let string_of_vector (v : vector) =
    let string_of_double (f : float) =
        let s = string_of_float f in
        let l = (String.length s) - 1 in
        if (String.get s l) <> '.' then s else s ^ "0" in
    "<" ^ (String.concat "," [(string_of_double v.x) ; (string_of_double v.y) ; (string_of_double v.z)]) ^ ">"