FUNCTION base_axis

(* SCHEMA STRUCTURAL_FRAME_SCHEMA; *)

(* Modified for LPM/6 *)
FUNCTION base_axis
  (dim : INTEGER; axis1, axis2, axis3 : direction) : LIST [2:3] OF direction;
  LOCAL
    u      : LIST [2:3] OF direction;
    factor : REAL;
    d1, d2 : direction;
  END_LOCAL;
  
  IF (dim = 3) THEN
    d1 := NVL(normalise(axis3),  dummy_gri || direction([0.0,0.0,1.0]));
    d2 := first_proj_axis(d1,axis1);
    u := [d2, second_proj_axis(d1,d2,axis2), d1];
  ELSE
     IF EXISTS(axis1) THEN
      d1 := normalise(axis1);
      u := [d1, orthogonal_complement(d1)];
      IF EXISTS(axis2) THEN
        factor := dot_product(axis2,u[2]);
        IF (factor < 0.0) THEN
          u[2].direction_ratios[1] := -u[2].direction_ratios[1];
          u[2].direction_ratios[2] := -u[2].direction_ratios[2];
        END_IF;
      END_IF;
    ELSE
      IF EXISTS(axis2) THEN
        d1 := normalise(axis2);
        u := [orthogonal_complement(d1), d1]; 
        u[1].direction_ratios[1] := -u[1].direction_ratios[1];
        u[1].direction_ratios[2] := -u[1].direction_ratios[2];
      ELSE
        u := [dummy_gri || direction([1.0, 0.0]), dummy_gri ||
                                                direction([0.0, 1.0])];
      END_IF;
    END_IF;
  END_IF;
  RETURN(u);
END_FUNCTION;  (*  STEP Part 42 (modified in 2nd edition)  *)

Referenced By

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