[geos-devel] [GEOS] #1081: TopologyPreservingSimplifier / GEOSTopologyPreserveSimplify on Windows

[GEOS]

#1081: TopologyPreservingSimplifier / GEOSTopologyPreserveSimplify on Windows
------------------------+--------------------------
 Reporter:  Mike Taves  |      Owner:  geos-devel@…
     Type:  defect      |     Status:  new
 Priority:  blocker     |  Milestone:  3.9.0
Component:  Unit Tests  |    Version:  master
 Severity:  Unassigned  |   Keywords:
------------------------+--------------------------
 As discussed on mail list: https://lists.osgeo.org/pipermail/geos-
 devel/2020-November/009856.html

 With GEOS 3.9.0beta1 for Windows, both C++ and C API versions of
 !TopologyPreservingSimplifier and GEOSTopologyPreserveSimplify,
 respectively, provide sometimes random incorrect results.

 In the test suite, this can be run using the command:
 {{{
 test_geos_unit "geos::simplify::TopologyPreservingSimplifier"
 }}}
 which will fail most of the time for test 14, but not always. Similar
 behavior can be found using a simple C or C++ program that uses `geos.dll`
 and `geos_c.dll`.

 With Shapely:
 {{{
 from shapely import wkt, geos

 print(geos.geos_version_string)
 g = wkt.loads('MULTILINESTRING((0 0, 50 0, 70 0, 80 0, 100 0), (0 0, 50 1,
 60 1, 100 0))')
 simplified = g.simplify(10.0, preserve_topology=True)
 print(simplified.wkt)
 }}}
 Using a stable GEOS build, this is the expected result:
 {{{
 3.8.0-CAPI-1.13.1
 MULTILINESTRING ((0 0, 100 0), (0 0, 50 1, 100 0))
 }}}
 while using `geos_c.dll`/`geos.dll` built from 3.9.0beta1 only shows the
 incorrect result:
 {{{
 3.9.0-CAPI-1.14.0
 MULTILINESTRING ((0 0, 100 0), (0 0, 100 0))
 }}}

 A PostGIS equivalent is be:
 {{{
 SELECT ST_AsText(ST_SimplifyPreserveTopology(
     'MULTILINESTRING((0 0, 50 0, 70 0, 80 0, 100 0), (0 0, 50 1, 60 1, 100
 0))', 10.0));
 }}}
 which returns mostly the incorrect result, but sometimes the correct
 result. Fun!

 ----
 This appears to be a Windows-only issue, which may have been introduced
 between 4 to 6 months ago. It is difficult to pin-down an exact commit
 from the !AppVeyor build history, as it was obscured by an unrelated
 preceding error in the CI workflow.

-- 
Ticket URL: <https://trac.osgeo.org/geos/ticket/1081>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).