diff --git a/simgear/scene/tgdb/ReaderWriterSTG.cxx b/simgear/scene/tgdb/ReaderWriterSTG.cxx
index 0f80079..db77e95 100644
--- a/simgear/scene/tgdb/ReaderWriterSTG.cxx
+++ b/simgear/scene/tgdb/ReaderWriterSTG.cxx
@@ -92,6 +92,17 @@ static bool hasOptionalValue(sg_gzifstream &in)
     }
 }

+static double getGroundElevation(const double &lon, const double &lat, double &elev)
+{
+
+    SG_LOG( SG_TERRAIN, SG_ALERT,
+          "Compute Ground Elevation with lon=" << lon << " lat=" << lat << " offset=" << elev );
+
+    elev = 0.0; // Just for test, we need to implement the calcul
+
+    return elev;
+}
+
 ReaderWriterSTG::ReaderWriterSTG()
 {
     supportsExtension("stg", "SimGear stg database format");
@@ -273,7 +284,7 @@ ReaderWriterSTG::readStgFile(const std::string& absoluteFileName,
             in >> lon >> lat >> elev >> hdg;

             // Always OK to load
-            if ( token == "OBJECT_STATIC" ) {
+            if ( token == "OBJECT_STATIC" || token == "OBJECT_STATIC_AGL" ) {
                 if (!onlyTerrain) {
                     osg::ref_ptr<SGReaderWriterOptions> opt;
                     opt = new SGReaderWriterOptions(*staticOptions);
@@ -299,7 +310,7 @@ ReaderWriterSTG::readStgFile(const std::string& absoluteFileName,
                     }
                 }

-            } else if ( token == "OBJECT_SHARED" ) {
+            } else if ( token == "OBJECT_SHARED" || token == "OBJECT_SHARED_AGL" ) {
                 if (!onlyTerrain) {
                     osg::ref_ptr<SGReaderWriterOptions> opt;
                     opt = new SGReaderWriterOptions(*sharedOptions);
@@ -320,18 +331,25 @@ ReaderWriterSTG::readStgFile(const std::string& absoluteFileName,
                     }
                 }

-            } else if ( token == "OBJECT_SIGN" ) {
+            } else if ( token == "OBJECT_SIGN" || token == "OBJECT_SIGN_AGL" ) {
                 int size(-1);

                 if ( hasOptionalValue(in) ){
                     in >> size;
                 }
-                if (!onlyTerrain)
+                if (!onlyTerrain) {
+                    if ( token == "OBJECT_SIGN_AGL" )
+                        elev = getGroundElevation(lon, lat, elev);
+
                     signBuilder.addSign(SGGeod::fromDegM(lon, lat, elev), hdg, name, size);
+                }
             } else {
                 SG_LOG( SG_TERRAIN, SG_ALERT, absoluteFileName
                         << ": Unknown token '" << token << "'" );
             }
+
+            if ( token == "OBJECT_STATIC_AGL" || token == "OBJECT_SHARED_AGL" )
+                 elev = getGroundElevation(lon, lat, elev);

             if (node.valid()) {
                 osg::Matrix matrix;