union_adjacent_contours_xld — Compute the union of contours whose end points are close together.
union_adjacent_contours_xld unifies all
contours of the input XLD contour array (
end points are close together.
The unified contour consists of the concatenation of the contour
points of the input contours.
If necessary, the order of these input contour points is flipped, so
that the end points of the contours that have to be connected are
direct neighbors in the resulting point list.
This operation is repeated until there are no more unconnected
adjacent contours left.
As a result all the contours that are newly created by unification,
as well as the input contours that could not be connected with any
other contour, are returned in
MaxDistRel are used to
define the conditions for the proximity of two contours. In principle, the
measures for these parameters depend on the order in which each pair of
contours is evaluated, i.e., which contour is used as reference contour
that is to be joined with the second contour. To avoid this dependency, the
respective measures are evaluated in both directions and the order of
contours is chosen that results in the smaller value for these measures.
Note that in the illustrations below, the contour on the left is always
used as the reference contour. The parameter
Mode controls the
handling of the attributes of the input contours.
MaxDistAbs defines the maximum accepted
absolute distance between the two contours. The distance is
measured along the regression line of the reference contour. Thus, it
is the length of the projection of the gap between the two contours
onto the regression line of the reference contour.
MaxDistRel defines the maximum accepted
relative distance between the two contours. The relative distance is
calculated by dividing the distance a (see the description of the
MaxDistAbs) by the length b of the reference
The order for connecting adjacent contours depends mainly on the distance of the neighbored end points: the contours with the smallest distance are connected first. If there are two pairs of contours with the same distance, first the contour pair that does not contain the shortest contour is connected.
Finally, by the parameter
Mode it is possible to control
how to handle the attributes that may come with input contours.
For example, the operator
edges_sub_pix attaches to every
contour point attributes like the local orientation, the edge
response, and the edge direction.
Choosing the default value 'attr_keep', all attributes are
copied to the output, and - if a contour has to be flipped for
connecting it with another one - they are adapted to the new
With a great number of input contours, however, it may be sensible
to ignore the attributes for performance reasons, if they are not
needed for further calculations.
For this the value 'attr_forget' has to be passed.
Input XLD contours.
Output XLD contours.
Maximum distance of the contours' end points.
Default value: 10.0
Typical range of values:
Maximum distance of the contours' end points in relation to the length of the longer contour.
Default value: 1.0
Typical range of values:
Mode describing the treatment of the contours' attributes.
Default value: 'attr_keep'
List of values: 'attr_forget', 'attr_keep'