On Wed, Sep 7, 2022 at 3:18 PM Sandro Santilli <s...@kbt.io> wrote: > On Tue, Sep 06, 2022 at 02:37:37PM -0700, Martin Davis wrote: > > I've started to build out operations on Polygonal Coverages in JTS ([1], > > [2]). > > [...] > > > 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) > > Could a coverage datatype allow performing operations on PostGIS Topologies > w/out building the polygons for each face ?
The short answer is "yes, probably, if suitable builders are defined for the coverage datatype". But that starts getting complex (in particular, it probably requires a concept of a Face, which might also have to be exposed). This is quite a bit more design than the current work requires. The other question is: what operations? Edge-based operations like simplification (and maybe smoothing) don't really require a coverage at all - they can simply operate on edge linework. That would be even easier to use from PostGIS Topology, I expect. In fact, I'm considering factoring out the "Topology-Preserving Line Simplification" part from the CoverageSimplifier, so it can be used standalone. > There's an ISO standard > representation of topologies, maybe such representation could be used > to transfer those topologies back and forth with GEOS ? > Not familiar with that representation. How does it handle identity for Faces of topologies? What we need to define is a C-based API for Coverage. It's not a huge design space, so there would probably be similarities.
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