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Multiple Problems with exporting Elevation Data as CVS File from a Point Grid - Global Mapper 17

In Global Mapper 17, I have been trying to export elevation data from a point grid within a polygon. I am trying to extract point elevation data from the lidar DEMs from the Louisiana Atlas GIS web site for statistical analysis. The first problem is the exported elevation attributes all came out as "-99999.99" in an area of Allen Parish, Louisiana that is between 85 and 160 feet in elevation. The other tools in Global Mapper continued to provide elevations consistent with local topographic maps. Finally, as I was working this problem, the "EXPORT - Export Selected Layer(s) to New File..." link disappeared from the menu to the point grid layer obtained by right clicking in the control center. Below is an excerpt from a csv showing anomalous elevations.

Best Answer

  • bmg_bobbmg_bob Global Mapper Programmer Posts: 2,328
    Answer ✓
    Hello,

    -99999.9 is the "no data" value for elevations, so it appears that Global Mapper is not detecting the elevation in the area where you are seeing those values. It is not immediately obvious from your description why that might be. How did you create your point grid? 

    I suggest that you download the latest version of Global Mapper and activate a trial license to see if your workflow does what you need. We have added numerous new features and bug fixes in the years since Global Mapper 17 was released.

    Cheers,
    Bob

Answers

  • What was so frustrating this situation is that the first time that I tried it on Global Mapper 17, it worked fine and I got some amazing point elevation data in the csv files. The data produced remarkable graphs and I could reconstruct and define and deeply dissected terrace surface. Then for some reason, it started producing -99999.99. 

    I tried Global Mapper 22 and it worked like a dream.  

    You asked, "How did you create your point grid?"

    1. I selected the polygon using the digitizer tool.

    2. Opened the "Grid Setup" box by right-clicking the selected polygon with the grid tool.
    no. of grid rows and columns = 100
    cell width and cell height = 10 m

    3. Selected "Crop to Selected Area Feature(s) in the Grid Bounds Box

    4. Selected "Crop Generated Grid to Selected Area Feature" in the Grid Set Box

    5. Selected "Create Points at Grid Line Intersections" in the Grid Set Box

    6. Pressed OK, which created the point grid within the polygon.

    7. right-clicked the User Created Grid Features layer in the control center
    and selected "EXPORT" from the menu and clicked  / open it.

    8. Choose CSV and clicked "open" to go to the CSV Export Options

    9. Under coordinate formatting choose "Include elevation values
    with each point" and under coordinate precision choose a decimal
    digit of "1". The rest were default values. then clicked "OK" to
    generate CSV file, which I named and saved.

    Regardless of what wrong, I bit the bullet and personally bought a single, multiple use license of version 22. I had already gotten my money's worth out of version 17, having used it as part of the process of mapping the geology of dozen or more 1:100,000 scale geologic maps, it was time to move on to version 22.
  • MicheleMichele Posts: 61
    Hi,

    Between step 6 and 7 you should add the elevations to the points attributes. You can do so by selecting all points -> right click -> Analysis/Measurement -> apply elevations to selected features

    Now each point has an elevation attribute that can be exported to csv.

    Best regards
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