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stephanfr / Cork

Cork Computational Library forked from source code by Gilbert Bernstein.
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Instability in intersection calculation #3

Open afalsafi opened 5 years ago

afalsafi commented 5 years ago

Hello, I would really appreciate if anyone could help me with the problem that I have encountered using cork. While using cork in order to calculate the intersection of two polyhedrons, The return polyhedron of cork intersection function becomes unstable when the external facets of the two input polyhedra coincide with each other in space. Has anyone else had such a problem with cork?? and is there anyone who can help me with this?

stephanfr commented 5 years ago

Cork is very sensitive to self-intersections or non-manifold models. I would check that first.

The test dataset I use has some very complex models and Cork runs fine on those but I am always interested in models that are correct but on which Cork fails.

If the models do not self intersect and are manifold, then if you send them to me I will take a look.

I am travelling right now through next week so it may take a day or two for me to respond.

Thanks !

Stephan

On Thu, May 9, 2019 at 6:31 AM afalsafi notifications@github.com wrote:

Hello, I would really appreciate if anyone could help me with the problem that I have encountered using cork. While using cork in order to calculate the intersection of two polyhedrons, The return polyhedron of cork intersection function becomes unstable when the external facets of the two input polyhedra coincide with each other in space. Has anyone else had such a problem with cork?? and is there anyone who can help me with this?

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/stephanfr/Cork/issues/3, or mute the thread https://github.com/notifications/unsubscribe-auth/AALH6M25ZOQY6QS4HJ5HNT3PUQRUBANCNFSM4HL2Q4HA .

stephanfr commented 5 years ago

Sorry, I just re-read your email.

"The return polyhedron of cork intersection function becomes unstable when the external facets of the two input polyhedra coincide with each other in space".

Yes - that is a problem and results in having non two manifold points or edges or self-intersecting surfaces. There is not a whole lot that can be done about it without changing the geometries themselves. Non two manifold surfaces are a problem for CSG libraries in general. Given the algorithm Cork uses, it is sensitive to self intersections and non two manifold meshes.

If you send me some examples, I can take a look. I added some code to better detect these error conditions, at a minimum even if I cannot fix the problem I would like to be sure that the right error message is returned instead of a broken polyhedron.

Beyond that, your best bet is simply to try to avoid self intersections or non two manifold points or edges in general.

Thanks !

Stephan

On Thu, May 9, 2019 at 5:49 PM Stephan Friedl stephanf01@gmail.com wrote:

Cork is very sensitive to self-intersections or non-manifold models. I would check that first.

The test dataset I use has some very complex models and Cork runs fine on those but I am always interested in models that are correct but on which Cork fails.

If the models do not self intersect and are manifold, then if you send them to me I will take a look.

I am travelling right now through next week so it may take a day or two for me to respond.

Thanks !

Stephan

On Thu, May 9, 2019 at 6:31 AM afalsafi notifications@github.com wrote:

Hello, I would really appreciate if anyone could help me with the problem that I have encountered using cork. While using cork in order to calculate the intersection of two polyhedrons, The return polyhedron of cork intersection function becomes unstable when the external facets of the two input polyhedra coincide with each other in space. Has anyone else had such a problem with cork?? and is there anyone who can help me with this?

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/stephanfr/Cork/issues/3, or mute the thread https://github.com/notifications/unsubscribe-auth/AALH6M25ZOQY6QS4HJ5HNT3PUQRUBANCNFSM4HL2Q4HA .

stephanfr commented 5 years ago

For clarity - the input to the algorithm is a pair of 3D, closed body, two manifold triangular meshes. The output is a 3D, closed body, two manifold triangular mesh.

Having the two bodies intersect at a point, line or surface results in an intersection output of a 1D point or 2D line or polygon. Those cannot be represented as a 3D body.

That is why this is not a failure of the code but an attempt to perform an operation that does not result in a solid geometry.

On Thu, May 9, 2019, 6:10 PM Stephan Friedl stephanf01@gmail.com wrote:

Sorry, I just re-read your email.

"The return polyhedron of cork intersection function becomes unstable when the external facets of the two input polyhedra coincide with each other in space".

Yes - that is a problem and results in having non two manifold points or edges or self-intersecting surfaces. There is not a whole lot that can be done about it without changing the geometries themselves. Non two manifold surfaces are a problem for CSG libraries in general. Given the algorithm Cork uses, it is sensitive to self intersections and non two manifold meshes.

If you send me some examples, I can take a look. I added some code to better detect these error conditions, at a minimum even if I cannot fix the problem I would like to be sure that the right error message is returned instead of a broken polyhedron.

Beyond that, your best bet is simply to try to avoid self intersections or non two manifold points or edges in general.

Thanks !

Stephan

On Thu, May 9, 2019 at 5:49 PM Stephan Friedl stephanf01@gmail.com wrote:

Cork is very sensitive to self-intersections or non-manifold models. I would check that first.

The test dataset I use has some very complex models and Cork runs fine on those but I am always interested in models that are correct but on which Cork fails.

If the models do not self intersect and are manifold, then if you send them to me I will take a look.

I am travelling right now through next week so it may take a day or two for me to respond.

Thanks !

Stephan

On Thu, May 9, 2019 at 6:31 AM afalsafi notifications@github.com wrote:

Hello, I would really appreciate if anyone could help me with the problem that I have encountered using cork. While using cork in order to calculate the intersection of two polyhedrons, The return polyhedron of cork intersection function becomes unstable when the external facets of the two input polyhedra coincide with each other in space. Has anyone else had such a problem with cork?? and is there anyone who can help me with this?

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/stephanfr/Cork/issues/3, or mute the thread https://github.com/notifications/unsubscribe-auth/AALH6M25ZOQY6QS4HJ5HNT3PUQRUBANCNFSM4HL2Q4HA .