Navigation :

ST_MinimumClearance

ST_MinimumClearance
Prev   8.9. Spatial Relationships and Measurements   Next

Name

ST_MinimumClearance — Returns the minimum clearance of a geometry, a measure of a geometry's robustness.

Synopsis

float ST_MinimumClearance ( geometry g ) ;

Description

It is not uncommon to have a geometry that, while meeting the criteria for validity according to ST_IsValid (polygons) or ST_IsSimple (lines), would become invalid if one of the vertices moved by a slight distance, as can happen during conversion to text-based formats (such as WKT, KML, GML GeoJSON), or binary formats that do not use double-precision floating point coordinates (MapInfo TAB).

A geometry's "minimum clearance" is the smallest distance by which a vertex of the geometry could be moved to produce an invalid geometry. It can be thought of as a quantitative measure of a geometry's robustness, where increasing values of minimum clearance indicate increasing robustness.

If a geometry has a minimum clearance of e , it can be said that:

  • No two distinct vertices in the geometry are separated by less than e .

  • No vertex is closer than e to a line segement of which it is not an endpoint.

If no minimum clearance exists for a geometry (for example, a single point, or a multipoint whose points are identical), then ST_MinimumClearance will return Infinity.

Availability: 2.3.0 - requires GEOS >= 3.6.0

Examples 

SELECT ST_MinimumClearance('POLYGON ((0 0, 1 0, 1 1, 0.5 3.2e-4, 0 0))');
 st_minimumclearance
---------------------
             0.00032

See Also

ST_MinimumClearanceLine

Prev   Up   Next
ST_Distance  Home  ST_MinimumClearanceLine