I WANT YOU TO MAKE THE SURFACE LOOK PRETTY!!!!!
Yes, we’ve all heard it before, Civil 3D makes contours that sometimes look like the recording of an earthquake on a Seismometer:
Seismometer Recording
Really, it’s not the fault of Civil 3D, it’s the data. Add the same data to any other civil design program and you’ll get the same results. This seems to crop up quite a bit when you have cross grades. In the following image you can see that there are two roads going opposite directions and this is where the jagged contours are coming from:
Jagged Contours
No contractor would build it this way so, let’s see what our options are.
Option 1: Smooth the Contours
You can smooth the contours of the surface. In the style the surface is using, you can toggle on the option to smooth the contours. This is a great way to make a drawing “look pretty”. It will take the contours and smooth them out. This is only editing the display of the surface. If you have a profile through this area, smoothing contours does nothing to the profile because we aren’t smoothing the surface, we are smoothing the display of the surface.
To smooth the contours, go into the style the surface is using and, on the contours tab, toggle the option to smooth the contours to True. Once you have this toggled on, you can select the type of smoothing you want to apply to the surface as well as how aggressive you want the contour smoothing to be. Play around with these settings and see what looks best for you. There isn’t a correct setting for this because your goal, when smoothing contours, is to make the contours look pretty.
Contour Smoothing Options
And here is the same area of that surface with the contour smoothing option set to True, the Smoothing Type set to “Add Vertices” and the contour smoothing maxed out.
Surface with Smoothed Contours
There are some things to be concerned with when smoothing contours, you are sacrificing the accuracy of the contours to make them “look pretty”. If you have a spot elevation that happens to fall very close to a contour or perhaps a point that was used in the surface creation that’s really close to the contour elevation, you might see some discrepancies. In the following image, I placed a spot elevation and snapped to the contour and you can see it’s not the exact same elevation as the contour:
Smoothed Contours Labeled
Another issue with smoothing contours is you might end up with contours that cross each other. You’ll see this sort of thing primarily where you have some really steep areas such as retaining walls.
Crossing Contours
Anyone that’s done any amount of surface modeling knows this is not allowed.
The last issue that I’m aware of with smoothing your contours is, it’s all or nothing. You can’t smooth just a portion of the contours of your surface. This is because it’s a part of the style.
Option 2: Smooth the Surface
The other option is to smooth the surface directly. This is an edit that is done to the surface and is found in the same place you can raise/lower the surface or paste in another surface.
Smooth Surface Command
There are two options when smoothing surfaces, “Natural neighbor interpolation” and “Kriging”. I’m not going to go into detail on how the different methods work or what settings to use. You’ll need to read the HELP FILE and do your own research to find out which method works best for your situation. In this example, I’m going to use the natural neighbor interpolation method.
Smothing Options
So, how does this differ from smoothing the contours? Well, when you smooth contours, you are smoothing the display of the surface. When you smooth the surface, you are actually editing the surface and not just the display. Here is an image of the surface with the smoothing edit applied to it:
Smoothed Surface
As you can see, the contours look much different then when the contour smoothing was applied. If you take a look at the triangles of the surface, you can get a better idea of what happened here (I did a 5′ grid in this example):
Smoothed Surface Triangles
A couple things to note here, I didn’t smooth the entire surface, just the area that needed it. Second, any data that was added to the surface was not modified in any way at all. If there are points, or breaklines, or corridors, or gradings, they are preserved (including the triangulation along the breaklines). This only affects the way the triangulation in the areas between data are calculated. Basically, instead of doing a straight grade between one point and the next, it rounds it out.
Something to be aware of, this can add a LOT of data to your surface and can make it very slow to work with so play around with the settings and get the results you want without adding too many points to the surface.
Hopefully this helps out when someone is complaining about your ugly contours!
Civil 3D Plus 
April 23, 2013 at 7:20 am
Great post for big issues that occur all the time.
One thing I’ve ran across though is some engineers don’t like using either of these methods in fear of providing inaccurate surface data, especially on roadways/intersections. So the 3rd option is to ADD MORE DATA!!
I typically go through and add additional feature lines to define these areas instead of having the software try an interpret it. There are times as well where I have drawn in actual polylines with arcs tracing a portion of contours, manually smoothing the contour with arcs and lines, setting it to an elevation, then adding it to the surface as contour data.
This method seems to work well, but can take some time depending on the surface. However, it allows you to manually set the grades and elevations instead of having the software calculate it out.
April 23, 2013 at 7:34 pm
Very good points. I personally would never use either of these in an area where extreme accuracy is important, such as a roadway, a swale, an intersection, etc. I would primarily use the Smooth Surface edit in the natural areas such as open space, parks, etc.
March 14, 2014 at 4:26 pm
Very nice post, just wondering what are the input parameters in the smooth surface menu where “point interpolation / extrapolation output” in grid X and grid Y? is there kind of a default value to avoid having to much data and also keeping the drowing accuracy?
March 27, 2014 at 3:50 pm
I don’t know. You’ll have to experiment with them and see what works well with your data.