Length 3D

proc _length3d {x1 y1 z1 x2 y2 z2} {
  # Procedure to determine 3d length of 2 point line.
  set dx [expr $x1 - $x2]
  set dy [expr $y1 - $y2]
  set dz [expr $z1 - $z2]
  return [expr sqrt((sqrt(($dx * $dx) + ($dy * $dy)) * sqrt(($dx * $dx) + ($dy * $dy))) + ($dz * $dz))]
}