I checked the TOPOZONE site and could easily come up with my QTH in
Corrales, NM. Decided to check accuracy so got my trusty GARMIN II Plus and
monitored the the output ( in UTM coordinates) resulting from internal
calculations. The map at TOPOZONE placed me at differennt coordinates than
what my GPS was reading. The error is NOT signifcant for amateur use (about
250 meters south and 200 meters west) of what the GPS readings incicated.
For about 2 hours I monitored the GPS readings and the difference in the GPS
readings was only 5 meters E-W and 3 meters N-S over the 2 hour period of
time.
Please note that I did not take into account the possible difference in
NAD27 and WGS84 (my GPS set for WGS84 currently)error that must be
determined when using a 7.5 minutes quad map. I have noticed as much as
about 100 meters difference on maps I use in SE Utah when 4X4ing. I do
notice that normally the topo maps are fairly good, but the GPS has helped
to determine my location easier then features on the map. BTW, on numerous
occasions several of us have compared GPS readings at the same spot (OK
vehicles may be with 5 meters of each other) and readings are always very
close. We use external antennas with gain to increase signal strength and
help maintain lock onto the satellites. Waypoints we make are often checked
on return route and very close to those recorded.
With TOPOZONE you can place cursor on your qth on the map and I got a UTM
reading above the map. This was the UTM I used to determine the info I got.
More playing with TOPOZONE is forth coming.
73 de Arne N7KA
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