Patent Publication Number: US-11035955-B2

Title: Registration calculation of three-dimensional scanner data performed between scans based on measurements by two-dimensional scanner

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 14/882,601, which is a continuation-in-part of U.S. patent application Ser. No. 14/559,290, filed Dec. 3, 2014, now U.S. Pat. No. 9,739,886, which claims the benefit of International Patent Application No. PCT/IB2013/003082, filed Sep. 27, 2013, which claims the benefit of German Patent Application No. 10 2012 109 481.0, filed Oct. 5, 2012 and of U.S. Provisional Patent Application No. 61/716,845, filed Oct. 22, 2012, the contents of all of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     U.S. Pat. No. 8,705,016 (&#39;016) describes a laser scanner which, through use of a rotatable mirror, emits a light beam into its environment to generate a three-dimensional (3D) scan. The contents of this patent are incorporated herein by reference. 
     The subject matter disclosed herein relates to use of a 3D laser scanner time-of-flight (TOF) coordinate measurement device. A 3D laser scanner of this type steers a beam of light to a non-cooperative target such as a diffusely scattering surface of an object. A distance meter in the device measures a distance to the object, and angular encoders measure the angles of rotation of two axles in the device. The measured distance and two angles enable a processor in the device to determine the 3D coordinates of the target. 
     A TOF laser scanner is a scanner in which the distance to a target point is determined based on the speed of light in air between the scanner and a target point. Laser scanners are typically used for scanning closed or open spaces such as interior areas of buildings, industrial installations and tunnels. They may be used, for example, in industrial applications and accident reconstruction applications. A laser scanner optically scans and measures objects in a volume around the scanner through the acquisition of data points representing object surfaces within the volume. Such data points are obtained by transmitting a beam of light onto the objects and collecting the reflected or scattered light to determine the distance, two-angles (i.e., an azimuth and a zenith angle), and optionally a gray-scale value. This raw scan data is collected, stored and sent to a processor or processors to generate a 3D image representing the scanned area or object. 
     Generating an image requires at least three values for each data point. These three values may include the distance and two angles, or may be transformed values, such as the x, y, z coordinates. In an embodiment, an image is also based on a fourth gray-scale value, which is a value related to irradiance of scattered light returning to the scanner. 
     Most TOF scanners direct the beam of light within the measurement volume by steering the light with a beam steering mechanism. The beam steering mechanism includes a first motor that steers the beam of light about a first axis by a first angle that is measured by a first angular encoder (or other angle transducer). The beam steering mechanism also includes a second motor that steers the beam of light about a second axis by a second angle that is measured by a second angular encoder (or other angle transducer). 
     Many contemporary laser scanners include a camera mounted on the laser scanner for gathering camera digital images of the environment and for presenting the camera digital images to an operator of the laser scanner. By viewing the camera images, the operator of the scanner can determine the field of view of the measured volume and adjust settings on the laser scanner to measure over a larger or smaller region of space. In addition, the camera digital images may be transmitted to a processor to add color to the scanner image. To generate a color scanner image, at least three positional coordinates (such as x, y, z) and three color values (such as red, green, blue “RGB”) are collected for each data point. 
     A 3D image of a scene may require multiple scans from different registration positions. The overlapping scans are registered in a joint coordinate system, for example, as described in U.S. Published Patent Application No. 2012/0069352 (&#39;352), the contents of which are incorporated herein by reference. Such registration is performed by matching targets in overlapping regions of the multiple scans. The targets may be artificial targets such as spheres or checkerboards or they may be natural features such as corners or edges of walls. Some registration procedures involve relatively time-consuming manual procedures such as identifying by a user each target and matching the targets obtained by the scanner in each of the different registration positions. Some registration procedures also require establishing an external “control network” of registration targets measured by an external device such as a total station. The registration method disclosed in &#39;352 eliminates the need for user matching of registration targets and establishing of a control network. 
     However, even with the simplifications provided by the methods of &#39;352, it is today still difficult to remove the need for a user to carry out the manual registration steps as described above. In a typical case, only 30% of 3D scans can be automatically registered to scans taken from other registration positions. Today such registration is seldom carried out at the site of the 3D measurement but instead in an office following the scanning procedure. In a typical case, a project requiring a week of scanning requires two to five days to manually register the multiple scans. This adds to the cost of the scanning project. Furthermore, the manual registration process sometimes reveals that the overlap between adjacent scans was insufficient to provide proper registration. In other cases, the manual registration process may reveal that certain sections of the scanning environment have been omitted. When such problems occur, the operator must return to the site to obtain additional scans. In some cases, it is not possible to return to a site. A building that was available for scanning at one time may be impossible to access at a later time. A forensics scene of an automobile accident or a homicide is often not available for taking of scans for more than a short time after the incident. 
     Accordingly, while existing 3D scanners are suitable for their intended purposes, what is needed is a 3D scanner having certain features of embodiments of the present invention. 
     BRIEF DESCRIPTION 
     According to one aspect of the invention, a method for measuring and registering three-dimensional (3D) coordinates comprises: locating a measuring device in a first position, the measuring device including a 3D scanner and a two-dimensional (2D) scanner, the 2D scanner configured to sweep a beam of light in a plane; obtaining with the 3D scanner in the first position, a first 3D coordinates on an object, the 3D scanner configured to determine the 3D coordinates based at least in part on a speed of light in air; obtaining by the 2D scanner a first plurality of 2D scan sets by sweeping a beam of light in the plane while the measuring device moves from the first position to a second position, each of the first plurality of 2D scan sets being a set of 2D coordinates of points on the object, each of the first plurality of 2D scan sets being acquired by the 2D scanner at a different position relative to the first position; determining for the measuring device a first value corresponding to a first direction, a second value corresponding to a second direction, and a first rotation value, wherein the first value, the second value, and the first rotation value are determined based at least in part on a fitting of the first plurality of 2D scan sets according to a first mathematical criterion; obtaining with the 3D scanner, while in the second position, a second 3D coordinates on the object; determining by the measuring device, while the measuring device moves from the second position to a third position, a correspondence among registration targets present in both the first 3D coordinates and the second 3D coordinates, the correspondence based at least in part on the first value, the second value, and the first rotation value; and storing in a memory the first value, the second value, and the first value. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of a laser scanner in accordance with an embodiment of the invention; 
         FIG. 2  is a side view of the laser scanner illustrating a method of measurement; 
         FIG. 3  is a schematic illustration of the optical, mechanical, and electrical components of the laser scanner; 
         FIG. 4  depicts a planar view of a 3D scanned image; 
         FIG. 5  depicts an embodiment of a panoramic view of a 3D scanned image generated by mapping a planar view onto a sphere; 
         FIGS. 6A, 6B and 6C  depict embodiments of a 3D view of a 3D scanned image; 
         FIG. 7  depicts an embodiment of a 3D view made up of an image of the object of  FIG. 6B  but viewed from a different perspective and shown only partially; 
         FIG. 8  is a perspective view of a 3D measuring device according to an embodiment; 
         FIG. 9  is a block diagram depicting a 2D scanner accessory and a processor system according to an embodiment; 
         FIG. 10  is a schematic representation of a 3D scanner measuring an object from two registration positions according to an embodiment; 
         FIG. 11  is a schematic representation of a 2D scanner measuring the object from a plurality of intermediate positions according to an embodiment; 
         FIG. 12  shows a 2D scanner capturing portions of the object from a plurality of positions according to an embodiment; 
         FIG. 13  shows the 2D scanner capturing portions of the object from a plurality of positions, as seen from a frame of reference of the 2D scanner, according to an embodiment; 
         FIGS. 14A, 14B, and 14C  illustrate a method for finding changes in the position and orientation of the 2D scanner over time according to an embodiment; 
         FIG. 15  includes steps in a method for measuring and registering 3D coordinates with a 3D measuring device according to an embodiment; 
         FIG. 16  is a perspective view of a 3D measuring device that includes a 3D scanner, 2D scanner, computing devices, and moveable platform according to an embodiment; and 
         FIG. 17  includes steps in a method for measuring and registering 3D coordinates with a 3D measuring device according to an embodiment. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION 
     The present invention relates to a device that includes a 3D scanner and a 2D scanner working cooperatively to provide automatic registration of 3D scans. 
     Referring now to  FIGS. 1-3 , a laser scanner  20  is shown for optically scanning and measuring the environment surrounding the laser scanner  20 . The laser scanner  20  has a measuring head  22  and a base  24 . The measuring head  22  is mounted on the base  24  such that the laser scanner  20  may be rotated about a vertical axis  23 . In one embodiment, the measuring head  22  includes a gimbal point  27  that is a center of rotation about the vertical axis  23  and a horizontal axis  25 . The measuring head  22  has a rotary mirror  26 , which may be rotated about the horizontal axis  25 . The rotation about the vertical axis may be about the center of the base  24 . The terms vertical axis and horizontal axis refer to the scanner in its normal upright position. It is possible to operate a 3D coordinate measurement device on its side or upside down, and so to avoid confusion, the terms azimuth axis and zenith axis may be substituted for the terms vertical axis and horizontal axis, respectively. The term pan axis or standing axis may also be used as an alternative to vertical axis. 
     The measuring head  22  is further provided with an electromagnetic radiation emitter, such as light emitter  28 , for example, that emits an emitted light beam  30 . In one embodiment, the emitted light beam  30  is a coherent light beam such as a laser beam. The laser beam may have a wavelength range of approximately 300 to 1600 nanometers, for example 790 nanometers, 905 nanometers, 1550 nanometers, or less than 400 nanometers. It should be appreciated that other electromagnetic radiation beams having greater or smaller wavelengths may also be used. The emitted light beam  30  is amplitude or intensity modulated, for example, with a sinusoidal waveform or with a rectangular waveform. The emitted light beam  30  is emitted by the light emitter  28  onto the rotary mirror  26 , where it is deflected to the environment. A reflected light beam  32  is reflected from the environment by an object  34 . The reflected or scattered light is intercepted by the rotary mirror  26  and directed into a light receiver  36 . The directions of the emitted light beam  30  and the reflected light beam  32  result from the angular positions of the rotary mirror  26  and the measuring head  22  about the axes  25  and  23 , respectively. These angular positions in turn depend on the corresponding rotary drives or motors. 
     Coupled to the light emitter  28  and the light receiver  36  is a controller  38 . The controller  38  determines, for a multitude of measuring points X, a corresponding number of distances d between the laser scanner  20  and the points X on object  34 . The distance to a particular point X is determined based at least in part on the speed of light in air through which electromagnetic radiation propagates from the device to the object point X. In one embodiment the phase shift of modulation in light emitted by the laser scanner  20  and the point X is determined and evaluated to obtain a measured distance d. 
     The speed of light in air depends on the properties of the air such as the air temperature, barometric pressure, relative humidity, and concentration of carbon dioxide. Such air properties influence the index of refraction n of the air. The speed of light in air is equal to the speed of light in vacuum c divided by the index of refraction. In other words, c air =c/n. A laser scanner of the type discussed herein is based on the time-of-flight (TOF) of the light in the air (the round-trip time for the light to travel from the device to the object and back to the device). Examples of TOF scanners include scanners that measure round trip time using the time interval between emitted and returning pulses (pulsed TOF scanners), scanners that modulate light sinusoidally and measure phase shift of the returning light (phase-based scanners), as well as many other types. A method of measuring distance based on the time-of-flight of light depends on the speed of light in air and is therefore easily distinguished from methods of measuring distance based on triangulation. Triangulation-based methods involve projecting light from a light source along a particular direction and then intercepting the light on a camera pixel along a particular direction. By knowing the distance between the camera and the projector and by matching a projected angle with a received angle, the method of triangulation enables the distance to the object to be determined based on one known length and two known angles of a triangle. The method of triangulation, therefore, does not directly depend on the speed of light in air. 
     In one mode of operation, the scanning of the volume around the laser scanner  20  takes place by rotating the rotary mirror  26  about axis  25  relatively quickly while rotating the measuring head  22  about axis  23  relatively slowly, thereby moving the assembly in a spiral pattern. In an exemplary embodiment, the rotary mirror rotates at a maximum speed of 5820 revolutions per minute. For such a scan, the gimbal point  27  defines the origin of the local stationary reference system. The base  24  rests in this local stationary reference system. 
     In addition to measuring a distance d from the gimbal point  27  to an object point X, the scanner  20  may also collect gray-scale information related to the received optical power (equivalent to the term “brightness.”) The gray-scale value may be determined at least in part, for example, by integration of the bandpass-filtered and amplified signal in the light receiver  36  over a measuring period attributed to the object point X. 
     The measuring head  22  may include a display device  40  integrated into the laser scanner  20 . The display device  40  may include a graphical touch screen  41 , as shown in  FIG. 1 , which allows the operator to set the parameters or initiate the operation of the laser scanner  20 . For example, the screen  41  may have a user interface that allows the operator to provide measurement instructions to the device, and the screen may also display measurement results. 
     The laser scanner  20  includes a carrying structure  42  that provides a frame for the measuring head  22  and a platform for attaching the components of the laser scanner  20 . In one embodiment, the carrying structure  42  is made from a metal such as aluminum. The carrying structure  42  includes a traverse member  44  having a pair of walls  46 ,  48  on opposing ends. The walls  46 ,  48  are parallel to each other and extend in a direction opposite the base  24 . Shells  50 ,  52  are coupled to the walls  46 ,  48  and cover the components of the laser scanner  20 . In the exemplary embodiment, the shells  50 ,  52  are made from a plastic material, such as polycarbonate or polyethylene for example. The shells  50 ,  52  cooperate with the walls  46 ,  48  to form a housing for the laser scanner  20 . 
     On an end of the shells  50 ,  52  opposite the walls  46 ,  48  a pair of yokes  54 ,  56  are arranged to partially cover the respective shells  50 ,  52 . In the exemplary embodiment, the yokes  54 ,  56  are made from a suitably durable material, such as aluminum for example, that assists in protecting the shells  50 ,  52  during transport and operation. The yokes  54 ,  56  each includes a first arm portion  58  that is coupled, such as with a fastener for example, to the traverse  44  adjacent the base  24 . The arm portion  58  for each yoke  54 ,  56  extends from the traverse  44  obliquely to an outer corner of the respective shell  50 ,  52 . From the outer corner of the shell, the yokes  54 ,  56  extend along the side edge of the shell to an opposite outer corner of the shell. Each yoke  54 ,  56  further includes a second arm portion that extends obliquely to the walls  46 ,  48 . It should be appreciated that the yokes  54 ,  56  may be coupled to the traverse  42 , the walls  46 ,  48  and the shells  50 ,  52  at multiple locations. 
     The pair of yokes  54 ,  56  cooperate to circumscribe a convex space within which the two shells  50 ,  52  are arranged. In the exemplary embodiment, the yokes  54 ,  56  cooperate to cover all of the outer edges of the shells  50 ,  52 , while the top and bottom arm portions project over at least a portion of the top and bottom edges of the shells  50 ,  52 . This provides advantages in protecting the shells  50 ,  52  and the measuring head  22  from damage during transportation and operation. In other embodiments, the yokes  54 ,  56  may include additional features, such as handles to facilitate the carrying of the laser scanner  20  or attachment points for accessories for example. 
     On top of the traverse  44 , a prism  60  is provided. The prism extends parallel to the walls  46 ,  48 . In the exemplary embodiment, the prism  60  is integrally formed as part of the carrying structure  42 . In other embodiments, the prism  60  is a separate component that is coupled to the traverse  44 . When the mirror  26  rotates, during each rotation the mirror  26  directs the emitted light beam  30  onto the traverse  44  and the prism  60 . Due to non-linearities in the electronic components, for example in the light receiver  36 , the measured distances d may depend on signal strength, which may be measured in optical power entering the scanner or optical power entering optical detectors within the light receiver  36 , for example. In an embodiment, a distance correction is stored in the scanner as a function (possibly a nonlinear function) of distance to a measured point and optical power (generally unscaled quantity of light power sometimes referred to as “brightness”) returned from the measured point and sent to an optical detector in the light receiver  36 . Since the prism  60  is at a known distance from the gimbal point  27 , the measured optical power level of light reflected by the prism  60  may be used to correct distance measurements for other measured points, thereby allowing for compensation to correct for the effects of environmental variables such as temperature. In the exemplary embodiment, the resulting correction of distance is performed by the controller  38 . 
     In an embodiment, the base  24  is coupled to a swivel assembly (not shown) such as that described in commonly owned U.S. Pat. No. 8,705,012 (&#39;012), which is incorporated by reference herein. The swivel assembly is housed within the carrying structure  42  and includes a motor that is configured to rotate the measuring head  22  about the axis  23 . 
     An auxiliary image acquisition device  66  may be a device that captures and measures a parameter associated with the scanned volume or the scanned object and provides a signal representing the measured quantities over an image acquisition area. The auxiliary image acquisition device  66  may be, but is not limited to, a pyrometer, a thermal imager, an ionizing radiation detector, or a millimeter-wave detector. 
     In an embodiment, a camera (first image acquisition device)  112  is located internally to the scanner and may have the same optical axis as the 3D scanner device. In this embodiment, the first image acquisition device  112  is integrated into the measuring head  22  and arranged to acquire images along the same optical pathway as emitted light beam  30  and reflected light beam  32 . In this embodiment, the light from the light emitter  28  reflects off a fixed mirror  116  and travels to dichroic beam-splitter  118  that reflects the light  117  from the light emitter  28  onto the rotary mirror  26 . The dichroic beam-splitter  118  allows light to pass through at wavelengths different than the wavelength of light  117 . For example, the light emitter  28  may be a near infrared laser light (for example, light at wavelengths of 780 nm or 1150 nm), with the dichroic beam-splitter  118  configured to reflect the infrared laser light while allowing visible light (e.g., wavelengths of 400 to 700 nm) to transmit through. In other embodiments, the determination of whether the light passes through the beam-splitter  118  or is reflected depends on the polarization of the light. The digital camera  112  takes 2D photographic images of the scanned area to capture color data to add to the scanned image. In the case of a built-in color camera having an optical axis coincident with that of the 3D scanning device, the direction of the camera view may be easily obtained by simply adjusting the steering mechanisms of the scanner—for example, by adjusting the azimuth angle about the axis  23  and by steering the mirror  26  about the axis  25 . 
       FIG. 4  depicts an example of a planar view of a 3D scanned image  400 . The planar view depicted in  FIG. 4  maps an image based on direct mapping of data collected by the scanner. The scanner collects data in a spherical pattern but with data points collected near the poles more tightly compressed than those collected nearer the horizon. In other words, each point collected near a pole represents a smaller solid angle than does each point collected nearer the horizon. Since data from the scanner may be directly represented in rows and column, data in a planar image is conveniently presented in a rectilinear format, as shown in  FIG. 4 . With planar mapping described above, straight lines appear to be curved, as for example the straight fence railings  420  that appear curved in the planar view of the 3D image. The planar view may be a 3D unprocessed scanned image displaying just the gray-scale values received from the distance sensor arranged in columns and rows as they were recorded. In addition, the 3D unprocessed scanned image of the planar view may be in full resolution or reduced resolution depending on system characteristics (e.g., display device, storage, processor). The planar view may be a 3D processed scanned image that depicts either gray-scale values (resulting from the light irradiance measured by the distance sensor for each pixel) or color values (resulting from camera images which have been mapped onto the scan). Although the planar view extracted from the 3D scanner is ordinarily a gray-scale or color image,  FIG. 4  is shown as a line drawing for clarity in document reproduction. The user interface associated with the display unit, which may be integral to the laser scanner, may provide a point selection mechanism, which in  FIG. 4  is the cursor  410 . The point selection mechanism may be used to reveal dimensional information about the volume of space being measured by the laser scanner. In  FIG. 4 , the row and column at the location of the cursor are indicated on the display at  430 . The two measured angles and one measured distance (the 3D coordinates in a spherical coordinate system) at the cursor location are indicated on the display at  440 . Cartesian XYZ coordinate representations of the cursor location are indicated on the display at  450 . 
       FIG. 5  depicts an example of a panoramic view of a 3D scanned image  600  generated by mapping a planar view onto a sphere, or in some cases a cylinder. A panoramic view can be a 3D processed scanned image (such as that shown in  FIG. 5 ) in which 3D information (e.g., 3D coordinates) is available. The panoramic view may be in full resolution or reduced resolution depending on system characteristics. It should be pointed out that an image such as  FIG. 5  is a 2D image that represents a 3D scene when viewed from a particular perspective. In this sense, the image of  FIG. 5  is much like an image that might be captured by a 2D camera or a human eye. Although the panoramic view extracted from the 3D scanner is ordinarily a gray-scale or color image,  FIG. 5  is shown as a line drawing for clarity in document reproduction. 
     The term panoramic view refers to a display in which angular movement is generally possible about a point in space, but translational movement is not possible (for a single panoramic image). In contrast, the term 3D view as used herein refers to generally refers to a display in which provision is made (through user controls) to enable not only rotation about a fixed point but also translational movement from point to point in space. 
       FIGS. 6A, 6B and 6C  depict an example of a 3D view of a 3D scanned image. In the 3D view a user can leave the origin of the scan and see the scan points from different viewpoints and angles. The 3D view is an example of a 3D processed scanned image. The 3D view may be in full resolution or reduced resolution depending on system characteristics. In addition, the 3D view allows multiple registered scans to be displayed in one view.  FIG. 6A  is a 3D view  710  over which a selection mask  730  has been placed by a user.  FIG. 6B  is a 3D view  740  in which only that part of the 3D view  710  covered by the selection mask  730  has been retained.  FIG. 6C  shows the same 3D measurement data as in  FIG. 6B  except as rotated to obtain a different view.  FIG. 7  shows a different view of  FIG. 6B , the view in this instance being obtained from a translation and rotation of the observer viewpoint, as well as a reduction in observed area. Although the 3D views extracted from the 3D scanner are ordinarily a gray-scale or color image,  FIGS. 6A-C  and  7  are shown as line drawings for clarity in document reproduction. 
       FIGS. 8 and 9  show an embodiment of a 3D measuring device  800  that includes a 3D scanner  20 , a two-dimensional (2D) scanner accessory  810 , a processor system  950 , and an optional moveable platform  820 . The 3D measuring device  800  may be a 3D TOF scanner  20  as described in reference to  FIG. 1 . The 2D scanner accessory  810  includes a 2D scanner  910  and may optionally include, as shown in  FIG. 9 , a 2D processor  940 , a position/orientation sensor  920 , and a network connection module  930 . 
     The processor system  950  includes one or more processing elements that may include a 3D scanner processor (controller)  38 , 2D processor  940 , an external computer  970 , and a cloud computer  980 . The processors may be microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), and generally any device capable of performing computing functions. The one or more processors have access to memory for storing information. In an embodiment illustrated in  FIG. 9 , the controller  38  represents one or more processors distributed throughout the 3D scanner. Also included in the embodiment of  FIG. 9  are 2D processor  940  for the 2D scanner accessory  810 , an external computer  970 , and one or more cloud computers  980  for remote computing capability. In an alternative embodiment, only one or two of the processors  38 ,  960 ,  970 , and  980  is provided in the processor system. Communication among the processors may be through wired links, wireless links, or a combination of wired and wireless links. In an embodiment, the connection between the processor of the 2D scanner accessory and the 3D scanner is made by IEEE 802.11 (Wi-Fi) through the network connection module  930 . In an embodiment, scan results are uploaded after each scanning session to the cloud (remote network) for storage and future use. 
     The 2D scanner accessory  810  measures 2D coordinates in a plane. In most cases, it does this by steering light within a plane to illuminate object points in the environment. It collects the reflected (scattered) light from the object points to determine 2D coordinates of the object points in the 2D plane. In an embodiment, the 2D scanner scans a spot of light over an angle while at the same time measuring an angle value and corresponding distance value to each of the illuminated object points. 
     Examples of 2D scanners  910  that might be included in the 2D scanner accessory  810  include 2D scanners from the Sick LMS100 product family and 2D scanners from Hoyuko such as the Hoyuko models URG-04LX-UG01 and UTM-30LX. The scanners in the Sick LMS100 family measure angles over a 270 degree range and over distances up to 20 meters. The Hoyuko model URG-04LX-UG01 is a low-cost 2D scanner that measures angles over a 240 degree range and distances up to 4 meters. The Hoyuko model UTM-30LX is a 2D scanner that measures angles over a 270 degree range and to distances up to 30 meters. Many other types of 2D scanners are also available. 
     The optional position/orientation sensor  920  in the 2D scanner accessory  810  may include inclinometers (accelerometers), gyroscopes, magnetometers, and altimeters. Usually devices that include one or more of an inclinometer and gyroscope are referred to as an inertial measurement unit (IMU). In some cases, the term IMU is used in a broader sense to include a variety of additional devices that indicate position and/or orientation—for example, magnetometers that indicate heading based on changes in magnetic field direction relative to the earth&#39;s magnetic north and altimeters that indicate altitude (height). An example of a widely used altimeter is a pressure sensor. By combining readings from a combination of position/orientation sensors with a fusion algorithm that may include a Kalman filter, relatively accurate position and orientation measurements can be obtained using relatively low-cost sensor devices. 
     The optional moveable platform  820  enables the 3D measuring device  20  to be moved from place to place, typically along a floor that is approximately horizontal. In an embodiment, the optional moveable platform  820  is a tripod that includes wheels  822 . In an embodiment, the wheels  822  may be locked in place using wheel brakes  824 . In another embodiment, the wheels  822  are retractable, enabling the tripod to sit stably on three feet attached to the tripod. In another embodiment, the tripod has no wheels but is simply pushed or pulled along a surface that is approximately horizontal, for example, a floor. In another embodiment, the optional moveable platform  820  is a wheeled cart that may be hand pushed/pulled or motorized. 
     In an embodiment, the 2D scanner accessory  810  is mounted between the moveable platform  820  and the 3D scanner  20  as shown in  FIG. 8 . In another embodiment, the 2D scanner accessory  810  is integrated into the 3D scanner  20 . In another embodiment, the 2D scanner accessory  810  is mounted on the moveable platform  820 , for example, on a leg of a tripod or between the legs of the tripod. In another embodiment, the 2D scanner accessory  810  is mounted on the body of the 3D scanner, for example, in a position similar to that of element  70  in  FIG. 1 . In another embodiment, the 2D scanner  910  is attached to a leg of a tripod while other parts of the 2D scanner accessory  810  are internal to the 3D scanner  20 . 
     In an embodiment, the 2D scanner  910  is oriented so as to scan a beam of light over a range of angles in a horizontal plane. At instants in time the 2D scanner  910  returns an angle reading and a corresponding distance reading to provide 2D coordinates of object points in the horizontal plane. In completing one scan over the full range of angles, the 2D scanner returns a collection of paired angle and distance readings. As the 3D measuring device  800  is moved from place to place, the 2D scanner  910  continues to return 2D coordinate values. These 2D coordinate values are used to locate the position of the 3D scanner  20  at each stationary registration position, thereby enabling more accurate registration. 
       FIG. 10  shows the 3D measuring device  800  moved to a first registration position  1112  in front of an object  1102  that is to be measured. The object  1102  might for example be a wall in a room. In an embodiment, the 3D measuring device  800  is brought to a stop and is held in place with brakes, which in an embodiment are brakes  824  on wheels  822 . The 3D scanner  20  in the 3D measuring device  800  takes a first 3D scan of the object  1102 . In an embodiment, the 3D scanner  20  may if desired obtain 3D measurements in all directions except in downward directions blocked by the structure of the 3D measuring device  800 . However, in the example of  FIG. 10 , in which 3D scanner  20  measures a long, mostly flat structure  1102 , a smaller effective FOV  1130  may be selected to provide a more face-on view of features on the structure. 
     When the first 3D scan is completed, the processor system  950  receives a signal indicating that 2D scan data is being collected. This signal may come from the position/orientation sensor  920  in response to the sensor  920  detecting a movement of the 3D measuring device  800 . The signal may be sent when the brakes are released, or it may be sent in response to a command sent by an operator. The 2D scanner accessory  810  may start to collect data when the 3D measuring device  800  starts to move, or it may continually collect 2D scan data, even when the 2D scanner accessory  810  is stationary. In an embodiment, the 2D scanner data is sent to the processor system  950  as it is collected. 
     In an embodiment, the 2D scanner accessory  810  measures as the 3D measuring device  800  is moved toward the second registration position  1114 . In an embodiment, 2D scan data is collected and processed as the scanner passes through a plurality of 2D measuring positions  1120 . At each measuring position  1120 , the 2D scanner collects 2D coordinate data over an effective FOV  1140 . Using methods described in more detail below, the processor system  950  uses 2D scan data from the plurality of 2D scans at positions  1120  to determine a position and orientation of the 3D scanner  20  at the second registration position  1114  relative to the first registration position  1112 , where the first registration position and the second registration position are known in a 3D coordinate system common to both. In an embodiment, the common coordinate system is represented by 2D Cartesian coordinates x, y and by an angle of rotation θ relative to the x or y axis. In an embodiment, the x and y axes lie in the plane of the scanner and may be further based on a direction of a “front” of the 2D scanner  910 . An example of such an (x, y, θ) coordinate system is the coordinate system  1410  of  FIG. 14A . 
     On the object  1102 , there is a region of overlap  1150  between the first 3D scan (collected at the first registration position  1112 ) and the second 3D scan (collected at the second registration position  1114 ). In the overlap region  1150  there are registration targets (which may be natural features of the object  1102 ) that are seen in both the first 3D scan and the second 3D scan. A problem that often occurs in practice is that, in moving the 3D scanner  20  from the first registration position  1112  to the second registration position  1114 , the processor system  950  loses track of the position and orientation of the 3D scanner  20  and hence is unable to correctly associate the registration targets in the overlap regions to enable the registration procedure to be performed reliably. By using the succession of 2D scans, the processor system  950  is able to determine the position and orientation of the 3D scanner  20  at the second registration position  1114  relative to the first registration position  1112 . This information enables the processor system  950  to correctly match registration targets in the region of overlap  1150 , thereby enabling the registration procedure to be properly completed. 
       FIG. 12  shows the 2D scanner  910  collecting 2D scan data at selected positions  1120  over an effective FOV  1140 . At different positions  1120 , the 2D scanner captures a portion of the object  1102  marked A, B, C, D, and E.  FIG. 12  shows 2D scanner moving in time relative to a fixed frame of reference of the object  1102 . 
       FIG. 13  includes the same information as  FIG. 12  but shows it from the frame of reference of the 2D scanner  910  rather than the frame of reference of the object  1102 . This figure makes clear that in the 2D scanner frame of reference, the position of features on the object change over time. Hence it is clear that the distance traveled by the 2D scanner  910  can be determined from the 2D scan data sent from the 2D scanner accessory  810  to the processor system  950 . 
       FIG. 14A  shows a coordinate system that may be used in  FIGS. 14B and 14C . In an embodiment, the 2D coordinates x and y are selected to lie on the plane of the 2D scanner  910 . The angle θ is selected as a rotation angle relative to an axis such as x or y.  FIGS. 14B, 14C  represent a realistic case in which the 2D scanner  910  is moved not exactly on a straight line, for example, nominally parallel to the object  1102 , but also to the side. Furthermore, the 2D scanner  910  may be rotated as it is moved. 
       FIG. 14B  shows the movement of the object  1102  as seen from the frame of reference of the 2D scanner  910 . In the 2D scanner frame of reference (that is, as seen from the 2D scanner&#39;s point of view), the object  1102  is moving while the 2D scanner  910  is fixed in place. In this frame of reference, the portions of the object  1102  seen by the 2D scanner  910  appear to translate and rotate in time. The 2D scanner accessory  810  provides a succession of such translated and rotated 2D scans to the processor system  950 . In the example shown in  FIGS. 14A , B, the scanner translates in the +y direction by a distance  1420  shown in  FIG. 14B  and rotates by an angle  1430 , which in this example is +5 degrees. Of course, the scanner could equally well have moved in the +x or −x direction by a small amount. To determine the movement of the 2D scanner  910  in the x, y, θ directions, the processor system  950  uses the data recorded in successive scans as seen in the frame of reference of the 2D scanner  910 , as shown in  FIG. 14B . In an embodiment, the processor system  950  performs a best-fit calculation using methods well known in the art to match the two scans or features in the two scans as closely as possible. 
     As the 2D scanner  910  takes successive 2D readings and performs best-fit calculations, the processor system  950  keeps track of the translation and rotation of the 2D scanner, which is the same as the translation and rotation of the 3D scanner  20  and the measuring device  800 . In this way, the processor system  950  is able to accurately determine the change in the values of x, y, θ as the measuring device  800  moves from the first registration position  1112  to the second registration position  1114 . 
     It is important to understand that the processor system  950  determines the position and orientation of the 3D measuring device  800  based on a comparison of the succession of 2D scans and not on fusion of the 2D scan data with 3D scan data provided by the 3D scanner  20  at the first registration position  1112  or the second registration position  1114 . 
     Instead, the processor system  950  is configured to determine a first translation value, a second translation value, and a first rotation value that, when applied to a combination of the first 2D scan data and second 2D scan data, results in transformed first 2D data that matches transformed second 2D data as closely as possible according to an objective mathematical criterion. In general, the translation and rotation may be applied to the first scan data, the second scan data, or to a combination of the two. For example, a translation applied to the first data set is equivalent to a negative of the translation applied to the second data set in the sense that both actions produce the same match in the transformed data sets. An example of an “objective mathematical criterion” is that of minimizing the sum of squared residual errors for those portions of the scan data judged to overlap. Another type of objective mathematical criterion may involve a matching of multiple features identified on the object. For example, such features might be the edge transitions  1103 ,  1104 , and  1105  shown in  FIG. 11B . The mathematical criterion may involve processing of the raw data provided by the 2D scanner accessory  810  to the processor system  950 , or it may involve a first intermediate level of processing in which features are represented as a collection of line segments using methods that are known in the art, for example, methods based on the Iterative Closest Point (ICP). Such a method based on ICP is described in Censi, A., “An ICP variant using a point-to-line metric,” IEEE International Conference on Robotics and Automation (ICRA) 2008. 
     In an embodiment, the first translation value is dx, the second translation value is dy, and the first rotation value dθ. If the first scan data is collected with the 2D scanner  910  having translational and rotational coordinates (in a reference coordinate system) of (x 1 , y 1 , θ 1 ), then when the second 2D scan data is collected at a second location the coordinates are given by (x 2 , y 2 , θ 2 )=(x 1 +dx, y 1 +dy, θ 1 +dθ). In an embodiment, the processor system  950  is further configured to determine a third translation value (for example, dz) and a second and third rotation values (for example, pitch and roll). The third translation value, second rotation value, and third rotation value may be determined based at least in part on readings from the position/orientation sensor  920 . 
     The 2D scanner  910  collects 2D scan data at the first registration position  1112  and more 2D scan data at the second registration position  1114 . In some cases, these scans may suffice to determine the position and orientation of the 3D measuring device at the second registration position  1114  relative to the first registration position  1112 . In other cases, the two sets of 2D scan data are not sufficient to enable the processor system  950  to accurately determine the first translation value, the second translation value, and the first rotation value. This problem may be avoided by collecting 2D scan data at intermediate scan locations  1120 . In an embodiment, the 2D scan data is collected and processed at regular intervals, for example, once per second. In this way, features are easily identified in successive 2D scans  1120 . If more than two 2D scans are obtained, the processor system  950  may choose to use the information from all the successive 2D scans in determining the translation and rotation values in moving from the first registration position  1112  to the second registration position  1114 . Alternatively, the processor may choose to use only the first and last scans in the final calculation, simply using the intermediate 2D scans to ensure proper correspondence of matching features. In most cases, accuracy of matching is improved by incorporating information from multiple successive 2D scans. 
     The first translation value, the second translation value, and the first rotation value are the same for the 2D scanner, the 3D scanner, and the 3D measuring device since all are rigidly held relative to the others. 
     The 3D measuring device  800  is moved to the second registration position  1114 . In an embodiment, the 3D measuring device  800  is brought to a stop and brakes are locked to hold the 3D scanner stationary. In an alternative embodiment, the processor system  950  starts the 3D scan automatically when the moveable platform is brought to a stop, for example, by the position/orientation sensor  920  noting the lack of movement. The 3D scanner  20  in the 3D measuring device  800  takes a 3D scan of the object  1102 . This 3D scan is referred to as the second 3D scan to distinguish it from the first 3D scan taken at the first registration position. 
     The processor system  950  applies the already calculated first translation value, the second translation value, and the first rotation value to adjust the position and orientation of the second 3D scan relative to the first 3D scan. This adjustment, which may be considered to provide a “first alignment,” brings the registration targets (which may be natural features in the overlap region  1150 ) into close proximity. The processor system  950  performs a fine registration in which it makes fine adjustments to the six degrees of freedom of the second 3D scan relative to the first 3D scan. It makes the fine adjustment based on an objective mathematical criterion, which may be the same as or different than the mathematical criterion applied to the 2D scan data. For example, the objective mathematical criterion may be that of minimizing the sum of squared residual errors for those portions of the scan data judged to overlap. Alternatively, the objective mathematical criterion may be applied to a plurality of features in the overlap region. The mathematical calculations in the registration may be applied to raw 3D scan data or to geometrical representations of the 3D scan data, for example, by a collection of line segments. 
     Outside the overlap region  1150 , the aligned values of the first 3D scan and the second 3D scan are combined in a registered 3D data set. Inside the overlap region, the 3D scan values included in the registered 3D data set are based on some combination of 3D scanner data from the aligned values of the first 3D scan and the second 3D scan. 
       FIG. 15  shows elements of a method  1500  for measuring and registering 3D coordinates. 
     An element  1505  includes providing a 3D measuring device that includes a processor system, a 3D scanner, a 2D scanner, and a moveable platform. The processor system has at least one of a 3D scanner controller, a 2D scanner processor, an external computer, and a cloud computer configured for remote network access. Any of these processing elements within the processor system may include a single processor or multiple distributed processing elements, the processing elements being a microprocessor, digital signal processor, FPGA, or any other type of computing device. The processing elements have access to computer memory. The 3D scanner has a first light source, a first beam steering unit, a first angle measuring device, a second angle measuring device, and a first light receiver. The first light source is configured to emit a first beam of light, which in an embodiment is a beam of laser light. The first beam steering unit is provided to steer the first beam of light to a first direction onto a first object point. The beam steering unit may be a rotating mirror such as the mirror  26  or it may be another type of beam steering mechanism. For example, the 3D scanner may contain a base onto which is placed a first structure that rotates about a vertical axis, and onto this structure may be placed a second structure that rotates about a horizontal axis. With this type of mechanical assembly, the beam of light may be emitted directly from the second structure and point in a desired direction. Many other types of beam steering mechanisms are possible. In most cases, a beam steering mechanism includes one or two motors. The first direction is determined by a first angle of rotation about a first axis and a second angle of rotation about a second axis. The first angle measuring device is configured to measure the first angle of rotation and the second angle measuring device configured to measure the second angle of rotation. The first light receiver is configured to receive first reflected light, the first reflected light being a portion of the first beam of light reflected by the first object point. The first light receiver is further configured to produce a first electrical signal in response to the first reflected light. The first light receiver is further configured to cooperate with the processor system to determine a first distance to the first object point based at least in part on the first electrical signal, and the 3D scanner is configured to cooperate with the processor system to determine 3D coordinates of the first object point based at least in part on the first distance, the first angle of rotation and the second angle of rotation. The 2D scanner accessory includes a 2D scanner having a second light source, a second beam steering unit, a third angle measuring device, and a second light receiver. The second light source is configured to emit a second beam of light. The second beam steering unit is configured to steer the second beam of light to a second direction onto a second object point. The second direction is determined by a third angle of rotation about a third axis, the third angle measuring device being configured to measure the third angle of rotation. The second light receiver is configured to receive second reflected light, where the second reflected light is a portion of the second beam of light reflected by the second object point. The second light receiver is further configured to produce a second electrical signal in response to the second reflected light. The 2D scanner is configured to cooperate with the processor system to determine a second distance to the second object point based at least in part on the second electrical signal. The 2D scanner is further configured to cooperate with the processor system to determine 2D coordinates of the second object point based at least in part on the second distance and the third angle of rotation. The moveable platform is configured to carry the 3D scanner and the 2D scanner. The 3D scanner is fixed relative to the 2D scanner, and the moveable platform is configured for motion on a plane perpendicular to the third axis. 
     An element  1510  includes determining with processor system, in cooperation with the 3D scanner, 3D coordinates of a first collection of points on an object surface while the 3D scanner is fixedly located at a first registration position. 
     An element  1515  includes obtaining by the 2D scanner in cooperation with the processor system a plurality of 2D scan sets. Each of the plurality of 2D scan sets is a set of 2D coordinates of points on the object surface collected as the 2D scanner moves from the first registration position to a second registration position. Each of the plurality of 2D scan sets is collected by the 2D scanner at a different position relative to the first registration position. 
     An element  1520  includes determining by the processor system a first translation value corresponding to a first translation direction, a second translation value corresponding to a second translation direction, and a first rotation value corresponding to a first orientational axis, wherein the first translation value, the second translation value, and the first rotation value are determined based at least in part on a fitting of the plurality of 2D scan sets according to a first mathematical criterion. 
     An element  1525  includes determining with the processor system, in cooperation with the 3D scanner, 3D coordinates of a second collection of points on the object surface while the 3D scanner is fixedly located at the second registration position. 
     An element  1535  includes identifying by the processor system a correspondence among registration targets present in both the first collection of points and the second collection of points, the correspondence based at least in part on the first translation value, the second translation value, and the first rotation value. 
     An element  1545  includes determining 3D coordinates of a registered 3D collection of points based at least in part on a second mathematical criterion, the correspondence among the registration targets, the 3D coordinates of the first collection of points and the 3D coordinates of the second collection of points. An element  1550  includes storing the 3D coordinates of the registered 3D collection of points. 
     In most methods used today for scanning large objects (for example, large buildings), data is collected at each registration position and the quality of the registration evaluated later. One problem with this approach is that it provides no way to detect a failure in registration, which might be easily corrected on site, but is difficult to correct at a later time when access to the scan site may no longer be available. In addition, there is the need with this method to register the multiple scans in software run on an external computer. In some cases, natural or artificial targets observed by the scanner at consecutive registration locations may be automatically recognized and matched by the software, but in many cases the scans must be hand registered. In many cases, the time and effort in registering and processing 3D scan data greatly outweighs the time required to collect the scan data on site. 
     In an embodiment described herein, processing of 2D and 3D scanner data is performed as the measurement is taking place, thereby eliminating time-consuming post processing and further ensuring that required scan data has been collected before leaving a site. 
     An example of a measuring device  800  that may be used to perform this measurement was described herein above with reference to  FIG. 8 . Another example of a measuring device  1600  that may be used to perform this measurement is now described with reference to  FIG. 16 . Included in the 3D measuring device  1600  is a 3D TOF scanner  20  that measures distance based at least in part on a speed of light in air. This type of scanner also measures two angles using angle transducers such as angular encoders. The two measured angles and one measured distance provide 3D coordinates of points on an object. In an embodiment, the scanner includes motors and a servo system to drive a beam of light to any desired point on an object. In an embodiment described herein above with respect to  FIGS. 1-3 , the scanner may also include a mode for rapidly directing the beam of light over a continually varying pattern, thereby enabling rapid collection of 3D coordinates over a large volume. 
     Also included in the 3D measuring system  1600  is a 2D laser scanner  1610 , which in an embodiment is configured to emit a beam of light in a horizontal plane  1622 . In an embodiment, the beam of light sweeps over an angle of 270 degrees at a rate of 30 Hz. In an embodiment, the beam of light receives reflected light from an object and determines a collection of distances to the object based on the reflected light. In an embodiment, the 2D scanner  1610  measures distances as a function of swept angle. In an embodiment, the swept beam of light is a part of an assembly  1620  that further includes a computing device  1630  that receives 2D scan sets, which might include distances versus angles, from the 2D scanner  1610  and 3D coordinate data from the 3D scanner  20 . In an embodiment, the computing device  1630  further performs processing of 2D and 3D scan data to determine a correspondence among targets measured at the first registration position and the second registration position. In other embodiments, other computing devices, such as a computer  1640  or an external computer  1650  not attached to the 3D measuring device may be used to determine the correspondence among targets measured at the first and second registration positions. 
     Communication channels to transfer information among the 2D scanner, 3D scanner, and computing devices may be wireless or wired communication channels  1660 . In an embodiment, a wireless access point (AP) is contained within the 3D scanner  20 . In an embodiment the AP connects to wireless devices such as the 2D scanner  1610  and one or more of computing devices  1630 ,  1640 , and  1650 . In an alternative embodiment, the 3D scanner  20  includes an automation adapter having an Ethernet interface and a switch. The automation adapter connects with Ethernet cables of the 2D scanner  1610  and computing devices such as  1630 ,  1640 , and  1650 . The automation interface enables wired communication among the elements of the measuring device  1600  and external computing devices. In an embodiment, the 3D scanner  20  includes both an AP and an automation adapter to provide both wireless and wired communication among different components of the system. In other embodiments, the AP and automation adapter are not included in the 3D scanner  20  but elsewhere in the system. 
     The measuring device further includes a moveable platform  1605 , which may be pushed by an operator or moved under computer control by motorized wheels. The 3D scanner and the 2D scanner are mounted on the moveable platform  1605 . 
     In an embodiment, a first 3D scan is taken at a first registration position. The scanner moves between the first registration position and the second registration position, either under its own power using motorized wheels or being pushed by an operator. As it moves between the first and second registration positions, the 2D scanner obtains 2D scan data, which is then evaluated mathematically to determine a movement vector (distance in each of two directions) and an angle of rotation, as explained herein above. At the second registration position, the 3D scanner  20  takes a second 3D scan. As explained herein above, one of the computing devices (i.e., processors) uses the plurality of collected 2D scan sets to determine a correspondence among registration targets seen by the 3D scanner in the first registration position and the second registration position. At a later time, a computing device performs any other steps needed to complete combining and processing of the 3D data collected at the first and second registration positions. This process of combining may further include additional collected data such as color data obtained from an internal color camera within the scanner. 
     The measuring device  1600  moves to successive registration positions, taking a 3D measurement at each registration position and collecting 2D data from the 2D scanner  1610  between the registration positions. An aspect of the present invention is that processing is carried out between the second and third registration position to determine the correspondence between the registration targets observed at the first and second registration positions. This processing uses the 2D data collected between the first and second registration positions in combination with 3D data obtained at the first and second registration positions. 
     Hence, when the scanner reaches the third registration position, the computing device will have determined (at least partially if not completely) the correspondence among the targets in the first and second registration positions. If a correspondence was not successfully established by the computing device, a notice may be given indicating that the problem is present. This may result in an operator being notified or it may result in the measurement suspended. In an embodiment, the failure to register the targets observed by the 3D scanner at the first and second registration positions results in the scanner being returned to an earlier step to repeat measurements. 
     In an embodiment, when the computing device has determined the correspondence among the targets in the overlap region of the first and second registration positions, the measuring device further determines a quality of the correspondence. In an embodiment, the measuring device provides a notification when the quality of the correspondence is below a quality threshold. The notification may be a notification to the user, a computer message, an emitted sound, an emitted light, or a stopping of the inspection procedure, for example. 
     In an embodiment, the scanner may determine the distance to move the measuring device  1600  between the first registration position and the second registration position based at least in part on one of the 2D scan sets. Each of the 2D scan sets includes information about features observable in a horizontal 2D scan. Examples of such features are the features  1102 - 1105  in  FIG. 11 . In an embodiment, the decision on the distance to be moved between the first registration position and the second registration position is based entirely on the first 2D scan set collected between the first and second registration positions. In another embodiment, the decision on the distance to be moved is based on a plurality of the first 2D scan sets, with the decision on the distance to be moved made during the movement between the first and second registration positions. 
     In an embodiment, the computing device  1640  is a laptop or notebook computer that provides a user an interface to a computer program enabling advanced processing and viewing of scan data. In an embodiment, use of the computing device  1640  is optional and simply is provided to give the operator more analysis tools. In another embodiment, the computing device  1640  is used to perform correspondence calculations described herein above or to perform other 3D processing steps. 
     In an embodiment, a computing device  1630  continually computes the position of the measuring device  1600  based at least in part on data from the 2D scanner and, optionally, on data provided by a position/orientation sensor, which might include a multi-axis inclinometer, a multi-axis gyroscope, and a magnetometer (electronic compass) to provide heading information. In an embodiment, data from the 2D scanner is acquired at a rate of 30 Hz. In an embodiment, after each scan, a difference is calculated with respect to one or more 2D scans obtained previously. In an embodiment, this information is provided to a Kalman filter that performs “intelligent averaging” calculations that smooth out noise within constraints imposed by movement geometry. 
     In an embodiment, application software runs on a notebook computer  1640  or similar device. In an embodiment, the user selects a button on the user interface of the application software to begin processing of the collected data. In an embodiment, after collecting after collecting 3D scan data at the second registration position, the software requests 2D position information from processed 2D scan data, which might be provided for example from the computing device  1630 . The processed 2D scan data may be provided as metadata to the 3D scan. The software uses a registration algorithm to determine a correspondence among the registration targets in the overlap region between the first and second registration positions. The software completes the 3D registration by combining 3D coordinates obtained at the first and second registration positions. 
     In other embodiments, the calculations are performed without the user needing to press a button on the user interface of an application program running on a notebook computer  1640 . In an embodiment, measurements are carried out in an integrated and automatic way without requiring assistance of an operator. In an embodiment, additional calculations, which may involve including additional mathematical operations such as meshing registered 3D data, and adding and texture to registered 3D data may be carried out following the registration step. In an embodiment, these later processing steps may be carried out in parallel, for example, by network computers to provide finished 3D scans at the end of data collection by the measuring device  1600 . 
       FIG. 17  is a flow chart of a method  1700  that may be carried out according to the description given herein above. In the element  1705 , the measuring device  1600  is fixedly located in a first registration position such as the position  1112  in  FIG. 10 . The measuring device includes a 3D scanner  20  and a 2D scanner  1610 , both mounted on a moveable platform  1605 , which in  FIG. 16  is a tripod mounted on a platform having three wheels. In an embodiment, the 2D scanner emits a beam of light that sweeps in different directions in a horizontal plane  1622 . 
     In the element  1710 , the 3D scanner, while in the first registration position, obtains 3D coordinates of a first collection of points on an object, which in an embodiment illustrated in  FIGS. 10 and 11  is the side of a building. In an embodiment, the 3D scanner is a TOF scanner, which may be of a variety of types. An example of a possible TOF scanner is the scanner  20  discussed in reference to  FIGS. 1-3 . 
     In the element  1715 , the 2D scanner  1610  obtains a first plurality of 2D scan sets while the first measuring device moves from the first registration position to the second registration position. Each of the first plurality of 2D scan sets includes a set of 2D coordinates of points on the object. The 2D coordinates of points on the object may be given in any coordinate system, for example, as x-y values or as distance and angle values. Each of the first plurality of 2D scan sets is collected by the 2D scanner at a different position relative to the first registration position. 
     In the element  1720 , the measuring device determines a first translation value corresponding to a first translation direction, a second translation value corresponding to a second translation direction, and a first rotation value corresponding to a first orientational axis. The first translational direction and the second translational direction might be, for example, x-y coordinates in a coordinate system established with respect to the object being measured. For example, the x-y coordinates might correspond to coordinates along a floor on which the measuring device moves. Other coordinate systems may alternatively be used to represent the first translational direction and the second translational direction. The first orientational axis has a given direction in relation to the first and second translation directions. A convenient choice for the first orientational axis is a direction perpendicular to the plane containing vectors along the first and second translational directions. The first translation value, the second translation value, and the first rotation angle provide the information needed to obtain a good initial estimate of the pose of the scanner at the second registration position relative to the pose of the scanner at the first registration position. This provides a good basis for matching the registration targets, whether natural targets or artificial targets, seen from the first and second registration positions. The determining of the first translation value, the second translation value, and the first rotation angle is carried out according to a first mathematical criterion. Such a mathematical criterion is also referred to as an objective mathematical criterion. The most commonly used such mathematical criterion is a least-squares criterion. In this case, for this criterion, the 2D features observed in the first collection of 2D scan sets are aligned so as to minimize the sum of squares of residual errors in the matching of the features. 
     In the element  1725 , the 3D scanner, while in the second registration position, obtains 3D coordinates of a second collection of points on the object. In general, the first collection of points measured by the 3D scanner at the first registration position are not exactly the same points as the second collection of points measured by the 3D scanner at the second registration position. However, the points provide the information needed to identify the target features, which might be natural features or artificial features. 
     In the element  1730 , the measuring device, while moving from the second registration position to a third registration position, determines a correspondence among registration targets seen in the first collection of 3D points observed at the first registration position and the registration targets seen in the second collection of 3D points observed at the second registration position. This registration is based at least in part on the first translation value, the second translation value, and the first rotation value, which provide the initial conditions from which the mathematical matching of 3D feature is carried out. 
     In the element  1735 , the first translation value, the second translation value, and the first rotation value are stored. 
     Terms such as processor, controller, computer, DSP, FPGA are understood in this document to mean a computing device that may be located within an instrument, distributed in multiple elements throughout an instrument, or placed external to an instrument. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.