MACRO(USE_OSSIMPLANET)
  FIND_PACKAGE(OSSIMPLANET)
  IF ((NOT OSSIMPLANET_FOUND) AND (${ARGC} LESS 1))
    USING_MESSAGE("Skipping because of missing OSSIMPLANET")
    RETURN()
  ENDIF((NOT OSSIMPLANET_FOUND) AND (${ARGC} LESS 1))
  IF(NOT OSSIMPLANET_USED AND OSSIMPLANET_FOUND)
    SET(OSSIMPLANET_USED TRUE)
    INCLUDE_DIRECTORIES(SYSTEM ${OSSIMPLANET_INCLUDE_DIR})
    SET(EXTRA_LIBS ${EXTRA_LIBS} ${OSSIMPLANET_LIBRARIES})
  ENDIF()
ENDMACRO(USE_OSSIMPLANET)