Definition of origin: indices_to_points and points_to_indices for voxel

[wkentaro]

If I run below code

import numpy as np
import trimesh
import trimesh.transformations as tf


matrix = np.ones((2,)*3, dtype=bool)
centers = trimesh.voxel.matrix_to_points(matrix, pitch=0.5, origin=(0,)*3)
print(centers)
centers = trimesh.voxel.matrix_to_points(matrix, pitch=0.5, origin=(0.5/2,)*3)
print(centers)
centers = trimesh.voxel.matrix_to_points(matrix, pitch=0.5, origin=(0.5,)*3)
print(centers)

the output is

[[-0.25 -0.25 -0.25]
 [-0.25 -0.25  0.25]
 [-0.25  0.25 -0.25]
 [-0.25  0.25  0.25]
 [ 0.25 -0.25 -0.25]
 [ 0.25 -0.25  0.25]
 [ 0.25  0.25 -0.25]
 [ 0.25  0.25  0.25]]
[[0.  0.  0. ]
 [0.  0.  0.5]
 [0.  0.5 0. ]
 [0.  0.5 0.5]
 [0.5 0.  0. ]
 [0.5 0.  0.5]
 [0.5 0.5 0. ]
 [0.5 0.5 0.5]]
[[0.25 0.25 0.25]
 [0.25 0.25 0.75]
 [0.25 0.75 0.25]
 [0.25 0.75 0.75]
 [0.75 0.25 0.25]
 [0.75 0.25 0.75]
 [0.75 0.75 0.25]
 [0.75 0.75 0.75]]

This shows currently, the definition of origin is right top corner of the first element. (①in the figure)

Maybe this is too late (since -0.5 is added for a while ago), but for me ② or ③ looks more reasonable as origin. By flipping sign of +-0.5 or removing it.
What do you think about this?

trimesh/trimesh/voxel.py

Line 657 in f785528

points = (indices - 0.5) * pitch + origin

trimesh/trimesh/voxel.py

Line 629 in f785528

indices = np.round((points - origin) / pitch + 0.5).astype(int)

[mikedh]

Not sure what the right answer here is. I think generally we probably want "points" to refer to the center of the voxel box?

[wkentaro]

I agree that design is the least confusing. In that case, we need to remove -0.5 and 0.5 and that is not backward compatible.

[mikedh]

Closed by #388