Tying Corridors and Feature Lines Together Dynamically

Time flies when you are having fun and the EECast yesterday was incredibly fun. I was very excited to show dynamic feature line extraction from corridors and some ideas on how you might tie shared-site feature lines together.

I could see lightbulbs going on all over the place as the live questions and comments kept coming in… Since we only had 60 minutes together, I thought I would put up a few summary diagrams of the intersection. (I’ll do the lot grading one later.) Keep in mind that while Civil 3D 2008 has the same ability to have one feature line “drive” another on the same site, the dynamic corridor extraction are 2009 only.

Also note that next week, James will be doing an EECast on a different dynamic intersection modeling idea that uses the EEPropack and dynamically linked profiles, and on June 4, I will be doing an EECast on Building Better Terrain Models.

See the diagram after the jump.

Start with a corridor. (Note that dynamic feature line extraction only works across regions where the feature line is continuous, and a few other ways which I will talk about in another post sometime.)


Extract ETW Feature Lines using Create Grading Feature Line from Corridor.


Draw feature lines for your EOP, being sure to touch the dynamic FLs and putting them on the same site.


If you would like to model curbs or other features as feature lines,  use Grading>Edit Feature Line Elevations> Adjacent Elevations by Reference. **I had mistakenly said this was a dynamic relationship. I sincerely apologize and hope it hasn’t caused any problems for you. It would be easy to quickly go back and reapply this tool upon grading changes. OR use a grading object instead.**


Build your surface- be sure to add that Marked Point feature line (for more on how surfaces are built from links, points and feature lines, check out pages 384-391 of Mastering Civil 3D for a very robust discussion.


Then add your EOP featurelines as breaklines to that surface. Don’t forget to tweak your mid-ord distance!

After some face flipping (which should stick through your iterations unless you make radical changes to your sampling interval which would cause more points needing triangles), you get something like this:



I haven’t tested this in all situations, but hopefully this gets your ideas flowing for other applications.

James is doing a webcast on an alternative workflow for intersections that involves tying profiles together using the EE Propack. Sign up for that EECast here. Learn more about the ProPack and download a trial version here. Watch an EEcast that shows the EEProPack here.

For more on feature lines and grading interaction, check out Dave’s AU Class. There used to be a white paper on grading best practices that has been taken down. I was upset until I realized that it has been included as part of the Civil 3D 2009 help file. READ THAT. It’s extremely helpful.


  1. Paul Markas says:

    Dana – Great webcast yesterday! I have a question about ‘Adjacent Elevations by Reference’ You said this is dynamic, but it doesn’t seem to be for me. I’ve tried editing the FL with quick edit and Elevation Editor, but the second line does not change. I’m assuming this command is a general one in terms of FL and not corridor specific? Any thoughts? Thanks.


  2. DANG. I had misunderstood that command, and I sincerely apologize for the mistake. It would be very quick to go back and reapply that command when the intersection changed. Or better yet- try a grading object. Maybe next week’s EECast workflow will be better for you if this is a deal breaker. Basically, this command is a way to reapply a stepped offset without having to reoffset. That way, your surface can keep the same breaklines.

  3. Tom McCrate says:

    Two thoughts on the webcast discussion.
    1. The top of curb does not influence intersection drainage, so adjust the corridors to achieve good intersection drainage,add the top of curb when finished.
    2. When you connect the corridor to the building pads, can you connect the two front corners? If so, the front edge of the pads would automatically conform with the street slope. The balance of the pad grading would generally be fairly consistent so you could set the relative slopes for one pad and copy to each lot.