compare discrete points to LAS gridded surface

treedtreed Global Mapper UserPosts: 2
edited September 2013 in Elevation Data
Hi, I would like to compare discrete ground surveyed points with a gridded surface. Is there a script that can help? I know I can create a surface from the surveyed points but do not have sufficient data in most cases for a valid surface. For example I have a string of shots collected down a road, or profiles down both sides of the road that do not show the road crown.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited September 2013
    What you can do is select the points with the Digitizer Tool and edit them to rename the existing elevation attribute to something other than ELEVATION (assuming that's what it is). Then right-click and choose the Analyze submenu option to add elevation attributes from the loaded terrain. This should add an ELEVATION attribute from the terrain. You can then right-click on the layer in the Control Center and select the calculate attribute option, then subtract those 2 elevation attributes to get the difference.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • treedtreed Global Mapper User Posts: 2
    edited September 2013
    Thank you Mike. I modified your suggestion just a bit and it worked well. Some of my steps may not be necessary, just wanted to document this for later use and for someone else who might be attempting the same.

    1. Load LAS data, creating Elevation Grid on the load.
    2. Open my CSV file of XYZ survey shots, selecting "point only" and unchecking "treat 3rd coordinate as elevation". That still brings in the surveyed elevation as an attribute.
    3. In Overlay Control Center right click the CSV file and "Select all features with digitizer tool".
    4. Right click anywhere on the screen, select "Attribute/Style Functions", then "Apply Elevations from Terrain Layers to Selected Features".
    5. Turn off LAS file in Control Center.
    6. Export Vector / CSV format using default settings.
    7. Calc the deltas in excel.
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