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Exported dxf geometry x,y, z scaling issue

migonaccimigonacci Global Mapper UserPosts: 4
edited June 2010 in Technical Support
Whenever I export terrain data from any one of the online sources to DXF MESH FILE, the resulting file has the entire mesh scaled in x y z to almost a single line of mesh. If I manually scale the mesh in x y and z, you can see that the entire mesh was exported but its always compressed in x y z. I was thinking it might be a X Y spacing issue, but I'm not sure. Has anyone experienced this?

Comments

  • migonaccimigonacci Global Mapper User Posts: 4
    edited June 2010
    Forgot to add link to the sample DXF file.

    http://dl.dropbox.com/u/4619977/TEST_FILE.rar
  • Frank2Frank2 Super Moderator Posts: 105
    edited June 2010
    Looking at the extents, I'm guessing you're exporting a geographic DXF with feet/meters elevations. You either want to use a projected system so all your units are the same, or make sure your other software can deal with the difference in units.
  • migonaccimigonacci Global Mapper User Posts: 4
    edited June 2010
    Frank2 wrote: »
    Looking at the extents, I'm guessing you're exporting a geographic DXF with feet/meters elevations. You either want to use a projected system so all your units are the same, or make sure your other software can deal with the difference in units.


    I am using 30m NED elevation data from the online data source. In Global Mapper the data projection is in meters, and I export it in meters. Projection system is set to Geographic(longitude/latitude) under configure.

    I changed the projection type to UTM and exported the data and it seemed to work. I noticed that the sampling space units also changed from arc degrees to feet, but this also distorted the terrain slightly (elongated). Maybe the issue is that sampling space units when exporting to DXF are in arc degrees?

    X: 0.000335785843014374 arc degrees
    Y: 0.000277777777777778 arc degrees

    I'm importing the DXF into rhino.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited June 2010
    As Frank said, the issue was that your elevation (Z) units (meters) were linear, while your projection (XY) units were angular units of arc degrees. Switching to a projected system with matching XY units (like UTM meters) is necessary so that software that can't deal with different XY and Z units can properly display the data. Note that a rectangular area in lat/lon will not be rectangular in many projected systems, like UTM. Assuming an appropriate projected system is selected, the projected display will almost always be more representative of ground truth than data displayed in the (very distorted away from the equator) lat/lon system.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • migonaccimigonacci Global Mapper User Posts: 4
    edited June 2010
    Thanks for the info.
  • Frank2Frank2 Super Moderator Posts: 105
    edited June 2010
    If you want to get the same data already in a UTM projection, so that you have square cells, you can use this site:
    http://datagateway.nrcs.usda.gov/

    You can find a tutorial here:
    http://datagateway.nrcs.usda.gov/Gateway_5_tutorial_14MAY2010.pdf
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