Offset via RhinoCommon

### Curve.Offset Method (Plane, Double, Double, CurveOffsetCornerStyle)
# off_crv_b = new_crv.Offset(off_plane, (-1) * offset_value, off_tolerance, off_type)

### Curve.Offset Method (Point3d, Vector3d, Double, Double, CurveOffsetCornerStyle)
off_crv_b = new_crv.Offset(pt_start, Vector3d.ZAxis, (-1) * offset_value, off_tolerance, off_type)