I'm getting an error with the ST_Intersection() function that makes no sense to me. The error is: If you look at the example below, there is a Polygon and a MultiPolygon and I am checking whether or not they intersect. I believe all of the polygons involved are closed (i.e., start==end), but the error implies otherwise. ------------------------------------------------------------------------------------------------- DROP TABLE IF EXISTS Test_GeometryPart; CREATE TABLE Test_GeometryPart ( "GEO_ID" BIGINT NOT NULL, "GEOMETRY" ST_Geometry(SRID=4269) NOT NULL, ) IN "system"; INSERT INTO "DBA"."Test_GeometryPart" ("GEO_ID","GEOMETRY") VALUES(43055,'Polygon ((-80.490979899999999 43.490733200000001, -80.491207399999993 43.490490100000002, -80.491187199999999 43.490479700000002, -80.491133399999995 43.490449599999998, -80.491082000000006 43.4904175, -80.490839100000002 43.490647500000001, -80.490960900000005 43.490721600000001, -80.490979899999999 43.490733200000001))'); INSERT INTO "DBA"."Test_GeometryPart" ("GEO_ID","GEOMETRY") VALUES(1485884,'MultiPolygon (((-80.491187230078907 43.490479716207119, -80.49115111388835 43.490459908120179, -80.491116014830851 43.490439150960938, -80.491081981067708 43.490417473797557, -80.49083911081506 43.490647468049133, -80.490960867340746 43.490721593241055, -80.491187230078907 43.490479716207119)), ((-80.491187231297985 43.490479717105607, -80.491187230086396 43.490479715314088, -80.491187230078907 43.490479716207119, -80.491187231297985 43.490479717105607)))'); COMMIT; SELECT gp.* ,gp.GEOMETRY.ST_Transform(3857) AS GP_3857 ,zp.* ,zp.GEOMETRY.ST_Transform(3857) AS ZP_3857 ,GP_3857.ST_Intersection(ZP_3857) AS INTERSECTION FROM Test_GeometryPart gp, Test_GeometryPart zp WHERE gp.GEO_ID = 43055 AND zp.GEO_ID = 1485884; ------------------------------------------------------------------------------------------------- I'm running SQL Anywhere 16.0.0.1948 Developer Edition under Windows 7 (I believe it is the latest version since 'Check-for-Updates' reports no updates). Is this a bug? Has anyone else seen this? Terry |
One possible cause of this type of error is that the input geometries are invalid. Checking for invalid geometries is not performed when a geometry is loaded/created. From
Note the zp_3857 is not valid. From:
We can see that:
has the error: Curve 0 of polygon is not a ring (near "Polygon ((-8960237.976 5357495.7335, -8960237.9758 5357495.7332, -8960237.9758 5357495.7333, -8960237.976 5357495.7335))") Hmm... This ring looks closed to me (start point is exactly end point). I will look further. It looks to me as if, when calculating ZP_3857 the ST_Transform() function breaks the polygon. That is, zp.GEOMETRY is valid but ZP_3857 is not?
(19 Nov '14, 12:34)
Terry Wilkinson
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Agreed that before the ST_Transform the geometry is reported as valid and after the ST_Transform it is not valid. We are looking further.
(19 Nov '14, 12:41)
Ian McHardy
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I'm no spatial expert at all but I (wildly!) guess the error may result from the fact that the spatial transformation seems to turn the closed polygons into a not really closed one.
If you test for intersection with the original 4269 SRID you do not get that error (though I can't tell whether the result is correct):
Another wild guess: When simply viewing the original geometries in the Spatial Viewer with SRID 3857, the second row seems to return an error, at least with 16.0.0.1915 (SQLCODE -1486 "Invalid polygon: ring has zero area (near '%1')").
Clearly, I'm not a spatial expert either, and your suggestion is just what I needed. Thanks a lot.