Include end bound in `pv.voxelize()` and `pv.voxelize_volume()` to avoid cropping the mesh

[GuillaumeBroggi]

Describe the feature you would like to be added.

Voxelizing a mesh with pv.voxelize() or pv.voxelize_volume() will crop the mesh.

For instance, for a simple cube with the default parameters, the mesh bounds are [-0.5, 0.5]:

import pyvista as pv
cube = pv.Cube()
cube

Header	Data Arrays
PolyData Information N Cells 6 N Points 8 N Strips 0 X Bounds -5.000e-01, 5.000e-01 Y Bounds -5.000e-01, 5.000e-01 Z Bounds -5.000e-01, 5.000e-01 N Arrays 3	Name Field Type N Comp Min Max Normals Points float32 3 -1.000e+00 1.000e+00 TCoords Points float32 2 -1.000e+00 1.000e+00 FaceIndex Cells int64 1 0.000e+00 5.000e+00

After voxelization, the mesh bounds are [-0.5, 0.3], the missing 0.2 corresponding to a missing row of cells:

pv.voxelize(cube, density=0.2)

Header	Data Arrays
UnstructuredGrid Information N Cells 64 N Points 125 X Bounds -5.000e-01, 3.000e-01 Y Bounds -5.000e-01, 3.000e-01 Z Bounds -5.000e-01, 3.000e-01 N Arrays 2	Name Field Type N Comp Min Max vtkOriginalPointIds Points int64 1 0.000e+00 1.240e+02 vtkOriginalCellIds Cells int64 1 0.000e+00 6.300e+01

One could expect the cube mesh to remain whole. Even if cropping is the intended behavior, there is no straightforward method to obtain a complete voxelized mesh of the cube.

As mentioned in https://github.com/pyvista/pyvista/issues/4312#issuecomment-1516994440, using np.linspace() instead of np.arange() would implement the proposed feature. Would a PR implementing this be welcome, or would it bring unwanted side effects?

Note

https://github.com/pyvista/pyvista/pull/6514 does not implement this behavior, instead the mesh is padded to enclose the cube:

pv.voxelize(cube, density=0.2, enclosed=True)

Header	Data Arrays
UnstructuredGrid Information N Cells 216 N Points 343 X Bounds -6.000e-01, 6.000e-01 Y Bounds -6.000e-01, 6.000e-01 Z Bounds -6.000e-01, 6.000e-01 N Arrays 2	Name Field Type N Comp Min Max vtkOriginalPointIds Points int64 1 0.000e+00 3.420e+02 vtkOriginalCellIds Cells int64 1 0.000e+00 2.150e+02

[tkoyama010]

Thank you for your suggestion. How about add it as an new option first? If the new method is better, we can make anothor breaking-change and make it the default. Pull requests are always welcome.

[GuillaumeBroggi]

In that case, I can start with the following signature that will not break anything:

voxelize(mesh, density=None, check_surface=True, enclosed=False, include_end_bound=False)

Maybe it could be made into a more generic function in the future, something like (just writing down some ideas):

voxelize(mesh, density=None, check_surface=True, range=["include", "exclude"])

where the behavior are defined for each bound:

• float: explicit value for the bound
• "exclude": exclude the bound
• "include": include the bound
• "enclosed": pad the mesh to ensure the bound is enclosed

The current behavior would be achieved with range=["include", "exclude"]. Using range=[float, float] or range=["include", "include"] would update the density if required to accommodate both bounds.

[tkoyama010]

Awesome. Let's try it!

[GuillaumeBroggi]

Implemented in both #6610 and #6611