| Bug #64649 | ST_Difference() returns invalid polygons with self tangency | ||
|---|---|---|---|
| Submitted: | 14 Mar 2012 15:30 | Modified: | 5 Oct 2012 17:11 |
| Reporter: | Benjamin Morel | Email Updates: | |
| Status: | Closed | Impact on me: | |
| Category: | MySQL Server: GIS | Severity: | S3 (Non-critical) |
| Version: | 5.6.4-m7, 5.6.5-m8 | OS: | Any |
| Assigned to: | CPU Architecture: | Any | |
| Tags: | Geometry, gis, polygon, spatial, ST_Difference | ||
[14 Mar 2012 15:49]
Valeriy Kravchuk
Thank you for the bug report. Same with 5.6.5:
macbook-pro:trunk openxs$ bin/mysql -uroot test
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Welcome to the MySQL monitor. Commands end with ; or \g.
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Server version: 5.6.5-m8-debug Source distribution
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Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> SET @a = ST_GeomFromText('POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))', 4326);
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT ST_AsText(ST_Difference(@a, @a));
+---------------------------------------------------------------+
| ST_AsText(ST_Difference(@a, @a)) |
+---------------------------------------------------------------+
| MULTIPOLYGON(((0 0,0 1,0 0)),((0 0,1 0,1 1,0 1,1 1,1 0,0 0))) |
+---------------------------------------------------------------+
1 row in set (0.00 sec)
[5 Oct 2012 17:11]
Paul DuBois
Noted in 5.6.8, 5.7.0 changelogs. ST_Difference() could incorrectly produce empty polygons in the result.
Description: ST_Difference() wrongly keeps the rings of the polygons involved in the calculation. In the example below, we're computing the difference of a polygon with itself; this should return an empty Geometry (behavior verified on PostGIS). Instead, the geometry returned is composed of invalid polygons with zero area. How to repeat: SET @a = ST_GeomFromText('POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))', 4326); SELECT ST_AsText(ST_Difference(@a, @a)); Expected result: GEOMETRYCOLLECTION EMPTY Actual result: MULTIPOLYGON(((0 0,0 1,0 0)),((0 0,1 0,1 1,0 1,1 1,1 0,0 0)))