pgr_alphaShape - pgRouting Manual (3.8)

Migration of pgr_alphaShape

Starting from v3.8.0

Before Deprecation: The following was calculated:

• An alphaShape was calculated

After Deprecation:

PostGIS has two ways of generating alphaShape.

If you have SFCGAL, which you can install using

CREATE EXTENSION postgis_sfcgal

• Since PostGIS 3.5+ use CG_AlphaShape

• For PostGIS 3.5+ use the old name ST_AlphaShape

Other PostGIS options are * ST_ConvexHull * ST_ConcaveHull

Description

Returns the polygon part of an alpha shape.

Characteristics

• Input is a geometry and returns a geometry

• Uses PostGis ST_DelaunyTriangles

• Instead of using CGAL’s definition of alpha it use the spoon_radius

  • \(spoon\_radius = \sqrt alpha\)

• A Triangle area is considered part of the alpha shape when \(circumcenter\ radius < spoon\_radius\)

• The alpha parameter is the spoon radius

• When the total number of points is less than 3, returns an EMPTY geometry

Boost Graph Inside

Signatures

Example :

passing a geometry collection with spoon radius \(1.5\) using the return variable geom

SELECT ST_Area(pgr_alphaShape((SELECT ST_Collect(geom)
      FROM vertices), 1.5));
WARNING:  pgr_alphashape(geometry,double precision) deprecated function on v3.8.0
 st_area
---------
    9.75
(1 row)

Parameters

Return Value

See Also

• pgr_drivingDistance

• Sample Data

• ST_ConcaveHull

Indices and tables

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