So I haven't been doing much with Radiance for the last year and a half or so, and suddenly something came up at work where it seemed the best solution. And actually, I've got a secret plan to make better and more widespread use of it where I work (Gensler). My day job is being their firmwide Revit guy, and the more folks we got using Revit, the more complete and nice models we've got to run design analysis tools on, Radiance being one of them.
Anyways, I figured out how to go from Revit to Radiance somewhat-quickly by using 3D Studio Max as an $3000 converter. Revit only exports DWG, DXF, DGN, and SAT's, and Max is the only 3D application that can import those DWG's and leave the Revit materials all intact (so you don't have to re-map stuff). So I then export out of Max as an .Obj, grouped by material, and I get a nice Radiance-ready OBJ file. Or so I'd hoped. I've got two issues, and I'll start with the first big one:
1. Revit likes to model glass as a solid plate, not a flat surface. So a bit of glass is a rectangular solid, not a flat plane. So when I try to make the windows into Illum's so that they spread light into the room, I'm getting errors and problems because I think it's looking for a flat plane with the normal pointing into the building. How important is it to have the Windows be a lightsource for interior renderings? Is there some way, via Mkillum or something, that I could quickly work around this issue? I can flatten the glass in Max, but that's an extra step and one that seems to also cause issues with zero-area light surfaces.
2. When I export out of Max, I get a .OBJ and a corresponding .MTL materials file. I currently use Grep and such to pull out all the material definition names out of the RAD file I get from OBJ2RAD, and then creating the .MAT radiance material file by hand. I'd love to hear a way to take the exported .MTL file and turn it into a starting point for my .MAT (short of having to write my own tool to do so...).
Now, we're just designers, and looking for design feedback not hard numbers. We'd be happy with something somewhat-accurate, for if/when we need 'real numbers' we'll typically turn to a lighting designer who know how to generate accurate numbers. But I figure, heck, we're generating these models anyways, why not try to put that to better use?
And sorry for the long post. As payback for all the help I've gotten here by lurking over the years I'll answer any Revit questions you might wanna ask...