pgr_alphaShape
pgr_alphaShape
— Polygon part of an alpha shape.
Availability
- Version 3.0.0
- Breaking change on signature
- Old signature no longer supported
- Boost 1.54 & Boost 1.55 are supported
- Boost 1.56+ is preferable
- Boost Geometry is stable on Boost 1.56
- Version 2.1.0
- Added alpha argument with default 0 (use optimal value)
- Support to return multiple outer/inner ring
- Version 2.0.0
- Official function
- Renamed from version 1.x
Support
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
Parameter |
Type |
Default |
Description |
geometry |
geometry |
|
Geometry with at least \(3\) points |
spoon_radius |
FLOAT |
|
The radius of the spoon |
Return Value
Kind of geometry |
Description |
GEOMETRY COLLECTION |
A Geometry collection of Polygons |
See Also
Indices and tables