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 (Row, Column), the orientation of the main axis Phi, the length of the larger half axis Radius1, and the length of the smaller half axis Radius2. Different measures for the distance of a contour point X = (Xi,Yi) to the ellipse are available (Mode):

'algebraic':
The distance is measured by the algebraic distance
a*Xi^2 + b*Xi*Yi + c*Yi^2 + d*Xi + e*Yi + f, where the
parameters a - f describing the ellipse are normalized in order
to obtain 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.

'geometric':
The distance is measured by the deviation XF1 + XF2 - 2a,
where F1,F2 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.

'bisec':
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 very good approximation of
the orthogonal distance from X to the ellipse.

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 artefacts in the pre-processing the start and end points of a contour might be faulty. Therefore, it is possible to exclude ClippingEndPoints points at the beginning and at the end of a contour from the computation.

read_image (Image, 'caltab')
find_caltab (Image, Caltab, 'caltab_big.descr', 3, 112, 5)
reduce_domain (Image, Caltab, 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
    Object_Selected := EdgesMarks[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.

dist_ellipse_contour_xld is local and processed completely exclusively without parallelization.

fit_ellipse_contour_xld

Sub-pixel operators