WIP: Features: Corendering and Isosurface Rendering

Feature 1: Corendreing of two or more volumes with MIP and Composite transfer functions. Specific applications to PET-CT visualization and visualization of labelled segmentations along with the data. The datasets need not have the same resolution or pixel type or extents in physical space. Interpolation into the two volumes during ray casting can be different as is the case with corendering segmentations and data.

Feature 2: Isosurface ray casting and difference isosurface highlights with specfic applications to CT Colonography. This adds the ability to perform isosurface ray casting with the interpolation method to achieve endoluminal visualization as in Virtual Colonoscopy/bronchoscopy. More than one volume can be specified for isosurface rendering with the use case being allowing (binary) switching between a cleansed colonic surface and un-cleansed colonic surface. The Difference isosurface highlight allows one to perform isosurface rendering on the cleansed volume (volume 2) with fragments of the surface that are digitally cleansed (different from volume 1 - the uncleansed volume) in a different color.