Working with User Features (UDFs):  Getting Started

User Features are used to encapsulate a geometric or technological construct. In some cases, depending on the selected input, and especially in an automation context, the User Feature  may be in error, with no possibility to determine what's wrong with it.

This section gives information concerning the following topics:

• Designing a robust User Feature: Some Hints
• Using Conditional Geometry
• Catching Errors
• Providing Explanations For Errors

Designing a robust User Feature : Some Hints

• First of all, it is recommended to make a prototype of your User Feature  in a Power Copy. The latter is much more flexible. After defining the Power Copy, it can be modified, whereas the first definition of the User Feature is the last one because it cannot be modified. This way your design can be made in several steps and you don't have to start again from scratch. At instantiation, it is also easier to handle possible troubles (update ….) thanks to the visibility provided by the Power Copy features.
• If the User Feature embeds a sketch, this sketch has to be iso-constrained. Thus, when instantiating the User Feature  and making changes in its new context, you will avoid uncontrolled modifications of the sketch geometry that you won't be able to manage because the User Feature  is a "black box". For the same reason, make sure that your sketch is "attached", and for that, always use the creation of sketch "With absolute axis definition". This way, you are sure that the sketch is at the right position.
• If the User Feature embeds contextual geometrical items like a draft or a fillet, it has to be resolved. It means that the base of their constructions has to be embedded too and must not be considered as an input of the User Feature. For example a fillet on the edge of a pad depends on the geometry of the sketch of the pad. If this sketch is in input of the User Feature  and changes from square to round, the fillet inside the User Feature will be broken and the User Feature will be in error.
• Don't embed datum or geometrical elements with external links to other documents (Copy\Paste as result with link).
  Don't try to embed a Body into a User Feature, it is impossible. Because a Body is a package which can be empty or can contain Knowledge features for example. Whereas a User Feature  is a geometrical feature. To make it compliant, you have to transform the Body into a geometrical feature with a boolean operation like Assemble, Remove, Intersect …. After this, you can select the boolean operation when defining the User Feature  and the associated Body is automatically embedded. To know what can be embedded, see Getting Familiar With Templates.

Using Conditional Geometry

To evaluate the environment of the User Feature (its inputs) and to make decisions, Knowledge Advisor provides 3 main functionalities:

Some measures (distance, angle, area, length, center of gravity, …) that can be used to evaluate the inputs. For more information, see Measures.
Some geometric parameters that can be valuated by other geometries. For more information, see Point Constructors, Line Constructors, Circle Constructors, Direction Constructors, Wireframe Constructors, Plane Constructors, and Surface Constructors.
If / then / else keywords allow you to choose how to validate those geometric parameters depending on the measure results.

Catching Errors

Usually, if an update error is raised inside a rule, the rule execution is stopped and the rule sends an evaluation error message.

The Do not catch evaluation errors option which is available by right-clicking the relation in the specification tree and selecting the Properties command enables you:
To create features in error To know (through an error message) if a feature is in error and To make changes (or not) in case of errors.
This capability can be used to perform a geometric computation (like intersection) and to decide what to do if there is no result.

For more information, see Knowledge Advisor User's Guide.

Providing Explanations For Errors

It is possible to associate a .CATNls file with a User Feature type to translate the names of its inputs, published parameters, outputs and multiple valued parameters in different languages.

This file can be used to override the update error message: in this message, you can provide explanations about how to avoid update errors. For more information, see Creating and Instantiating a NLS User Feature (UDF).

Controlling the Orientation of User Feature Inputs
Defining an Object Type Based on a User-Defined Feature
Creating a NLS User Feature
Instantiating a User Feature From a Macro