I have a macro that creates an oriented bounding box around a part given 2 co-planar linear edges as input. I've been testing the edges for linearity with ICurve.IsLine.  My problem is that sometimes the edge curve is a BCurve so IsLine fails. Is there a way to test a BCurve for linearity as a work around?

The selected edges in the following screenshot fail the IsLine test yet the 3 faces shown are planar and mutually perpendicular.