[GRASS-user] Determining Datum From Projection Coordinates [SOLVED]

Michael Perdue michael_perdue at yahoo.ca
Wed Mar 2 21:46:33 EST 2011

Hate to be a wet blanket, but both NAD27 and NAD83 UTM coordinates are supposed to be in meters. The False Easting for the UTM zones are defined to be 500000m regardless of datum. So, the presence of meters in your DB is not a solid indication that it is in NAD83. As the lat/long in you're file appears to be rounded to 2 decimal places (about a km) and is undefined with regards to datum, it will be difficult (if not impossible) to determine whether the data is NAD83 or NAD27. If you can live with the ~150-300m error then it shouldn't be a problem, otherwise ...


On 2011-03-02, at 5:43 PM, Rich Shepard wrote:

> On Wed, 2 Mar 2011, Thomas D. Dean wrote:
>> Look at
>> http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system
>> Some calculations should show you if it is meters ot not.
> tom,
>  The magnitude of the values is also indicative; for the NAD27 values in
> feet they'd be much larger.
>  Interesting article that confirms what I thought was the case.
> Thanks,
> Rich
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