[CMake] External project source

[Nicholas Yue]

Hi,

     There is an existing project I have access to that already have 
CMake configuration file but the way it is written requires alot of 
preprocessing steps (python, shell etc) before it is usable.

     I wanted to investigate a cleaner (truer to CMake original design 
purpose) usage of CMake,

     So, I have an  original-project directory which contains both the 
source and the CMakeLists.txt in a nested directory structure.

     I want to create my own CMake hierarchy (structure the same way) 
but reference the source code in the original-project directory location.

     How do I tell CMake to refer to source code at some other top level 
directory as a starting point.

     Is there such a concept in CMake ?

     At the risks of confusing matter, my closest example would be 
something vaguely resembling VPATH

Regards

-- 
Nicholas Yue
Graphics - RenderMan, Visualization, OpenGL, HDF5
Custom Dev - C++ porting, OSX, Linux, Windows
http://au.linkedin.com/in/nicholasyue