void vik_viewport_set_center_screen ( VikViewport *vvp, int x, int y );
void vik_viewport_center_for_zonen ( VikViewport *vvp, struct UTM *center, int zone);
gchar vik_viewport_leftmost_zone ( VikViewport *vvp );
gchar vik_viewport_rightmost_zone ( VikViewport *vvp );
void vik_viewport_set_center_screen ( VikViewport *vvp, int x, int y );
void vik_viewport_center_for_zonen ( VikViewport *vvp, struct UTM *center, int zone);
gchar vik_viewport_leftmost_zone ( VikViewport *vvp );
gchar vik_viewport_rightmost_zone ( VikViewport *vvp );