visit export database sometimes duplicates vertices (STL binary format only)

[kkiesling]

I cannot fully figure out why this is happening, but in some cases, when exporting the isovolume surface from Visit in the first step of the process, the volume has extra vertices slightly off from other vertices. Furthermore, these extra vertices/surfaces ONLY occur if the surface is exported to a binary STL file (which is the current method). But it does not happen if exported to an ascii STL file.

In the example that an isosurface is a cube, one would expect 8 vertices, like is depicted by this 2D rendering: (o=vertex, ----=surface/face):

o ---------- o
|            |
|            |
o ---------- o

What we actually get, on occasion (it doesn't happen in all cases), is one surface disconnected from the rest of the surfaces, introducing extra vertices, like this (x= extra vertices created that are almost in the same location as the ones we would expect):

o ---------- o   x
|                |
|                |
o ---------- o   x

My current solution is to export the isosurfaces from visit as STLs but in ascii format, rather than binary, because that makes it disappear.

This is not reproducible in all cases, but is reproducible in one of my mesh files when using certain values.

[kkiesling]

to add: this causes issues because the merging of surfaces in adjacent volumes doesn't necessarily get the correct surface and will end up not recognizing that there is a surface there? I honestly don't quite get what is happening despite all my debugging.