dist_ellipse_contour_xld — Compute the distance of contours to an ellipse.
dist_ellipse_contour_xld determines the distance
between the contours in
Contours and an ellipse
specified by the center (
orientation of the main axis
the length of the larger half axis
Radius1, and the
length of the smaller half axis
measures for the distance of a contour point
to the ellipse are
The underlying distance measure is the geometric distance between a point on the contour and the ellipse. This measure is also called orthogonal or Euclidian distance.
The distance is measured by the algebraic distance
, where the
parameters a - f describing the ellipse are normalized in order
Radius2 as distance of the center of the
ellipse. This measure shows a high curvature bias: Near points of
high curvature on the ellipse (like the poles on the main axis)
the distance is smaller than near points with low curvature.
The distance is measured by the deviation
where are the focal points and a corresponds to
Radius1. This measure shows a low curvature bias:
Near points of high curvature on the ellipse (like the poles on the main
axis) the distance is larger than near points with low curvature.
The distance is measured by the distance between X and the intersection of the angular bisector of the two lines through X and the focal points with the ellipse. This is a good approximation of the orthogonal distance from X to the ellipse. The accuracy of the approximation depends on both the aspect ratio of the ellipse and the distance.
The operator returns the minimum absolute distance
the maximum absolute distance
MaxDist, the average
AvgDist, and the standard deviation of
the absolute distances
SigmaDist of all contour points.
To reduce the computational load, the computation of the distances
can be restricted to a subset of the contour points: If a value other
than -1 is assigned to
MaxNumPoints, only up to
MaxNumPoints points - uniformly distributed over the
contour - are used.
Due to artifacts in the pre-processing the start and end points
of a contour might be faulty. Therefore, it is possible to
ClippingEndPoints points at the beginning and at
the end of a contour from the computation.
Method for the determination of the distances.
Default value: 'geometric'
List of values: 'algebraic', 'bisec', 'focpoints', 'geometric'
Maximum number of contour points used for the computation (-1 for all points).
Default value: -1
MaxNumPoints >= 3
Number of points at the beginning and the end of the contours to be ignored for the computation of distances.
Default value: 0
ClippingEndPoints >= 0
Row coordinate of the center of the ellipse.
Column coordinate of the center of the ellipse.
Orientation of the main axis in radian.
Phi >= 0 && Phi <= 6.283185307
Length of the larger half axis.
Radius1 > 0
Length of the smaller half axis.
Radius2 >= 0 && Radius2 <= Radius1
Standard deviation of the distance.
read_image (Image, 'caltab') find_caltab (Image, CalPlate, 'caltab_big.descr', 3, 112, 5) reduce_domain (Image, CalPlate, ImageReduced) edges_sub_pix (ImageReduced, Edges, 'lanser2', 0.5, 20, 40) select_contours_xld (Edges, EdgesClosed, 'closed', 0, 2.0, 0, 0) select_contours_xld (EdgesClosed, EdgesMarks, 'contour_length', 20, 100, \ 0, 0) fit_ellipse_contour_xld (EdgesMarks, 'fitzgibbon', -1, 2, 0, 200, 3, 2.0, \ Row, Column, Phi, Radius1, Radius2, StartPhi, \ EndPhi, PointOrder) for i := 0 to |Row|-1 by 1 select_obj (EdgesMarks, ObjectSelected, i+1) dist_ellipse_contour_xld (ObjectSelected, 'bisec', -1, 0, Row[i], \ Column[i], Phi[i], Radius1[i], Radius2[i], \ MinDist, MaxDist, AvgDist, SigmaDist) endfor
dist_ellipse_contour_xld returns 2 (H_MSG_TRUE) if all parameter
values are correct. If necessary, an exception is raised.