Smooth a Surface

Again, this is a re-post on a topic that was already covered in 2007 on, Surface Smoothing Simplified.  However, this tip may be a little more simplistic – not giving as much in-depth detail – making it a little easier to distribute around the office.  Also, maybe some folks missed the 2007 posts… you never know.

Creating a nice smooth surface in the computer has always been a somewhat difficult task; until now!  With Civil 3D you can apply a surface edit (call “Smooth Surface…”) that will run some extra algorithms on your surface and make nice smooth contours were you don’t have that much definition to build the surface. 

Check it out…

The below image shows a typical finished grade (FG) surface that after adding the main elements (road, pond, daylight perimeter) is still not that smooth in the grass areas between these main elements.

2009.05.25-Not Smooth

In the past we would add “smoother contours” but that takes time and if updates were made to the road or pond grades you would have to redo the “smoother contours”.

A much faster way now in Civil 3D is to simply apply the “Smooth Surface…” edit by expanding the surface Definitions category in Prospector and right-clicking on “Edits” (see below).

2009.05.25-Smooth Surface

You will be presented with the following dialog (below).

CLICK the “” (ellipsis) button in the “Select output region” row and choose the entire surface (EG surface maybe) or Regions – need to have close polylines first – of your proposed surface where you would like to smooth.  For example, on a proposed surface you would only smooth grass areas or maybe a large parking lot.  You would NOT want to smooth the entire surface for a FG surface.

2009.05.25-Smoother dialog [start] 

Next, you will need to set your grid X and Y spacing for the smoothing.  The lower the number the more detailed the smoothing will be BUT don’t go crazy!  Note below on the dialog the number of surface points that will be added.  You need to keep this number at a reasonable value.  A good grid spacing value to start with is 10-feet; 5-feet maybe if you have a small site.  Mega sites – you want to go larger than 10-feet if possible.

2009.05.25-Smoother dialog [end]

CLICK “OK” and you should be set to go with a nice smooth surface!  Best of all, if you make edits to the pond featurelines, road corridor, etc… there is no redo work at all to have a smooth surface once again.  Laughing

2009.05.25-Very Smooth

If you want to smooth more in certain areas you can have two sets of smoothing areas and grid spacing.  Maybe some areas are a 10-foot grid and others are 5-foot.  As always, you can still add “smoother contours” in combination with surface smoothing to get the desired results as well.

Keep in mind that the ‘Smooth Surface’ edit needs to be near the bottom of the ‘Definition’ order in ‘Surface Properties’ (below).  If you add, re-add, or remove data you may need to give some attention to the order again to make sure everything works correctly.  Also note you can TURN OFF surface smoothing simply by un-checking the box!  Nice option…

2009.05.25-Smoother edit order


  1. Josh Petersen says:

    Great writeup! Distributing around the office right now.

  2. Mark Spatz says:

    Yeah, I have the posts from my companies internal site that I setup and post to so I figured I might as well upload it after reading

  3. Matt Anderson, PE says:

    I’ve been doing this all day today! Good post!

  4. José Ponce says:

    Que buena Herramienta!. Es lo que estaba buscando.

  5. Mark Spatz says:

    It is one of those things that makes you excited the first time you use it, isn’t it.

    It’s like “BOOM! all smooth…”

    Then when you get into the details you realize you need to make smoothing regions to make it all work for finished grade surfaces, but still a great thing.

  6. Tony says:

    Good post. I do this most often at curb returns where there is not a smooth contour arc.