[vtkusers] Unstructured grid and coincident face rendering

Miorelli, Federico Federico.Miorelli at CGG.COM
Tue Aug 16 11:28:33 EDT 2016

Dear All,

I need to render a 3D grid which is horizontally structured but vertically unstructured (a corner-point grid with vertical pillars).
This is made of columns on a regular grid, each column is made up of a possibly different number of voxels whose Z coordinates are different from the neighboring columns. Voxels are displaced only in Z, so their faces are always perfectly vertical and touch the adjacent columns.

/     /|
*-----* o-----o
|     |/     /|
|     o-----o |
|     |     | |
*-----*     | o
|     |     |/
|     o-----o
|     |/

I am using vtkUnstructuredGrid with VTK_VOXEL cells to represent this. In each column I have (Nz+1)*4 points to represent the voxel edges, so that 4 points are shared between two vertically adjacent voxels. I cannot share points laterally because the Z values are different.

My problem is that I get very bad surface rendering artifacts at the boundaries between two columns, probably because both faces are rendered (see attached screenshot).

The only way I could get the correct rendering is by using OSPray in Paraview, but it's very slow on my hardware.

-    Is vtkUnstructuredGrid the best way to do this?

-    Is there a way to hint VTK that some faces are partially coincident, as to avoid double rendering?

I can provide code samples or data if needed.

Thank you for your help,
Best Regards


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