VolumeController widget function


The VolumeController of vtk.js looks like this:

In the lower box, a sort of grey sort of mountain landshape is displayed in the background. I noticed that this is different for each data. Does someone know what the function of this is and what this means?

I also have another question. On the vtk.js volumeviewer page is mentioned that a Gaussian is created for the opacity transfer function when clicking on a specific location in the lower box. Why is specifically a gaussian created? What is the purpose of this?
Thanks a lot in advance!

The grey area is the histogram of the volume, so you can see where the data is and use that information when adjusting your transfer function. Gaussian is just what we picked to easily modify the transfer function (width height center) so just a few parameters that can easily be mapped to mouse events. But nothing special about it.