message: ENH: Prevent build against an ITK install tree
diff: @@ -226,6 +226,10 @@ configure_file(cmake/RTKConfigVersion.cmake.in RTKConfigVersion.cmake @ONLY)
  # Configure and build ITK external module
  #=========================================================
  if(NOT ITK_SOURCE_DIR)
  + if(NOT EXISTS ${ITK_CMAKE_DIR}/ITKModuleMacros.cmake)
  + message(FATAL_ERROR "Modules can only be built against an ITK build tree; they cannot be built against an ITK install tree.")
  + endif()
  +
  list(APPEND CMAKE_MODULE_PATH ${ITK_CMAKE_DIR})
  include(ITKModuleExternal)
  else()
  