Values for UTM & LL out of sync
anticus
Global Mapper User
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
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
-
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 -
The Ocotepque datum is specified in the marginalia.
Clarke 1866 is the correct ellipsoid, as entered. -
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 -
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 -
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 -
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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