Wednesday, December 10, 2008

Criss-Crossed Cross Sections


Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2008. All rights reserved.

It happens to the best of us. Occasionally, we import GIS cross sections that we accidentally drew in backwards (i.e. right-to-left looking downstream, instead of the required left-to-right). As a result, you can get a criss-cross deal where the correctly drawn and incorrectly drawn cross sections are located (see figure). You can also tell something's wrong when the River Station label is on the right side of the cross section (looking downstream). RAS always places that label on what it thinks is the left side of the cross section.
It's very easy to fix. Simply left-click on the cross section you want to fix and select "Reverse XS Stationing". Of course you could always go back to your GIS application and redraw (or reverse) each cross section, but who wants to do that?

6 comments:

  1. I'm seeing a bizarre issue with some cross sections ending up reversed (mirror image of correct), but everything else appears OK (correct labeling unlike the image above, etc.). I'm generating them in Geo-RAS (for ArcMAP 10), and drawing them correctly from left to right. Any suggestions?

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  2. Hmmm. That's a good question. Are your stream centerlines and flow lines all drawn in from upstream to downstream? That might be the cause. Otherwise, I'm not sure. I'll keep thinking about it. Please post a reply here if you figure it out.

    Thanks

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  3. Thanks Chris. Yes, they're drawn up to down, and what's more strange is that cross sections above and below the mirrored ones turn out just fine. I laid these cutlines over a surface about a year ago using ArcMAP 9.3 and it worked OK, then I replaced the surface recently, now using ArcMAP 10, and this occurred.

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  4. I'm having a problem where a few of the cross sections I entered into Hec-Ras have reversed stationing and after using the reverse stationing tool on those few cross sections, I now have the criss-cross issue you show above.

    The stationing is now correct but I still have the criss-cross issue. Do you have any suggestions on how to get rid of the criss-cross without changing the stationing? Thanks.

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    Replies
    1. You may have to still reverse your Cross Section cutline coordinates. Go to the GIS Tools menu item in the geometry window and select XS Cutlines Table. If you scroll to the affected cross sections and then just "flip" the table, that may fix your problem. Good Luck.
      @RASModel

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  5. Reversing the XS stations did not work for me (4.1) - it mirrored the points but didn't flip the cross section orientation around. The solution for me was to left-click and "Move Cut Line Upstream/Downstream", then choose the existing location as the 'new' location. This caused the program to flip the orientation of the cross section.

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