ES|QL ST_SIMPLIFY function
geometry- Expression of type
geo_point,geo_shape,cartesian_pointorcartesian_shape. Ifnull, the function returnsnull. tolerance-
Tolerance for the geometry simplification, in the units of the input SRS
Simplifies the input geometry by applying the Douglas-Peucker algorithm with a specified tolerance. Vertices that fall within the tolerance distance from the simplified shape are removed. Note that the resulting geometry may be invalid, even if the original input was valid.
| geometry | tolerance | result |
|---|---|---|
| cartesian_point | double | cartesian_point |
| cartesian_point | float | cartesian_point |
| cartesian_point | integer | cartesian_point |
| cartesian_point | long | cartesian_point |
| cartesian_shape | double | cartesian_shape |
| cartesian_shape | float | cartesian_shape |
| cartesian_shape | integer | cartesian_shape |
| cartesian_shape | long | cartesian_shape |
| geo_point | double | geo_point |
| geo_point | float | geo_point |
| geo_point | integer | geo_point |
| geo_point | long | geo_point |
| geo_shape | double | geo_shape |
| geo_shape | float | geo_shape |
| geo_shape | integer | geo_shape |
| geo_shape | long | geo_shape |
ROW wkt = "POLYGON ((7.998 53.827, 9.470 53.068, 15.754 53.801, 16.523 57.160, 11.162 57.868, 8.064 57.445, 6.219 55.317, 7.998 53.827))"
| EVAL simplified = ST_SIMPLIFY(TO_GEOSHAPE(wkt), 0.7)
| wkt:keyword | simplified:geo_shape |
|---|---|
| POLYGON ((7.998 53.827, 9.470 53.068, 15.754 53.801, 16.523 57.160, 11.162 57.868, 8.064 57.445, 6.219 55.317, 7.998 53.827)) | POLYGON ((9.47 53.068, 15.754 53.801, 16.523 57.16, 8.064 57.445, 6.219 55.317, 9.47 53.068)) |
Low tolerance keeps almost every vertex
With a small tolerance, only collinear or near-collinear vertices are removed.
Mid tolerance smooths out the bumps
A tolerance of 0.2 is large enough to remove the small dents along each edge, leaving the underlying square.
Simplifying a circle with tolerance 0.5
Higher tolerances drop more vertices and the circle becomes a rough polygon.
Simplifying a circle to an octagon
Tolerance 1.0 reduces the circle to a regular octagon.
Simplifying a coastline at moderate tolerance
France's coastline simplified at tolerance 0.1 (roughly 10 km). Small bays and peninsulas survive but the coastline is noticeably smoother.
Simplifying a coastline at coarse tolerance
France's coastline simplified at tolerance 0.5 (roughly 50 km). Only the high-level shape of the country remains.
