Add an offset boundary line to a corridor

May 13, 2013 at 12:40 pm 1 comment

I got a question of one of my students of how to create a land acquisition boundary line from the outer limits of a corridor at an offset of 0.50m outside the daylight cut or fill feature lines.

My first reaction was to do it by extracting a feature line from the corridor and then stepped offset it with a distance of 0.50m and a grade of 0.00% to the outside of the corridor, assign elvations from surface, assign it a style and you’re done. But then you have to recreate it over and over again every time when the corridor is rebuild.

If you want to automate this, the solution lies within the corridor itself. In fact, within the assembly it’s built from. So this is how I solved it: add a LinkWidthAndSlope subassembly placed at the end of any daylight or LinkSlopeToSurface subassembly, add 0.50m to the Width value and 0.00% to the Slope value.

Last but not the least: Omit the link, so it will not be used by the corridor for creating corridor surfaces. And you should also name the P2 point code to a more appropriate name like: Boundary or OffsetPoint, and incorporate this code to your code set style where you assign it a feature line style.

Now every time you recreate the corridor, the boundary is updated.

But this is not quite what I was looking for. It works great for plan view purposes only. But if I want to have information of the existing ground surface for stake-out purposes for example, then I want to have the boundary line to follow the exisiting ground conditions. So I added an extra subassembly to determine the exact daylight point at the applied offset. And I added the LinkSlopeToSurface subassembly with a cut or fill slope of 99999% which is near to vertical placed at the end of the outer LinkWidthAndSlope subassembly.


Don’t forget to Omit the link. This will show a total different layout than when it’s not omitted.


Rebuild the corridor and you’ll see like in below picture in Plan view and in Section view how the boundary line looks like.


In cross section view I added a guardrail markerpoint to see it more clearly of where the boundary line will follow the exisiting ground.


So by going horizontal first and then going vertical next answered the question.

If there’s a better way to do this, please respond. I’m open to any suggestion.


Note: There is a LinkOffsetToSurface subassembly, but that one offsets only from the Assembly Baseline and not from the attached point of the subassembly itself. I’ve tried to use it instead of the above solution by using (turning on) the Use option with the assembly which should transfer the value of another subassembly value. I’ve tried to copy/use the LinkWidthAndSlope.Offset End value but that one failed.


Entry filed under: AutoCAD Civil 3D, Code Set Style, Corridor. Tags: , , , , , , .

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1 Comment Add your own

  • 1. Brian Wallace  |  May 12, 2016 at 9:15 pm

    I realize it’s been years since this was posted, hopefully you will see this. I’ve been playing with various ways to achieve this and even using your exact method before stumbled across it. The problems I’ve encountered are that even tho I tell C3D to Omit Links it still occasionally triangulates oddly outside the original corridor border. Have you had any more luck with this? It sure would be easy if C3D had a generic LinkWidthtoSurface subassembly. This could be used to tie to the daylight then go a distance (width) to the target surface, no matter what the slope to get there is. That is what we need.


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