[vtkusers] Multiple volumes rendering with vtkGPUVolumeRayCastMapper or similar

amdelaossa adelaossa at gmail.com
Fri Aug 26 06:39:39 EDT 2016

Hi Álvaro,

Thanks a lot for your prompt answer!
See my comments below. 

> as you have noticed, multi-volume rendering is currently not supported in the vtkGPUVolumeRayCastMapper.  If you are building VTK with OpenGL2 however, it supports independent components so (depending on your use case) you might be able to render up to 4 volumes (one per component), provided you can arrange them in a four component array (this has the limitation that each component will need to have the same dimensions).  That said, we are working on giving support for multiple volumes in the next VTK release.

It is great to read that you are working on this feature for future releases of VTK. 
I think that it will be very useful for many people. 
In the mean time I would like to try your proposed approach of defining multiple components in one volume. 
Let me ask you something:
If data1, data2, data3 are my three independent three-dimensional data arrays, should I merge them first in a four-dimensional array where the first index is the component index?

> With regards to the solution you mentioned (https://github.com/bozorgi/VTKMultiVolumeRayCaster <https://github.com/bozorgi/VTKMultiVolumeRayCaster>), you could use it temporarily if it would solve your problem better than fitting the volumes as independent components.  It seems to implement a similar approach as we would do (connecting various inputs/ properties to the mapper) so it should not be extremely difficult to migrate to the official implementation in the future.  I have not tried it myself but please do let us know if you have any remarks once you try it.  As far as I know, if the python bindings are not explicitly disabled for these new classes then they should be also wrapped.

Alright. However this solution is currently not useful to me since it was implemented for VTK 5 (I think) and it fails to compile against VTK 7. 
So I am temporarily stuck here. I’d like to try your approach with the multi-components…

Could you give an rough estimation of when multiple volumes rendering with vtkGPUVolumeRayCastMapper will be available in VTK?

Thanks a lot!


> Regads,
> Álvaro
> ---------- Forwarded message ----------
> From: amdelaossa <adelaossa at gmail.com <mailto:adelaossa at gmail.com>>
> Date: Thu, Aug 25, 2016 at 10:00 AM
> Subject: [vtkusers] Multiple volumes rendering with vtkGPUVolumeRayCastMapper or similar
> To: vtkusers at vtk.org <mailto:vtkusers at vtk.org>
> Dear all, 
> we (a research team <http://plasma.desy.de/research/simulation_and_theory/index_eng.html> in DESY, Germany) are strongly interested in rendering multiple data volumes in the same view with VTK. 
> We chose VTK for our 3D visualisation project on beam-plasma interactions due to its extended functionality and features, 
> its open source character and because it is written in C++ with bindings for python.
> However, we will require to show multiple volumes in the same view (representing the data of different particle species in our simulations).
> We are currently using a vtkGPUVolumeRayCastMapper object for each data set, which is then connected to a vtkVolume. 
> The different vtkVolume objects are then added to the vtkRenderer.
> We have tried to use different vtkRenderer objects for the different vtkVolumes, 
> but still only the first volume on the first vtkRenderer is displayed. 
> Searching in the web, we have found the following (potential) solution:
> https://github.com/bozorgi/VTKMultiVolumeRayCaster <https://github.com/bozorgi/VTKMultiVolumeRayCaster>
> which is published here:
> http://www.ncbi.nlm.nih.gov/pubmed/24841148 <http://www.ncbi.nlm.nih.gov/pubmed/24841148>
> It consists on new vtk classes to handle multiple volumes rendering.
> As it might work well for our purposes, we would like to ask your opinion about this new classes.
> Are you planning to incorporate something like this in the official VTK distribution soon?
> If not, we will be interested in incorporating this new class into our personal VTK installation.
> Then the question is: Will be the python bindings automatically generated for these new classes?
> Thanks a lot for your support!
> Best regards,
> Alberto
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