Selection Method for Volume Rendering

Dear Advacned programmers,

I am developing a Advanced Volume Rendering application. My Dataset is fo size 512512174. I use 3D Texture mapping(glTexImage3D) for generating volme.Since the size is huge,I have divided the entire volume into cells of size (323232) and each cell overlaps each other.

Now I need to find a region inside a volume.How to
use selection method for this finding/getting a region.

With regards

Write the texcoords into the colorbuffer. and read the needed pixel back.

Depends what you mean with a region. If you want to visualize an ISOsurface, you might want to create a Ray caster with a specified transfer function.

Good luck