Lidar data and contour generation along rivers

kp50
kp50 Global Mapper User
in Features Discussion
The contours I generate along rivers from the Terrain Grid (Bin DTM) using classified ground lidar points are inconsistent with contours going all through the river in a sporadic manner (see attached screen shot). Is there a way of creating a break-line along the river edges or some other fix?

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  • bmg_bob
    bmg_bob Global Mapper Programmer
    Answer ✓
    Hello,

    You can't use a break line, per se, but you can adjust your generated grid to give the area covered by the river a constant elevation that makes sense in the context of the location you are working with.  This will ensure that you don't get the random contours in the river.

    The simplest way to flatten the river is:
    1. Use the Digitizer to draw an area feature covering the river
    2. Select the new area feature
    3. Right-click and choose Edit Feature
    4. Add an attribute called ELEVATION and give it a value of the elevation value you want to use
    5. Use Analysis->Create Elevation Grid from 3D Vector Lidar Data to create a grid from the area (it will be in the User Create Features layer.)
    Cheers,

    Bob
  • kp50
    kp50 Global Mapper User
    Thanks Bob, that helps. My river is dropping about a foot every 200 feet or so and I've got miles to go. Using your idea however I exported a corridor of the river with ground and water lidar points and the associated orthophoto. I was then able to import into AutoCAD and run a 3D breakline along the river edges. I used that to form the Terrain Grid in GM for generating contours.
    Thanks a lot for the idea. 
    Do you anticipate GM will have a breakline creation utility in the near future?

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