AutoCAD Civil 3D 2018 – What’s a Relative Feature Line?

Civil 3D

As you’ve hopefully heard, AutoCAD Civil 3D 2018 is now shipping and we’re really excited to see how you begin putting all of the new tools into practical use. There are a number of blog posts, videos and forum discussions that will help you quickly become acquainted with all the new functionality so I’ll avoid duplicating what others have already done. Rather, I thought I’d share a little background on how some of these improvements became reality. There’s quite a bit in this release so I’ll break this into a series of blog posts.

The first improvement area that I’ll cover is with the new “relative feature line” capability. Here’s the back story…

Just about every Autodesk University class or production example demonstrating grading using in AutoCAD Civil 3D starts with generating a reference surface (e.g., drainage, rough site grading, etc.) and then projecting feature lines so that they’re draped at the correct location in 3D. This works great as a starting point but there were areas that we felt we could improve this workflow. These improvements included:

  1. Make it easier for people to make system-wide changes to the grading scheme. In other words, I want to make a change to how water flows across a parking lot or I want to raise/lower part of a site to balance my earthworks.
  2. Give people a way to build more of the detailed features in a site while retaining a link to the site’s rough grading. For example, I want to add features like top/bottom or curb, gutter edge, etc and have them all remain vertically connected if I need to make a major change.
  3. Give people a way to hold elevations at key points on a design feature regardless of changes that they may need when modifying their rough grading. For example, I may want to hold elevations at key drainage locations, building walks/entrances or existing road connections.

The way we implemented this in Civil 3D 2018 was to allow you to maintain a persistent link to a surface when controlling a feature line’s elevation. You can also set a vertical displacement for some/all of the elevation controls along the feature line. Finally, you can specify that some/all of those elevation nodes will remain relative to a surface or that they’re remain at an absolute elevation.

relative feature line explanation

This approach gives you the flexibility to progressively refine a design while retaining the ability to make system wide changes very efficiently. I’m looking forward to seeing Autodesk University 2017 classes that leverage these changes when coupled with other improvements such as the ability to create a corridor from feature lines (R2017) and the corridor bowtie resolution tools (R2017 and R2018).

Here are some resources that you can check out to learn more about this R2018 improvement:



Dave Simeone



Add comment

There are no comments