find_marks_and_poseT_find_marks_and_posefind_marks_and_poseFindMarksAndPoseFindMarksAndPose (Operator)

Name

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

Signature

Description

find_marks_and_posefind_marks_and_posefind_marks_and_poseFindMarksAndPoseFindMarksAndPose is used to determine the necessary input data for the subsequent camera calibration (see calibrate_camerascalibrate_camerascalibrate_camerasCalibrateCamerasCalibrateCameras or camera_calibrationcamera_calibrationcamera_calibrationCameraCalibrationCameraCalibration): First, the 2D center points [RCoordRCoordRCoordRCoordRCoord,CCoordCCoordCCoordCCoordCCoord] of the calibration marks within the region CalTabRegionCalTabRegionCalTabRegionCalTabRegioncalTabRegion 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_posecreate_poseCreatePoseCreatePose for more information about 3D poses).

In the input image ImageImageImageImageimage an edge detector is applied (see edges_imageedges_imageedges_imageEdgesImageEdgesImage, mode 'lanser2') to the region CalTabRegionCalTabRegionCalTabRegionCalTabRegioncalTabRegion, which can be found by applying the operator find_caltabfind_caltabfind_caltabFindCaltabFindCaltab. 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 CalTabDescrFileCalTabDescrFileCalTabDescrFileCalTabDescrFilecalTabDescrFile and the contours have to be ellipticly 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_pixedges_sub_pixEdgesSubPixEdgesSubPix) 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 CalTabDescrFileCalTabDescrFileCalTabDescrFileCalTabDescrFilecalTabDescrFile, since this fixes the correspondences between extracted image marks and known model marks (given by caltab_pointscaltab_pointscaltab_pointsCaltabPointsCaltabPoints)! If a triangular orientation mark is defined in a corner of the plate by the plate description file (see gen_caltabgen_caltabgen_caltabGenCaltabGenCaltab), 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_calibrationcamera_calibrationCameraCalibrationCameraCalibration.

Parallelization

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Processed without parallelization.

Parameters

*  read calibration image
read_image(Image, 'calib-01')
*  find calibration pattern
find_caltab(Image,Caltab1, 'caltab.descr', 3, 112, 5)
*  find calibration marks and start pose
find_marks_and_pose(Image, Caltab, 'caltab.descr' , \
                    [0.008, 0.0, 0.000011, 0.000011, 384, 288, 768, 576], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

*  read calibration image
read_image(Image, 'calib-01')
*  find calibration pattern
find_caltab(Image,Caltab1, 'caltab.descr', 3, 112, 5)
*  find calibration marks and start pose
find_marks_and_pose(Image, Caltab, 'caltab.descr' , \
                    [0.008, 0.0, 0.000011, 0.000011, 384, 288, 768, 576], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

HTuple StartCamPar, RCoord, CCoord, StartPose;
// read calibration image
HImage Image("calib-01");
// find calibration pattern
HRegion Caltab = Image.FindCaltab("caltab.descr", 3, 112, 5);
// read internal camera parameters from file
read_cam_par("campar.dat", &StartCamPar);
// find calibration marks and start pose
RCoord = Image.FindMarksAndPose(Caltab, "caltab.descr", StartCamPar,
                                128, 10, 18, 0.9, 15.0, 100.0,
                                &RCoord, &CCoord, &StartPose);

*  read calibration image
read_image(Image, 'calib-01')
*  find calibration pattern
find_caltab(Image,Caltab1, 'caltab.descr', 3, 112, 5)
*  find calibration marks and start pose
find_marks_and_pose(Image, Caltab, 'caltab.descr' , \
                    [0.008, 0.0, 0.000011, 0.000011, 384, 288, 768, 576], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

*  read calibration image
read_image(Image, 'calib-01')
*  find calibration pattern
find_caltab(Image,Caltab1, 'caltab.descr', 3, 112, 5)
*  find calibration marks and start pose
find_marks_and_pose(Image, Caltab, 'caltab.descr' , \
                    [0.008, 0.0, 0.000011, 0.000011, 384, 288, 768, 576], \
                    128, 10, 18, 0.9, 15.0, 100.0, RCoord, CCoord, StartPose)

Result

find_marks_and_posefind_marks_and_posefind_marks_and_poseFindMarksAndPoseFindMarksAndPose 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_caltabfind_caltabFindCaltabFindCaltab

Possible Successors

camera_calibrationcamera_calibrationcamera_calibrationCameraCalibrationCameraCalibration

See also

find_caltabfind_caltabfind_caltabFindCaltabFindCaltab, camera_calibrationcamera_calibrationcamera_calibrationCameraCalibrationCameraCalibration, disp_caltabdisp_caltabdisp_caltabDispCaltabDispCaltab, sim_caltabsim_caltabsim_caltabSimCaltabSimCaltab, read_cam_parread_cam_parread_cam_parReadCamParReadCamPar, read_poseread_poseread_poseReadPoseReadPose, create_posecreate_posecreate_poseCreatePoseCreatePose, pose_to_hom_mat3dpose_to_hom_mat3dpose_to_hom_mat3dPoseToHomMat3dPoseToHomMat3d, caltab_pointscaltab_pointscaltab_pointsCaltabPointsCaltabPoints, gen_caltabgen_caltabgen_caltabGenCaltabGenCaltab, edges_sub_pixedges_sub_pixedges_sub_pixEdgesSubPixEdgesSubPix, edges_imageedges_imageedges_imageEdgesImageEdgesImage

Module

Foundation