[postgis-tickets] [PostGIS] #4289: A multipolygon is inverted in ST_AsMVTGeom in some cases

[PostGIS]

#4289: A multipolygon is inverted in ST_AsMVTGeom in some cases
----------------------+-------------------------
  Reporter:  ajolma   |      Owner:  pramsey
      Type:  defect   |     Status:  new
  Priority:  medium   |  Milestone:
 Component:  postgis  |    Version:  trunk
Resolution:           |   Keywords:  vector tile
----------------------+-------------------------

Comment (by Algunenano):

 This comes from the issues that geos has clipping geometries using the
 fast and dirty `lwgeom_clip_by_rect`, and although I made an attempt to
 fix it in
 https://github.com/postgis/postgis/commit/35db4ea0c0b02b15090f1e916c8fdb8ff6c5cc22
 (done for #4183) it doesn't work for this polygon.

 Coincidentally, as part of https://github.com/postgis/postgis/pull/356 I
 decided to switch the function order and clip the geometry after
 transforming it into mvt coordinates (instead of before). This should make
 it more robust but it still won't be bulletproof; the underlying problems
 in GEOS will still be there, but I don't think they will pop as often as
 there won't be points as close to each other after snapping them to the
 grid.

 You can see the current output and the output with the change in the
 `mvt_bug.png` image attached above. I guess that change is interesting for
 older releases, so I'll try to separate it from the introduction of the
 alternative library (for clipping and validation) and backport it to 2.4
 and 2.5.

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4289#comment:4>
PostGIS <http://trac.osgeo.org/postgis/>
The PostGIS Trac is used for bug, enhancement & task tracking, a user and developer wiki, and a view into the subversion code repository of PostGIS project.