ECEF - Elevation Data export formats do not match each other

veddycent
veddycent Global Mapper User
in Elevation Data

HI all,

I have a gridded terrain (elevation set to 0m, sea level) which I'm exporting as elevation (DXF 3D Face) and points which I export as (Vector CSV). Both are using the same projection (Transverse Mercator and WGS84) and both have Export ECEF ticked.

The issue I'm having is the XYZ of the points from both exports are widely different even though they should be in the same location.

For example:

DXF = 4544717.350, 2326459.340, 5103626.990

CSV = 3812523.318, -380795.818, 5081952.011

I've attached a screenshot of the export settings used.

image.png

I've never used ECEF before and I'm trying to get my head around how to incorporate it into our work flow.

ECEF - Test File.zip


I've attached the GM file with the terrain and points.

Using: GM v20.1 (b022519)


Any help/guidance would be appreciated!

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Answers

  • bmg_mike
    bmg_mike Global Mapper Guru Moderator, Trusted User
    Answer ✓

    I took a look and discovered that while the CSV export to ECEF is correct, the DXF 3D Face export was doing a double conversion and generating incorrect ECEF coordinates.

    I have fixed this for the next v23.1 daily build at https://www.bluemarblegeo.com/products/global-mapper-daily-builds.php , but there isn't much to be done for v20.1.

    Your only workaround might be to export a DXF 3D face without using the ECEF option, then load that back in. It should come in as 3D triangles. Then, export that to a vector DXF with the ECEF option. I believe that will do the correct conversion.

    Thanks,

    Mike

    Global Mapper Guru

  • veddycent
    veddycent Global Mapper User

    Thanks for the response.

    I'll have a go with the work around and see what I can come up with.

    Good that the bug was found and fixed!

    Thanks

    Ved

  • veddycent
    veddycent Global Mapper User

    As a reference for anyone else to comes across this issue and doesn't have the latest version with a fix.

    The method Mike mentioned above worked for me and to expand on it this is the method that worked for me:

    • Global Mapper (GM) file with all data loaded in and visually in the correct location (the projection I used is Transverse Mercator, WGS84).
    • Export points as CSV with ECEF enabled.
    • For any terrains/elevation grids we need to convert to points so we can export as XYZ. Do do this select the layers/group = Layer Menu = Create Point Features at Elevation Grid Cell Centres.
    • Turn everything else off apart from the points we just made then export as Vector = XYZ (Simple ASCII) text file with ECEF selected and Elevations checked.
    • Import the XYZ we just exported back into the same GM file with Elevation Grid selected in the Import Type. Don't worry if it's in the wrong place, it will export in the correct location.
    • Export as elevation grid = DXF 3D Face but do NOT check ECEF.

    That's it!

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