Archived discussion

Difference in number of STL triangles between versions

Data Exchange and Application FrameworkMon, 11/13/2017 - 08:101 reply

QuestionAuthorMon, 11/13/2017 - 08:10

I am converting STEP files to STL using, among other helper functions, the BRepMesh_IncrementalMesh function from OCC. I've performed the conversion from STEP to STL using version 6.8.0 and version 6.9.1. For shapes like cube and tetrahedron, the conversion generates the same number of STL triangles when using either version. But for curved shapes, like cylinder and sphere, the number of STL triangles is higher for version 6.9.1. Could someone please comment on or point me to the changes in algorithm/parameters between the two versions, that might be causing the difference in the number of STL triangles?

Discussion

1 archived reply

Posts are displayed in their archived order.

01Commenter-1Mon, 11/13/2017 - 12:25

point me to the changes in algorithm/parameters between the two versions

The changes between OCCT versions can be found in Release Notes document coming with each official release.
Category "Mesh" in the document describes changes related to BRepMesh, though changes in other domains potentially may also affect results.

But for curved shapes, like cylinder and sphere, the number of STL triangles is higher for version 6.9.1.

You haven't specified what is the scale of this increase in percents, so it is difficult to say if you are telling about modest fluctuation (which is perfectly fine after some modifications in algorithms) or noticeable change.
In the latter case, this usually means, that previous version of OCCT generated triangulation less-reliable to required deflection parameters; so that increase of amount of triangles was a result of a bugfix.