Name
ST_FrechetDistance — Retorna a menor linha 3-dimensional entre duas geometrias
Synopsis
float ST_FrechetDistance(geometry g1, geometry g2, float densifyFrac = -1);
Descrição
Implements algorithm for computing the Fréchet distance restricted to discrete points for both geometries, based on Computing Discrete Fréchet Distance. The Fréchet distance is a measure of similarity between curves that takes into account the location and ordering of the points along the curves. Therefore it is often better than the Hausdorff distance.
When the optional densifyFrac is specified, this function performs a segment densification before computing the discrete Fréchet distance. The densifyFrac parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equal-length subsegments, whose fraction of the total length is closest to the given fraction.
Units are in the units of the spatial reference system of the geometries.
![[Note]](../images/note.png)
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A implementação atual suporta somente vértices como as localizações completas. Isto poderia ser expandido para permitir densidade arbitrária de pontos a serem usados. |
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The smaller densifyFrac we specify, the more acurate Fréchet distance we get. But, the computation time and the memory usage increase with the square of the number of subsegments. |
Desempenhado pelo módulo GEOS.
Availability: 2.4.0 - requires GEOS >= 3.7.0
Exemplos
postgres=# SELECT st_frechetdistance('LINESTRING (0 0, 100 0)'::geometry, 'LINESTRING (0 0, 50 50, 100 0)'::geometry);
st_frechetdistance
--------------------
70.7106781186548
(1 row)
SELECT st_frechetdistance('LINESTRING (0 0, 100 0)'::geometry, 'LINESTRING (0 0, 50 50, 100 0)'::geometry, 0.5);
st_frechetdistance
--------------------
50
(1 row)