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 \(circumcenter\ radius < spoon\_radius\)
• When the total number of points is less than 3, returns an EMPTY geometry

Signatures¶

Summary

pgr_alphaShape(geometry,   [spoon_radius])
RETURNS geometry

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

SELECT ST_Area(pgr_alphaShape((SELECT ST_Collect(the_geom) FROM edge_table_vertices_pgr), 1.5));
 st_area
---------
    9.75
(1 row)

Parameters¶

Return Value¶

See Also¶

• pgr_drivingDistance
• Sample Data network.
• ST_ConcaveHull

Indices and tables

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