From the course: Autodesk Civil 3D 2025 Essential Training

Understand corridors - AutoCAD Civil 3D Tutorial

From the course: Autodesk Civil 3D 2025 Essential Training

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Understand corridors

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- [Instructor] Corridors are used to model 3D linear features like roads, ditches, dams, and many others. Before we dig into creating corridors, let's learn a little bit about how they work. Over the last two chapters, actually four chapters, you've been learning about how alignments and profiles work. You learn that the alignment represents the 2D path of an object, and a profile adds the third dimension to that path. Now, if you combine an alignment and a profile together in Civil 3D, it creates an object that actually not a lot of people know about, even experienced civil 3D users don't know about it. It's called a 3D chain. And if I zoom into this 3D view of a corridor, you'll actually see two 3D chains here. This one represents the sampling of the existing ground surface, and this one represents our design or the proposed ground elevations for our road. So again, that's the combination of the alignment, the 2D path, the horizontal path, and the profiles, the vertical elevations assigned to that path. Now, the way a corridor is built is we take something called an assembly shown here in this viewport. An assembly is the proposed cross section of the road. And you can see this one, even though it's really simple, you can see the components of the road, the lanes, the curbs, and these figures represent how we tie into existing ground from the proposed elevation at the back of the curb. So we've got some static and some dynamic components to the assembly. Now, this, as I said, is a fairly simple assembly. In a real design situation, this lane would probably have strata in it, representing the different layers of the road construction. We might have sub drains, and guardrails, and ditches behind this tie in slope, and lots of other detail going into this assembly. But it's all basically the same idea. The proposed cross section of the road is represented by this assembly. So the way that civil 3D builds a corridor, and if I switch down to this view, you probably already see it. Here's an insertion of that assembly right here. I know it's shown in black, and this one is shown in different colors. And as you might guess, that's a function of the style. But what's actually happening is this assembly is being inserted precisely along the 3D chain, the combination of alignment and profile again and again at increments to build out kind of the framework of the corridor. So you take that proposed cross section and just drop it in again and again and again along that 3D chain, and you've got the 3D formation of the corridor. There are also feature lines that connect between the assembly insertions. You can see these magenta lines here, I believe, that represent the connection points between points on each assembly insertion. So that kind of fills out the longitudinal geometry of that corridor. And then we can do something like build a surface on that corridor. We can select the surface built for this corridor, right-click and open Object Viewer, make sure we have this set to shaded view. And you can see the three dimensional representation of that corridor in surface form. One other thing I wanted to show you is the 3D representation of the 3D chain. Let's select that, right-click, and go to Object Viewer. It's a pretty simple-looking object, but this again is the combination of the horizontal alignment and the vertical profile all wrapped into one entity. So that's how a corridor is constructed. An alignment and profile come together to establish that three dimensional path. And then we insert assemblies along that path, attaching those assembly insertions to that 3D chain, feature lines connect the different assembly insertions, forming the longitudinal construction of the corridor. And then as an added bonus, we can create a surface out of that corridor and kind of stretch a skin over that framework that's being built by the assembly insertions and the feature lines between them. So you've just learned the anatomy of a corridor. In the next video, we'll begin by building an assembly.

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