For what 3D software? My UV Editor (Maya) has exactly this feature. It can be found here: http://www.creativecrash.com/maya/downloads/scripts-plugins/texturing/c/nightshade-uv-editor You specify a TD value (pixels per centimeter) and a texture map size, and it scales the selected UV shells accordingly.
I would like a script that scales the texel density of my uv shells to a number I type in without distorting the uvs, much like normalize in textools does, but with a type in of say 8px per 1 generic max unit. I tried the type in in textools, but its scaling some of my shells differently from the rest resulting in uneven…