Issue & Reason
For background, Avizo 3D delivers 3D images to the viewer using a proprietary C++ codebase called OpenInventor. This codebase is, in turn, using OpenGL to do a lot of the management of the scene.
Formally, two overlapping Volume Rendering modules are not a supported function. That is because it is not supported by OpenInventor or OpenGL. Normally, the application tries to prevent the user from doing this by disallowing the creation of two Volume Rendering modules for the same data set. In practice, there are times when you may want to do this and try to get around the limitation.
The reason we do not have a support document on this topic is that it is not just ‘advanced usage,’ but it is not supported usage of the software. That does not make it impossible, but you will probably encounter a poor rendering or rendering less than desirable.
Suggested Solutions
1. The classic solution to this problem is to instead use Volren. This module uses a different rendering pipeline than Volume Rendering. However, the rendering is less accurate and may not fit your application.
2. Another common method is to mix a Surface View (or IsoSurface) with a Volume Rendering. Some known interactions between shadows and transparency are not always going to look correct, but otherwise, this is a practical way to see two datasets at once.
3. One could also use a shared clipping plane between two Volren (or even Volume Rendering) modules.
Reference: https://www.thermofisher.com/software-em-3d-vis/xtra-library/xtras/how-to-set-up-a-two-sided-clipping
4. If you are intent on using two Volume Rendering modules for the same data, I recommend using the Tcl console:
- Open it by clicking the “>” icon on the bottom-right of the interface
- You will need to create an additional Volume Rendering module and a Volume Rendering Settings module. Two commands do this:
- create HxVolumeRender2
- create HxVolumeRenderingSettings
- This should create two unattached modules in the "Project View". You will need to connect the two modules by pointing the Common Settings port of the Volume Rendering module to the Volume Rendering Settings module.
- Then, you can point the Volume Rendering Settings module to the data of your choice. This bypasses the GUI limits on attaching two or more Volume Rendering modules to one data set.