how to install gendaylit?

dear all,

I'm new to Ubuntu.

after download "gendaylit.tar.Z" file and uncompress it, I get a folder named
"gendaylit", and then how to install it?
from the readme file, it seem I should edit the "makefile", but how to edit it?
my operating system is Ubuntu8.04, radiance 3.8

if can show step by step, it would be a great help.