12.18.5.3. Functions That Create New Geometries from Existing Ones

The following sections describe functions that take geometry values as arguments and return new geometry values.

12.18.5.3.1. Geometry Functions That Produce New Geometries

Section 12.18.5.2, "Geometry Property Functions", discusses several functions that construct new geometries from existing ones. See that section for descriptions of these functions:

OpenGIS proposes a number of other functions that can produce geometries. They are designed to implement spatial operators.

Buffer(g,d)

Returns a geometry that represents all points whose distance from the geometry value g is less than or equal to a distance of d.

Buffer() supports negative distances for polygons, multipolygons, and geometry collections containing polygons or multipolygons. For point, multipoint, linestring, multilinestring, and geometry collections not containing any polygons or multipolygons, Buffer() with a negative distance returns NULL.

The OpenGIS specification also defines the following functions, which MySQL does not implement:

ConvexHull(g)

Returns a geometry that represents the convex hull of the geometry value g.
Difference(g1,g2)

Returns a geometry that represents the point set difference of the geometry value g1 with g2.
Intersection(g1,g2)

Returns a geometry that represents the point set intersection of the geometry values g1 with g2.
SymDifference(g1,g2)

Returns a geometry that represents the point set symmetric difference of the geometry value g1 with g2.
Union(g1,g2)

Returns a geometry that represents the point set union of the geometry values g1 and g2.