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https://issues.apache.org/jira/browse/MATH-780?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13264594#comment-13264594
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Luc Maisonobe commented on MATH-780:
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I have made some progress analyzing this issue.
First, I confirm there is a problem in the code.
It appears that during the build, a very thin triangle occurs on a facet. In
the facet plane, the coordinates of the three vertices of this triangle are
(0.9999999997583233 -0.999998986721039), (-1.0000000000000002
-0.9999989867210387) and (-1.0000000000000002 -1.0). While extracting the
vertices of this triangle, the public getVertices method in PolygonsSet first
build the segments and then calls the private followLoop method to identify
their topology (i.e. how they connect to each other). The segments are properly
built and identified, but the followLoop method fails to connect them. It hits
a dedicated conditional statement considering the loop is below some predefined
threshold (despite it really is above this threshold) and it ignores the
triangle completely. Later, this breaks things as a node in the tree without a
boundary must be a leaf node which must contain a boolean attribute. However,
here we are not a a leaf node, we are at an internal node with an ignored
boundary.
So I think there are two bugs here. One bug for not identifying correctly the
triangle, and one bug for misclassifying an internal node as a leaf node.
The triangle identification bug will probably take some time to fix. The
internal/leaf node bug will probably be easy to fix.
I'll look into that, hopefully in the next few days.
> 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, 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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