let boolX = r.GetDirection.X >= 0.0
        let boolY = r.GetDirection.Y >= 0.0
        let boolZ = r.GetDirection.Z >= 0.0

        let tx =  match boolX with
                  |true -> (lowPoint.X - r.GetOrigin.X)/r.GetDirection.X
                  |false -> (highPoint.X - r.GetOrigin.X)/r.GetDirection.X
        let tx' = match boolX with
                  |true -> (highPoint.X - r.GetOrigin.X)/r.GetDirection.X
                  |false -> (lowPoint.X - r.GetOrigin.X)/r.GetDirection.X
        let ty =  match boolY with
                  |true -> (lowPoint.Y - r.GetOrigin.Y)/r.GetDirection.Y
                  |false -> (highPoint.Y - r.GetOrigin.Y)/r.GetDirection.Y
        let ty' = match boolY with
                  |true -> (highPoint.Y - r.GetOrigin.Y)/r.GetDirection.Y
                  |false -> (lowPoint.Y - r.GetOrigin.Y)/r.GetDirection.Y
        let tz =  match boolZ with
                  |true -> (lowPoint.Z - r.GetOrigin.Z)/r.GetDirection.Z
                  |false -> (highPoint.Z - r.GetOrigin.Z)/r.GetDirection.Z
        let tz' = match boolZ with
                  |true -> (highPoint.Z - r.GetOrigin.Z)/r.GetDirection.Z
                  |false -> (lowPoint.Z - r.GetOrigin.Z)/r.GetDirection.Z


        let t = max tx (max ty tz)

        let t' = min tx' (min ty' tz')

        match (t < t' && t' > 0.0) with
        |true -> Some(t, t')
        |false -> None