Inconsistent rendering of point data in hexahedrall cells

ParaView Support
1

Hi,

When I load a vtkUnstrucuredGrid and color by scalars, I was expecting the coloring to be symetrical, but it looks like there is an interpolation error:

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here’s my data:

# vtk DataFile Version 4.2
vtk output
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 16 float
0	0	0
0.1	0	0
0.1	0.1	0
0	0.1	0
0	0	0.1
0.1	0	0.1
0.1	0.1	0.1
0	0.1	0.1

0.2	0	0
0.3	0	0
0.3	0.1	0
0.2	0.1	0
0.2	0	0.1
0.3	0	0.1
0.3	0.1	0.1
0.2	0.1	0.1

CELLS 2 18
8 0 1 2 3 4 5 6 7
8 8 9 10 11 12 13 14 15

CELL_TYPES 2
12
12

POINT_DATA 16
SCALARS active_set int 1
LOOKUP_TABLE default
0 1 1 0
0 0 0 0
1 0 0 1
0 0 0 0

I’m using ParaView 5.9.0 on Windows 10

Thank you!
- Jorge

2

This is a known issue that is discussed at length here: Unsymmetric contour rendered by symmetric data.

The issue is that as an optimization step, rendering systems will divide primitives into triangles, and that causes the interpolation to change from non-simplexes. Normally the difference is minor, but when you have large cells with dramatically changing data, as is your case, then the difference is much greater.

1 Like
3

Oh, I see
Thank you for your answer! @Kenneth_Moreland