On Mon, 2 May 2022 at 19:05, Martin Davis <[email protected]> wrote:
> That blog post does provide useful queries for finding polygon overlaps > and gaps. > > Overlaps are found via testing if polygon interiors intersect, using the > DE-9IM relate mask 2********. > > Gaps are found by identifying holes in the union of the set of polygons. > One issue with this is that computing the union of large datasets can be > slow. Lars' solution provides some ideas for dealing with this. > > > I think that matters are rather more complex than this. For instance, I found 2 lines meet with each other at both ends. In this case, 2 intersections are both a point. One will find two lines form an enclosed area. When 2 lines intersect or meet/touch more than 2 times, intersection will return more than 2 points. For instance, when two lines meet at 3 points, one would get 2 gap polygons. Given 2 zigzagging lines, how to write a function to return overlaps and gaps is an interesting matter. Regards, David
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