Using LinkWidthAndSlope to Tie Into Existing Ground

I was working on a video yesterday using the dataset that I put together for this post: More Conceptual Design: Using Surface Analysis for Pole Placement based on this story: El Dorado County DOT uses Civil 3D.

The idea is that the road redesign project required staying within irregular purchased right-of-way limits (meaning it isn’t always an even 100’, etc.) The location at elevation at the right of way is fixed, and it almost doesn’t matter what slope I use to tie into existing ground- I just really need to hit the elevation at the right of way.

Here is an image I used in a post called Conceptual Road Design Ideas that shows the concept.

There are probably thousands of ways to combine the tools in Civil 3D to get this result. There is no right or wrong way, and how you approach it really depends on what you are trying to accomplish. Leave a comment if you’ve used a different approach that you really like.

You need two main ingredients:

1. A 3D polyline or feature line that runs along the right of way limits at existing ground surface elevation.
2. A road assembly that includes LinkWidthAndSlope or another daylight type subassembly that supports a target.

I just took the polylines I had drawn at the extents of the right-of-way and used Create Feature Lines from Objects. You could do some more clever things- like use survey figures from field data, or extract polylines from GIS then replace them later with surveyed info.

Depending on your constraints, you could also do something slick like create a temporary corridor and extract dynamic feature lines from it to use as targets. That way, if your existing ground surface changed, or your right of way changed shapes, you could probably work it out to be mostly automatically updated. You could use offset alignments and sampled profiles. You could extract the boundary from a corridor surface and target that, or target a corridor surface itself.

As I sit here and write this, I am wondering if maybe using alignments with sampled surface profiles might be the most flexible and dynamic targets in this scenario. Try it and let me know.

If you want to use the surface elevations, make sure you assign them.

When I made the corridor, I targeted the LinkWidthAndSlope to the right-of-way limits for both Width and Elevation.

Now, when I make changes to my profile (or anything else for that matter) my corridor will rebuild and always hit existing ground exactly where I need it. The image below shows a surface analysis on the corridor surface. The idea is that areas that are too steep for pole placement are shown in red.

This might be a good idea for a first draft design or a conceptual scenario, but in most cases you will need to use one of the more parametric daylight subassemblies that checks for different conditions and uses different slopes (or even better, use Subassembly Composer to make something that does exactly what you need.)

Here are two more posts about combining Civil 3D tools, temporary corridors, and targets that might also get you thinking:

Leveraging a Temporary Corridor for Stream Projects

Using Temporary Corridors and Surfaces to Drive Design

Comments

[TimStalin]

LinkOffsetOnSurface subassembly.

With this subassembly you can leave the targets as polylines and target the surface for the elevations. If the surface updates so will the corridor.

Similar to your idea using offset alignments and profiles but fewer steps.

[Dana Probert, P.E.]

Well, shoot!! Of course it does! Thanks for the comment and I shall blog that one today.