C# - Sweep single point / 3d curve offset using perpendicular frame coordinates

Hi,

I can't seem to find anything on this... I'm trying to do something (seemingly) simple: I'm sweeping a series of rectangular profiles along a 3d curve and this is done easily by orienting them to the perpendicular frame of the curve (Transform.PlaneToPlane()) and then sweeping them.

What I would like to then do is also get the center line of each of those profiles as they are swept, so the same thing as sweeping a point along that same curve, using the same perpendicular frame as the profiles do to control its position along the curve.

Is that possible? Am I missing something very obvious?

Thanks!

T