I’m trying to merge two adjacent large 3D independently meshed volume meshes at a single face, such that there is only overlap is right at that face and the nodes aren’t guaranteed to overlap. I could obviously retriangulate with Delaunay the entire merged mesh, but that would be very wasteful since I only need to retriangulate the boundary face. Is there a way with CGAL that I can force retriangulation on only the boundary nodes?
Perhaps I need to select the boundary nodes and all nodes within some alpha distance from the boundary, triangulate that and then merge that into the larger mesh.
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I have two meshes Mesh1 and Mesh2. Mesh1 does not necessarily have the same amount of vertices or faces as Mesh2.
What is the best way to "transition" between these two meshes smoothly?
Obviously, I could do a linear interpolation of some sort. But there are some problems beyond this that I need to solve. One problem that I'm facing is the "not necessarily have the same amount of vertices or faces" part. Maybe I need to bypass this restriction by taking one of my faces in one of the meshes and subdividing it until there's the same amount of faces in both meshes (would this adjust the result in a weird way, like an "explosion" in the subdivided part?)
However, the main problem is choosing which faces on Mesh1 correspond to Mesh2. Is there any algorithm that can accomplish this?
I have a file that contains many identical surfaces overlapped. How could I check if two surfaces are identical and overlapped and delete one of them using VBA functions?
As gdir said there is no direct way.
However you can compare some properties which you can measure such as surface area, length of boundary, number of verticies on the boundary, various extremum points, center of gravity, moments of inertia, etc.
Although these properties don't mathematically prove or disprove that two surfaces are the identical/different in most cases some combination of them will suffice.
I have been using the cgal library to generate convex hulls which are further used for discrete element simulations. Currently, I am trying to make the polyhedral particles break, which is right now implemented as plane clipping of the polyhedron. The problem is that after several (sometimes even one) clipping, the polyhedrons start having "bad" attributes, such as nearly degenerate faces, nearly coplanar edges or nearly degenerate edges, which cause problems in the contact calculation. I have been looking at CGAL/Surface_mesh_simplification routines and used the edge_collapse function, but it does not preserve convexity of the particles. Is there any way to use routines from cgal for convex polyhedra simplifications while preserving convexity?
You can try using the function isotropic_remeshing(). While there is no guarantee that the output will stay convex, the points are guaranteed to be on the input mesh. If you have some sharp edges you want to preserve, you can specify it to the function and it will take them into account.
I have 3 sets of point cloud that represent one surface. I want to use these point clouds to construct triangular mesh, then use the mesh to represent the surface. Each set of point cloud is collected in different ways so their representation to this surface are different. For example, some sets can represent the surface with smaller "error". My questions are:
(1) What's the best way to evaluate such mesh-to-surface "error"?
(2) Is there a mature/reliable way to convert point cloud to triangular mesh? I found some software doing this but most requests extensive manual adjustment.
(3) After the conversion I get three meshes. I want to use a fourth mesh, namely Mesh4, to "fit" the three meshes, and get an "average" mesh of the three. Then I can use this Mesh4 as a representation of the underlying surface. How can I do/call this "mesh to mesh" fitting? Is it a mature technique?
Thank you very much for your time!
Please find below my answers for point 1 and 2:
as a metric for mesh-to-surface error you can use Hausdorff distance. For example, you could use Libigl to compare two meshes.
To obtain a mesh from a point cloud, have a look at PCL
I need to generate a tetrahedral (volume) mesh of thin-walled object object. Think of objects like a bottle or a plastic bowl, etc, which are mostly hollow. The volumetric mesh is needed for an FEM simulation. A surface mesh of the outside surface of the object is available from measurement, using e.g. octomap or KinectFusion. Therefore the vertex spacing is relatively regular. The inner surface of the object can be calculated from the outside surface by moving all points inside, since the wall thickness is known.
So far, I have considered the following approaches:
Create a 3D Delaunay triangulation (which would destroy the existing surface meshes) and then remove all tetrahedra which are not between the two original surfaces. For this check, it might be required to create an implicit surface representation of the 2 surfaces.
Create a 3D Delaunay triangulation and remove tetrahedra which are "inside" (in the hollow space) or "outside" (of the outer surface) with Alphashapes.
Close the outside and inside meshes and load them into tetgen as the outside hull and as a hole respectively.
These approaches seem to be a bit inelegant to me, and they still have some pitfalls. I would probably need several libraries/tools for them. For 1 and 2, probably tetgen or another FEM meshing tool would still be required to create well-conditioned tetrahedra. Does anyone have a more straight-forward solution? I guess this should also be a common problem in 3D printing.
Concerning tools/libraries, I have looked into PCL, meshlab and tetgen so far. They all seem to do only part of the job. Ideally, I would like to use only open source libraries and avoid tools which require manual intervention.
One way is to:
create triangular mesh of surface points,
extrude (move) that surface to inner for a given thickness. That produces volume (triangular prism) mesh of a wall,
each prism can be split in three tetrahedrons.
The problem I see is aspect ratio.
A single layer of tetrahedra will not reproduce shell or bending behavior very well. A single element through the thickness will already require a large mesh. Putting more than one will likely break the bank in order to keep aspect ratios and angles acceptable.
I'd prefer brick or thick shell elements to tetrahedra in this case. I think the modeling will be easier and the behavior will be more faithful to the physics.