Creating Pipes, Part Piggyback

Since Dana was kind enough to start writing on pipes, I wanted to jump on her momentum and throw out a nugget of knowledge discovered this week during training and working on some pipes questions from GBA in Kansas City.

First, a couple of assumptions: 1. You’ve written your pipe rules, and worked through the parts list, labeling isn’t an issue, and the world is well. 2. Your pipe networks are typically stationed such that 0+00 is the downstream end, whether is be a storm line outfall, or a connection to an existing sanitary sewer.

So let’s talk about those pipes. Because you’re a die hard reader, you know that when laying out pipes using the layout tools, it’s best to work downstream.

But now it’s time to profile. You’re like many engineers and designers I work with, and want to profile exaclty along the CL of the pipe, so doesn’t it make sense to just use the tools that Autodesk gave us in the package? After all, there is a Create Alignment from Network Parts command, right?

So you go to the bottom of the network, because that’s where you want your 0+00 to be, and begin clicking and picking your way up the hill. You finish picking, the nifty create dialog pops up (look at that, we can even make the profile and profile view in this step!) and you pick, pick, pick until you wind up with a nive profile view on screen.

But something isn’t right. This isn’t what I was expecting? And why does my alignment jump back and forth like that? Something is rotten in the state of Darcy Weisbach! After running into this a few times, I knew it wasn’t just a quirk of the dataset. So after a quick e-mail exchange, I have an answer to share….

When you laid out the pipes, you went from high-to-low to create pipe network that worked fairly well based on rules of your creation and to get a good initial design. But when you created your alignment, you picked in the other direction! When creating the alignment, if you choose begin and end structures in the order OPPOSITE their initial creation order, AND pick structure, pipe, structure, pipe… then the alignment will double back as I’ve shown in this image.

The solution? Create that alignment from top to bottom, then reverse it. Simple as pie, and no more fighting with the loopback alignment.


  1. Trevor says:

    Okay, so I am a die hard reader and I’m struggling to remember why it is that when laying out pipes with the layout tools, it’s best to work downstream. Care to suggest a link to where I can refresh my memory?

    And thanks for the heads-up on that issue, James.

  2. i dont remember it either 🙂

  3. Oops.

    Really thought we had covered that. Or that one of my cohorts had. I’ll see if I can get something together tonight on the plane.

  4. Jason Hickey says:

    wow, that’s a good little trick. I’ll have to try it later today.