void gis_viewer_set_location(GisViewer *viewer, gdouble lat, gdouble lon, gdouble elev);
void gis_viewer_get_location(GisViewer *viewer, gdouble *lat, gdouble *lon, gdouble *elev);
void gis_viewer_set_location(GisViewer *viewer, gdouble lat, gdouble lon, gdouble elev);
void gis_viewer_get_location(GisViewer *viewer, gdouble *lat, gdouble *lon, gdouble *elev);