[postgis-tickets] r16558 - ensure that polygons are CW coming out of the ASMVTGEOM process

[Paul Ramsey]

Author: pramsey
Date: 2018-05-07 11:04:57 -0700 (Mon, 07 May 2018)
New Revision: 16558

Modified:
   branches/2.4/postgis/mvt.c
Log:
ensure that polygons are CW coming out of the ASMVTGEOM process
Closes #4079


Modified: branches/2.4/postgis/mvt.c
===================================================================
--- branches/2.4/postgis/mvt.c	2018-05-07 17:59:57 UTC (rev 16557)
+++ branches/2.4/postgis/mvt.c	2018-05-07 18:04:57 UTC (rev 16558)
@@ -734,22 +734,27 @@
 
 	/* if polygon(s) make valid and force clockwise as per MVT spec */
 	if (lwgeom_out->type == POLYGONTYPE ||
-		lwgeom_out->type == MULTIPOLYGONTYPE) {
-		lwgeom_out = lwgeom_make_valid(lwgeom_out);
+	    lwgeom_out->type == MULTIPOLYGONTYPE) {
+	    lwgeom_out = lwgeom_make_valid(lwgeom_out);
+		/* Because we are in image coordinates, we need to go to CCW in */
+		/* order to get a CW output in image space */
 		lwgeom_force_clockwise(lwgeom_out);
+		lwgeom_reverse(lwgeom_out);
 	}
 
 	/* if geometry collection extract highest dimensional geometry type */
 	if (lwgeom_out->type == COLLECTIONTYPE) {
 		LWCOLLECTION *lwcoll = lwgeom_as_lwcollection(lwgeom_out);
-		lwgeom_out = lwcollection_as_lwgeom(
-			lwcollection_extract(lwcoll, max_type(lwcoll)));
+		lwgeom_out = lwcollection_as_lwgeom(lwcollection_extract(lwcoll, max_type(lwcoll)));
 		lwgeom_out = lwgeom_homogenize(lwgeom_out);
 		/* if polygon(s) make valid and force clockwise as per MVT spec */
 		if (lwgeom_out->type == POLYGONTYPE ||
-			lwgeom_out->type == MULTIPOLYGONTYPE) {
-			lwgeom_out = lwgeom_make_valid(lwgeom_out);
+		    lwgeom_out->type == MULTIPOLYGONTYPE) {
+		    lwgeom_out = lwgeom_make_valid(lwgeom_out);
+			/* Because we are in image coordinates, we need to go to CCW in */
+			/* order to get a CW output in image space */
 			lwgeom_force_clockwise(lwgeom_out);
+			lwgeom_reverse(lwgeom_out);
 		}
 	}