Fetching: proj4rb-0.4.3.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing proj4rb:
        ERROR: Failed to build gem native extension.

        /usr/bin/ruby1.9.1 extconf.rb
checking for proj_api.h... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=/usr/bin/ruby1.9.1
        --with-proj-dir
        --without-proj-dir
        --with-proj-include
        --without-proj-include=${proj-dir}/include
        --with-proj-lib
        --without-proj-lib=${proj-dir}/lib
extconf.rb:6:in `<main>': Cannot find proj_api.h header (RuntimeError)


Gem files will remain installed in /var/lib/gems/1.9.1/gems/proj4rb-0.4.3 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/proj4rb-0.4.3/ext/gem_make.out