DXF Export Question

KyudosKyudos Global Mapper UserPosts: 12Trusted User
edited March 2011 in Vector Data
I'm am trying to deal with a Global Mapper produced DXF file, which gives us some problems when importing into our software. The DXF file contains mostly contours as polylines. I have a number of questions:

1) The file has Projection: Geographic (Latitude/Longitude), Datum: NAD83, Ground Units: arc degrees. This appears to make "X" the Long and "Y" the Lat, which generally seems backwards. Is that a feature of NAD83, or of exporting projected data in DXF?

2) This is a technical DXF question - the contour polylines in the file store their elevation under group code 30, but they appear to be malformed when compared with a 'real' DXF file (though AutoCAD does interpret the GM DXFs correctly). An R12 DXF exported from AutoCAD includes a group code 10, 20, and 30 entry for the POLYLINE entity and for each vertex - this is what our import routine expects, causing it to trip up on the Global Mapper DXF. Autocad exports to more recent DXF version formats use the LWPOLYLINE with the elevation in group code 38. Is there a reason GlobalMapper uses the 'old style'?

3) With 2) in mind, and only having here the non-exporting trial version of GlobalMapper, do any of the DXF export settings change the format/group code output in a way which might allow us to import the GM DXF?

Thanks!

Comments

  • KyudosKyudos Global Mapper User Posts: 12Trusted User
    edited March 2011
    Kyudos wrote: »
    1) The file has Projection: Geographic (Latitude/Longitude), Datum: NAD83, Ground Units: arc degrees. This appears to make "X" the Long and "Y" the Lat, which generally seems backwards. Is that a feature of NAD83, or of exporting projected data in DXF?

    Actually, thinking more about this, it does make sort of make sense.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited March 2011
    I would expect X to be longitude and Y to be latitude, that is how your normally draw a lat/lon grid.

    If you check the box to generate 3D DXF files on export you should get the separate 30 entry for each VERTEX of the POLYLINE, although for contour lines this is very wasteful since the 30 group code value is the same for every VERTEX. I would recommend supported either method of elevation storage rather than requiring a separate 30 for each VERTEX.

    Global Mapper tries to export a DXF file that will function in as many formats as possible. Since the POLYLINE entity has been around forever and there isn't anything in the LWPOLYLINE entity that Global Mapper needs, there isn't any reason to use it.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • KyudosKyudos Global Mapper User Posts: 12Trusted User
    edited March 2011
    Thanks Mike,

    I can certainly fix out DXF import routine to deal with this extra case, but it is good to know that we might be able to jerry-rig a solution in the meantime.
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