Values for UTM & LL out of sync

anticus
anticus Global Mapper User
edited August 2008 in Technical Support
I am georeferencing a chart over Costa Rica that uses the Ocotepque datum.
I'm using the UTM projection, Clarke 1866 spheroid.
If I georeference to the UTM values these values are displayed accurately but the Lat/Lon values are off by over 400 meters. If I reference to the Lat Lon values the UTM values are off but the Lat Lon are correct.
Is this a datum problem ? The Molodensky transformation values for the Ocotepque datum are: 204 , 96 and -98.

thanks for any help

John

Comments

  • global_mapper
    global_mapper Administrator
    edited August 2008
    John,

    It sounds to me like perhaps the UTM grid on the map and the lat/lon grid on the map are based on different datums or else you did not use the correct ellipsoid when creating the datum. How do you know that the chart is based on the Ocotepque datum?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • anticus
    anticus Global Mapper User
    edited August 2008
    The Ocotepque datum is specified in the marginalia.

    Clarke 1866 is the correct ellipsoid, as entered.
  • global_mapper
    global_mapper Administrator
    edited August 2008
    It's possible that the UTM grid is in the Ocotepque datum and the lat/lon grid may use WGS84 (or some other datum). Is it possible for you to provide me with the chart to take a look?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • anticus
    anticus Global Mapper User
    edited August 2008
    I can't provide the chart (LIMDIS) but here is the relevant legend info verbatim:

    Spheroid........................................... Clark 1866
    Grid................................................. (North American 1927) UTM
    1,000 Meter Zone 16
    Projection........................................... Lambert
    Vertical Datum ..................................... MSL
    Horizontal Datum .................................. Ocotopeque Fundamental
  • global_mapper
    global_mapper Administrator
    edited August 2008
    Can you perhaps provide a screenshot illustrating the problem?

    The legend indicates a (North American 1927) grid, which is usually the NAD27 datum. Perhaps the UTM grid is in NAD27 and the lat/lon grid uses Ocotopeque?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • anticus
    anticus Global Mapper User
    edited August 2008
    Can't do a screenshot (restrictions).
    I'll try the georeferincing using NAD 1927 for the UTM values and see what happens.

    thanks

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