Working with MultiPolygons in MariaDB: Alternatives to MultiPolygonFromWKB

• Well-Known Binary (WKB)
  WKB is a standard format for storing spatial data in binary form. It's a way to represent geometric objects like points, lines, polygons, and multipolygons in a compact and efficient manner.
• Multipolygon
  A multipolygon is a geometric object that can consist of one or more polygons. Each polygon is defined by a closed ring of linear coordinates.

MariaDB GEOMETRY object
MariaDB supports storing and manipulating spatial data using the GEOMETRY data type. The GEOMETRY object represents various geometric shapes, including polygons and multipolygons.

Function Usage

MultiPolygonFromWKB is not actually a built-in function in MariaDB. The information you found might be outdated. There is no official documentation for MultiPolygonFromWKB on the MariaDB website.

However, MariaDB provides similar functionalities through the ST_GeomFromWKB function. This function can handle various geometries, including multipolygons, by recognizing the geometry type encoded in the WKB.

SET @wkt_polygon = <your_multipolygon_wkt_string_here>;

SELECT ST_GeomFromWKB(@wkt_polygon) AS multipolygon;

Alternative Approach

1. Split your WKB multipolygon string into individual polygon WKB strings.
2. Use ST_PolygonFromWKB to convert each individual WKB string into a polygon GEOMETRY object.
3. Use GEOMCOLLECT to combine the individual polygon objects into a single multipolygon GEOMETRY object.

This approach offers more flexibility if you need to manipulate individual polygons within the multipolygon data.

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Example 1: Using ST_GeomFromWKB

SET @wkt_multipolygon = 
  <your_multipolygon_wkt_string_here>;

SELECT ST_GeomFromWKB(@wkt_multipolygon) AS multipolygon;

This code assumes you have a Well-Known Text (WKT) string representing your multipolygon data. You'll need to replace <your_multipolygon_wkt_string_here> with the actual WKT string. The ST_GeomFromWKB function will convert this WKT string into a MariaDB GEOMETRY object representing the multipolygon.

Example 2: Using ST_PolygonFromWKB and GEOMCOLLECT

SET @wkt_multipolygon = 
  <your_multipolygon_wkt_string_here>;

-- Split the WKT multipolygon string into individual polygon strings
SELECT SUBSTRING(@wkt_multipolygon, 
                  INSTR(@wkt_multipolygon, '(') + 1, 
                  INSTR(@wkt_multipolygon, ')') - INSTR(@wkt_multipolygon, '(') - 1)
  AS individual_polygon_wkt
FROM (SELECT @wkt_multipolygon) AS t
WHERE LOCATE('(', @wkt_multipolygon) > 0;

-- Convert individual WKT strings to polygon geometries
SELECT ST_PolygonFromWKB(individual_polygon_wkt) AS polygon
FROM (SELECT individual_polygon_wkt FROM (SELECT @wkt_multipolygon) AS t WHERE LOCATE('(', @wkt_multipolygon) > 0);

-- Combine polygon geometries into a multipolygon
SELECT GEOMCOLLECT(polygon) AS multipolygon
FROM (
  SELECT ST_PolygonFromWKB(individual_polygon_wkt) AS polygon
  FROM (SELECT individual_polygon_wkt FROM (SELECT @wkt_multipolygon) AS t WHERE LOCATE('(', @wkt_multipolygon) > 0)
);

This code first splits the WKT multipolygon string into individual polygon WKT strings. Then, it uses ST_PolygonFromWKB to convert each individual WKT string into a polygon GEOMETRY object. Finally, it combines all the polygon objects into a single multipolygon GEOMETRY object using GEOMCOLLECT.

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1. ST_GeomFromWKB
   This is the recommended approach. ST_GeomFromWKB is a versatile function that can handle various geometries, including multipolygons. It automatically recognizes the geometry type encoded in the WKB and creates the corresponding MariaDB GEOMETRY object.

SET @wkt_multipolygon = <your_multipolygon_wkt_string_here>;

SELECT ST_GeomFromWKB(@wkt_multipolygon) AS multipolygon;

1. ST_PolygonFromWKB and GEOMCOLLECT
   This approach offers more flexibility if you need to manipulate individual polygons within the multipolygon data.

• Combine polygon objects into a multipolygon
  Use GEOMCOLLECT to combine all the individual polygon objects into a single multipolygon GEOMETRY object.
• Convert individual WKB strings to polygons
  Use ST_PolygonFromWKB to convert each individual WKB string into a separate polygon GEOMETRY object.
• Split the WKB multipolygon string
  You can use string manipulation functions like SUBSTRING and LOCATE to extract individual polygon WKB strings from the main multipolygon WKB string.

SET @wkt_multipolygon = <your_multipolygon_wkt_string_here>;

-- Split the WKT multipolygon string into individual polygon strings
SELECT SUBSTRING(@wkt_multipolygon, 
                  INSTR(@wkt_multipolygon, '(') + 1, 
                  INSTR(@wkt_multipolygon, ')') - INSTR(@wkt_multipolygon, '(') - 1)
  AS individual_polygon_wkt
FROM (SELECT @wkt_multipolygon) AS t
WHERE LOCATE('(', @wkt_multipolygon) > 0;

-- Convert individual WKT strings to polygon geometries
SELECT ST_PolygonFromWKB(individual_polygon_wkt) AS polygon
FROM (SELECT individual_polygon_wkt FROM (SELECT @wkt_multipolygon) AS t WHERE LOCATE('(', @wkt_multipolygon) > 0);

-- Combine polygon geometries into a multipolygon
SELECT GEOMCOLLECT(polygon) AS multipolygon
FROM (
  SELECT ST_PolygonFromWKB(individual_polygon_wkt) AS polygon
  FROM (SELECT individual_polygon_wkt FROM (SELECT @wkt_multipolygon) AS t WHERE LOCATE('(', @wkt_multipolygon) > 0)
);

• If you need to access or manipulate individual polygons within the multipolygon, then the ST_PolygonFromWKB and GEOMCOLLECT approach offers more flexibility.
• If you only need to create a multipolygon object from a WKB string and don't need to manipulate individual polygons, then ST_GeomFromWKB is the simpler and recommended approach.