Importing Quad Mesh from *.obj or *.ply

I would like to use Trelis to process an existing open quadrilateral mesh, but I am struggling to import the mesh. Specifically, while the file I import is a *.obj (or *.ply) object with quadrilateral elements (see attached image), when I import to Trelis, the object is immediately triangulated (again, see attached image). How does one go about importing a (open) quadrilateral mesh into Trelis?


While the mesh contains quads, an .OBJ file is made up of triangles. Each quad element will be saved as two triangles when exporting to .OBJ format. You can see this in the picture of triangles.

Often the triangle facets of an .OBJ or .STL file are not ideal for analysis, so deleting the mesh and re-meshing with Trelis will give you a much nicer mesh. When you import the .OBJ file, you can check the Create Geometry option and then delete the mesh to get the facet-based geometry. Set the meshing scheme on the facet geometry and mesh it with a new mesh.

Also, facet geometry in Trelis is not a solid like a .STEP, SolidWorks, or Parasolid file would be, so you will be limited in what you can do t0 the model in Trelis. For example, you cannot cut the model or remove surface like you could a solid model.

Thanks for your reply.

I agree that formats such as STL indeed are saved as triangulations. However, perhaps I am mistaken, but I do not believe that OBJ (or PLY) files save as triangles. Specifically, by associating more than three vertices to one face, one arrives at a polygonal (e.g. quad) object (see e.g. For example, a basic square mesh can be described in OBJ format as a single (quad) element as:

v 0 0 0
v 0 1 0
v 1 1 0
v 1 0 0
f 1 2 3 4

Saving the above as an OBJ file and importing into Trelis will yield a two-element triangulation. However, importing the above into other software (such as Rhinoceros 6) gives a single-quad mesh. Similarly, PLY files should support quads.

Am I correct in understanding, then, that Trelis does not currently support importing of quad meshes in OBJ and PLY formats?

We can take a look at it. Are you able to share the file? Either on the forum or send it to

Of course. Thank you.