About UDF Placement Using an On-Surface Coordinate System
To place a UDF through an on-surface coordinate system, you must construct the UDF in one of the two following ways:
• The on-surface coordinate system must be the first feature of the UDF.
• Any type of coordinate system must be the only external reference of the UDF, and all other references must be internal references.
The coordinate system serves both as an origin and a reference point for the UDF. It can be compared to a pin holding an add-on in place on the model surface by its axis.
When you create the UDF, the on-surface coordinate system must be the first defined feature. The placement point that you choose for the coordinate system is the placement point for the UDF on the model. If you do not place the UDF first, it is treated like any other feature, in which case the references of the coordinate system are listed in the Placement tab of the User Defined Feature Placement dialog box.