ST_Simplify

Simplify a geometry using the Douglas-Peucker algorithm. This function reduces the number of vertices in a geometry while preserving its general shape, useful for rendering maps.

ST_Simplify is available from MariaDB 12.0.

Syntax

ST_Simplify(g, max_distance)

Description

Takes as input a geometry (g) and a double (max_distance). It applies the Ramer–Douglas–Peucker algorithm on g and returns the resulting geometry.

The goal of the Douglas-Peucker algorithm is to provide generalized simplifications by returning a geometry that is similar to g but uses only a subset of points. To perform the simplification, all the vertices that are shorter than max_distance are removed.

The algorithm may produce self-intersections and therefore result in invalid geometries. ST_IsValid can be used to test validity of the result.

If the max_distance is not positive or is NULL, an ER_WRONG_ARGUMENT will occur.

Examples

SELECT ST_AsText(ST_Simplify(ST_GeomFromText('LINESTRING(0 0,0 2,2 2,2 4,4 4,4 6,6 6)'), 0.5));
+-----------------------------------------------------------------------------------------+
| ST_AsText(ST_Simplify(ST_GeomFromText('LINESTRING(0 0,0 2,2 2,2 4,4 4,4 6,6 6)'), 0.5)) |
+-----------------------------------------------------------------------------------------+
| LINESTRING(0 0,0 2,2 2,2 4,4 4,4 6,6 6)                                                 |
+-----------------------------------------------------------------------------------------+

SELECT ST_AsText(ST_Simplify(ST_GeomFromText('LINESTRING(0 0,0 2,2 2,2 4,4 4,4 6,6 6)'), 1));  
+---------------------------------------------------------------------------------------+
| ST_AsText(ST_Simplify(ST_GeomFromText('LINESTRING(0 0,0 2,2 2,2 4,4 4,4 6,6 6)'), 1)) |
+---------------------------------------------------------------------------------------+
| LINESTRING(0 0,0 2,2 2,2 4,6 6)                                                       |
+---------------------------------------------------------------------------------------+

See Also

• Geometry Constructors

• ST_AsText

• ST_GeomFromText

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