Save building and shadows only?

[hereagain]

Im trying to compose a birds eye view of a site where a new building is to be located. I have the basic model done in Max, but now i'm trying to figure out how to:

 

1. Set up the camera view so it most closely resembles the site photo I already have

 

2. Save out only the building and the shadow cast by the building

 

I know this has something to do with alpha channels and shadow matte material, both of which I know nothing about. Thanks for the help.

 

P.S. I'm rendering with Vray, if that makes any difference.

[kippu]

this is for (2)give the ground plane a basic vray material ... go into vray properties of that material ... switch on the matte object ... affect shadows ..alpha contribution -1(or)0 and save it as .tga

 

for (1) i would usually put the image in the environment slot and make it viewable in the viewport and adjust the camera to come close

 

hope it helps