rework of world altitude calculation.

src/engine/net/client/handlers/PlaceAssetMsgHandler.java

@@ -792,10 +792,11 @@ public class PlaceAssetMsgHandler extends AbstractClientMsgHandler {
         ZoneManager.addPlayerCityZone(zoneObject);
         serverZone.addNode(zoneObject);
 
-        zoneObject.generateWorldAltitude();
+        zoneObject.worldAltitude = ZoneManager.caclulateWorldAltitude(zoneObject);
 
         cityObject.setParent(zoneObject);
         cityObject.setObjectTypeMask(MBServerStatics.MASK_CITY); // *** Refactor : should have it already
+
         //Link the tree of life with the new zone
 
         treeObject.setObjectTypeMask(MBServerStatics.MASK_BUILDING);