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From "Andrew Willis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-780) BSPTree class and recovery of a Euclidean 3D BRep
Date Sun, 22 Apr 2012 15:39:34 GMT

    [ https://issues.apache.org/jira/browse/MATH-780?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13259154#comment-13259154
] 

Andrew Willis commented on MATH-780:
------------------------------------

By the output, the index values displayed are all factors of 2. This seems to indicate you
are running the constructor for 2D shapes which is commented out with an if (false) {} statement
in the main() function.
I you use the constructor:

public BSPMesh2(float[] coords, int[] indices)

Then your indices should be factors of 3.

If you run the 2D shape constructor on the 3D points (cubeIndices, cubeCoords) strange things
will occur as you mention.

I've attached yet another BSPMesh2.java with all extraneous code stripped out.

The code constructs a cube from a set of triangles. Each face (having 4 vertices) is triangulated
by adding an edge across the diagonal of the face, i.e., a quad face with vertex indices 0
1 2 3 becomes the following two triplets of indices {0 1 2} {2 1 3} as two triangles.
Hence each face (normally 4 SubLines has 6 subLines (one redundant across the diagonal and
these redundant lines have opposing directions (subline 1 2 and subline 2 1)). I am working
towards converting generic triangular meshes to BSPTrees (and back to meshes). This is a standard
for triangular mesh representations.

I hope this helps clarify.
                
> BSPTree class and recovery of a Euclidean 3D BRep
> -------------------------------------------------
>
>                 Key: MATH-780
>                 URL: https://issues.apache.org/jira/browse/MATH-780
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>         Environment: Linux
>            Reporter: Andrew Willis
>              Labels: BSPTree, euclidean.threed
>         Attachments: BSPMesh2.java, BSPMesh2.java, BSPMesh2.java, BSPMesh2.java
>
>
> New to the work here. Thanks for your efforts on this code.
> I create a BSPTree from a BoundaryRep (Brep) my test Brep is a cube as represented by
a float array containing 8 3D points in(x,y,z) order and an array of indices (12 triplets
for the 12 faces of the cube). I construct a BSPMesh() as shown in the code below. I can construct
the PolyhedronsSet() but have problems extracting the faces from the BSPTree to reconstruct
the BRep. The attached code (BSPMesh2.java) shows that a small change to 1 of the vertex positions
causes/corrects the problem.
> Any ideas?

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