System with ignition-math2 and ignition-math3 versions installed
 - find_package(SDFormat)
 - find_package(ignition-math2)

rivero@nium build $ (master) cmake .
-- Looking for ignition-math10
-- Looking for ignition-math9
-- Looking for ignition-math8
-- Looking for ignition-math7
-- Looking for ignition-math6
-- Looking for ignition-math5
-- Looking for ignition-math4
-- Looking for ignition-math3
--   - Found!
-- ignition-math3
-- /usr/include/ignition/math3
-- Boost version: 1.58.0
-- SDFORMAT variables
-- /usr/include/sdformat-4.3;/usr/include/ignition/math3;/usr/include
-- /usr/lib/x86_64-linux-gnu/libsdformat.so;ignition-math3
-- /usr/lib/x86_64-linux-gnu;/usr/lib/x86_64-linux-gnu;/usr/lib
-- ------------------
-- Ign3 variables
-- ignition-math3
-- /usr/include/ignition/math3
-- ------------------
-- Configuring done
-- Generating done
-- Build files have been written to: /home/jrivero/code/cmake_experiments/ign2_ign3/build


jrivero@nium build $ (master) cmake .. -DIGN_MATH_VERSION_TO_USE=2
-- /usr/lib/x86_64-linux-gnu/libignition-math2.so
-- /usr/include/ignition/math2
-- Boost version: 1.58.0
-- SDFORMAT variables
-- /usr/include/sdformat-4.3;/usr/include/ignition/math2;/usr/include
-- /usr/lib/x86_64-linux-gnu/libsdformat.so;/usr/lib/x86_64-linux-gnu/libignition-math2.so
-- /usr/lib/x86_64-linux-gnu;/usr/lib/x86_64-linux-gnu;/usr/lib
-- ------------------
-- Ign3 variables
-- /usr/lib/x86_64-linux-gnu/libignition-math2.so
-- /usr/include/ignition/math2
-- ------------------
-- Configuring done
-- Generating done
-- Build files have been written to: /home/jrivero/code/cmake_experiments/ign2_ign3/build