The structures, functions, and macros in the UF_FORGEO module allow you
to define your own surfaces for use inside NX. You can use this
module in conjuction with the UF_BREP module to aid in the creation an
inquiry of foreign surfaces. The functionality of this module is for
users who have proprietary surface definitions which cannot be duplicated
using NX modeling techniques.

To use this functionality you must first register a set of functions,
like a UDO (see the uf_udobj.h chapter or header file), which is called
when your foreign surface is processed. You then create the surface using
the routines in the UF_BREP module.

The mechanism for loading the foreign surface library is identical to
that used to load and initialize User Defined Objects. You will build a
library containing everything you need to process your foreign surfaces.
This library will also contain the function ufsta(). You will put your
foreign surface library in your $UGII_SITE_DIR/udo directory. During
NX startup this library will be loaded and ufsta will be
invoked. Your ufsta function must call UF_FORGEO_register_surface() to
register the functions required to process foreign surfaces. The
functions you register will be called when NX needs to process
a foreign surface. You must call UF_initialize before the call to
register your callbacks and UF_terminate after. If your callbacks call
Open API functions then they too must UF_initialize and UF_terminate.

Refer to function pointers for a discussion on them