About aplha shapes

[DmitryMedvedev]

Hello, friends!
I need some help with concave shape.
I have random set of points(>300 points) with high density which i want to turn in concave shape.
The problem appears when i try to do it with one of dyn4j Decomposer.
SweepLine.decompose and Bayazit gives me exceptions
Smth like this

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java.lang.NullPointerException
   at org.dyn4j.geometry.decompose.SweepLine.regular(SweepLine.java:258)
   at org.dyn4j.geometry.decompose.SweepLine.createTriangulation(SweepLine.java:128)
   at org.dyn4j.geometry.decompose.SweepLine.triangulate(SweepLine.java:79)

or this

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java.lang.IllegalArgumentException: A simple polygon cannot have crossing edges.

Even triangulation falls with exception.

Looks like i have "wrong" input points, right?

I beleive any cloud of points can be turned to concave polygon through maybe aplha shape method. Is dyn4j support it?
If not how can i get decomposition for my points clowd closest to alpha shape? Should i implement delaunay triangulation or this is already done in dyn4j? Any help very appreciated!

[William]

The dyn4j decomposition algorithms only support Simple Polygons without holes, not point clouds. There's no algorithm in dyn4j to build concave shapes from point clouds (there are classes to build convex shapes, but I don't think that's what you are looking for).

If you'd like to contribute a Delaunay triangulation that would be awesome.

William

[DmitryMedvedev]

Thx for fast responce! I like dyn4j and even it hasn't what i need i will try to do it by myself. I am newby user of this library, but if i will have acceptable solution for alpha shape i will make a contribution to support this lib.