Parameters of the equivalent ellipse.

The operator elliptic_axis_xld calculates the radii and the orientation of the ellipse having the ``same orientation'' and the ``same aspect ratio'' as the input contour. The closed input contour must not intersect itself, otherwise the resulting parameters are not meaningful. Several input contours can be passed in XLD as tuples. The length of the major radius Ra and the minor radius Rb as well as the orientation of the main axis with regard to the horizontal (Phi) are determined. The angle is indicated in radians.

Calculation:

        If the moments M20, M02 and M11 are
        normalized to the area (see moments_xld),
        the radii Ra and Rb are calculated as:

        Ra = sqrt(8.0*(M20+M02+sqrt((M20-M02)^2+4.0*M11^2)))/2.0
        Rb = sqrt(8.0*(M20+M02-sqrt((M20-M02)^2+4.0*M11^2)))/2.0

        The orientation Phi is defined by:

        Phi = -0.5 * atan2(2.0 * M11,M02 - M20)

If more than one contour is passed the results are stored in tuples, the index of a value in the tuple corresponding to the index of a contour in the input.

If N is the number of contour points, the runtime complexity is O(N).

elliptic_axis_xld returns 2 (H_MSG_TRUE) if the input is not empty. If the input is empty the behavior can be set via set_system(::'no_object_result',<Result>:). If necessary, an exception is raised.

elliptic_axis_xld is reentrant and automatically parallelized (on tuple level).

gen_contours_skeleton_xld, edges_sub_pix, threshold_sub_pix, gen_contour_polygon_xld

area_center_xld, gen_ellipse_contour_xld

smallest_rectangle2

moments_xld, smallest_circle_xld, smallest_rectangle1_xld, smallest_rectangle2_xld, shape_trans_xld

R. Haralick, L. Shapiro ``Computer and Robot Vision'' Addison-Wesley, 1992, pp. 73-75

Sub-pixel operators