Same STL file, but different vertices count for Rhino and other CAD codes


I have a STL file to import into Rhino, and it counts 162035 vertices. However, when the same STL file is imported into other CAD codes (like Paraveiw, hypermesh, ICEM), it counts 112094 vertices. And more surprising: Rhino and other codes count the same cell (face) numbers.
What’s the issue? Could anyone give some clues?
Thanks a lot!

Hello - if you Weld the mesh on opening in Rhino, at say 90 degrees, then check the vertex count, it should go down.


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Hi @pascal, thank you so much for your lightening (< 1 min) reply!
Yes, your method works! And I tried several time until with 180 degrees :slight_smile:
Thanks again!

It is important to note that STL files are simply a list of vertexes that make up independent mesh triangles. No face normals, no join information. There is not information if a collection of triangles make up which objects. In this way is a poor format in that it loses so much information that normally travels with mesh formats. On the other hand, it is quite simple to write.

Because there is no information on joins, each program must pre-process and STL file to guess at what is joined, what is welded, etc. So many times there could be quite a difference between one application and another in how the values are read.

Almost any other format contains more information about the meshes they contain.

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Thank you for your detailed explanation, @scottd!