// VBA style
Dim dP(0 To 2) As Double
dP(0) = line.EndPoint.X - line.StartPoint.X
dP(1) = line.EndPoint.Y - line.StartPoint.Y
dP(2) = line.EndPoint.Z - line.StartPoint.Z
Dim length_dP As Double
length_dP = (dPX * dPX + dPY * dPY + dPZ * dPZ)^0.5
Dim L(0 To 2) As Double
L(0) = 1.5 * (dP(0) / length_dP)
L(1) = 1.5 * (dP(1) / length_dP)
L(2) = 1.5 * (dP(2) / length_dP)
Dim p1(0 To 2) As Double
Dim p2(0 To 2) As Double
p1(0) = line.StartPoint.X - L(0)
p1(1) = line.StartPoint.Y - L(1)
p1(2) = line.StartPoint.Z - L(2)
p2(0) = line.EndPoint.X + L(0)
p2(1) = line.EndPoint.Y + L(1)
p2(2) = line.EndPoint.Z + L(2)