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find_marks_and_poseT_find_marks_and_poseFindMarksAndPoseFindMarksAndPose (Operator)

Name

find_marks_and_poseT_find_marks_and_poseFindMarksAndPoseFindMarksAndPose — Extract rectangularly arranged 2D calibration marks from the image and calculate initial values for the external camera parameters.

Signature

find_marks_and_pose(Image, CalPlateRegion : : CalPlateDescr, StartCamParam, StartThresh, DeltaThresh, MinThresh, Alpha, MinContLength, MaxDiamMarks : RCoord, CCoord, StartPose)

Herror T_find_marks_and_pose(const Hobject Image, const Hobject CalPlateRegion, const Htuple CalPlateDescr, const Htuple StartCamParam, const Htuple StartThresh, const Htuple DeltaThresh, const Htuple MinThresh, const Htuple Alpha, const Htuple MinContLength, const Htuple MaxDiamMarks, Htuple* RCoord, Htuple* CCoord, Htuple* StartPose)

void FindMarksAndPose(const HObject& Image, const HObject& CalPlateRegion, const HTuple& CalPlateDescr, const HTuple& StartCamParam, const HTuple& StartThresh, const HTuple& DeltaThresh, const HTuple& MinThresh, const HTuple& Alpha, const HTuple& MinContLength, const HTuple& MaxDiamMarks, HTuple* RCoord, HTuple* CCoord, HTuple* StartPose)

HTuple HImage::FindMarksAndPose(const HRegion& CalPlateRegion, const HString& CalPlateDescr, const HCamPar& StartCamParam, Hlong StartThresh, Hlong DeltaThresh, Hlong MinThresh, double Alpha, double MinContLength, double MaxDiamMarks, HTuple* CCoord, HPose* StartPose) const

HTuple HImage::FindMarksAndPose(const HRegion& CalPlateRegion, const char* CalPlateDescr, const HCamPar& StartCamParam, Hlong StartThresh, Hlong DeltaThresh, Hlong MinThresh, double Alpha, double MinContLength, double MaxDiamMarks, HTuple* CCoord, HPose* StartPose) const

HTuple HCamPar::FindMarksAndPose(const HImage& Image, const HRegion& CalPlateRegion, const HString& CalPlateDescr, Hlong StartThresh, Hlong DeltaThresh, Hlong MinThresh, double Alpha, double MinContLength, double MaxDiamMarks, HTuple* CCoord, HPose* StartPose) const

HTuple HCamPar::FindMarksAndPose(const HImage& Image, const HRegion& CalPlateRegion, const char* CalPlateDescr, Hlong StartThresh, Hlong DeltaThresh, Hlong MinThresh, double Alpha, double MinContLength, double MaxDiamMarks, HTuple* CCoord, HPose* StartPose) const

HTuple HPose::FindMarksAndPose(const HImage& Image, const HRegion& CalPlateRegion, const HString& CalPlateDescr, const HCamPar& StartCamParam, Hlong StartThresh, Hlong DeltaThresh, Hlong MinThresh, double Alpha, double MinContLength, double MaxDiamMarks, HTuple* CCoord)

HTuple HPose::FindMarksAndPose(const HImage& Image, const HRegion& CalPlateRegion, const char* CalPlateDescr, const HCamPar& StartCamParam, Hlong StartThresh, Hlong DeltaThresh, Hlong MinThresh, double Alpha, double MinContLength, double MaxDiamMarks, HTuple* CCoord)

static void HOperatorSet.FindMarksAndPose(HObject image, HObject calPlateRegion, HTuple calPlateDescr, HTuple startCamParam, HTuple startThresh, HTuple deltaThresh, HTuple minThresh, HTuple alpha, HTuple minContLength, HTuple maxDiamMarks, out HTuple RCoord, out HTuple CCoord, out HTuple startPose)

HTuple HImage.FindMarksAndPose(HRegion calPlateRegion, string calPlateDescr, HCamPar startCamParam, int startThresh, int deltaThresh, int minThresh, double alpha, double minContLength, double maxDiamMarks, out HTuple CCoord, out HPose startPose)

HTuple HCamPar.FindMarksAndPose(HImage image, HRegion calPlateRegion, string calPlateDescr, int startThresh, int deltaThresh, int minThresh, double alpha, double minContLength, double maxDiamMarks, out HTuple CCoord, out HPose startPose)

HTuple HPose.FindMarksAndPose(HImage image, HRegion calPlateRegion, string calPlateDescr, HCamPar startCamParam, int startThresh, int deltaThresh, int minThresh, double alpha, double minContLength, double maxDiamMarks, out HTuple CCoord)

Description

find_marks_and_posefind_marks_and_poseFindMarksAndPoseFindMarksAndPoseFindMarksAndPose is used to determine the input data for a subsequent camera calibration using a calibration plate with rectangularly arranged marks (see calibrate_camerascalibrate_camerasCalibrateCamerasCalibrateCamerasCalibrateCameras or camera_calibrationcamera_calibrationCameraCalibrationCameraCalibrationCameraCalibration): First, the 2D center points [RCoordRCoordRCoordRCoordRCoord,CCoordCCoordCCoordCCoordCCoord] of the calibration marks within the region CalPlateRegionCalPlateRegionCalPlateRegionCalPlateRegioncalPlateRegion of the input image ImageImageImageImageimage are extracted and ordered. Secondly, a rough estimate for the external camera parameters (StartPoseStartPoseStartPoseStartPosestartPose) is computed, i.e., the 3D pose (= position and orientation) of the calibration plate relative to the camera coordinate system (see create_posecreate_poseCreatePoseCreatePoseCreatePose for more information about 3D poses).

In the input image ImageImageImageImageimage an edge detector is applied (see edges_imageedges_imageEdgesImageEdgesImageEdgesImage, mode 'lanser2') to the region CalPlateRegionCalPlateRegionCalPlateRegionCalPlateRegioncalPlateRegion, which can be found by applying the operator find_caltabfind_caltabFindCaltabFindCaltabFindCaltab. The filter parameter for this edge detection can be tuned via AlphaAlphaAlphaAlphaalpha. Use a smaller value for AlphaAlphaAlphaAlphaalpha to achieve a stronger smoothing effect. In the edge image closed contours are searched for: The number of closed contours must correspond to the number of calibration marks as described in the calibration plate description file CalPlateDescrCalPlateDescrCalPlateDescrCalPlateDescrcalPlateDescr and the contours have to be elliptically shaped. Contours shorter than MinContLengthMinContLengthMinContLengthMinContLengthminContLength are discarded, just as contours enclosing regions with a diameter larger than MaxDiamMarksMaxDiamMarksMaxDiamMarksMaxDiamMarksmaxDiamMarks (e.g., the border of the calibration plate).

For the detection of contours a threshold operator is applied on the resulting amplitudes of the edge detector. All points with a high amplitude (i.e., borders of marks) are selected.

First, the threshold value is set to StartThreshStartThreshStartThreshStartThreshstartThresh. If the search for the closed contours or the successive pose estimate fails, this threshold value is successively decreased by DeltaThreshDeltaThreshDeltaThreshDeltaThreshdeltaThresh down to a minimum value of MinThreshMinThreshMinThreshMinThreshminThresh.

Each of the found contours is refined with subpixel accuracy (see edges_sub_pixedges_sub_pixEdgesSubPixEdgesSubPixEdgesSubPix) and subsequently approximated by an ellipse. The center points of these ellipses represent a good approximation of the desired 2D image coordinates [RCoordRCoordRCoordRCoordRCoord,CCoordCCoordCCoordCCoordCCoord] of the calibration mark center points. The order of the values within these two tuples must correspond to the order of the 3D coordinates of the calibration marks in the calibration plate description file CalPlateDescrCalPlateDescrCalPlateDescrCalPlateDescrcalPlateDescr, since this fixes the correspondences between extracted image marks and known model marks (given by caltab_pointscaltab_pointsCaltabPointsCaltabPointsCaltabPoints)! If a triangular orientation mark is defined in a corner of the plate by the plate description file (see gen_caltabgen_caltabGenCaltabGenCaltabGenCaltab), the mark will be detected and the point order is returned in row-major order beginning with the corner mark in the (barycentric) negative quadrant with respect to the defined coordinate system of the plate. Else, if no orientation mark is defined, the order of the center points is in row-major order beginning at the upper left corner mark in the image.

Based on the ellipse parameters for each calibration mark, a rough estimate for the external camera parameters is finally computed. For this purpose the fixed correspondences between extracted image marks and known model marks are used. The estimate StartPoseStartPoseStartPoseStartPosestartPose describes the pose of the calibration plate in the camera coordinate system as required by the operator camera_calibrationcamera_calibrationCameraCalibrationCameraCalibrationCameraCalibration.

Execution Information

Parameters

ImageImageImageImageimage (input_object)  singlechannelimage → objectHImageHImageHobject (byte / uint2)

Input image.

CalPlateRegionCalPlateRegionCalPlateRegionCalPlateRegioncalPlateRegion (input_object)  region → objectHRegionHRegionHobject

Region of the calibration plate.

CalPlateDescrCalPlateDescrCalPlateDescrCalPlateDescrcalPlateDescr (input_control)  filename.read → HTupleHTupleHtuple (string) (string) (HString) (char*)

File name of the calibration plate description.

Default value: 'caltab.descr' "caltab.descr" "caltab.descr" "caltab.descr" "caltab.descr"

List of values: 'caltab.descr'"caltab.descr""caltab.descr""caltab.descr""caltab.descr", 'caltab_100mm.descr'"caltab_100mm.descr""caltab_100mm.descr""caltab_100mm.descr""caltab_100mm.descr", 'caltab_10mm.descr'"caltab_10mm.descr""caltab_10mm.descr""caltab_10mm.descr""caltab_10mm.descr", 'caltab_200mm.descr'"caltab_200mm.descr""caltab_200mm.descr""caltab_200mm.descr""caltab_200mm.descr", 'caltab_30mm.descr'"caltab_30mm.descr""caltab_30mm.descr""caltab_30mm.descr""caltab_30mm.descr"

File extension: .descr

StartCamParamStartCamParamStartCamParamStartCamParamstartCamParam (input_control)  campar → HCamPar, HTupleHTupleHtuple (real / integer / string) (double / int / long / string) (double / Hlong / HString) (double / Hlong / char*)

Initial values for the internal camera parameters.

StartThreshStartThreshStartThreshStartThreshstartThresh (input_control)  number → HTupleHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Initial threshold value for contour detection.

Default value: 128

Suggested values: 80, 96, 112, 128, 144, 160

Restriction: StartThresh > 0

DeltaThreshDeltaThreshDeltaThreshDeltaThreshdeltaThresh (input_control)  number → HTupleHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Loop value for successive reduction of StartThreshStartThreshStartThreshStartThreshstartThresh.

Default value: 10

Suggested values: 6, 8, 10, 12, 14, 16, 18, 20, 22

Restriction: DeltaThresh > 0

MinThreshMinThreshMinThreshMinThreshminThresh (input_control)  number → HTupleHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Minimum threshold for contour detection.

Default value: 18

Suggested values: 8, 10, 12, 14, 16, 18, 20, 22

Restriction: MinThresh > 0

AlphaAlphaAlphaAlphaalpha (input_control)  real → HTupleHTupleHtuple (real) (double) (double) (double)

Filter parameter for contour detection, see edges_imageedges_imageEdgesImageEdgesImageEdgesImage.

Default value: 0.9

Suggested values: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1

Typical range of values: 0.2 ≤ Alpha Alpha Alpha Alpha alpha ≤ 2.0

Restriction: Alpha > 0.0

MinContLengthMinContLengthMinContLengthMinContLengthminContLength (input_control)  real → HTupleHTupleHtuple (real) (double) (double) (double)

Minimum length of the contours of the marks.

Default value: 15.0

Suggested values: 10.0, 15.0, 20.0, 30.0, 40.0, 100.0

Restriction: MinContLength > 0.0

MaxDiamMarksMaxDiamMarksMaxDiamMarksMaxDiamMarksmaxDiamMarks (input_control)  real → HTupleHTupleHtuple (real) (double) (double) (double)

Maximum expected diameter of the marks.

Default value: 100.0

Suggested values: 50.0, 100.0, 150.0, 200.0, 300.0

Restriction: MaxDiamMarks > 0.0

RCoordRCoordRCoordRCoordRCoord (output_control)  real-array → HTupleHTupleHtuple (real) (double) (double) (double)

Tuple with row coordinates of the detected marks.

CCoordCCoordCCoordCCoordCCoord (output_control)  real-array → HTupleHTupleHtuple (real) (double) (double) (double)

Tuple with column coordinates of the detected marks.

StartPoseStartPoseStartPoseStartPosestartPose (output_control)  pose → HPose, HTupleHTupleHtuple (real / integer) (double / int / long) (double / Hlong) (double / Hlong)

Estimation for the external camera parameters.

Number of elements: 7

Example (HDevelop)

* Read calibration image.
read_image(Image, 'calib/calib_distorted_01')
* Find calibration pattern.
find_caltab(Image,CalPlate, 'caltab_100mm.descr', 3, 112, 5)
* Find calibration marks and start pose.
find_marks_and_pose(Image, CalPlate, 'caltab_100mm.descr' , \
                    ['area_scan_division', 0.008, 0.0, \
                     0.000011, 0.000011, 384, 288, 640, 512], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

Example (HDevelop)

* Read calibration image.
read_image(Image, 'calib/calib_distorted_01')
* Find calibration pattern.
find_caltab(Image,CalPlate, 'caltab_100mm.descr', 3, 112, 5)
* Find calibration marks and start pose.
find_marks_and_pose(Image, CalPlate, 'caltab_100mm.descr' , \
                    ['area_scan_division', 0.008, 0.0, \
                     0.000011, 0.000011, 384, 288, 640, 512], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

Example (HDevelop)

* Read calibration image.
read_image(Image, 'calib/calib_distorted_01')
* Find calibration pattern.
find_caltab(Image,CalPlate, 'caltab_100mm.descr', 3, 112, 5)
* Find calibration marks and start pose.
find_marks_and_pose(Image, CalPlate, 'caltab_100mm.descr' , \
                    ['area_scan_division', 0.008, 0.0, \
                     0.000011, 0.000011, 384, 288, 640, 512], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

Example (HDevelop)

* Read calibration image.
read_image(Image, 'calib/calib_distorted_01')
* Find calibration pattern.
find_caltab(Image,CalPlate, 'caltab_100mm.descr', 3, 112, 5)
* Find calibration marks and start pose.
find_marks_and_pose(Image, CalPlate, 'caltab_100mm.descr' , \
                    ['area_scan_division', 0.008, 0.0, \
                     0.000011, 0.000011, 384, 288, 640, 512], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

Example (HDevelop)

* Read calibration image.
read_image(Image, 'calib/calib_distorted_01')
* Find calibration pattern.
find_caltab(Image,CalPlate, 'caltab_100mm.descr', 3, 112, 5)
* Find calibration marks and start pose.
find_marks_and_pose(Image, CalPlate, 'caltab_100mm.descr' , \
                    ['area_scan_division', 0.008, 0.0, \
                     0.000011, 0.000011, 384, 288, 640, 512], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

Result

find_marks_and_posefind_marks_and_poseFindMarksAndPoseFindMarksAndPoseFindMarksAndPose returns 2 (H_MSG_TRUE) if all parameter values are correct and an estimation for the external camera parameters has been determined successfully. If necessary, an exception is raised.

Possible Predecessors

find_caltabfind_caltabFindCaltabFindCaltabFindCaltab

Possible Successors

camera_calibrationcamera_calibrationCameraCalibrationCameraCalibrationCameraCalibration

See also

find_caltabfind_caltabFindCaltabFindCaltabFindCaltab, camera_calibrationcamera_calibrationCameraCalibrationCameraCalibrationCameraCalibration, disp_caltabdisp_caltabDispCaltabDispCaltabDispCaltab, sim_caltabsim_caltabSimCaltabSimCaltabSimCaltab, read_cam_parread_cam_parReadCamParReadCamParReadCamPar, read_poseread_poseReadPoseReadPoseReadPose, create_posecreate_poseCreatePoseCreatePoseCreatePose, pose_to_hom_mat3dpose_to_hom_mat3dPoseToHomMat3dPoseToHomMat3dPoseToHomMat3d, caltab_pointscaltab_pointsCaltabPointsCaltabPointsCaltabPoints, gen_caltabgen_caltabGenCaltabGenCaltabGenCaltab, edges_sub_pixedges_sub_pixEdgesSubPixEdgesSubPixEdgesSubPix, edges_imageedges_imageEdgesImageEdgesImageEdgesImage

Module

Foundation

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