Andy,

At the moment you can rotate the volume and zoom the image. However, the volume is always centered in the screen and pivots around the image origin. It would not be hard to implement this, you would just want to modify the procedure "SetOrtho()" in gl_core_3d (if you are building for OpenGL 3.3 Core) or gl_legacy_3d (if you care building for legacy OpenGL 2.1). I am pretty busy right now, but if this is important to you, why not go to github and generate a "new issue" which you can label as an enhancement.

Your toolbox looks fantastic!