[geos-devel] [GEOS] #959: Reversed result in GEOSClipByRect

GEOS geos-trac at osgeo.org
Mon Mar 11 16:57:09 PDT 2019

#959: Reversed result in GEOSClipByRect
 Reporter:  Algunenano   |       Owner:  geos-devel@…
     Type:  defect       |      Status:  closed
 Priority:  major        |   Milestone:  3.5.2
Component:  Default      |     Version:  3.5.0
 Severity:  Significant  |  Resolution:  invalid
 Keywords:               |
Changes (by Algunenano):

 * status:  new => closed
 * resolution:   => invalid


 > Is the wagyu quick_clip all that is needed for clipping MVT polygons? If
 so, that's easy to port. If not, then it's not the real comparison.

 Yes and no, wagyu guarantees that the output will always be valid (it does
 a pass later for force validation with int coordinates). In exchange it
 might drop small triangles of a multipolygon, which you can't get away
 with in MVTs as it's normal for things to pop up/out and you zoom in/out.

 It doesn't make much sense to port that clipping algorithm without the
 whole paraphernalia (quick validation with int coordinates). I found and
 even harder issue around mvts today [1] where making a polygon valid
 changed some of its coordinates to floats (against the mvt spec), then
 snapping them to ints turned it invalid (against the mvt spec), and so on.

 Based on this, I think I'll keep dropping geometries when this happens and
 push to make wagyu the default for 3.0.

 Thanks a lot for the comments @mdavis.

 1 - https://trac.osgeo.org/postgis/ticket/4348

Ticket URL: <https://trac.osgeo.org/geos/ticket/959#comment:7>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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