api:dk11:net:tatukgis.ndk.tgis_topology.concavehull_tgis_shape_double

DK11 for .NET
| TatukGIS.NDK.TGIS_Topology.**ConcaveHull**
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Creates a concave hull based on the provided shape and edge length.

// C# public TGIS_ShapePolygon ConcaveHull( TGIS_Shape _shape, double _alpha );

' VisualBasic Public Function ConcaveHull( ByVal _shape As TGIS_Shape, ByVal _alpha As Double ) As TGIS_ShapePolygon

// Oxygene public function ConcaveHull( _shape : TGIS_Shape; _alpha : Double ) : TGIS_ShapePolygon;

Name | Type | Description |
---|---|---|

_shape | TGIS_Shape | source shape |

_alpha | double Double | maximum edge length |

Type | Description |
---|---|

TGIS_ShapePolygon | concave hull as a polygon |

The alpha parameter (maximum edge length) tells the algorithm that the length of each edge of the concave hull should not exceed this value. The algorithm starts with finding the convex hull and then attempts to “shrink” it by eliminating edges of length greater than alpha. It is not guaranteed that the concave hull will consist only of edges shorter than alpha because it may not be possible to eliminate some “long” edges in a reasonable manner. However, the output shape is guaranteed to be topologically correct (i.e. no self crossings, contains all input points).

The difference between a convex and a concave hull (sample data unit is kilometer, sample data size is 100×100 km):

Convex Hull | Concave Hull, alpha=1 | Concave Hull, alpha=20 |

2022/11/30 19:27