Expressions and API Functionality | Autodesk Civil 3D Subassembly Composer

In this post, we'll be reviewing expressions and API functionality that can help enhance your subassemblies in Subassembly Composer.

If you want to watch a video of this post, click here.

A review of expressions:

  • Used within Subassembly Composer (SAC) properties.
  • Expressions allow you to use a mathematical formula to convert information such as X/Y location, slope and elevation. You can use expressions to set a property value based on the result of the equation.
  • Expressions are typically used in the properties of a variety of geometry elements.
    For example, a Switch uses an expression to tell it if the switch has a certain type (like displaying one valley gutter over another). By defining this in an expression, the subassembly will use it as part of the parameters.
    Civil 3D Subassembly Composer Expression
  • Expressions are entered in the properties panel. When a property can accept an expression, the property displays a [...] button. Click the [...] button to open the Expression Editor window.
  • Most expressions are built on standard MSDN math functions. the MSDN Math Class .NET framework provides constants and static methods for trigonometric, logarithmic and other common mathematical functions, in which you can see the different types of functionalities and operations you can use within your expressions.
    MSDN math functions

A review of API Functions:

  • API (Application Programming Interface) Functions are a set of commands, protocal and objects that use .NET API to extend the functionality of your expressions. 
  • The most common API functions you will use in SAC are surface, auxiliary points, auxiliary links, elevation targets, offset/width targeting, decision making and more.
    Civil 3D Subassembly Composer API Functions

Previously, we've reviewed packet settings, how to create a simple SAC using basic tools, how to create a rounded shoulderdaylight roundingswitcheslooping geometry sequencing and importing PKT files into Civil 3D.

It's that easy! To learn more about Subassembly Composer, click here.
To learn more about expressions in Civil 3D, click here


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