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/*
 *   NAME
 *     coord_system
 *
 *   PURPOSE
 *     Create unit vector cartesian coordinate system from two points
 *
 *   NOTES
 *     
 *
 *   HISTORY
 *      wiener - May 8, 1995: Created.
 */

#include <euclid/copyright.h>
#include <euclid/geometry.h>

/*
 * Create coordinate system unit vectors given two points.  Origin is
 * assumed to be p1.  The vector u1 will have the same direction as the
 * vector from p1 to p2.  The unit vector u2 will be perpendicular to u2.
 * Returns the length of the vector from p1 to p2.
 */
double EG_coord_system(Point_d *p1, Point_d *p2, Point_d *u1, Point_d *u2)
{
  double ret;
  Point_d vect;
  
  EG_vect_sub(p2, p1, &vect);
  ret = EG_unit_vector(&vect, u1);
  u2->x = -u1->y;
  u2->y = u1->x;
  return(ret);
}