How to determine GPS accuracy?

Hi,

I got a Nuvi 250 for Christmas, and that was my first GPS. I'm curious
about it's accuracy. I'm also in Canada, so finding pre-determined
locations to check against isn't possible (I don't think). The arrow
seems to match my location on street maps, but I'd like to verify
accuracy as a measure of +/- 20', or +/- 30' etc. Any ideas?

Thanks,

Norm

Norm

This is not the final answer -- but you can easily
experiment until you determine where the nearest 'real'
geodetic marker is and use that to compare with your Garmin.

Anyway using http://maps.google.com or Google Earth, find
a spot near your house where you can zoom in and really
find a small spot that you will actually be able to get to -
- and read the latitude and longitude.

For getting coordinates from Google see:
Garmin GPS - Tricks, Tips, Work Arounds, Hints, Secrets
and Ideas
Article:

ARE YOU COORDINATED? -
Obtaining and Using Coordinates in Your GPS

Now, go to that spot (with your antenna up/or in active
GPS mode) and read from your instrument what your Garmin is
reflecting as the coordinates.
See Garmin GPS Tricks, Tips, etc.........
Article:

WHERE AM I? BY THE NUMBERS -
Coordinates of Your PRESENT Position

Make a comparison of the coordinates.

You might walk around the spot, watching the coordinates
change until they match what Google maps said (assuming
Google was the most accurate of coordinate indicators in
the world) and eye ball or measure the straight line
difference.

You could even plan a route by making the Google
coordinates a destination and your reality position as the
starting point and let your GPS tell you how many feet your
are away from your destination. You would read the distance
from a 'Where to?' inner screen. [I didn't try this but it
should work -- somewhat.]

I hope that some of this is some help. Eh?

Read more about
Garmin GPS Tricks, Tips, Work Arounds, Secrets and Hints at

**********************
http://snipurl.com/garmin_gps_tricks
**********************

Gary Hayman

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

Don't bet on the accuracy of Google Earth. The mapping is approximate at
best.

Google does pretty good on their accuracy. Last year I had "The Google
Guy" charter a Floatplane, and fly out to my, very isolated Inlet,
here in alaska, to take Survey Grade GPS Fixes, of specific geographic
locations, that could be seen, and Identified, on upgraded SAT based
Photos. He said that the updated Registrations would be available in
about 6 months. Sure enough, about six months later, the High Resolution
Pictures were incorporated, and the GPS Registrations were "Right On"
One of the Points, he Registered, was a USGS Monument that was Survey'd
in by the USGS a few years back, as a Primary Survey Monument in our
area.

--
Bruce in alaska

While they aren't too bad in general, if you look closely at the photos,
you will often see mismatches at the mosaic boundaries. Roads can jog
perhaps 50 or 100 feet at times. Those jogs can only mean there are
errors. I have also seen political boundaries several hundred feet from
where they should be.

If someone was trying to look at the accuracy of their GPS, they would
have to recognize that those sorts of errors can exist in the Google
data.