[vtkusers] The order of indexes in tetrahedrons defined in VTK files

[Pearu Peterson]

Hi,

I have noticed that the order of indices matters when defining
tetrahedrons in a *.vtk file. For example, the two files given below
produce differently looking scenes in mayavi (when using SurfaceMap
module with opacity set to 0.65). The only difference in these files is
the ordering of indices in the CELLS section. In both cases there appear
artificial planes (in different places for different
ordering cases) that are supported by the sides of the cells.
When the grid is more dense, these artificial planes will disturb the
scene considerably.

My question is: is there any rule about the ordering of the indices such
that there will be no artificial planes?

Any hints about how to improve the quality of the case is appreciated.

Thanks,
	Pearu

File: cells1.vtk
# vtk DataFile Version 2.0
A12
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 7 float
0.0 0.765894022913 1.39781344961
0.497944830482 0.765894022913 1.39781344961
0.0 0.267949192431 1.39781344961
0.0 1.26383885339 1.89575828009
0.995889660964 1.26383885339 1.89575828009
0.0 0.267949192431 1.89575828009
0.0 0.267949192431 0.899868619128
CELLS 4 20
4 0 1 2 6
4 2 3 4 5
4 1 2 3 4
4 0 1 2 3
CELL_TYPES 4
10 10 10 10
POINT_DATA 7
SCALARS Scalars0 float 1
LOOKUP_TABLE default
1.0 3.63890178935e-17 1.0 1.0 1.10259829524e-17 1.0 1.0

File: cells2.vtk
# vtk DataFile Version 2.0
A12
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 7 float
0.0 0.765894022913 1.39781344961
0.497944830482 0.765894022913 1.39781344961
0.0 0.267949192431 1.39781344961
0.0 1.26383885339 1.89575828009
0.995889660964 1.26383885339 1.89575828009
0.0 0.267949192431 1.89575828009
0.0 0.267949192431 0.899868619128
CELLS 4 20
4 6 2 1 0
4 5 4 3 2
4 4 3 2 1
4 3 2 1 0
CELL_TYPES 4
10 10 10 10
POINT_DATA 7
SCALARS Scalars0 float 1
LOOKUP_TABLE default
1.0 3.63890178935e-17 1.0 1.0 1.10259829524e-17 1.0 1.0