Learn about POLYGON properties in MariaDB Server. This section details SQL functions for retrieving attributes of polygonal spatial objects, such as area, perimeter, and the number of rings.
A synonym for ST_CENTROID.
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A synonym for ST_AREA.
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A synonym for ST_ExteriorRing.
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A synonym for ST_InteriorRingN.
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A synonym for ST_NumInteriorRings.
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ST_Area(poly)
Area(poly)Returns as a double-precision number the area of the Polygon value poly, as measured in its spatial reference system.
ST_Area() and Area() are synonyms.
SET @poly = 'Polygon((0 0,0 3,3 0,0 0),(1 1,1 2,2 1,1 1))';
SELECT Area(GeomFromText(@poly));
+---------------------------+
| Area(GeomFromText(@poly)) |
+---------------------------+
| 4 |
+---------------------------+This page is licensed: GPLv2, originally from fill_help_tables.sql
ST_Centroid(mpoly)
Centroid(mpoly)Returns a point reflecting the mathematical centroid (geometric center) for the MultiPolygon mpoly. The resulting point will not necessarily be on the MultiPolygon.
ST_Centroid() and Centroid() are synonyms.
SET @poly = ST_GeomFromText('POLYGON((0 0,20 0,20 20,0 20,0 0))');
SELECT ST_AsText(ST_Centroid(@poly)) AS center;
+--------------+
| center |
+--------------+
| POINT(10 10) |
+--------------+This page is licensed: CC BY-SA / Gnu FDL
ST_ExteriorRing(poly)
ExteriorRing(poly)Returns the exterior ring of the Polygon value poly as a LineString.
ST_ExteriorRing() and ExteriorRing() are synonyms.
SET @poly = 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';
SELECT AsText(ExteriorRing(GeomFromText(@poly)));
+-------------------------------------------+
| AsText(ExteriorRing(GeomFromText(@poly))) |
+-------------------------------------------+
| LINESTRING(0 0,0 3,3 3,3 0,0 0) |
+-------------------------------------------+This page is licensed: GPLv2, originally from fill_help_tables.sql
ST_InteriorRingN(poly,N)
InteriorRingN(poly,N)Returns the N-th interior ring for the Polygon value poly as a LineString. Rings are numbered beginning with 1.
ST_InteriorRingN() and InteriorRingN() are synonyms.
SET @poly = 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';
SELECT AsText(InteriorRingN(GeomFromText(@poly),1));
+----------------------------------------------+
| AsText(InteriorRingN(GeomFromText(@poly),1)) |
+----------------------------------------------+
| LINESTRING(1 1,1 2,2 2,2 1,1 1) |
+----------------------------------------------+This page is licensed: GPLv2, originally from fill_help_tables.sql
ST_NumInteriorRings(poly)
NumInteriorRings(poly)Returns an integer containing the number of interior rings in the Polygon value poly.
Note that according the OpenGIS standard, a POLYGON should have exactly one ExteriorRing and all other rings should lie within that ExteriorRing and thus be the InteriorRings. Practically, however, some systems, including MariaDB's, permit polygons to have several 'ExteriorRings'. In the case of there being multiple, non-overlapping exterior rings ST_NumInteriorRings() will return 1.
ST_NumInteriorRings() and NumInteriorRings() are synonyms.
SET @poly = 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';
SELECT NumInteriorRings(GeomFromText(@poly));
+---------------------------------------+
| NumInteriorRings(GeomFromText(@poly)) |
+---------------------------------------+
| 1 |
+---------------------------------------+Non-overlapping 'polygon':
SELECT ST_NumInteriorRings(ST_PolyFromText('POLYGON((0 0,10 0,10 10,0 10,0 0),
(-1 -1,-5 -1,-5 -5,-1 -5,-1 -1))')) AS NumInteriorRings;
+------------------+
| NumInteriorRings |
+------------------+
| 1 |
+------------------+This page is licensed: GPLv2, originally from fill_help_tables.sql