code: public static double angleBetween( LineSegment l1, LineSegment l2 ) {
          double azimuth1 = azimuth(l1.p0, l1.p1);
          double azimuth2 = azimuth(l2.p0, l2.p1);
  
          if (azimuth1 < azimuth2) {
              return azimuth2 - azimuth1;
          } else {
              return 360 - azimuth1 + azimuth2;
          }
      }
docs: Calculates the angle between two {@link LineSegment}s.
  
  @param l1 the first segment.
  @param l2 the second segment.
  @return the angle between the two segments, starting from the first segment
  moving clockwise.