On Wed, Apr 26, 2023 at 12:45:41PM -0700, Paul Ramsey wrote: > I am tempted to change the contract and document that > a validity check is a precondition for getting "sensible" results on > output.
Where's the contract ? I was curious to understand what would ST_CoverageUnion do for me but only found these short paragraphs: https://github.com/libgeos/geos/blob/62c928c9f37957c62fab8db69e6c8efd26ce4085/include/geos/coverage/CoverageUnion.h#L33-L40 https://github.com/libgeos/geos/blob/62c928c9f37957c62fab8db69e6c8efd26ce4085/include/geos/coverage/CoverageUnion.h#L48-L53 Those two paragraphs boils down to: Unions a polygonal coverage in an efficient way. Valid polygonal coverage topology allows merging polygons in a very efficient way. Takes: the polygons in the coverage (a vector of Geometry pointers) Returns: the union of the coverage polygons (a Geometry unique pointer) Questions I have are: - What is a "valid polygonal coverage" ? - Do shared edges need to contain the exact same vertices ? The answer seem to be in the PostGIS pull request to expose the functionality [1], but it would be useful to have it in the GEOS (and JTS?) side too. For easier porting of JTS fixes I also find it useful to encode the "last commit of JTS" in a comment in the top of each file. [1] https://github.com/postgis/postgis/pull/731#issue-1683980686 In general GEOS functions are (not sure if documented as such) expected to take a valid input for their return to be defined. There should be very few exceptions to this, maybe only the recent MakeValid. --strk; _______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/geos-devel
