Volume problems

Hi Marco, sorry to be opening so many issues…

I was playing around with the Volume class and found a couple small issues.

Threshold in range

There seems to be something weird with volume.threshold, if I only pass vmin or vmax it works as expected, but if I pass both it just returns the full volume and which particular values I use doesn’t change anything (in fact I can even pass vmax > vmin).

bug in volume.resample

  File "/Users/federicoclaudi/Documents/Github/BrainRender/workspace.py", line 41, in <module>
    vol.resample([.1, .1, .1])
  File "/Users/federicoclaudi/miniconda3/envs/brainrender/lib/python3.7/site-packages/vtkplotter/volume.py", line 291, in resample
    oldsp = self.GetSpacing()
AttributeError: 'Volume' object has no attribute 'GetSpacing'

setting volume transparency.

I have these volumes that are 0 in empty voxels and >0 where there’s something. The actual scalar value in non-empty voxels doesn’t matter, it’s just to label voxels belonging to different structures. So when rendering the volume I wanted all the 0 voxels to have alpha=0 and all the non-zero voxels to have alpha=1, but I couldn’t find an easy way to do that with the alpha argument of Volume. I ended up doing this which works fine:

    otf = vol.GetProperty().GetScalarOpacity()
    otf.RemoveAllPoints()
    otf.AddPoint(vmin, 0) # set to transparent
    otf.AddPoint(vmin+.1, alpha) # set to opaque
    otf.AddPoint(data.max(), alpha)

but I thought perhaps you wanted to build this possibility into the Volume class.

All the best, Fede

P.s.: The slicers in the latest release look awesome!

[marcomusy]

In the latest push this should be possible check: vtkplotter -ir interpolateVolume

line: # vol.alpha([(0.3,0.3), (0.9,0.9)]) # alternative way, by specifying (xscalar, alpha)

[FedeClaudi]

yep I think that would work, awesome thanks!