How the IsRing() function works in Mariadb?

The MariaDB IsRing() function is used to assess whether a given LINESTRING is a ring. A ring is defined as a closed and simple curve, meaning it forms a complete loop without crossing itself.

Syntax

MariaDB IsRing() function’s syntax is as follows:

IsRing(g)

or

ST_IsRing(g)

Where g is the LINESTRING geometry to be tested. The function returns true if g is both closed (its start and end points are coincident) and simple (the line does not intersect itself at any point).

Examples

Example 1: Simple Closed LineString

This example checks whether a closed LINESTRING is a ring.

SELECT IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 0 1, 0 0)'));

The output for this statement is:

+-----------------------------------------------------------+
| IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 0 1, 0 0)')) |
+-----------------------------------------------------------+
|                                                         1 |
+-----------------------------------------------------------+

This indicates that the LINESTRING is a ring.

Example 2: Non-Closed LineString

Here, we check a LINESTRING that is not closed.

SELECT IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 0 1)'));

The output for this statement is:

+------------------------------------------------------+
| IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 0 1)')) |
+------------------------------------------------------+
|                                                    0 |
+------------------------------------------------------+

This result confirms that the LINESTRING is not a ring because it is not closed.

Example 3: Self-Intersecting LineString

To demonstrate IsRing() with a self-intersecting LINESTRING.

SELECT IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 1 0, 0 1, 0 0)'));

The output for this statement is:

+----------------------------------------------------------------+
| IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 1 0, 0 1, 0 0)')) |
+----------------------------------------------------------------+
|                                                              0 |
+----------------------------------------------------------------+

This shows that the LINESTRING is not a ring because it intersects itself.

Example 4: Valid Ring with Multiple Points

This example checks a valid ring with multiple defined points.

SELECT IsRing(ST_GeomFromText('LINESTRING(0 0, 2 0, 2 2, 0 2, 0 0)'));

The output for this statement is:

+----------------------------------------------------------------+
| IsRing(ST_GeomFromText('LINESTRING(0 0, 2 0, 2 2, 0 2, 0 0)')) |
+----------------------------------------------------------------+
|                                                              1 |
+----------------------------------------------------------------+

This confirms that the LINESTRING forms a valid ring.

Example 5: LineString with Repeated Points

IsRing() can also be used to check for repeated points in a LINESTRING.

SELECT IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 1 1, 0 0)'));

The output for this statement is:

+-----------------------------------------------------------+
| IsRing(ST_GeomFromText('LINESTRING(0 0, 1 1, 1 1, 0 0)')) |
+-----------------------------------------------------------+
|                                                         1 |
+-----------------------------------------------------------+

This indicates that the LINESTRING is not a ring because it has repeated points, violating the simplicity requirement.

Related Functions

Below are a few functions related to MariaDB IsRing():

• MariaDB ST_IsClosed() function is used to determine if a LINESTRING is closed.
• MariaDB ST_IsSimple() function is used to determine if a geometry has no self-intersections.
• MariaDB ST_GeometryType() function is used to return the geometry type of the input as a string.

Conclusion

The IsRing() function is an important tool in spatial analysis within MariaDB, allowing for the validation of LINESTRING geometries as rings. Understanding how to use IsRing() in conjunction with related functions can greatly enhance spatial data integrity and the accuracy of spatial operations. Ensuring that geometries meet the criteria of being both closed and simple is crucial for their correct usage in spatial computations.