take the edge off CIVIL 3D

We’ve had some interesting questions about some interesting intersections in Civil 3D 2010 recently and have been testing some ambitious ideas with marked points and invisible generic links.

We’re pleasently surprised at how well all this works - it takes time to set up the assemblies etc , but once they are done, the intersection can be formed as quickly as a simple road intersection and the geometry is quite robust. The alignments can be dragged etc and the intersection/corridor updated like a standard Civil 3D intersection.

This example in this case is a tunnel. It’s an interesting example in general and also showcases the marked points / invisible generic links in the assembly sets.

[More:]

The Logic:

Essentially it is a road with a roof and walls. The logic in general is to build the road and set some (nearly) vertical links on the edges to house the roof.

• So, to get started, we build a road assembly with vertical components on the CL and both edges. We set the CL vertical link to invisible - it is going to act as a Reference Point for the roof.

• We then place Marked Points on the top right and top left as in the diagram below.

• Now we use the LinktoMarkedPoint generic link to form the ‘roof’ component.
  These are inserted on the reference point (mentioned above). The offset, direction and slope are taken care of by specifying the marked point to link to. We insert one for “TopLeft” and one for “TopRight". The aesthetics of these are a bit confusing on the screen as they will both point towards the right - this is only a conceptual view - the assembly will work fine even though it looks strange.
  (the diagram below is not a screen capture - it’s a sketch)

The purpose of this:

The principle is that when the road is stretched, the roof comes with it. The diagram below illustrates this.

When you think about it, it should work the same way for the intersections and it does.

The Tunnel Intersection Assembly Set:

This takes some iteration and there are a few things to look out for but it isn’t really that difficult. It’s more of an exercise in patience than hardcore technical work.

Copying the assembly from above and removing the relevant links is easy enough. The Kerb Return needs to have codes and the marked point name renamed as the CL vertical link becomes the left wall (for left hand drive systems).

In terms of the link codes, we found it best to use the code of ‘body’ for the road and walls so that a surface model can be formed easily. The roof links can have a separate code (roof for example) so a separate surface can be formed. More on all this on a later post.