MeshSplit Bug Example

Hi,

I am having some trouble accurately splitting/trimming the mesh in this file.

MeshSplit Error.3dm (140.3 KB)

The result does not follow the polyline at the corner, almost creating a fillet at this point. I need a corner here!

Additionally, projecting the polyline to the mesh follows this contour created by MeshSplit however placing a point at this corner and projecting it to the mesh gives an accurate result.

Does anyone know of a workaround for this?

Thanks

Hi Waltzie- I see that, thanks - it is the Projection part that is messing up. Workaround: Extrude the curve through the mesh, Mesh the result, MeshIntersect to get a new curve in place and and use that curve to split the mesh with SplitMeshWithCurve (not MeshSplit) …

thanks,

-Pascal

Hi Pascal,

Thanks for that. I see that it also works if I use MeshSplit with the extruded curve (surface). Is this a fluke? Is your method the most reliable way of achieving an accurate result or can I just use the surface without meshing it and intersecting the meshes? I will be placing this into a script and I want it to work every time.

Thanks for the help.

Hi wattzie- I got the same discrepancy when I used the extruded curve directly in MeshSplit and had to resort to SplitMeshWithCurve - I’ll double check how that worked but I’d say this is a bug/weakness… Rhino’s mesh intersection/split/trim stuff is not all that reliable in many cases.

-Pascal

Hi Pascal,

Is this being looked at for V6?

Thanks

I am lobbying for this… yes.

-Pascal

Thanks. I think that rhino is a great program however it often falls down with the mesh tools. I am using stl meshes obtained from 3d scans quite extensively in rhino and I keep encountering little bugs like this in the mesh tools in Rhino and RhinoPython.

Thanks for the help

Hi Pascal,

I have been trying to implement this in python and it seems like most of these commands ( _Mesh, _MeshIntersect and _SplitMeshWithCurve ) are not available in there. Do you have any idea how i could do this reliably in python?

Thanks

Well, however you invoke it, the underlying code is, well, weak, so it will not be any better or worse, in terms of success, than the Rhino commands I would say.

-Pascal

Hello,

Same for me. I find myself trying to implement a robust semi-automatic design workflow based on meshes from surface laser scans and the curve/mesh, mesh/mesh intersections are really the weakest point of Rhino.

Please, use CGAL or another robust geometric library to re implement the core algorithms of your mesh objects.

See

http://discourse.mcneel.com/t/projectcurvetomesh-bug-on-triangle-edges/24760

for the possibility of using CGAL to bypass these problems.