gen_parallels_xldgen_parallels_xldGenParallelsXldGenParallelsXldGenParallelsXldgen_parallels_xld examines the XLD polygons passed in
PolygonsPolygonsPolygonsPolygonspolygonspolygons for parallelism. The resulting parallel
polygons are returned in ParallelsParallelsParallelsParallelsparallelsparallels. If the parameter
MergeMergeMergeMergemergemerge is set to 'true'"true""true""true""true""true", adjacent parallel polygons
are returned in a single parallel relation. Otherwise, one parallel
relation is returned for each pair of parallel line segments.
Only polygon segments longer than LenLenLenLenlenlen are taken into account.
Whether two polygon segments are parallel depends on a maximum allowed
angle difference AlphaAlphaAlphaAlphaalphaalpha (in radians).
Furthermore, the projections of the two segments onto their angle bisector
have to overlap.
Finally, the overlap on the angle bisector is reprojected onto the two
segments. If the maximal distance of the reprojections is smaller than
DistDistDistDistdistdist, the segments are stored in ParallelsParallelsParallelsParallelsparallelsparallels。
As a side effect, a quality factor is calculated for each pair of
parallels, compare mod_parallels_xldmod_parallels_xldModParallelsXldModParallelsXldModParallelsXldmod_parallels_xld。It is based on the
normalized angular difference and the
normalized length of the overlap:
Here, is the angle difference of the
polygon segments, is the length of the overlap,
and the lengths of the polygon
segments, and the resulting quality factor.
The quality factor is a measure of parallelism (the larger its
value, the “more parallel” the polygons). Finally, the quality
factors of all parallel polygon segments contained in a single
polygon are added, weighted with their length of the overlapping
area. Note that you can query the range for the quality
factor with info_parallels_xldinfo_parallels_xldInfoParallelsXldInfoParallelsXldInfoParallelsXldinfo_parallels_xld。