Smooth Surface versus Smooth Contours in Civil 3D

September 18, 2019 Bryant Quinney

Many times, the concern or question comes about where a user wants to know the differences between smoothing the surface versus smoothing the contours within Autodesk Civil 3D. Also, I get asked if it affects the volume calculations. To address this, lets first dig into what you get from each of the two choices. First, the easier of the two:

Contour Smoothing:

Found in the surface style > Contour tab, enabling Contour Smoothing allows you to alter the visual appeal of the surface contours. Note that this does not modify the TIN, only the contour lines. Once in the tab, expand Contour Smoothing and set the value to “True” and choose how the contours should round out, by adding vertices or splining curves. You can adjust the amount of smoothing using the slider along the bottom.


Notice the “rounding out” of the contours after enabling smoothing, where they no longer show a jagged appearance.

Smoothing disabled:


Smoothing enabled:



As I mentioned, the TIN is not modified from a visual-only setting, so any volume calculations based on the surface do not change.

Up next, Smooth Surface


Surfaces (in Prospector) > Definition > Edits > Smooth Surface:

This method does modify the definition of the surface TIN, so here are a couple of notes about it:

  • Achieves a more gradually defined terrain from the surface by reducing the amount of sudden deviations in surface face transitions.
  • Uses Natural Neighbor Interpolation or Kriging methods to calculate smoothness, allowing the user to choose the x-axis and y-axis grid spacing, along with grid orientation.
  • Note: This operation makes the surface more complex and is the fundamental opposite of simplifying the surface.

Using the Kriging method, you are presented with a behavioral preview at the bottom, once you have chosen the points to adjust. You can choose from a selection of points, random points, or all points of the surface. It is necessary to have the current style showing the surface points in order to select them. When prompted to select the points, you have options of sampling a region, choosing a rectangle, polygon, or the complete surface as your selection.

Note: If your selection has more than 4000 points, you are given an error, prompting you to choose a smaller sample group for kriging.

Once you are returned to the dialog box, the model preview at the bottom shows how the surface points are generally treated, differing between the Semivariogram models:











In each model type, the parameter to the left represent:

  • Parameter A: The scale factor of the variogram
  • Parameter C: The range factor of the variogram
  • Nugget effect: This value is always greater than zero (0) and represents the amount of discontinuity at the origin of the model.

Specify an output region for the solution, whether located by:

  • Grid-based
  • Centroid locations
  • Random points
  • Edge midpoints

Press OK. Once the smoothing operation is completed, the entry shows in the preview window of the surface, with the type of smoothing done.


The modification triggers the need to update the volume surface (if applicable).

Pre-adjusted Volume:


Post-adjusted Volume:


There you have it. If you merely want to clean up the appearance of contour data, then Smooth Contours may be for you. However, if refining the data of your surface is the task, then Smooth Surface is the option for you.

About the Author

Bryant Quinney

Civil Solutions Applications Expert<br><br>Working with clients to implement various technologies and techniques within civil engineering disciplines. With my travels, I teach/train, troubleshoot, solve, configure, and implement solutions based on client needs. Drawing on many years of experience across various types of projects, I continue to enjoy doing this type of work.

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