The issue regarding the number of permutations of point sets

[sxs505]

In the code, when observing the ground truth part, if there are 20 points in a line element of a vectors, why are there 38 relations corresponding to it, given that according to maptr's viewpoint, the permutation of point sets should result in 2N?

[woodfrog]

This part is from StreamMapNet. If I remember correctly: because the first and last points of a polygon are the same (duplicated), there are only 19 different coordinates, so we have 38=19*2 permutations. For polylines, there will be only 2 permutations. All things are equivalent to MapTR's viewpoint.