Make install doesn't install libraries nor headers

[Mapniv]

I configured gravity with cmake -DCMAKE_INSTALL_PREFIX=/home/user/installdir/gravity and then ran make -j2. Gravity was built with no warnings. Then I ran make install and only /home/user/installdir/gravity/bin/gravity was installed. I copied static library to its destination but now I have no idea where to find header files. I think that either make install should install libraries and headers or there should be target named install-dev that would do it.

I really would like to embed Gravity in my project as it seems to meet all my requirements. However without header files I can't even write a simple test program.