To reproduce the issue use this GeoPackage containing 6 geometries (valid) with a counterclockwise (CCW) winding order.
Description: When determining polygon winding order for the set of geometries in the provided GeoPackage the function ST_IsPolygonCCW returns 0 for all geometries while it should return 1. The function ST_IsPolygonCW does produce the correct result
The winding order of the polygons can be visualized with the following QGIS Layer definition file, which shows the winding order of the polygons is in fact CCW (warning: this QGIS style uses a geometry generator, which is quite computionally heavy when viewing larger geometries):
See the below steps to reproduce the issue:
Run in Bash shell:
wget https://www.dropbox.com/s/h2tf7vob53wpib3/ccw-issue-spatialite.gpkg
sqlite3 ccw-issue-spatialite.gpkgRun following SQL commands in sqlite shell:
select load_extension('mod_spatialite');
select 'spatialite_version', spatialite_version();
select 'geos_version', geos_version();
select 'count ST_IsValid', count(*) from protected_site where ST_IsValid(GeomFromGPB(geom)) = 1;
select 'count ST_IsPolygonCCW = 0', count(*) from protected_site where ST_IsPolygonCCW(GeomFromGPB(geom)) == 0;
select 'count ST_IsPolygonCCW = 1', count(*) from protected_site where ST_IsPolygonCCW(GeomFromGPB(geom)) == 1;
select 'count ST_IsPolygonCW = 0', count(*) from protected_site where ST_IsPolygonCW(GeomFromGPB(geom)) == 0;
select 'count ST_IsPolygonCC = 1', count(*) from protected_site where ST_IsPolygonCW(GeomFromGPB(geom)) == 1;This will output the following result:
spatialite_version|5.0.1
geos_version|3.10.2-CAPI-1.16.0
count ST_IsValid|6
count ST_IsPolygonCCW = 0|6
count ST_IsPolygonCCW = 1|0
count ST_IsPolygonCW = 0|6
count ST_IsPolygonCCW = 1|0Forcing the geoms a CCW orientation does not work using ST_ForcePolygonCCW:
update protected_site set geom = AsGPB(ST_ForcePolygonCCW(GeomFromGPB(geom)));Rerunning select count(*) from protected_site where ST_IsPolygonCCW(GeomFromGPB(geom)) == 1; still returns a count of 0.