static gboolean _coord_to_mapcoord ( VikMapSource *self, const VikCoord *src, gdouble xzoom, gdouble yzoom, MapCoord *dest );
static void _mapcoord_to_center_coord ( VikMapSource *self, MapCoord *src, VikCoord *dest );
static gboolean _coord_to_mapcoord ( VikMapSource *self, const VikCoord *src, gdouble xzoom, gdouble yzoom, MapCoord *dest );
static void _mapcoord_to_center_coord ( VikMapSource *self, MapCoord *src, VikCoord *dest );