When placing a UDF interactively, it is possible to select a single axis of a coordinate system as reference. How can this be done programmatically with TOOLKIT or OTK? The problem is: The coordinate system axis is not a Modelitem and cannot be directly converted to a Selection.
Just in case you are still looking for an answer on this, here goes. Typically a UDF needs to be placed relative to geometry so that it aligns and references properly so I would expect the UDF placement to prompt me to specify the new alternative placements. Unless of course the by some method you have been able to constrain all of the geometry to a CSYS. I doubt you are doing that. You also mention the axis of a CSYS, ther is no axis on a CSYS for it to be an axis it would need to be defined as such. CSYS show directional vectors on screen, these are not axes, though they may look like that to you.
If you don't have experience of UDF placement. You should tick the advanced reference control icon when you attempt to place your UDF. This will allow you to see on one screen the source file and on the other the destination geometry so that you can choose the correct alternative placements. For example tou may have dtm1 in the source file but want to use dtm8 in the destination.
I hope that this helps you.
Thanks for the answer. I am aware that the X, Y and Z 'axes' of a coordinate system in Creo are not geometry items like the axis of a cylinder or that of an axis feature. And that exactly is my problem. When defining the reference of an UDF (or any other feature) programmatically with TOOLKIT or OTK, I have to select a geometry item. However when interactively placing an axis for example with a coordinate system reference, I can additionally select if it should be aligned to X, Y or Z.