+/* To be implemented by subclasses */
+void gis_viewer_center_position(GisViewer *viewer,
+ gdouble lat, gdouble lon, gdouble elev);
+
+void gis_viewer_project(GisViewer *viewer,
+ gdouble lat, gdouble lon, gdouble elev,
+ gdouble *px, gdouble *py, gdouble *pz);
+
+void gis_viewer_clear_height_func(GisViewer *self);
+void gis_viewer_set_height_func(GisViewer *self, GisTile *tile,
+ GisHeightFunc height_func, gpointer user_data,
+ gboolean update);
+
+void gis_viewer_begin(GisViewer *viewer);
+void gis_viewer_end (GisViewer *viewer);
+
+gpointer gis_viewer_add(GisViewer *self, GisObject *object,
+ gint level, gboolean sort);
+void gis_viewer_remove(GisViewer *self, gpointer ref);
+