[geos-devel] OverlayNG for Testing

[Paul Ramsey]

OK, as requested it is now possible to test OverlayNG using C clients.

https://github.com/libgeos/geos/commit/c6774a6a48b2

For autotools, use

  --enable-overlayng

For cmake, add

  -DDISABLE_OVERLAYNG=OFF

No guarantees, this is completely untested, except insofar as it all still compiles in the default state (which is overlayng off).

The goal, of course, is to get to a point before release where the default state can be overlayng on.

Some things we already know don't work:

- 3D! GEOS uniquely has supported adding in Z coordinates to introduced coordinates, and that code hasn't been added to JTS (and thus overlayng). How this will affect existing expectations for 3D output is unknown, but it's sure to be broken in some way.
- Union on linestrings! OverlayNG extracts maximal length linestrings from the unioned graph. Old overlay extracted minimal length linestrings. This change is probably "for the best" but it's a change which might impact existing logic.

ATB,

P