FUNCTION first_proj_axis

(* SCHEMA STRUCTURAL_FRAME_SCHEMA; *)

(* Modified for LPM/6 *)
FUNCTION first_proj_axis
	(z_axis, arg : direction) : direction;
  LOCAL
    x_axis : direction;
    v      : direction;
    z      : direction;
    x_vec  : vector;
  END_LOCAL;
  
  IF (NOT EXISTS(z_axis)) THEN
    RETURN (?) ;
  ELSE
    z := normalise(z_axis);
    IF NOT EXISTS(arg) THEN
      IF ((z.direction_ratios <> [1.0,0.0,0.0]) AND
          (z.direction_ratios <> [-1.0,0.0,0.0]))  THEN
        v :=  dummy_gri || direction([1.0,0.0,0.0]);
      ELSE
        v := dummy_gri || direction([0.0,1.0,0.0]);
      END_IF;
    ELSE
      IF  (arg.dim <> 3) THEN
        RETURN (?) ;
      END_IF;
      IF ((cross_product(arg,z).magnitude) = 0.0) THEN
        RETURN (?);
      ELSE
        v := normalise(arg);
      END_IF;
    END_IF;
    x_vec := scalar_times_vector(dot_product(v, z), z);
    x_axis := vector_difference(v, x_vec).orientation;
    x_axis := normalise(x_axis);
  END_IF;
  RETURN(x_axis);
END_FUNCTION;  (*  STEP Part 42 (modified in 2nd edition)  *)

Referenced By

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2023-03-25T00:11:39-04:00