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Sample C# code implementing medial axis transform of a polygon using Voronoi diagram. In order to compile this code, download and reference NetTopologySuite, an open source spatial analysis library.
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using System; | |
using System.Collections.Generic; | |
using GeoAPI.Geometries; | |
using NetTopologySuite.Geometries; | |
using NetTopologySuite.IO; | |
using NetTopologySuite.Densify; | |
using NetTopologySuite.Triangulate; | |
namespace Skeleton | |
{ | |
class MainClass | |
{ | |
public static void Main (string[] args) | |
{ | |
IGeometryFactory gfactory = GeometryFactory.Fixed; | |
WKTReader greader = new WKTReader (gfactory); | |
//Create a new polygon instance | |
IGeometry polygon = greader.Read ("POLYGON((0 0, 0 10, 20 10, 20 20, 25 20, 25 10, 40 10, 40 0, 0 0))"); | |
//Densify polygon and store vertices in point array | |
IGeometry densification = Densifier.Densify (polygon, 1); | |
IGeometry[] points = new IGeometry[densification.NumPoints - 1]; | |
for (int i = 0; i <= points.GetUpperBound (0); i++) { | |
points[i] = gfactory.CreatePoint (densification.Coordinates[i]); | |
} | |
//Create a new point collection | |
IGeometryCollection pointsCollection = gfactory.CreateGeometryCollection (points); | |
//Build Voronoi diagram from point collection | |
VoronoiDiagramBuilder voronoiBuilder = new VoronoiDiagramBuilder (); | |
voronoiBuilder.SetSites (pointsCollection.Coordinates); | |
IGeometryCollection diagram = voronoiBuilder.GetDiagram (gfactory); | |
//Intersect Voronoi diagram with target polygon to get crust | |
IGeometry crust = diagram.Intersection (polygon); | |
//Create an empty geometry collection for the skeleton | |
IList<IGeometry> skeleton = new List<IGeometry> (); | |
//Populate skeleton from edges in crust | |
for (int i = 0; i < crust.NumGeometries; i++) { | |
IGeometry g = crust.GetGeometryN (i); | |
for (int j = 1; j < g.Coordinates.Length; j++) { | |
//For each polygon in crust get each edge | |
IGeometry edge = gfactory.CreateLineString (new Coordinate[] {g.Coordinates[j-1], g.Coordinates[j]}); | |
if (!edge.Touches (polygon.Boundary) && edge.Within (polygon)) { | |
skeleton.Add (edge); //If this edge does not touch polygon perimeter add to skeleton | |
} | |
} | |
} | |
} | |
} | |
} |
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maybe try moments of inertia/ellipsoid of inertia/principal axes?