If any argument is NULL, the return value is NULL.

If any geometry argument is not a syntactically well-formed geometry, an ER_GIS_INVALID_DATA error occurs.

If any geometry argument has an SRID value that refers to an undefined spatial reference system (SRS), an ER_SRS_NOT_FOUND error occurs.

For functions that take multiple geometry arguments, if those arguments do not have the same SRID, an ER_GIS_DIFFERENT_SRIDS error occurs.

If any geometry argument has an SRID value for a geographic SRS, an ER_NOT_IMPLEMENTED_FOR_GEOGRAPHIC_SRS error occurs.

Otherwise, the return value is non-NULL.

ST_Buffer(g, d[, strategy1[, strategy2[, strategy3]]])

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

If the geometry argument is empty, ST_Buffer() returns an empty geometry.

If the distance is 0, ST_Buffer() returns the geometry argument unchanged:

mysql> SET @pt = ST_GeomFromText('POINT(0 0)');
mysql> SELECT ST_AsText(ST_Buffer(@pt, 0));
+------------------------------+
| ST_AsText(ST_Buffer(@pt, 0)) |
+------------------------------+
| POINT(0 0)                   |
+------------------------------+

ST_Buffer() supports negative distances for Polygon and MultiPolygon values, and for geometry collections containing Polygon or MultiPolygon values. The result may be an empty geometry.

ST_Buffer() permits up to three optional strategy arguments following the distance argument. Strategies influence buffer computation. These arguments are byte string values produced by the ST_Buffer_Strategy() function, to be used for point, join, and end strategies:

Up to one strategy of each type may be specified, and they may be given in any order.

ST_Buffer() handles its arguments as described in the introduction to this section, with these exceptions:

mysql> SET @pt = ST_GeomFromText('POINT(0 0)');
mysql> SET @pt_strategy = ST_Buffer_Strategy('point_square');
mysql> SELECT ST_AsText(ST_Buffer(@pt, 2, @pt_strategy));
+--------------------------------------------+
| ST_AsText(ST_Buffer(@pt, 2, @pt_strategy)) |
+--------------------------------------------+
| POLYGON((-2 -2,2 -2,2 2,-2 2,-2 -2))       |
+--------------------------------------------+

mysql> SET @ls = ST_GeomFromText('LINESTRING(0 0,0 5,5 5)');
mysql> SET @end_strategy = ST_Buffer_Strategy('end_flat');
mysql> SET @join_strategy = ST_Buffer_Strategy('join_round', 10);
mysql> SELECT ST_AsText(ST_Buffer(@ls, 5, @end_strategy, @join_strategy))
+---------------------------------------------------------------+
| ST_AsText(ST_Buffer(@ls, 5, @end_strategy, @join_strategy))   |
+---------------------------------------------------------------+
| POLYGON((5 5,5 10,0 10,-3.5355339059327373 8.535533905932738, |
| -5 5,-5 0,0 0,5 0,5 5))                                       |
+---------------------------------------------------------------+

ST_Buffer_Strategy(strategy[, points_per_circle])

This function returns a strategy byte string for use with ST_Buffer() to influence buffer computation.

Information about strategies is available at Boost.org.

The first argument must be a string indicating a strategy option:

If the first argument is 'point_circle', 'join_round', 'join_miter', or 'end_round', the points_per_circle argument must be given as a positive numeric value. The maximum points_per_circle value is the value of the max_points_in_geometry system variable.

For examples, see the description of ST_Buffer().

ST_Buffer_Strategy() handles its arguments as described in the introduction to this section, with these exceptions:

ST_ConvexHull(g)

Returns a geometry that represents the convex hull of the geometry value g.

This function computes a geometry's convex hull by first checking whether its vertex points are colinear. The function returns a linear hull if so, a polygon hull otherwise. This function processes geometry collections by extracting all vertex points of all components of the collection, creating a MultiPoint value from them, and computing its convex hull.

ST_ConvexHull() handles its arguments as described in the introduction to this section, with this exception:

mysql> SET @g = 'MULTIPOINT(5 0,25 0,15 10,15 25)';
mysql> SELECT ST_AsText(ST_ConvexHull(ST_GeomFromText(@g)));
+-----------------------------------------------+
| ST_AsText(ST_ConvexHull(ST_GeomFromText(@g))) |
+-----------------------------------------------+
| POLYGON((5 0,25 0,15 25,5 0))                 |
+-----------------------------------------------+

ST_Difference(g1, g2)

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

ST_Difference() handles its arguments as described in the introduction to this section.

mysql> SET @g1 = Point(1,1), @g2 = Point(2,2);
mysql> SELECT ST_AsText(ST_Difference(@g1, @g2));
+------------------------------------+
| ST_AsText(ST_Difference(@g1, @g2)) |
+------------------------------------+
| POINT(1 1)                         |
+------------------------------------+

ST_Intersection(g1, g2)

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

ST_Intersection() handles its arguments as described in the introduction to this section.

mysql> SET @g1 = ST_GeomFromText('LineString(1 1, 3 3)');
mysql> SET @g2 = ST_GeomFromText('LineString(1 3, 3 1)');
mysql> SELECT ST_AsText(ST_Intersection(@g1, @g2));
+--------------------------------------+
| ST_AsText(ST_Intersection(@g1, @g2)) |
+--------------------------------------+
| POINT(2 2)                           |
+--------------------------------------+

ST_SymDifference(g1, g2)

Returns a geometry that represents the point set symmetric difference of the geometry values g1 and g2, which is defined as:

g1 symdifference g2 := (g1 union g2) difference (g1 intersection g2)

Or, in function call notation:

ST_SymDifference(g1, g2) = ST_Difference(ST_Union(g1, g2), ST_Intersection(g1, g2))

ST_SymDifference() handles its arguments as described in the introduction to this section.

mysql> SET @g1 = Point(1,1), @g2 = Point(2,2);
mysql> SELECT ST_AsText(ST_SymDifference(@g1, @g2));
+---------------------------------------+
| ST_AsText(ST_SymDifference(@g1, @g2)) |
+---------------------------------------+
| MULTIPOINT((1 1),(2 2))               |
+---------------------------------------+

ST_Transform(g, target_srid)

Transforms a geometry from one spatial reference system (SRS) to another. The return value is a geometry of the same type as the input geometry with all coordinates transformed to the target SRID, target_srid. Transformation support is limited to geographic SRSs, unless the SRID of the geometry argument is the same as the target SRID value, in which case the return value is the input geometry for any valid SRS.

ST_Transform() handles its arguments as described in the introduction to this section, with these exceptions:

ST_SRID(g, target_srid) and ST_Transform(g, target_srid) differ as follows:

mysql> SET @p = ST_GeomFromText('POINT(52.381389 13.064444)', 4326);
mysql> SELECT ST_AsText(@p);
+----------------------------+
| ST_AsText(@p)              |
+----------------------------+
| POINT(52.381389 13.064444) |
+----------------------------+
mysql> SET @p = ST_Transform(@p, 4230);
mysql> SELECT ST_AsText(@p);
+---------------------------------------------+
| ST_AsText(@p)                               |
+---------------------------------------------+
| POINT(52.38208611407426 13.065520672345304) |
+---------------------------------------------+

ST_Union(g1, g2)

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

ST_Union() handles its arguments as described in the introduction to this section.

mysql> SET @g1 = ST_GeomFromText('LineString(1 1, 3 3)');
mysql> SET @g2 = ST_GeomFromText('LineString(1 3, 3 1)');
mysql> SELECT ST_AsText(ST_Union(@g1, @g2));
+--------------------------------------+
| ST_AsText(ST_Union(@g1, @g2))        |
+--------------------------------------+
| MULTILINESTRING((1 1,3 3),(1 3,3 1)) |
+--------------------------------------+

ST_Envelope(g)

ST_StartPoint(ls)

ST_EndPoint(ls)

ST_PointN(ls, N)

ST_ExteriorRing(poly)

ST_InteriorRingN(poly, N)

ST_GeometryN(gc, N)