How the ST_IsRing() function works in MariaDB?

The ST_IsRing() function in MariaDB is used to determine whether a given linestring geometry forms a closed ring. A linestring is considered a ring if it is closed, meaning that the start and end points of the linestring are the same. This function is particularly useful when working with polygons, as the outer and inner rings of a polygon must be valid closed rings.

Syntax

The syntax for the MariaDB ST_IsRing() function is as follows:

ST_IsRing(l)

• l: The linestring geometry to be checked for being a ring.

The function returns 1 if the linestring forms a closed ring, and 0 if it does not.

Examples

Example 1: Checking if a linestring is a ring

This example demonstrates how to check if a linestring geometry forms a closed ring.

SELECT ST_IsRing(ST_GEOMFROMTEXT('LINESTRING(0 0, 1 1, 2 0, 0 0)'));

The following is the output:

1

The linestring defined by the coordinates (0 0, 1 1, 2 0, 0 0) forms a closed ring, as the start and end points are the same (0 0). Therefore, the function returns 1.

Example 2: Checking if a linestring is not a ring

This example shows how to check if a linestring geometry does not form a closed ring.

SELECT ST_IsRing(ST_GEOMFROMTEXT('LINESTRING(0 0, 1 1, 2 0, 3 0)'));

The following is the output:

0

The linestring defined by the coordinates (0 0, 1 1, 2 0, 3 0) does not form a closed ring, as the start and end points are different. Therefore, the function returns 0.

Example 3: Checking if a polygon’s outer ring is valid

This example demonstrates how to check if the outer ring of a polygon geometry is a valid closed ring.

SELECT ST_IsRing(ST_ExteriorRing(ST_POLYGONFROMTEXT('POLYGON((0 0, 10 0, 10 10, 0 10, 0 0))')));

The following is the output:

1

The outer ring of the polygon defined by the coordinates (0 0, 10 0, 10 10, 0 10, 0 0) forms a valid closed ring, so the function returns 1.

Example 4: Checking if a polygon’s inner ring is valid

This example shows how to check if an inner ring of a polygon geometry is a valid closed ring.

SELECT ST_IsRing(ST_InteriorRingN(ST_POLYGONFROMTEXT('POLYGON((0 0, 10 0, 10 10, 0 10, 0 0), (2 2, 4 2, 4 4, 2 4, 2 2))'), 1));

The following is the output:

1

The inner ring of the polygon defined by the coordinates (2 2, 4 2, 4 4, 2 4, 2 2) forms a valid closed ring, so the function returns 1.

Example 5: Checking if a multilinestring geometry contains a ring

This example demonstrates how to check if a multilinestring geometry contains a linestring that forms a closed ring.

SELECT ST_IsRing(ST_GEOMFROMTEXT('MULTILINESTRING((0 0, 1 1, 2 0, 0 0), (3 3, 4 4, 5 3))'));

The following is the output:

1

The multilinestring geometry contains a linestring (0 0, 1 1, 2 0, 0 0) that forms a closed ring, so the function returns 1.

Related Functions

The following are some functions related to the MariaDB ST_IsRing() function:

• MariaDB ST_IsSimple() function is used to check if a given geometry is simple.
• MariaDB ST_IsValid() function is used to check if a given geometry is valid according to the OGC specifications.
• MariaDB ST_ExteriorRing() function is used to get the outer ring of a polygon geometry.
• MariaDB ST_InteriorRingN() function is used to get the Nth inner ring of a polygon geometry.
• MariaDB ST_NumInteriorRings() function is used to get the number of inner rings in a polygon geometry.

Conclusion

The ST_IsRing() function in MariaDB is a valuable tool for working with linestring geometries and validating the rings of polygon geometries. By determining whether a linestring forms a closed ring, you can ensure the validity of polygons and perform various spatial operations and analyses. The examples provided in this article demonstrate how to use the ST_IsRing() function effectively in different scenarios.