I've started to build out operations on Polygonal Coverages in JTS ([1], [2]). These will be ported to GEOS (started here with CoverageValidator etc in C++ [3]). Hopefully these will be exposed in PostGIS as well (and of course other downstream projects).
Here's some examples of coverage operations and their geometric signatures: - Validation: List of Polygons -> List of linear geometries for invalid locations - Cleaning: List of Polygons -> Coverage - Union: Coverage -> Polygonal geometry - Simplification: Coverage -> Coverage A key question is how to expose these operations in the GEOS C API. I see two options: 1) Model a Polygonal Coverage as an array of simple Polygons (and possibly MultiPolygons) 2) Provide a Polygonal Coverage datatype (which might contain internal topology) So far I've been favouring #1, both for the C API and for the underlying C++ and JTS APIs. Reasons are: - Simplicity of use and implementation - Some operations (such as validation and cleaning) have to operate on non-coverage lists of polygons anyway - A potential advantage of having a Coverage data model is that coverage operations could be chained without needing to convert back to the simple polygon representation - but it's not clear to me that this will be very common (and this is not an option for PostGIS, and maybe other downstream projects). - It seems more in the spirit of the Simple Features philosophy (if that's a thing) Any thoughts or comments on this? If Model #1 is used, what would the C API look like? Accept a Geometry array with a size parameter, and return a Geometry array? It will likely be good to have some support functions to free Geometry arrays too. [1] http://lin-ear-th-inking.blogspot.com/2022/07/polygonal-coverages-and-operations-in.html [2] http://lin-ear-th-inking.blogspot.com/2022/08/validating-polygonal-coverages-in-jts.html [3] https://github.com/libgeos/geos/commit/62c928c9f37957c62fab8db69e6c8efd26ce4085
_______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/geos-devel
