ST_TOUCHES

Description

Determine whether two geometric shapes have boundary contact only (i.e., there are common points on the boundaries, but no internal intersection). Specifically:

Returns 1 if the boundaries of the two shapes have at least one common point, and their interiors are completely non-intersecting (no overlapping areas). Returns 0 if there are no common points on the boundaries, or if there is an internal intersection (even if the boundaries are in contact).

This function is used to distinguish between "boundary-only contact" and "internal intersection" scenarios, such as shared edges of adjacent polygons (boundary-only contact) or tangent points between a line and a polygon (boundary-only contact).

Sytax

ST_TOUCHES( <shape1>, <shape2>)

Parameter

Parameter	Description
`<shape1>`	The first geometric shape used to determine contact, supporting types such as Point, LineString, Polygon, Circle, etc.
`<shape2>`	The second geometric shape used to determine contact, supporting types such as Point, LineString, Polygon, Circle, etc.

Return value

Returns 1: shape1 is in contact with shape2. Returns 0: shape1 is not in contact with shape2.

ST_TOUCHES has the following edge cases:

If any input parameter is NULL, returns NULL.
If the input geometric shape is invalid, returns NULL.
If the input is an empty geometric object (e.g., POINT EMPTY), returns NULL.
If one shape is completely contained within another (with internal intersection), returns 0 even if their boundaries are in contact.
When a point is in contact with the boundary of a shape (a point has no interior), returns 1 (the "boundary" of a point is itself, which coincides with the shape's boundary with no internal intersection).。

Example

Point on polygon boundary

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Point(0, 5));
+--------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Point(0, 5)) |
+--------------------------------------------------------------------------------------+
|                                                                                    1 |
+--------------------------------------------------------------------------------------+

Point not on polygon boundary (inside the geometric shape)

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Point(5, 5));
+--------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Point(5, 5)) |
+--------------------------------------------------------------------------------------+
|                                                                                    0 |
+--------------------------------------------------------------------------------------+

Lines touch at endpoints

mysql> SELECT ST_TOUCHES(  ST_Linefromtext("LINESTRING (0 0, 2 2)"),  ST_Linefromtext("LINESTRING (2 2, 4 0)"));
+---------------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Linefromtext("LINESTRING (0 0, 2 2)"),  ST_Linefromtext("LINESTRING (2 2, 4 0)")) |
+---------------------------------------------------------------------------------------------------+
|                                                                                                 1 |
+---------------------------------------------------------------------------------------------------+

Lines intersect internally (not boundary contact, returns 0)

mysql> SELECT ST_TOUCHES(  ST_Linefromtext("LINESTRING (0 0, 10 10)"),  ST_Linefromtext("LINESTRING (0 10, 10 0)"));
+-------------------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Linefromtext("LINESTRING (0 0, 10 10)"),  ST_Linefromtext("LINESTRING (0 10, 10 0)")) |
+-------------------------------------------------------------------------------------------------------+
|                                                                                                     0 |
+-------------------------------------------------------------------------------------------------------+

Line is tangent to polygon boundary

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Linefromtext("LINESTRING (10 5, 15 5)"));
+------------------------------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Linefromtext("LINESTRING (10 5, 15 5)")) |
+------------------------------------------------------------------------------------------------------------------+
|                                                                                                                1 |
+------------------------------------------------------------------------------------------------------------------+

Line passes through the interior of the polygon (internal intersection, returns 0)

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Linefromtext("LINESTRING (5 5, 15 5)"));
+-----------------------------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Linefromtext("LINESTRING (5 5, 15 5)")) |
+-----------------------------------------------------------------------------------------------------------------+
|                                                                                                               0 |
+-----------------------------------------------------------------------------------------------------------------+

Polygons share a boundary (boundary-only contact, returns 1)

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 5 0, 5 5, 0 5, 0 0))"),  ST_Polygon("POLYGON ((5 0, 10 0, 10 5, 5 5, 5 0))"));
+-----------------------------------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 5 0, 5 5, 0 5, 0 0))"),  ST_Polygon("POLYGON ((5 0, 10 0, 10 5, 5 5, 5 0))")) |
+-----------------------------------------------------------------------------------------------------------------------+
|                                                                                                                     1 |
+-----------------------------------------------------------------------------------------------------------------------+

Polygons partially overlap (internal intersection, returns 0)

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Polygon("POLYGON ((5 5, 15 5, 15 15, 5 15, 5 5))"));
+-----------------------------------------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Polygon("POLYGON ((5 5, 15 5, 15 15, 5 15, 5 5))")) |
+-----------------------------------------------------------------------------------------------------------------------------+
|                                                                                                                           0 |
+-----------------------------------------------------------------------------------------------------------------------------+

Empty shape and polygon (no contact, returns 0)

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_GeometryFromText("POINT EMPTY"))
    -> ;
+----------------------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_GeometryFromText("POINT EMPTY")) |
+----------------------------------------------------------------------------------------------------------+
|                                                                                                     NULL |
+----------------------------------------------------------------------------------------------------------+

Invalid self-intersecting polygon (returns NULL)

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 1 1, 0 1, 1 0, 0 0))"),ST_Point(0.5, 0.5));
+------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 1 1, 0 1, 1 0, 0 0))"),ST_Point(0.5, 0.5)) |
+------------------------------------------------------------------------------------+
|                                                                               NULL |
+------------------------------------------------------------------------------------+

Parameter is NULL (returns NULL)

mysql> SELECT ST_TOUCHES(NULL, ST_Point(5, 5));
+----------------------------------+
| ST_TOUCHES(NULL, ST_Point(5, 5)) |
+----------------------------------+
|                             NULL |
+----------------------------------+

mysql> SELECT ST_TOUCHES(ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"), NULL);
+-------------------------------------------------------------------------+
| ST_TOUCHES(ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"), NULL) |
+-------------------------------------------------------------------------+
|                                                                    NULL |
+-------------------------------------------------------------------------+

Circle is tangent to line

mysql> SELECT ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Linefromtext("LINESTRING (-10 5, 10 5)"));
+--------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Linefromtext("LINESTRING (-10 5, 10 5)")) |
+--------------------------------------------------------------------------------+
|                                                                              1 |
+--------------------------------------------------------------------------------+

Point intersects circle boundary

mysql> SELECT ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Point(5, 0));
+---------------------------------------------------+
| ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Point(5, 0)) |
+---------------------------------------------------+
|                                                 1 |
+---------------------------------------------------+

Two circles are tangent

mysql> SELECT ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Circle(10, 0, 5));
+--------------------------------------------------------+
| ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Circle(10, 0, 5)) |
+--------------------------------------------------------+
|                                                      1 |
+--------------------------------------------------------+

Point is inside circle (not tangent)

mysql> SELECT ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Point(4, 0));
+---------------------------------------------------+
| ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Point(4, 0)) |
+---------------------------------------------------+
|                                                 0 |
+---------------------------------------------------+

Line intersects circle, returns 0

mysql> SELECT ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Linefromtext("LINESTRING (-10 0, 10 0)"));
+--------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Circle(0, 0, 5),  ST_Linefromtext("LINESTRING (-10 0, 10 0)")) |
+--------------------------------------------------------------------------------+
|                                                                              0 |
+--------------------------------------------------------------------------------+

Circle is tangent to polygon

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Circle(15, 5, 5));
+-------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Circle(15, 5, 5)) |
+-------------------------------------------------------------------------------------------+
|                                                                                         1 |
+-------------------------------------------------------------------------------------------+

Circle intersects polygon, returns 0

mysql> SELECT ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Circle(8, 5, 3));
+------------------------------------------------------------------------------------------+
| ST_TOUCHES(  ST_Polygon("POLYGON ((0 0, 10 0, 10 10, 0 10, 0 0))"),  ST_Circle(8, 5, 3)) |
+------------------------------------------------------------------------------------------+
|                                                                                        0 |
+------------------------------------------------------------------------------------------+

Description​

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Return value​

Example​

Description

Sytax

Parameter

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Example