Resolving homography decomposition ambiguity based on viewing angle range

Abstract

The homography between captured images of a planar object is determined and decomposed into at least one possible solution, and typically at least two ambiguous solutions. The removal of the ambiguity between the two solutions, or validation of a single solution, is performed using a viewing angle range. The viewing angle range may be used by comparing the viewing angle range to the orientation of each solution as derived from the rotation matrix resulting from the homography decomposition. Any solution with an orientation outside the viewing angle range may be eliminated as a solution.

1 . A method comprising:
 capturing two images of a planar object with at least one camera from a first position and a second position;   determining a homography between the two images;   decomposing the homography to obtain at least one possible solution for the second position;   using a viewing angle range to eliminate the at least one possible solution; and   storing any remaining solution for the second position.   
     
     
         2 . The method of  claim 1 , wherein a plurality of possible solutions are obtained and the viewing angle range is used to eliminate at least one of the plurality of possible solutions. 
     
     
         3 . The method of  claim 1 , wherein decomposing the homography produces a rotation matrix associated with the at least one possible solution, wherein using the viewing angle range comprises:
 extracting an orientation with respect to normal of the planar object from the rotation matrix;   comparing the orientation to the viewing angle range; and   eliminating any possible solution with the orientation outside the viewing angle range.   
     
     
         4 . The method of  claim 3 , wherein the viewing angle range is a predefined angular range between the planar object and the normal of the planar object. 
     
     
         5 . The method of  claim 3 , wherein the viewing angle range is between approximately 270° and 360°. 
     
     
         6 . The method of  claim 1 , the method further comprising:
 determining an orientation of the at least one camera with respect to gravity; and   using the orientation of the at least one camera with respect to gravity to define the viewing angle range.   
     
     
         7 . The method of  claim 1 , wherein using the viewing angle range to eliminate the at least one possible solution does not use prior knowledge of the planar object and does not use additional images of the planar object. 
     
     
         8 . The method of  claim 1 , wherein a plurality of possible solutions are obtained and each of the plurality of possible solutions are within the viewing angle range, the method further comprising tracking each of the plurality of possible solutions until a solution is outside the viewing angle range before using the viewing angle range to eliminate the solution that is outside the viewing angle range. 
     
     
         9 . An apparatus comprising:
 a camera for capturing images of a planar object; and   a processor coupled to receive two images captured from a first position and a second position, the processor configured to determine a homography between the two images, decompose the homography to obtain at least one possible solution for the second position, use a viewing angle range to eliminate the at least one possible solution, and store any remaining solution for the second position in a memory coupled to the processor.   
     
     
         10 . The apparatus of  claim 9 , wherein the at least one possible solution is a plurality of possible solutions and wherein the processor is configured to use the viewing angle range to eliminate at least one of the plurality of possible solutions. 
     
     
         11 . The apparatus of  claim 9 , wherein the processor is configured to produce a rotation matrix associated with the at least one possible solution, wherein the processor is configured to use the viewing angle range by being configured to:
 extract an orientation with respect to normal of the planar object from the rotation matrix;   compare the orientation to the viewing angle range; and   eliminate any possible solution with the orientation outside the viewing angle range.   
     
     
         12 . The apparatus of  claim 11 , wherein the viewing angle range is predefined and is between the planar object and the normal of the planar object. 
     
     
         13 . The apparatus of  claim 11 , wherein the viewing angle range is between approximately 270° and 360°. 
     
     
         14 . The apparatus of  claim 9 , further comprising orientation sensors coupled to the processor, the processor being further configured to determine an orientation of the camera with respect to gravity using the orientation sensors, and to use the orientation of the camera with respect to gravity to define the viewing angle range. 
     
     
         15 . The apparatus of  claim 9 , wherein the processor is configured to use the viewing angle range to eliminate the at least one possible solution without prior knowledge of the planar object and without additional images of the planar object. 
     
     
         16 . The apparatus of  claim 9 , wherein a plurality of possible solutions are obtained and each of the plurality of possible solutions are within the viewing angle range, wherein the processor is further configured to track each of the plurality of possible solutions until a solution is outside the viewing angle range before the processor uses the viewing angle range to eliminate the solution that is outside the viewing angle range. 
     
     
         17 . An apparatus comprising:
 means for capturing two images of a planar object with at least one camera from a first position and a second position;   means for determining a homography between the two images;   means for decomposing the homography to obtain at least one possible solution for the second position;   means for using a viewing angle range to eliminate the at least one possible solution; and   means for storing any remaining solution for the second position.   
     
     
         18 . The apparatus of  claim 17 , wherein the means for decomposing the homography produces a plurality of possible solutions and wherein the means for using the viewing angle range eliminates at least one of the plurality of possible solutions. 
     
     
         19 . The apparatus of  claim 17 , wherein the means for decomposing the homography produces a rotation matrix associated with the at least one possible solution, wherein the means for using the viewing angle range comprises:
 means for extracting an orientation with respect to normal of the planar object from the rotation matrix;   means for comparing the orientation to the viewing angle range; and   means for eliminating any possible solution with the orientation outside the viewing angle range.   
     
     
         20 . The apparatus of  claim 19 , wherein the viewing angle range is predefined and is between the planar object and the normal of the planar object. 
     
     
         21 . The apparatus of  claim 19 , wherein the viewing angle range is between approximately 270° and 360°. 
     
     
         22 . The apparatus of  claim 17 , the method further comprising:
 means for determining an orientation of the at least one camera with respect to gravity;   means for using the orientation of the at least one camera with respect to gravity to define the viewing angle range.   
     
     
         23 . The apparatus of  claim 17 , wherein the means for using the viewing angle range to eliminate the at least one possible solution does not use prior knowledge of the planar object and does not use additional images of the planar object. 
     
     
         24 . The apparatus of  claim 17 , wherein a plurality of possible solutions are obtained and each of the plurality of possible solutions are within the viewing angle range, the apparatus further comprising means for tracking each of the plurality of possible solutions until a solution is outside the viewing angle range before the means for eliminating eliminates the solution that is outside the viewing angle range. 
     
     
         25 . A non-transitory computer-readable medium including program code stored thereon, comprising:
 program code to determine a homography between two images of a planar object captured from different positions by at least one camera;   program code to decompose the homography to obtain at least one possible solution;   program code to use a viewing angle range to eliminate the at least one possible solution; and   program code to store any remaining solution.   
     
     
         26 . The non-transitory computer-readable medium of  claim 25 , wherein a plurality of possible solutions are obtained and the viewing angle range is used to eliminate at least one of the plurality of possible solutions. 
     
     
         27 . The non-transitory computer-readable medium of  claim 25 , wherein a rotation matrix is produced that is associated with the at least one possible solution, wherein the program code to use the viewing angle range comprises:
 program code to extract an orientation with respect to normal of the planar object from the rotation matrix;   program code to compare the orientation to the viewing angle range; and   program code to eliminate any possible solution with the orientation outside the viewing angle range.   
     
     
         28 . The non-transitory computer-readable medium of  claim 27 , wherein the viewing angle range is predefined and is between the planar object and the normal of the planar object. 
     
     
         29 . The non-transitory computer-readable medium of  claim 27 , wherein the viewing angle range is between approximately 270° and 360°. 
     
     
         30 . The non-transitory computer-readable medium of  claim 25 , further comprising:
 program code to determine an orientation of the at least one camera with respect to gravity;   program code to use the orientation of the at least one camera with respect to gravity to define the viewing angle range.   
     
     
         31 . The non-transitory computer-readable medium of  claim 25 , wherein the program code to use the viewing angle range to eliminate the at least one possible solution does not use prior knowledge of the planar object and does not use additional images of the planar object. 
     
     
         32 . The non-transitory computer-readable medium of  claim 25 , wherein a plurality of possible solutions are obtained and each of the plurality of possible solutions are within the viewing angle range, the non-transitory computer-readable medium further comprising program code to track each of the plurality of possible solutions until a solution is outside the viewing angle range before the solution that is outside the viewing angle range is eliminated.