Top/Bottom of flat surface contour

[Anonymous]

I run into this all the time and am not quite sure why. It usually happens when I infill a flat area created by grading object feature lines. It does not happen when I infill an area defined by a user feature line. How can I avoid having these incorrect contours across the top or bottom of my surfaces? What's weird is that the surface actually has the correct shape.

[redtransitconsultants]

It's a common issue if you're grading down to a specific elevation with a flat bottom. I will usually go an extra hundreth down to avoid this - so if bottom is 700, go down to 699.99. Yes, if you put a spot elevation on the bottom it's not going to read correctly - but helps to keep intact and achieve results.

You could also try going to the thousandth.

[troma · Accepted solution]

Or go down to 699.9999, and then all your labels will probably look right!

You may not be making a surface from polylines, but @BrianHailey 's blog post is still a good read to help understand the issue:

https://civil3dplus.wordpress.com/2011/08/13/adding-contours-to-a-surface-youre-doing-it-wrong/

[Anonymous]

Yeah, I've had to do this before. I've also read that blog post many times. I should really set my default to enable swapping edges when minimizing flat areas. Running the minimize flat areas and enabling the swapping edges feature did clean up the top wonky contours in the image I posted, the bottom wonky squiggle is still there though. 

[jmayo-EE]

Just to add to the great advice already provided. This particular fix may be as simple as placing a feature line in the same site at the center of the flat area .001 units up or down following the design intent.

[jmayo-EE]

Also note that if the feature lines are all in a surface the infill in not needed.

[Anonymous]

I disagree.

[jmayo-EE]

Try fitting that inside. You should be modeling a very slight ridge/depression. Your ridge is crossing the upper rim.

[Anonymous]

I don't follow. That is the same pond, I just had to start over to get rid of the infill I alrady put in there to show you that you have to add the infill. See how there's no pond bottom on the cross section. The white line is my section line.

[jmayo-EE]

OK I didn't see that was the sample line. Attached is what I was talking about. On fliine inside the infill on the same site. IF you didn't have a grading and the flines were instead directly in a surface, the infill would not be required.