Re: Point in Triangle

• To: Desiree Hilbring <hilbring@xxxxxxxxxxxxxxxxxxxx>
• Subject: Re: Point in Triangle
• From: Steve Emmerson <steve@xxxxxxxxxxxxxxxx>
• Date: Thu, 22 Feb 2001 10:06:01 -0700

Desiree,

I think that what you want to do can be done using the method 
SimpleSetIface.valueToInterp(float[][],int[][],float[][]).

Having said that, I'll now respond to your specific questions.

>Date: Thu, 22 Feb 2001 17:32:01 +0100 (MET)
>From: Desiree Hilbring <hilbring@xxxxxxxxxxxxxxxxxxxx>
>To: Steve Emmerson <steve@xxxxxxxxxxxxxxxx>
>Subject: Re: Point in Triangle 

The above message contained the following:

> thanks for your immediate answer.
> Unfortunately I am not familiar to Delaunay Triangulation.

Neither am I -- which makes this difficult.

> Ok, I understand the Delaunay Triangulation breaks up my set of points in
> a structure with triangles. I thinks this happens somewhere in Irregular2D
> set. But how are the triangles organized?

To answer that question, I believe that I would have to know what the
fields of the Delaunay class are (Edges, Tri, Vertices, Walk).  I don't.
The class visad.Delaunay has the following commentary, however:

  public int[][] Tri;        // triangles/tetrahedra --> vertices
                             //   Tri = new int[ntris][dim + 1]
  public int[][] Vertices;   // vertices --> triangles/tetrahedra
                             //   Vertices = new int[nrs][nverts[i]]
  public int[][] Walk;       // triangles/tetrahedra --> triangles/tetrahedra
                             //   Walk = new int[ntris][dim + 1]
  public int[][] Edges;      // tri/tetra edges --> global edge number
                             //   Edges = new int[ntris][3 * (dim - 1)];
  public int NumEdges;       // number of unique global edge numbers

> What is the method getNeighbours doing?  I am putting an 2D-array of
> floats in the the Irregular2D set, what is the int[][] array in get
> Neighbours? Does it somehow specify the indices,

IrregularSet.getNeighbors(int[][]) returns the neighboring sample points
for each sample point.  On input, "neighbors.length" must be greater
than or equal to "getLength()".  On output, "neighbors[i][j]" is the
index of the jth neighbor of sample point i.  I assume that each sample
point has, at most, 3 neighbors.

> which floats cooresponds to an triangle?
> Where can I find more Information about Irregular2D set?

At this point, I suggest that you start looking at the source code for
IrregularSet and Delaunay -- which is what I would have to do to answer
your questions.

I believe there are a couple of others on this list who know about
Delaunay triangulation.  Perhaps you'll hear from them.

Regards,
Steve Emmerson   <http://www.unidata.ucar.edu>