Parameters are used very oftens for models where not all dimensions are defined for sure (which ends up being a quite large percentage of the stuff that you might need to do). This page will go into how to generate and use parameters. For in-depth info on parametrization, you can see the documentation atAbout Parameters.
User parameters store some data in the form of a lenght, an integer, or a True/False value (amongst others). These parameters can be inserted into features
These are the parameters that you will make yourself, and connect to intrinsic parameters or features by using formulae. Here's a list of all the methods you can use to make parameters:
Creating a Parameter
Having an assembly where you might have a lot of common dimensions is a very common scenario; and, for one reason or another, you might not be able or want to use the skeleton design approach. Thus, it'd be very useful to have one parameter determining various features in different parts. However, if you tried to make a parameter inside of an assembly you'd get a error message. This situation is due to ordering rules. You can insert parameters inside of a 3DShape, but not inside of an 3DProduct (assembly).
To get around this, you can either insert a 3DShape in your assembly (already the case if you're modelling using the "skeleton approach" or create an Engineering Knowledge Specification. This serves as an item that can house, among other things, user parameters. You can read about them and how to create them in Creating Engineering Knowledge Specifications.
These parameters can now be used to set things like distances in Engineering Connections whitin the assembly. However, to be able to use these parameters for specific parts inside of the assembly, it's needed to
"import them" into said parts. This is done by adding them as external parameters.
If you need a parameter from one part (or an assembly) to act inside of a different part, you need to create an external parameter. The process is detailed in Creating External Parameters (in particular, we recommend the 2nd method).
When any feature is made, a series of parameters are created. So everything made in CATIA is parametrized, techincally. You can find all of these "intrinsic" parameters with the "Formula" browser under "Tools". However, modifying intrinsic parameters is not terribly practical as in any decently-sized model there is a very large amount of them. It's also noteworthy that messing around with the intrinsic parameters, and their naming schemes get increasingly complicated. Additionally, messing around with them can very much break your part. This is why these are usually not interacted with directly.
However, if you know what you are doing, you can link a user parameter ( to things like the "Activity" of a feature. This makes it so that it would be easy to deactivate a bunch of features very quickly, for instance.
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