There is more to this problem - a 200 meter discrepancy is too large
to be accounted for by a change from NAD27 to NAD83 alone. Also, the
problem seems to be isolated to UTM coordinates and not lat/long
geocoodinates. I have sent topozone a table of UTM coordinates and
geocoodinates taken from the paper map, their program, and my Topo!
CD-ROM.
Measurements using the USGS map grid agree with those from topozone
and Topo! NAD83, but none of these agree with Topo! NAD27 or
reality. I believe the paper map grid is NAD83 and topozone is
misinterpreting it as NAD27. Since only the UTM coordinates, and not
the geocoordinates, show a 200 meter change between NAD27 and NAD83,
I conclude that the UTM grid moved with respect to the geocoodinates
concurrently with the datum change.
And now I must rest my pointy head.
BJB
--- In BoundaryPoint@y..., michael donner <m@d...> wrote:
> cool
> this is almost exactly the difference between jacks & my njnyus
coords
>
> since i used topozone only to measure distances
> but usgs source materials to pin my points onto
> it is still possible that my cruder numbers are basically right
>
> glad you revisited the mdp source of everyones land too
> & trust you had a great one too
>
> m
>
>
> >
> >Anyone using www.topozone.com to acquire GPS coordinates should be
> >aware that they are using a mixture of NAD27 and NAD83 UTM
> >coordinates, but there is no way to tell which is which. They
> >believe all coordinates are NAD27. However, last week I relied on
> >this misinformation during a bushwhack from the Delaware Arc
monument
> >to the Delaware - Maryland - Pennsylvania tri-point and ended up
in a
> >hay field 200 meters north of the tri-state monument. Using the
same
> >target coordinates, but interpreting them using the NAD83 datum
> >yields the correct result.
> >
> >I have contacted topozone about this problem.
> >
> >Regards,
> >BJB
> >
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