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Extracting Y-Coordinates (Latitude) from Geospatial Data in MariaDB


ST_Y Function

In MariaDB, ST_Y is a spatial function used within SQL statements to extract the Y-coordinate (latitude) from a geometry value stored in a spatial data type column. It's particularly useful when working with geospatial data like points, lines, or polygons.

Key Points

  • Output
    A double-precision floating-point number representing the Y-coordinate (latitude) of the geometry
  • Input
    A geometry value representing a spatial object (point, line, polygon)
  • Function
    ST_Y(geometry_column)

Example

SELECT ST_Y(location) AS latitude
FROM geospatial_data
WHERE ST_X(location) > -122.4  -- Filter points west of -122.4 longitude

In this example:

  • The WHERE clause filters for points west of a specific longitude (-122.4).
  • The result is aliased as latitude for clarity.
  • ST_Y(location) extracts the Y-coordinate (latitude) from each geometry in the location column.
  • geospatial_data is a table containing a column named location that stores geometry values.

Synonyms

ST_Y has a synonym: Y(). Both functions work identically.

  • For the X-coordinate (longitude), you can use the ST_X function.
  • ST_Y assumes the spatial reference system (SRS) defined for the geometry column. Ensure your data and queries use compatible SRS for accurate results.

Finding Points Within a Specific Latitude Range

SELECT *
FROM geospatial_data
WHERE ST_Y(location) BETWEEN 45 AND 50;  -- Find points between 45 and 50 degrees latitude

This query retrieves all records from the geospatial_data table where the Y-coordinate (latitude) of the geometry in the location column falls within the range of 45 and 50 degrees (inclusive).

Ordering Points by Latitude (North to South)

SELECT *, ST_Y(location) AS latitude
FROM geospatial_data
ORDER BY latitude DESC;  -- Order by latitude in descending order (north to south)

This query selects all columns along with an alias latitude for the extracted Y-coordinate. The results are then ordered by latitude in descending order, effectively sorting points from north (higher latitude) to south (lower latitude).

Calculating Distance Between Points (Combining with Other Spatial Functions)

SELECT p1.id AS point1_id, p2.id AS point2_id,
  ST_Distance_Sphere(p1.location, p2.location) AS distance_in_meters
FROM points_of_interest p1, points_of_interest p2
WHERE p1.id <> p2.id;  -- Exclude points from calculating distance to themselves

This example showcases how ST_Y can be used in conjunction with other spatial functions. Here, it calculates the distance between pairs of points stored in the points_of_interest table.

  • The WHERE clause ensures points aren't compared to themselves by excluding records where p1.id is equal to p2.id.
  • ST_Distance_Sphere calculates the approximate distance between two geometries using the sphere model (suitable for short distances on Earth).

Using ST_AsText or ST_AsGeoJSON to Convert Geometry to Text Format

  • Within the text representation, you can parse the latitude component using regular expressions or string manipulation techniques.
  • ST_AsText and ST_AsGeoJSON convert a geometry value into a human-readable text representation, typically in the form of a WKT (Well-Known Text) or GeoJSON string.

Combining Spatial Functions

  • The extracted latitude value can then be obtained using ST_Y on the newly created point geometry.
  • ST_PointFromText or ST_PointFromGeoJSON can create a new geometry point object from a text representation containing latitude and longitude.

Utilizing Custom Functions or Libraries

  • This approach offers greater flexibility but may require additional programming expertise.
  • For more complex scenarios, you can develop custom functions or utilize specialized geospatial libraries to extract and manipulate latitude coordinates.
  • When dealing with complex geometries or text-based representations, consider alternative approaches based on your skillset and project requirements.
  • For simple latitude extraction, ST_Y is generally the most efficient and straightforward option.
  • Choosing the appropriate method depends on the specific context, data format, and desired outcome.