Patent Publication Number: US-9835726-B2

Title: Method for optically scanning and measuring an environment

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 15/419,334 filed on Jan. 30, 2017, which is a continuation-in-part application of U.S. application Ser. No. 15/140,909 filed on Apr. 28, 2016, which is a continuation application of U.S. application Ser. No. 13/697,031 filed on Apr. 29, 2013. U.S. application Ser. No. 13/697,031 is a National Stage Application of PCT Application No. PCT/EP2011/001662, filed on Apr. 1, 2011, which claims the benefit of U.S. Provisional Patent Application No. 61/362,810, filed on Jul. 9, 2010, and of German Patent Application No. DE 10 2010 020 925.2, filed on May 10, 2010, and which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The invention relates to a system and method for optically scanning and measuring an environment, and in particular, to a system and method for generating a display image from a point cloud. 
     Metrology devices, such as laser scanners for example, may generate large volumes of coordinate data of points located on the surfaces of the scanned area. These types of devices may be used to generate three-dimensional models of an area, such as a home or building, a crime scene, or an archeological site for example. Often with these types of scans, the data may be acquired from multiple positions to capture all of the desired surfaces and avoid having blank areas where a surface was in the “shadow” of another object. As a result in several data-sets of coordinate data are generated that are registered together to define a single data-set, sometimes colloquially referred to as a “point cloud” since the data is represented as a group of points in space without surfaces. 
     It should be appreciated that from a graphical display of a point cloud, it may be difficult to visualize the surfaces of the scanned area. This is due to the close proximity of points (from any user point of view) within the point cloud that may lie on different planes. For example, if the user point of view of the point cloud is looking down on a table, there will be points within the field of view from the table surface, along with the floor that is underneath the table surface or even the surface on the underside of the table. 
     Where the point cloud is relatively dense, meaning that the points on a surface are dense, the generation of surfaces in the displayed image for visualizing the scanned area may be created, albeit computationally intensive. However, in some applications, the point cloud may have a lower density of points resulting in gaps in the data set between the points of the point cloud. As a result, it may be difficult to generate a desired displayed image. 
     Accordingly, while existing metrology devices and point cloud display systems are suitable for their intended purposes the need for improvement remains, particularly in providing a system for filling in pixels on a graphical display to generate a displayed image of a point cloud. 
     SUMMARY 
     According to an embodiment of the present invention a method for optically scanning, measuring and displaying a point cloud is provided. The method includes emitting, by a light emitter of a laser scanner, an emission light beam. A light receiver receives a reflection light beam, wherein a reflection light beam of the emission light beam is reflected from an object. A control and evaluation device determines for measurement points projected on a plane corresponding to a screen on a display device, at least the distance from the object to a center of the laser scanner, wherein at least some measurement points are displayed on the display device. The points are visible are determined on the display device based at least in part on a viewpoint of the display device. One or more pixels are gap filled to generate a visual appearance of a surface on the display device. Wherein the gap filling includes a first horizontal search in a first direction of a first measured point of the measurement points followed by a second horizontal search in a second direction of the first measured point, the second direction being opposite the first direction. The gap filling further includes a first vertical search in a third direction of the measured point, the third direction being perpendicular to the first direction, followed by a second vertical search in a fourth direction, the fourth direction being opposite the third direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are explained in more detail below on the basis of exemplary embodiments illustrated in the drawings, in which 
         FIG. 1  is a schematic illustration of a laser scanner in the environment including a display device, and 
         FIG. 2  is a partial sectional illustration of the laser scanner. 
         FIG. 3  is a schematic illustration of a scanned area with measured points shown on surfaces; 
         FIG. 4  is a schematic illustration of the assignment and filling of the pixels with a view onto the plane, wherein the adjacent pixels are on the same surface; 
         FIG. 5  is a schematic illustration of the assignment and filling of the pixels, according to  FIG. 4 , with a view onto the plane, in accordance with an embodiment; 
         FIG. 6  is a schematic illustration of the assignment and filling of the pixels with a view onto the plane, wherein the adjacent pixels are located on different surfaces, in accordance with an embodiment; 
         FIG. 7  is a schematic illustration of the assignment and filling of the pixels, according to  FIG. 3 , with a view onto the plane, in accordance with an embodiment; 
         FIG. 8  is a flow diagram of a method of filling pixels in accordance with an embodiment; 
         FIG. 9 - FIG. 11  are flow diagrams of a method of performing a horizontal row pixel filling in accordance with an embodiment; 
         FIG. 12 - FIG. 16  are schematic illustrations of a sequence of horizontal and vertical pixel filling steps performed using the methods of  FIG. 6 ; 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  and  FIG. 2 , a laser scanner  10  is provided as a device for optically scanning and measuring the environment of the laser scanner  10 . The laser scanner  10  has a measuring head  12  and a base  14 . The measuring head  12  is mounted on the base  14  as a unit that can be rotated about a vertical axis. The measuring head  12  has a rotary mirror  16  that can be rotated about a horizontal axis. The point of intersection between the two axes of rotation is designated as the center C 10  of the laser scanner  10 . 
     The measuring head  12  also has a light emitter  17  for emitting an emission light beam  18 . The emission light beam  18  may be a laser beam in the range of wavelength of approximately 300 to 1600 nm, for example, 790 nm, 905 nm or less than 400 nm, but other electro-magnetic waves having, for example, a greater wavelength can be used. The emission light beam  18  may be amplitude-modulated with, for example, a sinusoidal or rectangular-waveform modulation signal. The emission light beam  18  is passed from the light emitter  17  onto the rotary mirror  16  where it is deflected and then emitted into the environment. A reception light beam  20 , which is reflected by or otherwise scattered from an object O, is captured again by the rotary mirror  16 , deflected and passed onto a light receiver  21 . The direction of the emission light beam  18  and of the reception light beam  20  results from the angular positions of the rotary mirror  16  and the measuring head  12 , which depend on the positions of their respective rotary drives which are, in turn, detected by a respective angular encoder. 
     A control and evaluation device  22  has a data link connection to the light emitter  17  and to the light receiver  21  in the measuring head  12 , parts thereof being arranged also outside the measuring head  12 , for example as a computer connected to the base  14 . The control and evaluation device  22  determines, for a multiplicity of measurement points X, the distance d of the laser scanner  10  from the illuminated point on the object O (e.g. the table T,  FIG. 3 ), and from the propagation times of emission light beam  18  and reception light beam  20 . In an embodiment, the distance d is determined by the control and evaluation device  22  based on the phase shift between the two light beams  18  and  20 . In another embodiment, the distance d is determined by the control and evaluation device based on a measured round trip time between an outgoing emission pulse of light  18  and a returning reception pulse of light  20 . In another embodiment, the distance d is determine by the control and evaluation device based on change in optical wavelength of a reception beam of light  20  relative to an emission beam of light, the emission beam of light having an optical wavelength that is linearly swept (chirped) in time. Many other methods are known in the art and may be used to determine the distance d. 
     Through use of the relatively rapid rotation of the mirror  16 , scanning takes place along a circular line. Also, through use of the relatively slow rotation of the measuring head  12  relative to the base  14 , the entire space is gradually scanned with the circular lines. The totality of the measurement points X of such a measurement may be referred to as a scan. The center C 10  of the laser scanner  10  defines for such a scan the origin of the local stationary reference system. The base  14  is stationary in this local stationary reference system. In other embodiments, a different type of beam steering method is used to direct the emission beam  18  to different points X in the environment. In an embodiment, a pair of galvanometer steering mirrors are used to rapidly direct the emission beam  18  to desired points X. In another embodiment, the emission beam  18  rotates along with the entire measuring head  12 . Many types of beam steering mechanisms are known in the art and may be used. 
     In addition to the distance d to the center C 10  of the laser scanner  10 , each measurement point X comprises a brightness value which may also be determined by the control and evaluation device  22 . Here the term brightness may be understood to refer to a level of optical power or a level of irradiance (optical power per unit area). The brightness is a gray-tone value which is determined, for example, by integration of the bandpass-filtered and amplified signal of the light receiver  21  over a measuring period which is assigned to the measurement point X. Through use of a color camera, it is optionally possible to generate pictures, by which colors (R, G, B) can be assigned as a value to the measurement points X in addition to the brightness or comprising the brightness. 
     A display device  30  is connected to the control and evaluation device  22 . The display device  30  can be integrated into the laser scanner  10 , for example into the measuring head  12  or into the base  14 , or it can be an external unit, for example part of a computer which is connected to the base  14 . The display device  30  has a graphics card  32  and a screen  34  which can be arranged separately from one another or as a structural unit. The control and evaluation device  22  provides 3D data of the scan. 
     It should be appreciated that when the measurement points X, which are positioned in a three-dimensional space, are displayed on a two-dimensional display device  30 , it may be difficult for the user to visualize the object O on the display. For example, referring to  FIG. 3  a table T has been scanned with the laser scanner  10  and the measurement points X have been acquired. When the user displays the measurement points X from a viewpoint V, the user will see not only the measurement points X T  from the tabletop, but also the measurement points X F . As a result, without a visual reference such as a surface of the table T or the surfaces of the legs of the table, it will be difficult for the user to distinguish between the measurement points X T  and the measurement points X F . It should be appreciated that in an embodiment where the measured object O is a structure, such as the inside of a building and the measured points may be on opposite sides of a wall. Accordingly, embodiments herein provide advantages generating on display device  30  an image representing surfaces on the object O by filling in the pixels between measured points. The method of filling in the pixels between the measured points may sometimes be referred to a gap filling or pixel filling. 
     In many cases, objects in an environment are scanned with a laser scanner  10  placed in a plurality of locations. This is illustrated in  FIG. 3 , where a scanner  10 A is located at a first location at a first time and the same or different scanner  10 B is located at a different location at a second time. In some embodiments, multiple scanners such as  10 A,  10 B are used simultaneously. In an embodiment, the scanner  10 A is positioned to scan the top side of the table T and to a lesser extent floor points to the side of the table. The scanner  10 B is positioned to scan mostly points beneath the table T rather than on top of the table. When the measurement points X T  are registered with the measurement points X F , the result is a point cloud having points distributed over three-dimensional space. From the perspective of a viewer V, such a collection of sparsely located points may not clearly indicate which points are closer to the viewer and which are farther from the viewer. Hence a display of the collected points in the point cloud may intersperse the floor points and the tabletop points, with the surfaces not clearly distinguished for the viewer V. 
     Referring now to  FIGS. 4-7 , with continuing reference to  FIG. 1  and  FIG. 2 , the graphic card  32  converts the 3-D data into 2-D data (e.g., rendering data), which are displayed on the screen  34 . The 3-D data are the measurement points X, wherein several scans from different positions of the laser scanner  10  can be assembled into one scene. For representing the 2-D data, there are pixels P, i.e., adjacent, small polygonal surfaces (e.g. squares or hexagons), which are arranged in a two-dimensional plane E which corresponds to the screen  34 . In an embodiment, a starting point for the representation on the screen  34  is the projection of the measurement points X onto a plane E with a viewer (e.g., eye, camera), at a certain viewpoint V. The projection appears to be in perspective (i.e., the viewpoint V is in the finite) or orthographical (i.e., the viewpoint V in is the infinite). In an embodiment, the projected measurement points X are assigned to single pixels P 0 , P 1 , P 2 . A Z-buffer, which is a two-dimensional array (field) of values for the pixels P. In this Z-buffer, a field element (depth z) is assigned to each pixel P. The depth z of each projected measurement point X corresponds to the distance of the measurement point X to the plane E with respect to the viewpoint V. The field of the pixels P and the Z-buffer may be treated in the same way as the images. 
     The viewpoint V may be arbitrary per se and is usually changed several times when regarding the scan and/or the scene. In other words, the user may elect to view the measurement point data from a variety of perspectives, with the changes to the displayed measurement points X re-rendered. 
     Since the measurement points X are punctiform, with gaps in between, and the pixels P usually, in the case of nearby objects O, have a higher density in the plane E than do the projections of the measurement points X, a gap-filling method is carried out to fill as many pixels P as possible for an improved visual representation for the user. In an embodiment, the graphic card  32  carries out this method by processing the 3-D data following a parallel method described further herein below, the parallel processing method based at least in part on the indication of the viewpoint V and of the plane E. 
     In an embodiment, initially only those pixels P are filled to which the projection of a measurement point X is assigned, i.e., which exactly cover one measurement point X, such as pixels P 0 , P 1 , P 2  for example. These pixels P are filled with the value of the assigned measurement point X, i.e., brightness (gray-scale value) and, where applicable, color. All other pixels P, which do not exactly correspond with a projection of a measurement point X, i.e., which are “in between” are empty at first, for example are set to a value of zero (e.g. empty or blank). Each of the depths z, i.e., the field elements of the Z-buffer, which are assigned to the initially filled pixels P, is set to that depth z 0 , z 1 , z 2 , which corresponds to the distance of the assigned measurement point X to the plane E. In an embodiment, sometimes referred to as perspective projection, the distance z 1  is marked from an object point to a point P 1  on a plane E along a line directed to a viewer point V. In this embodiment, the distance z 1  is the distance from the object point to point P 1 . In another embodiment, sometimes referred to as orthographic projection, the distance is a perpendicular distance from the object point to the point P 1  rather than along the line aimed toward V. 
     All other field elements of the Z-buffer (e.g., depths z) are set to a very large value (relative to the scale of the measured points), for example, to approximate an infinite depth. If, when the projection of the measurement points X is made, it turns out that two measurement points X are available for one pixel P, the measurement point having the smaller depth z is selected and the other one is rejected, so that covered surfaces and covered edges, such measurement points X F  on the floor of  FIG. 3  for example, are not visible. 
     According to an embodiment, the gap-filling method is performed in dependence on the depth z 0 , z 1 , z 2 , i.e., on the distance to the plane E. The graphic card  32  selects all pixels P in parallel with respect to time. By way of example, one selected pixel P 0  is regarded now. The assigned depth z, i.e., field element of the Z-buffer, contains the depth z 0 . For each selected pixel P 0  the adjacent pixels P 1 , P 2 , are searched consecutively, i.e., alternating between to the left and to the right, and above and below. If the adjacent pixel P 1  is not yet filled or if its depth z is bigger than the depth z 0  of the selected pixel P 0 , it is skipped and the second next pixel P is taken as adjacent pixel P 1 , if necessary iteratively. If an adjacent pixel P 1 , the depth z 1  of which is smaller than the depth z 0  of the selected pixel P 0 , is found in one of the directions, a change to the next direction takes place, and it is looked for the adjacent pixel P 2  (e.g., the depth z 2  of which is smaller than the depth z 0  of the selected pixel P 0 ). It is possible to define a maximum number of skipped pixels, i.e., if the adjacent pixel P 1  or P 2  is not yet found after skipping the maximum number of skipped pixels, the search for P 1  or P 2  is aborted. In one embodiment, the search for pixels to fill about an initial pixel P 0  is limited to those pixels within a radius R of the pixel P 0  on the two-dimensional pixel array. In another embodiment, the search is also limited by another radius in 3-D coordinates, perpendicular to the viewing direction. 
     If the adjacent pixels P 1  and P 2  to the selected pixel P 0  have been found in opposite directions, with the depths z 1  and z 2  of the adjacent pixels P 1  and P 2  being smaller than the depth z 0 , it is checked whether P 1  and P 2  are on the same plane, i.e, whether the amount of the difference of z 2  and z 1  is below a threshold value for the depth z crit , i.e.,
 
| z   2   −z   1   |&lt;z   crit  
 
applies. In such a case, the selected pixel P 0  is filled with the value which is interpolated between P 1  and P 2 , i.e., brightness (gray-scale level) and, if applicable color. The assigned field element of the Z-buffer is likewise set to the interpolated depth between z 1  and z 2 . Interpolation weights depend on the distance of the selected pixel P 0  from P 1  and P 2  in plane E.
 
     If the difference of the depths is too big, i.e., the condition
 
| z   2   −z   1   |&gt;z   crit  
 
applies, it is assumed that P 1  and P 2  are located on different planes. The selected pixel P 0  is then filled with the value, i.e., brightness and, if applicable color, of, for example, the more remote pixel P 1  or P 2 , and the assigned field element of the Z-buffer with the bigger depth z 1  or z 2 . In another embodiment, the value and the depth of pixel P 1  or P 2  having a larger depth z 1  or z 2  is transferred or assigned to the other pixel. In the case of more than two adjacent pixels P 1 , P 2 , the average value of the majority, i.e., of the adjacent pixels P 1 , P 2 , which are located on the same surface, can be transferred.
 
     Selected pixels P 0 , which are already filled with values of the measurement points, are overwritten by the interpolation of the values of the adjacent pixels P 1  and P 2 . In another embodiment, a selected pixel P 0 , which is already filled, remains unvaried if |z 0 −z 1  is smaller than a threshold, i.e. if P 0  and P 1  already belong to the same surface. 
     If pixels P have been skipped when finding the pixels P 1  and P 2 , because they were not filled or because their depth z was too big, their adjacent pixels P 1 , P 2  are the same as with the selected pixel P 0 , so that the skipped pixels P F  and the assigned field elements of the Z-buffer, within the framework of the selection taking place in parallel, are likewise filled either with a value which is interpolated between the pixels P 1  and P 2  and/or the depths z 1  and z 2  (depending on the distance of the selected pixel P 0  from P 1  and P 2  in plane E) or with the value and/or the depth z 1  or z 2  of the more remote one among pixels P 1  or P 2  (or the average value of the majority) as shown in  FIG. 7 . 
     Due to the selection taking place in parallel, filling with the value and/or the depth z 1  or z 2  of the more remote among the pixels P 1  or P 2  on account of a difference of depths which is too big, leads to the closer-by pixel P 1  or P 2  forming an edge. Even if no adjacent pixel P 1  or P 2  is found, the depth z 1  or z 2  of which is smaller than the depth z 0  of the selected pixel P 0 , since the selected pixel P 0  is at the side of the screen  34 , an edge is generated, since these selected pixels P 0  at the edge are not filled then. 
     Once the pixels along a horizontal row are filled, the same process may be used to fill the vertical gaps between the measurement points P 3 , P 4  in a similar manner to that described herein above for the horizontal gap filling. As will be discussed in more detail below, the gap-filling process may be iteratively performed until the image is created. 
     Gap-filling may take place in the control and evaluation device  22  or by software running on an external computer. Due to the savings in time by a parallel selection, the hardware-based gap-filling on the graphic card  32  may be used together with the programming interface of the latter. 
     Referring now to  FIG. 8  an embodiment is shown of a method  100  for acquiring measurement points and displaying the point cloud using gap filling of pixels. The method  100  begins in block  102  where the object O is scanned with a metrology device, such as but not limited to a laser scanner  10  for example. It should be appreciated that the scanned object O may comprise multiple objects, such as the interior rooms and hallways of a building for example. The step of scanning the object O results in the generation of a point cloud representing measured points X on the surfaces of the object O. 
     The method  100  then proceeds to block  104  where it is determined which of the measured points X are visible on the display device  30 . As discussed herein above the three-dimensional point cloud is projected onto the two-dimensional screen  34  of display device  30  to allow the user to view the point cloud. The method then proceeds to block  106  where the pixels are gap filled to provide the visual appearance of surfaces in the display device  30 . In an embodiment, the step of gap filling in block  106  includes a horizontal search to the left of a pixel containing measured point in block  108  and then a search to the right of the pixel in block  110 . The step of gap filling in block  106  further includes the steps of a vertical search above (e.g. towards the top of the display device  34 ) the pixel containing the measured point in block  112  and then a search below the pixel in block  114 . In an embodiment, the vertical search of blocks  112 ,  114  follow the horizontal search of blocks  108 ,  110 , it should be appreciated, however, that this is for exemplary purposes and the claims should not be so limited. In other embodiments, the vertical search precedes the horizontal search. In an embodiment, the vertical search is performed sequentially with the horizontal search. In another embodiment, the horizontal and vertical searches are performed simultaneously in both directions. 
     The gap filling steps may be performed for all of the pixels containing a measured point that are being displayed on the display device. In an embodiment, the pixel filling steps are the same as those described herein above with respect to  FIGS. 4-7 . Once the gap filling is performed, the method  100  then proceeds to query block  116  where it is determined whether all of the pixels have been evaluated for gap filling. As will be discussed in more detail below, gaps or empty pixels may occur in some cases where the pixel is not bounded by a pixel containing a measured point or a previously filled pixel. To resolve this issue, the gap filling of block  106  may be an iterative process. In one embodiment, the process performs for a fixed number of iterations. In another embodiment, the process performs until a stop condition is achieved. In one embodiment, the stop condition is that no additional pixels could be filled in the previous iteration. 
     When the query block  116  returns an affirmative, meaning that there are unevaluated pixels, the method loops back to block  106 . When query block  116  returns a negative, the method  100  proceeds to block  118  where the image is displayed on the display device  30 . 
     Referring now to  FIGS. 9-11 , an embodiment of a method  200  for the gap filling steps of blocks  108 - 110 . It should be appreciated that while method  200  is described with reference to horizontal gap filling, this is for exemplary purposes and the steps of method  200  may also be performed for vertical gap filling as well. 
     The method  200  begins in block  202  where a pixel P 0  is identified. The pixel P 0  is a pixel that contains an image of the measured point X that is projected from the three-dimensional point cloud onto the two-dimensional display device  30 . The method  200  then proceeds to block  204  where a search is performed of pixels to the left of the pixel P 0 . As used herein, the terms “left” and “right” indicate opposite sides in the row of pixel P 0 , this is done for clarity purposes and no intended orientation of the display device  34  or the point cloud data is intended. 
     The method  200  then proceeds to query block  206  where it is determined if a pixel P 1  is found within a radius R ( FIG. 7 ). In the exemplary embodiment, the radius R is initially a predetermined value defined by the user, such as five pixels for example. When the query block  206  returns a negative (no pixel P 1  found), the method  200  proceeds to block  208  and no gap filling is performed. When the query block  206  returns a positive (a pixel P 1  is found), the method proceeds to block  210  where a maximum search radius in pixels is determined where the radius is non-proportional or anti-proportional to a distance d 1 , where the distance d 1  is the same as z 1  of  FIG. 4 . The search is performed in pixel space. It should be appreciated that each pixel may represent a different size in 3D space. For example, if a ray extends through each pixel from the view point into space, the distance between the rays will increase with the distance or depth from the viewpoint (perspective projection). In an embodiment, the search re-projects the pixels into 3D space and objects within a predetermined distance. 
     The method  200  then proceeds to query block  212  where it is determined whether the distance (x0, y0), (x1, y1) is between the measured points of pixels P 0 , P 1 . When this distance is not within the radius determined in block  210 , the query block  212  returns a negative and proceeds to block  214  where the direct neighboring pixel P 1  to the left of (x0, y0) is evaluated in query block  216 . In query block  216 , it is determined whether the pixel is non-empty and has a depth less than the depth to the measured point X of P 0 . When query block  216  returns a negative, meaning either the pixel is empty or it has a depth greater than the measured point X of P 0 , the method  200  loops back to block  208 . When the query block  216  returns a positive, the method  200  proceeds to block  218  where the values of (x1, y1) and d 1  are set to this pixel (e.g. pixel P 1 ). Once the values of block  218  are set, or when the query block  212  returns a positive, the method  200  proceeds to block  211  ( FIG. 10 ). 
     In block  211 , a search is performed of the pixels to the right of the pixel P 0 . The method then proceeds to query block  213  where it is determined whether pixel P 2  is within the radius R (e.g. 5 pixels). When the query block  213  returns a negative, the method  200  proceeds to block  208  and no gap filling is performed. When the query block  213  returns a positive, the a maximum search radius is determined in block  215  that is non-proportional or anti-proportional to the distance d 2 , where the distance d 2  is equivalent to the distance z 2  of  FIG. 4 . The method  200  then proceeds to query block  217  where it is determined if the pixel distance (x0, y0), (x2, y2) is within the radius determined in block  215 . 
     When query block  217  returns a negative, the method  200  proceeds to block  219  where the direct neighboring pixel to the right of (x0, y0) is evaluated. This provides for more even gap filling even when the search criteria is not fulfilled. In an embodiment, for directly neighboring pixels, the 3D-criteria is ignored unless better pixels are identified. In query block  221 , it is determined if the pixel is non-empty and has a depth less than the depth to the measured point X of P 0 . When query block  221  returns a negative, meaning either the pixel is empty or it has a depth greater than the measured point X of P 0 , the method  200  loops back to block  208  and no gap filling is performed. When the query block  221  returns a positive, the method  200  proceeds to block  222  where the values of (x2, y2) and d 2  are set to this pixel (e.g. pixel P 2 ). Once the values of block  222  are set, or when the query block  217  returns a positive, the method  200  proceeds to block  224  ( FIG. 11 ). 
     In query block  224 , it is determined if the difference between the distances d 0  and d 1  (e.g. the distance from the viewpoint V to the measured points x0 and x1 of  FIG. 6 ) is greater than a threshold (e.g. Z crit ). In one embodiment, the threshold is 2.5 centimeters. When query block  224  returns a negative, indicating that that the measured points already lie on the same plane, the method  200  proceeds to block  208  and no gap filling is performed. When query block  224  returns a positive, the method  200  proceeds to query block  226  where it is determined whether the difference between the distances d 1  and d 2  (e.g. the distance from the viewpoint V to the measured points x1 and x2 of  FIG. 6 ) is less than a threshold. In one embodiment, the threshold of block  226  is 10 centimeters. 
     When query block  226  returns a positive, meaning the difference in the depths is less than the threshold and that the points lie on the same plane, the method  200  proceeds to block  228  where the depth and color of pixels P 1  and P 2  is interpolated and assigned to the intermediate or intervening pixels. In one embodiment, the depth and color interpolation is weighted with weights (1/r 1   2 ) and (1/r 2   2 ), where r 1  is the distance in pixel units from P 1  to P 0 , and r 2  is the distance in pixel units from P 2  to P 0 . 
     When query block  226  returns a negative, the method  200  proceeds to query block  230  where it is determined if the depth d 2  is greater than the depth d 1 . When the query block  230  returns a positive, the color and depth values from the pixel P 2  are used for gap filling the empty pixels between pixels P 1  and P 2 . When the query block  230  returns a negative, the color and depth values from the pixel P 1  are used for gap filling the empty pixels between pixels P 1  and P 2 . The purpose of block  230  is to avoid extending objects by additional pixels at their edges. 
     It should be appreciated that the method  200  may be repeated for the vertical gap filling as well. 
     Turning now to  FIGS. 12-16 , an example is illustrated of the iteration steps for gap filling, such as provided by query block  116  ( FIG. 8 ) for example.  FIG. 12  illustrates the horizontal gap filling that occurs in the first iteration, the blocks with the “x” represent pixels containing a measured point. The number “1” represents empty pixels that are filled in the first iteration, such as by method  100  for example. Once the horizontal gap filling is completed, the vertical gap filling is performed as shown in  FIG. 13 . The number “2” represents the pixels filled during the first iteration vertical gap filling. It should be noted empty pixels are only filled when they are bounded on opposite sides by either a pixel having a measurement point X or a previously filled pixel, for example pixel  300  is filled because it is bounded by the pixels  302 ,  304 . It should further be noted that once the first iteration is completed, there are a number pixels, such as pixels  306 ,  308  that have not been evaluated for gap filling because at least one side of the row in which the pixel is located was unbounded at the beginning of the first iteration vertical gap filling. 
     Referring now to  FIG. 14  a second gap filling iteration is initiated. The second iteration starts with a horizontal gap filling. In this iteration, the pixel  306  is evaluated and filled based on the bounding or end pixels  310 ,  312 . The number “3” represents pixels that were gap filled during the second iteration horizontal gap filling. It should be noted in an embodiment the gap filled pixels have an associated depth and color that was assigned during blocks  228 ,  232  or  234  of  FIG. 11 . This assigned depth and color allows the intermediate pixels to be evaluated and filled. With the second iteration horizontal gap filling completed, the second iteration vertical gap filling is performed as shown in  FIG. 15 . Here, the additional pixels are evaluated and filled (where appropriate), based on filled pixels that include those pixels filled during the second iteration horizontal gap filling. For example, pixel  308  is evaluated and filled based on end pixels  306  (filled in the second iteration horizontal gap filling) and pixel  312  (filled in the first iteration gap filling). 
     In the illustrated embodiment, when the second iteration vertical gap filling is completed, there remain no unevaluated bounded pixels. Therefore, the query block  116  would return a negative and the method  100  would proceed with displaying the image on the display device  34 . It should be appreciated that in other embodiments, more or less iterations may be performed. 
     It should be appreciated that while embodiments herein describe the creation of a displayed image by a gap-filling process with respect to data acquired by a laser scanning device, this is for exemplary purposes and the claims should not be so limited. In other embodiments, the displayed image may be created using point cloud data generated by any metrology device, such as a triangulation-type laser scanner device, a triangulation-type structured light scanner device, or a time-of-flight based scanner device for example.