execute_process(COMMAND svnversion $ENV{IGEP_ROOT}/uav_lib OUTPUT_VARIABLE SVN_REV)
string(REPLACE "\n" "" SVN_REV ${SVN_REV})
#set(SVN_REV "svnversion of $ENV{IGEP_ROOT}/uav_lib is ${SVN_REV}")

file(WRITE svnversion.h.txt "#define SVN_REV \"svnversion of $ENV{IGEP_ROOT}/uav_lib is ${SVN_REV}\\n\"\n")
# copy the file to the final header only if the version changes
# reduces needless rebuilds
execute_process(COMMAND ${CMAKE_COMMAND} -E copy_if_different
                        svnversion.h.txt @CMAKE_CURRENT_SOURCE_DIR@/src/unexported/svnversion.h)