opencv isn’t made for voxel data. one of the fundamental assumptions is that stuff is flat (a picture) and the third dimension is “attributes” (color).
the cv::Mat type, in C++, can carry a limited number of channels (512) but that still doesn’t mean the APIs (warpAffine) can just interpret data as multi-dimensional.
if you’re looking for speed, either write your kernel in python and slap numba on it, or some other thing like it.
or write your kernel as opencl or some other GPU-type thing.
GPUs are good at sampling in voxel data. trilinear interpolation is commonly available.
if you’re trying to visualize voxel data volumetrically, take a class on the subject. there are approaches that run well even on GPUs that are over a decade old.