How to get a list of lists of triangles using each vertex?

Question

Hi,
Its my first time working with Java3D, i just have experience with C++ and OpenGL, but im trying to implement a mesh simplification algorithm and get already problems with the data structures for the geometry info of the object.
I load an *.obj file with the object loader and now i dont know how to get the data i need.
I have to make loops over each vertex and get all triangles and their vertices used by that vertex. Is this possible with the given Java3D Functions or do i have to implement my own data structures for the triangle stuff?
What i need is following:
- List of vertex coordinates (thats the easy part, GeometryInfo.getCoordinates())
- List of triangle definitions
- List of lists of triangles using each vertex
I dont know how to get the last two, i tried around with IndexedTriangleArray but could not get anything to work..
The IndexTriangleArray should contain the triangle definitions if i understood that right. The first 3 entries in the array build the first triangle pointing to its vertices, the next 3 entries the second triangle,... Is that correct?
Does someone have an idea how to solve that problem?
Thanks a lot
spoertsch

Answer 1

I tried around a bit and figured something out, but with big objects with a lot of vertices it is quite inefficent and very slow...
I have the array of coordinates(GeometryInfo.getCoordinates) and the array of coordinate indices (GeometryInfo.getCoordinateIndices()). In the coordinate indice array each set of 3 indices builds an triangle.
CoordinateArray[CoordIndex] = Point3f (Vertex)
CoordinateIndiceArray[Index] = CoordIndex => Coordinate[CoordIndex] = Point3f . . . . . . }
CoordinateIndiceArray[Index + 1] = CoordIndex => Coordinate[CoordIndex] = Point3f . . . } triangle
CoordinateIndiceArray[Index + 2] = CoordIndex => Coordinate[CoordIndex] = Point3f . . . }
Now i iterate over each index of the coordinates array and search for this index in the indice array, to find out which triangle uses that vertex. If i find one i calculate the first index of the triangle and add it in an ArrayList<Integer>. So i get an ArrayList for each vertex in which the beginning indices of the triangles that uses that vertex are found. But these iterations are of course very slow for big objects with a lot of vertices, but i havent found a better way yet.
Does someone know a more efficent and faster way to do it?
Thanks
spoertsch
Edit: Sorry, just read about the movement of the forum, startet new Thread on java.net
Message was edited by:
spoertsch