaches a second detent, which is exactly 10 m from the first.  
         [0116]    Referring now to FIGS. 5 and 6, oblique exploded views of a possible stadia mount assembly and spring assembly, respectively, which are part of a field-deployable length standard for the receiver according to the invention are shown. These two figures show variants of what is envisioned as part of the invention. The field-deployable length standard can be mounted directly on, or made integral with, the receiver as previously described. Inside the field-deployable length standard, a spring tape SPT is reeled upon a center hub CNH, both residing in an inside reel, shown as portions or views inside reel left (IRL) and inside reel right (IRR). The inside reel (IRL, IRR) is in turn housed inside an inner reel, which acts as a housing for a reelable tape or spring tape SPT. Reelable tape or spring tape SPT is reeled upon a center hub CNH, both residing inside an inside reel, shown as portions or views inside reel left (IRL) and inside reel right (IRR). The inside reel is in turn housed inside an inner reel, which keeps the spring tape SPT reeled and deployable. Inner reel is shown as portions or views INL and INR. Spring tape SPT comprises a markable position, shown MARK, that provides a way of setting a the position of the receiver. As shown, a detent is used, but any other mechanism or technique can be used consistent with the definition above for markable position. The inside reel floats under bias using spring SC which is affixed to the inside reel as described. In practice, one deploys the reelable tape or spring tape SPT by posing or extending spring tape SPT, which can be affixed to a known feature in the field of measurement, and taking a position reading using the receiver, while the tape is unreeled and the inside reel is positioned upon a markable position. A receiver position reading (not shown) taken at an original position of the spring tape SPT with respect to the inside reel can provide, with the position obtain from the markable position, a distance standard as envisioned. To keep the tension or force loading of the reelable tape constant from measurement to measurement, the position of the inside reel can be monitored using an aperture in a reel housing (shown, OB and OCV), with or without use of a lens L as shown to allow better alignment of the inside reel with respect to the reel housing. The use of a detent as the markable position on the spring tape SPT can be facilitated by the use of a button BUT and button holder BUTH, as shown, which allow a spring pin SPP to engage or cause to engage that detent. In this way, a reproducible field-deployable length standard is provided that is compact and allows a fair degree of measurement reproducibility. Another embodiment is provided when the spring tape SPT comprises two markable positions, in which case the field-deployable length standard can be posed twice, with receiver position readings taken for each pose, thus providing a length standard as envisioned here.  
         [0117]    Now referring to FIG. 7, a portion of the cross-sectional view of FIG. 1, showing use of a labyrinth seal is shown. One embodiment of this invention provides for use of a labyrinth seal LS as shown, at or near the interface between the rotating laser head RH and the spindle assembly SP, in lieu of felt, rubber, or other rotary seals which have the disadvantages as cited above. The transmitter shown can also comprise a rotary transformer RT as discussed above, and shown in the figure inboard of the labyrinth seal LS. Contaminants CON are in the ambient environment around the transmitter, and entry of contaminants in the general direction shown by the arrow can potentially result in contamination of spindle shaft SFT and other critical components, resulting in opening up of tolerances and poor performance. The labyrinth seal LS incorporates a serpentine path SRP along a necessary path that the contaminants CON must take to enter critical areas. Such a labyrinth seal can be a separate component pressed or installed into the rotating laser head RH and spindle assembly SP, or can be formed therefrom by machining or other known processes.  
         [0118]    Referring now to FIG. 8, a closer cross-sectional view of FIG. 7 is shown. An interface volume IV as shown provides a narrow, serpentine necessary path for contaminants CON and thereby slows entry into spindle shaft SFT and related areas. The serpentine nature of the necessary path breaks up laminar flow of contaminants CON and provide sinks for accumulated contaminants that would otherwise have an opportunity to enter in an undesirable manner. Referring now to FIG. 9, the left side portion of the cross-sectional view of FIG. 8 is shown, showing use of a labyrinth seal and a rotary transformer having separate inductive portions RTO and RTI as shown. FIG. 10 shows a close view of the left side portion of the cross-sectional view of FIG. 9, but with non-serpentine labyrinth seals to illustrate two things: the rotary transformer RT can itself be modified, machined, or formed to operate as a labyrinth seal LS, and the labyrinth seal LS interface volume can be straight, that is, non-serpentine. Specifically, the labyrinth seal LS can have a non-serpentine interface volume IVLS and the rotary transformer RT can have a non-serpentine interface volume IVR, which individually (separately) or both (if both are made to be labyrinth seals) can serve to provide a discouraging necessary path for contaminants CON.  
         [0119]    [0119]FIG. 11 shows an end-on surface view of the labyrinth seal shown in FIG. 7, in a plane perpendicular to spindle shaft SFT. The concentric rings as shown are indicative of the serpentine nature of the necessary path for contaminants CON as they start to migrate across this figure toward the center O as shown.  
         [0120]    Referring now to FIG. 12, a conventional leveling of the operating axis of an autocollimator, a known process by which an autocollimator AC secured by an autocollimator foot ACF is leveled or plumbed to have its operating axis OA as shown to be in alignment with the gravitational vector. The output of the autocollimator is set upon a mercury pool HG and the autocollimator AC is adjusted in position (notably, its operating axis OA) until the operating axis OA of the autocollimator AC becomes a desired axis DA, which in this case is determined by gravity. This is done in a known manner by adjusting autocollimator AC and its operating axis OA until the place where the reflected beam from mercury pool HG hits a reticle ACR or functionally similar component or surface in the same projected location as the originating beam.  
         [0121]    Now referring to FIG. 13, a transmitter calibration technique is given for the present invention using a mirror affixed to the rotating laser head RH as shown. It does not matter whether the mirror M is flat on its underside, or whether it is not level with respect the rotating laser head RH. The mirror, once affixed to the rotating laser head RH, defines a rotor axis RA, which may or may not reflect well the rotation axis (not shown) of the rotating laser head RH, but the beauty of this method is it does not matter in terms of affecting the final result.  
         [0122]    Presumably, the rotating laser head RH needs calibration, and its rotation axis is not true or along a desired axis DA as shown. For example, after the transmitter levels itself, there may still be deviation about gimbal axis GA and the rotating laser head RH may be tilted with respect to the desired axis DA, with the positioning of the transmitter housing and components TH (shown) taken into account. One places mirror M on the rotating laser head RH, and shines the light output of autocollimator AC upon the mirror with the rotating laser head RH rotating in the normal manner. The resultant reflected light will give valuable and easily obtainable information.  
         [0123]    [0123]FIG. 14 shows a reticle inside the autocollimator of FIG. 12, illustrating the calibration technique of the present invention. The resultant reflected light forms a circle, circular arc or arc ARC which may be divined using the cross hairs CRH or the equivalent in the autocollimator AC, whose reticle may have gradations or rulings RSC as shown. In this method, the magnitude and direction of the deviation of the center GEO of the arc ARC indicates precisely the misalignment of the rotor spin axis RA, and the transmitter can be appropriately calibrated to bring the arc (ARC) center GEO into alignment with the operating axis OA of the autocollimator AC. The diameter of the arc indicates the amount of wobble and this information can be discarded, as it is not relevant to the calibration of the rotating laser head RH spin axis with the desired axis DA. FIG. 15 shows a transmitter calibration technique similar to that shown in FIG. 13, but for a transmitter in vertical mode, where the operating axis OA of the autocollimator AC is set to a desired axis DA that is other than gravitational, e.g., horizontal. For this purpose the autocollimator AC may be aligned using the known technique given, but this time using a pentaprism PP or other device in conjunction with mercury pool HG, as is known.  
         [0124]    To address the fourth requirement given in the background above, FIG. 16 shows a prior art configuration of strobe light emitting devices for azimuth synchronization, where a transmitter on a tripod TRR is set a ground plane GPL in a field of measurement and strobes are used to periodically light up the field using IREDs (infra-red emitting diodes) or other light emitting devices. The strobe devices shown here to illustrate have a half power beam angular width (HPBW) that is shown nominally at 25 degrees, resulting in a wide divergence DIV 1  and a wide radiant intensity distribution RID 1 . Such a distribution can be obtain using IRED devices under the tradename OPTEK290, for example. Radiant intensity distribution RID 1  results in a range (RANGE 1 ) which is not long range enough from the transmitter, and results in wasted energy WST 1  which typically spills onto the ground surface. In FIG. 17, a longer range prior art configuration of strobe light emitting devices for azimuth synchronization is shown, with a narrow divergence DIV 2  (using, for example, OPTEK295 IREDs), resulting in a narrow radiant intensity distribution RID 2 , giving a long range RANGE 2 , but resulting in wasted energy WST 2 , which actually is a lack of energy, and results in no appreciable strobe signal in the WST 2  area, limiting the fiduciary volume over which the spatial positioning system can function. A solution is shown in FIG. 18, where a configuration of strobe light emitting devices for azimuth synchronization according to the present invention is shown. One seeds the array of strobes with light emitting device of both narrow and wide divergence characteristics, namely, at least one wide divergence strobe providing a wide radiant intensity distribution, and at least one narrow divergence strobe providing a narrow radiant intensity distribution. The result, as shown, gives a mixed divergence characteristic DIV 3 , a long range RANGE 3 , and good coverage near the transmitter and minimal wasted energy WST 3 . Of course, it is envisioned that many strobes can be used, and FIG. 19 shows a unfolded 360 degree view of the strobe light emitting devices arrayed about a transmitter according to the present invention. A strobe set SS is shown, with the unfolded 360 degree view “flattened” into a strip S-STRIP for illustration purposes. In practice, the strobes are only arrayed about an angular field of 270 degrees, but this shall not be limiting in this disclosure. As shown, strobes having a narrow divergence distribution NDIST, shown with “X&#39;s” are placed throughout the array. Seeded among these devices, perhaps one for every three NDIST strobes, are wide distribution strobes WDIST, as envisioned above and in the appended claims.  
         [0125]    [0125]FIG. 20 shows the detector end of a receiver according to the present invention, with a detector DET, photodiodes PHT arrayed inside the detector DET, covered by an infra-red transmissive cover IRC. The detector DET rides on a photocell base PHB which is articulatable by a pivot shaft PIVS, and includes a position sensing switch and detent PSS, which indicates the the receiver electronics that the detector DET has been flipped up as shown. The photocell base PHB can include a marking point MRK as well known in the art.  
         [0126]    Now referring to FIG. 21, the detector end of a receiver according to the present invention, when used with a transmitter in a vertical mode, is shown. In this mode, the receiver is posed such that the detector DET “views” the field of measurement horizontally, in anticipation of detecting laser fans that are rotating in a vertical plane, as is known. Photocell base PHB is flipped down into the receiver housing RHO for this purpose. Instead of prior art transmitters, where a transmitter must be dedicated to vertical scanning, the invention allows that the transmitter electronics and/or the receiver electronics are “informed” of a vertical positioning of the transmitter by known position sensors in the unit, and the spatial positioning system is used in conjunction with the receiver thus described. The fan sweep frequency for the vertical and horizontal modes can be different to allow differentiation by processors and calculation engines. Appropriate vertical vials can be provided and sensed at the appropriate time. By communicating the vertical mode (by virtue of position sensing, and not by elaborate setup methods or by dedication of units) directly to processors, automatic vertical mode position sensing in the field of measurement, even for tall buildings, can be obtained.  
         [0127]    The setup cable described above obviates need for a “scale bar” to determine locations and give a scale to measurements already accumulated. In the case where there is no two-detector measurement wand or pole (stadia-type measurements), there is a need for quick field deployable means for easily setting scale. One can take numerous (redundant) measurements, which can then be averaged by processing algorithms. A “carpenter&#39;s” folding level is a possible embodiment for the posing of the field-deployable length standard.  
         [0128]    Typically, each laser transmitter scans light across a field extending 270 degrees horizontally and 60 degrees vertically. This scanning creates a detection or fiduciary volume over which the transmitter output may be detected by the receiver for position measurement. Two more transmitters can be positioned so that their detection volumes overlap. In the shared volume where the detection volumes overlap, three or more position variables may be obtained, typically two spatial coordinates (e.g., azimuth, elevation) per twin beam laser transmitter.  
         [0129]    All publications and references, including but not limited to patents and patent applications, cited in this specification are herein incorporated by reference in their entirety as if each individual publication or reference were specifically and individually indicated to be incorporated by reference herein as being fully set forth. Any patent application to which this application claims priority is also incorporated by reference herein in its entirety in the manner described above for publications and references.