public LineVO(double x, double y, double z, double a, double b, double c)
 {
     this.start = new PointVO(x, y, z);
     this.end   = new PointVO(a, b, c);
 }
 public LineVO(PointVO start, PointVO end)
 {
     this.start = start;
     this.end   = end;
 }