get_circle_poseT_get_circle_poseGetCirclePoseget_circle_poseGetCirclePoseGetCirclePose (Operator)

Name

get_circle_poseT_get_circle_poseGetCirclePoseget_circle_poseGetCirclePoseGetCirclePose — Determine the 3D pose of a circle from its perspective 2D projection.

Signature

Description

Each ellipse in an image can be interpreted as the perspective projection of a circle into the image. In fact, for a given radius of the circle, there exist two differently oriented circles in 3D that result in the same projection. get_circle_poseget_circle_poseGetCirclePoseget_circle_poseGetCirclePoseGetCirclePose determines the 3D positions and orientations of these two circles. First, each ContourContourContourContourContourcontour is approximated by an ellipse. Then, based on the internal camera parameters (CameraParamCameraParamCameraParamCameraParamCameraParamcameraParam) and the radius of the circle in 3D (RadiusRadiusRadiusRadiusRadiusradius), the 3D positions and orientations (Pose1Pose1Pose1Pose1Pose1pose1,Pose2Pose2Pose2Pose2Pose2pose2) are determined in camera coordinates.

Depending on the value of the parameter OutputTypeOutputTypeOutputTypeOutputTypeOutputTypeoutputType, the position and orientation is returned as a 3D pose (OutputTypeOutputTypeOutputTypeOutputTypeOutputTypeoutputType = 'pose'"pose""pose""pose""pose""pose") or in the form of the center of the 3D circle and the normal vector of the plane in which the circle lies (OutputTypeOutputTypeOutputTypeOutputTypeOutputTypeoutputType = 'center_normal'"center_normal""center_normal""center_normal""center_normal""center_normal"). In the former case, the angle for the rotation around the z axis is set to zero, because it cannot be determined. In the latter case, the first three elements of the output parameters Pose1Pose1Pose1Pose1Pose1pose1 and Pose2Pose2Pose2Pose2Pose2pose2 contain the position of the center of the circle. The following three elements contain the normal vector. The normal vectors are normalized and oriented such that they point away from the optical center which is the origin of the camera coordinate system. If OutputTypeOutputTypeOutputTypeOutputTypeOutputTypeoutputType is set to 'center_normal'"center_normal""center_normal""center_normal""center_normal""center_normal", the output parameters Pose1Pose1Pose1Pose1Pose1pose1 and Pose2Pose2Pose2Pose2Pose2pose2 contain only six elements which describe the position and orientation of the circle instead of the seven elements of the 3D pose that are returned if OutputTypeOutputTypeOutputTypeOutputTypeOutputTypeoutputType is set to 'pose'"pose""pose""pose""pose""pose".

If more than one contour is passed in ContourContourContourContourContourcontour, RadiusRadiusRadiusRadiusRadiusradius must either contain a tuple that contains a value for each contour or only one value which is then used for all contours. The resulting positions and orientations are stored one after another in Pose1Pose1Pose1Pose1Pose1pose1 and Pose2Pose2Pose2Pose2Pose2pose2, i.e., Pose1Pose1Pose1Pose1Pose1pose1 and Pose2Pose2Pose2Pose2Pose2pose2 contain first the pose or the position and the normal vector of the first contour, followed by the respective values for the second contour and so on.

Attention

The accuracy of the determined poses depends heavily on the accuracy of the extracted contours. The extraction of curved edges using relatively large filter masks leads to a slightly shifted edge position. Edge extraction approaches that are based on the first derivative of the image function (e.g., edges_sub_pixedges_sub_pixEdgesSubPixedges_sub_pixEdgesSubPixEdgesSubPix) yield edges that are shifted towards the center of curvature, i.e., extracted ellipses will be slightly to small. Approaches that are based on the second derivative of the image function (laplace_of_gausslaplace_of_gaussLaplaceOfGausslaplace_of_gaussLaplaceOfGaussLaplaceOfGauss followed by zero_crossing_sub_pixzero_crossing_sub_pixZeroCrossingSubPixzero_crossing_sub_pixZeroCrossingSubPixZeroCrossingSubPix) result in edges that are shifted away from the center of curvature, i.e., extracted ellipses will be slightly too large.

These effects increase with the curvature of the edge and with the size of the filter mask that is used for the edge extraction. Therefore, to achieve high accuracy, the ellipses should appear large in the image and the filter parameter should be chosen such that small filter masks are used (see info_edgesinfo_edgesInfoEdgesinfo_edgesInfoEdgesInfoEdges).

Parallelization

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

Parameters

Result

get_circle_poseget_circle_poseGetCirclePoseget_circle_poseGetCirclePoseGetCirclePose returns 2 (H_MSG_TRUE) if all parameter values are correct and the position of the circle has been determined successfully. If necessary, an exception is raised.

Possible Predecessors

edges_sub_pixedges_sub_pixEdgesSubPixedges_sub_pixEdgesSubPixEdgesSubPix

Alternatives

find_marks_and_posefind_marks_and_poseFindMarksAndPosefind_marks_and_poseFindMarksAndPoseFindMarksAndPose, camera_calibrationcamera_calibrationCameraCalibrationcamera_calibrationCameraCalibrationCameraCalibration

See also

get_rectangle_poseget_rectangle_poseGetRectanglePoseget_rectangle_poseGetRectanglePoseGetRectanglePose, fit_ellipse_contour_xldfit_ellipse_contour_xldFitEllipseContourXldfit_ellipse_contour_xldFitEllipseContourXldFitEllipseContourXld

Module

3D Metrology