Improving your Corridor Contour Tie In

You may have experienced some frustratation trying to get your daylighting contours to “tie in” to your existing ground contours.

(EG= Red Tones, FG=Blue Tones)

The reason this happens is that Civil 3D is tying your TINs together- NOT necessarily your contours. 

We are so used to looking at contours sometimes that we forget that contours are PRODUCT of TIN and won’t always wind up with that perfect Pentel Marking Pen flare at the end when we are dealing with the linear world of TIN theory. 

There is an easy solution to this problem, however.  You can have great contour tie in with an extra few steps.


It is very easy if you can live with showing your total final site grading without the EG contours peeking through, but if you like to see the distinction between tie in and distrubed ground, that’s OK too.

Make a new surface.  Paste your EG into the new surface. 

Paste your Corridor Surface into your new surface. 

Look at this new surface and note that I now get a really smooth tie in, because the TIN had a whole lot more room to blend in.

(EG= Red Tones, FG Composite=Blue Tones)

You might be happy at this point- and in fact this is the surface I would use as my rim targets for pipes and those types of things.

Now let’s say you need to show just how they tie in- similar to the very first image in this post, only a little smoother at those matching points.

Draw a boundary around your corridor surface footprint. I usually don’t make it very perfect, I just go about 5′ away from the ragged looking tie in to start. 

Add this boundary to your FG Composite Surface, and you wind up with something that looks like this:

Giving the TIN those few extra feet to “find” EG really makes a difference in the tie in. 

You may find you need to grip edit and finesse this boundary in order to get your blend as “blended” as you like, and of course this isn’t dynamic to your corridor or anything, but it is a pretty quick grip edit when you need to reblend.

Jason wrote a piece about some assembly rounding options that might also be useful in this post:

We originally decided that we didn’t quite like how that was working, but since then, we’ve had some chats with our friendly neighborhood corridor QA guy (the blogger formerly known as Nick Z) and we’ve decided to give it a second chance this week at Tech Camp.  In a few days, I may have a solution that doesn’t involve pasting surfaces, but in the meantime, I like the way these contours tie in far better than anything else I have tried.

One comment

  1. R.K. McSwain says:

    …sometimes that we forget that contours are PRODUCT of TIN

    I hear you…. Many people I deal with seem to think that the contours *are* the surface definition, rather than a *representation* of the surface.