AutoCAD Civil 3D General Discussion

AutoCAD Civil 3D General Discussion

Active Contributor
26 Posts
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Registered: ‎10-10-2012
Post 1 of 4

Smoothing Contours

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10-23-2012 01:26 PM

Hello All,


I'm drawing a topo and trying to figure out a way to manually smooth out my contours. I'm not talking about the little jagged edges that you can remove if you use the smooth surface option under surface properties but the big ugly looking jumps you see when contouring a relatively flat lot. In the ancient version of AutoCAD my company used the contours came in almost like splines and you could move the vertices around to make them look good. I know you can go in and delete some TIN lines and edit point elevations but that is very time consuming and I'm hoping there is a quicker way.


I know I can extract them into polylines but there are too many little segments to be useful. I've seen the SIMPLIFYSURFACE option and while that takes away some of the roughness it creates some as well. Is there some better option than extracting and then drawing a spline between the parts I want to smooth out? These contours don't need to be 100% accurate, I just need them to look simple, like if someone was drawing them by hand.


Thanks guys.

*Expert Elite*
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Registered: ‎12-18-2002
Post 2 of 4

Re: Smoothing Contours

10-23-2012 02:04 PM in reply to: dankoss

You can extract the polyline, and then weed the polylines of points by using the MAPCLEAN command. Using larger Distance and Angle weeding factors eliminates more points. Play with it.


After that you can use PEDIT (Multiple option) to Splinefit the polylines. You can then edit them by moving their control points.

Tim Corey, Owner
Delta Engineering Systems
Redding, CA
Autodesk Authorized Value-Added Reseller
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Registered: ‎12-10-2003
Post 3 of 4

Re: Smoothing Contours

10-23-2012 02:23 PM in reply to: dankoss

Contours are generated directly from the TIN lines - as you may be aware.


For example, a contour with elevation 100 is generated by connecting all the points on the TIN lines with elevation 100.  This is why, if you have many surface data points, you get contours with all the "jagged" edges, as you had described.


Surfaces created from "sparse" data tend to generate the larger "ugly looking jumps".  This is one reason why you can supplement breaklines with additional points - solely to generate more triangles to "pull" contours in the desired direction.


There are the smooth and simplify surface routines, that you mentioned, which can work - but I've found this to be a bit trial and error.


Some time ago, when faced with a similar challenge, I created a surface for display purposes only (to show nice, uniform contours).  To create this surface...


  1. Set points on a grid - say at 25m (or whatever you think would be appropriate given your data set) grid intervals (you can do this using the Points - On Grid Command - be sure to set prompt for elevations and prompt for descriptions to automatic).  When you create a surface from these points, you get a nice uniform distribution of triangle lines, and hence decent looking contours
  2. Create Display Only surface from these points - and assign a style that displays contours at the requried interval
  3. You can choose the grid increment for the points

So I had EG (CALC) which is not displayed (used for profiles, sections, grading etc.) and EG (DISPLAY) which is displayed for final plan production.  You can turn the points off using Point Group Sort Order or by using a layer.


It may not be the best option, but was a good one in my circumstance.  Maybe this will work for you?







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Registered: ‎12-14-2006
Post 4 of 4

Re: Smoothing Contours

10-25-2012 12:11 PM in reply to: dankoss

just draw the contours with a polyline where  you think they should be and add the data to the surface as a contour line.


try not to over think it :smileywink:


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