# Difference between surface and corridor section?

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Hi, can someone please help me out and explain the difference between a surface and a corridor section? I was given a cross sections file with: existing ground (assume correct location), corridor section (correct location), and finished ground (wrong location - shifted about 2' to one side). Why can't I calculate cut/fill from the existing ground surface, and the corridor section that's in the right location. any thoughts on what my next step should be. do I have to make another surface from the corridor section?

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If I remember correctly, there are a few steps to get a surface from a corridor, I can't check right now though. Ping me on monday if I forget and i should be able to help you.

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Hi, can someone please help me out and explain the difference between a surface and a corridor section? I was given a cross sections file with: existing ground (assume correct location), corridor section (correct location), and finished ground (wrong location - shifted about 2' to one side).

It is a bit hard to explain. A corridor section is looking at one cross section of your corridor, e.g. Chainage 100. Another corridor section might be Chainage 110. Now, your corridor is only defined at those points where the assembly was applied, it is not defined at the areas in-between the assemblies. For that, you need to create a surface from your corridor so that a surface is defined at all localities between assemblies, not just at the exact points assemblies are located.

The above image sort of shows this. Assemblies are applied at the dark blue corridor sections. A final mesh/dtm/surface still needs to be made by combining the position (x, y, z) and geometry of all these assemblies into one final road design. Otherwise, when the machine controlled grader goes to build the road, it will have geometry to build it at Ch100 & Ch1210, although come CH 100.01 - CH109.99, the machine has no elevation control and will either fail or try to grade the road to 0.00m elevation [i.e. machine control is then useless, which is how most projects are constructed these days].

do I have to make another surface from the corridor section?

Yes, you have to make a surface for your corridor. If you select the corridor, on the ribbon there will be a big button on the left called 'Surface' or something similar which you can use to create the surface for the corridor design, like Tiger I don't have access to Civil 3D at the moment. It's fairly simple and there will be lots of tutorials/videos online about it. Every Civil 3D book covers it also.

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• 10 years later...

isn't there any way that we can solve this by altering corridor property. i am also facing this problem only in 2 of my sample lines among more than 20.

https://ibb.co/JmFWhxH  the red surface is in right place while the corridor has shifted towards right.

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It's hard to tell from a picture. My guess is that something is off in the assembly, or you're targeting something that is not where you expect it to be. Have you verified the codes in your assemblies?

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