[BUG] Numpy array to openvdb conversion returns a shuffled volume

[Tomaubier]

Environment

Operating System: macOS 14.1.1
Version: Blender 4.0.2

Issue

I have a 3d numpy array containing results from a simulation which I want to render using Blender. When visualized using napari I get the expected result:

Using pyopenvdb’s copyFromArray function, I’ve attempted to import the same array within blender.

import bpy, os
import pyopenvdb as vdb
import numpy as np

# --- Scenario 3 -> .npy import of the actual array ---
actual_vol_path = '/Users/tomaubier/actual_volume.npy'
volume = np.load(actual_vol_path)

# numpy array to openvdb object
vecgrid = vdb.DoubleGrid()
vecgrid.name = 'density'
vecgrid.copyFromArray(volume)

# Saving the openvdb object
vdb_file_path = f'/Users/tomaubier/openvdb_volume.vdb'
vdb.write(vdb_file_path, grids=[vecgrid])

# Importing the volume within blender
bpy.ops.object.volume_import(filepath=vdb_file_path, files=[])

However this code gives me what looks like a array of shuffled values.

I then made up an arbitrary array defined as

# Making up a MWE volume
x = np.linspace(0, 5*np.pi, x_shape)
y = np.linspace(0, np.pi, y_shape)
z = np.linspace(0, .2*np.pi, z_shape)
X, Y, Z = np.meshgrid(x, y, z)
mwe_volume_presave = np.cos(X*Y*Z)

and got the expected result:

To check whether or not saving and loading the values in a .npy file could be at the root of this issue, I rendered the same dummy array after saving and loading it in a numpy file. As expected this test led to the same rendered output.

I currently don’t have any clues as to whats going on.. Do you guys have any ideas?
If anyone wants to perform tests with the data I used, I've created a repo with the blender file and .npy array.
Best.

[Dxyk]

Hi, I recently ran into the same problem. This might be a bit late, but I suspect there is an issue/implicit assumption with how OpenVDB copies data from Numpy arrays.

For what it's worth, what fixed it for me was making the array contiguous with np.ascontiguousarray before calling copyFromArray.

[Tomaubier]

Awesome that solved the issue!
No idea why this would be necessary though..