ENH: improve FindOssim script

CMake/FindOssim.cmake

@@ -14,14 +14,19 @@ endif()
 find_path( OSSIM_INCLUDE_DIR
            NAMES ossim/init/ossimInit.h )
 
-file(READ "${OSSIM_INCLUDE_DIR}/ossim/ossimVersion.h" _ossim_version_h_CONTENTS)
-string(REGEX REPLACE ".*# *define OSSIM_VERSION *\"([0-9.]+)\".*" "\\1" OSSIM_VERSION "${_ossim_version_h_CONTENTS}")
-string(REGEX REPLACE "([0-9]+)\\.([0-9]+)\\.([0-9]+)" "\\1" OSSIM_MAJOR_VERSION_NUMBER "${OSSIM_VERSION}")
-string(REGEX REPLACE "([0-9]+)\\.([0-9]+)\\.([0-9]+)" "\\2" OSSIM_MINOR_VERSION_NUMBER "${OSSIM_VERSION}")
-string(REGEX REPLACE "([0-9]+)\\.([0-9]+)\\.([0-9]+)" "\\3" OSSIM_PATCH_VERSION_NUMBER "${OSSIM_VERSION}")
-
-math(EXPR OSSIM_VERSION_NUMBER
-  "((${OSSIM_MAJOR_VERSION_NUMBER})*100+${OSSIM_MINOR_VERSION_NUMBER})*100+${OSSIM_PATCH_VERSION_NUMBER}")
+if(EXISTS "${OSSIM_INCLUDE_DIR}/ossim/ossimVersion.h")
+  file(READ "${OSSIM_INCLUDE_DIR}/ossim/ossimVersion.h" _ossim_version_h_CONTENTS)
+  string(REGEX REPLACE ".*# *define OSSIM_VERSION *\"([0-9.]+)\".*" "\\1" OSSIM_VERSION "${_ossim_version_h_CONTENTS}")
+  string(REGEX REPLACE "([0-9]+)\\.([0-9]+)\\.([0-9]+)" "\\1" OSSIM_MAJOR_VERSION_NUMBER "${OSSIM_VERSION}")
+  string(REGEX REPLACE "([0-9]+)\\.([0-9]+)\\.([0-9]+)" "\\2" OSSIM_MINOR_VERSION_NUMBER "${OSSIM_VERSION}")
+  string(REGEX REPLACE "([0-9]+)\\.([0-9]+)\\.([0-9]+)" "\\3" OSSIM_PATCH_VERSION_NUMBER "${OSSIM_VERSION}")
+  math(EXPR OSSIM_VERSION_NUMBER
+    "((${OSSIM_MAJOR_VERSION_NUMBER})*100+${OSSIM_MINOR_VERSION_NUMBER})*100+${OSSIM_PATCH_VERSION_NUMBER}")
+else()
+  if(NOT Ossim_FIND_QUIETLY)
+  message(WARNING "ossimVersion.h not found !")
+  endif()
+endif()
 
 find_library(OSSIM_LIBRARY
              NAMES ossim)