Dear Dirk,
Yes.
You can create a model curve or a detail curve, and both reside on a sketch plane.
If you care about efficiency, you might care to reuse the sketch plane as much as possible.
Note that some existing samples create a new sketch plane for each individual curve, which is not a nice thing to do.
The Building Coder provides a number of samples, e.g.:
- Model and Detail Curve Colour -- http://thebuildingcoder.typepad.com/blog/2010/01/model-and-detail-curve-colour.html
- Detail Curve Must Indeed lie in Plane -- http://thebuildingcoder.typepad.com/blog/2010/05/detail-curve-must-indeed-lie-in-plane.html
- Model Curve Creator -- http://thebuildingcoder.typepad.com/blog/2010/05/model-curve-creator.html
- Generating a MidCurve Between Two Curve Elements -- http://thebuildingcoder.typepad.com/blog/2013/08/generating-a-midcurve-between-two-curve-elements.html
Also included in The Building Coder samples:
https://github.com/jeremytammik/the_building_coder_samples
Cheers,
Jeremy