one more attempt...

GeoModelVisualization/GXHitDisplaySystems/CMakeLists.txt

@@ -11,6 +11,7 @@ target_link_libraries( GXHitDisplaySystems
    PUBLIC Coin::Coin GXBase 
    PRIVATE Qt5::Core Qt5::Widgets ${HDF5_LIBRARIES} )
 target_include_directories( GXHitDisplaySystems PUBLIC
+   ${HDF5_CXX_INCLUDE_DIRS} 
    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
    $<INSTALL_INTERFACE:include> )
 source_group( "GXHitDisplaySystems" FILES ${HEADERS} )