VolPack is an external volume rendering package which is necessary for the 3D version of Amrvis.
You can download VolPack using git by typing the following command.
git clone https://ccse.lbl.gov/pub/Downloads/volpack.git
Note that the VolPack software was developed elsewhere and is governed by the license found at
We release it here for use with the 3D Amrvis software as a convenience. You can find more information about VolPack at http://graphics.stanford.edu/software/volpack.