On Wed, 7 Sept 2022 at 07:37, Martin Davis <mtncl...@gmail.com> wrote: > > 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
This is exciting, I'm very happy to see this on the horizon. Thank you! > > 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) > > Any thoughts or comments on this? >From one downstream client perspective (QGIS) we could work with either with a similar level of work, and would be happy to adapt to whatever upstream decides is the best approach! > 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. This sounds fine to me! A must-have would be that the geometries are always guaranteed to be returned in the same order as the input geometries, so that we can easily link input->output geometries and re-attach non spatial attributes. One consideration for the "Simplification: Coverage -> Coverage" use case would be whether only a fixed set of simplification algorithms are permitted (eg Visvalingam/Douglas-peucker only), or whether custom simplification/modification operations would also be permitted (via some callback function or similar). I'd love to see support for custom operations, so eg I could write a coverage -> coverage operation which applies both simplification and smoothing to the boundaries. Nyall _______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/geos-devel
