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ST_REDUCEPRECISION ​

Returns a GEOGRAPHY object with reduced precision, achieved by rounding all coordinates to a specified grid size. Features smaller than the grid size may be removed or altered, but the output will be a valid GEOGRAPHY object.

This function is generally more accurate near the equator and for smaller geographic scales. For large-scale projections, it may introduce significant distortions.

Syntax ​

sql
ST_REDUCEPRECISION(<input>, <gridsize>)

Arguments ​

  • <input>: A GEOGRAPHY object whose precision will be reduced.
  • <gridsize>: A FLOAT8 value representing the grid tolerance in meters.

Returns ​

Returns a GEOGRAPHY object with reduced precision. All coordinates are rounded to the specified grid size, and features smaller than this tolerance may be removed or altered. The resulting object will be a valid GEOGRAPHY.

Example ​

sql
SELECT
  ROUND(ST_DISTANCE(p1, p2)::NUMERIC, 2) AS original_distance_m,
  ROUND(ST_DISTANCE(ST_REDUCEPRECISION(p1, 20), ST_REDUCEPRECISION(p2, 20))::NUMERIC, 2) AS distance_after_20m_grid,
  ROUND(ST_DISTANCE(ST_REDUCEPRECISION(p1, 100), ST_REDUCEPRECISION(p2, 100))::NUMERIC, 2) AS distance_after_100m_grid
FROM (
  SELECT
    ST_POINT(10.0001, 50.0001)::GEOGRAPHY AS p1,
    ST_POINT(10.0003, 50.0003)::GEOGRAPHY AS p2
) AS points;
-- original_distance_m | distance_after_20m_grid | distance_after_100m_grid
-- ---------------------+-------------------------+--------------------------
--                26.00 |                   20.00 |                     0.00