GPS coords. vs. topo map

I've visited the TopoZone website a few times, and one of the interesting
features is that it will tell you the exact coordinates of a point you
select in the crosshairs. I'd been curious about how accurate that was
compared to my GPS, so yesterday I checked it. I selected an intersection
about a mile from my house, and plugged the TopoZone coordinates into the
GPS. On my next errand run, I drove through that intersection to see how
close the coordinates would correspond. The result, almost dead on. Pretty
cool.

Joe F.

"rb608" wrote in message
...
I've visited the TopoZone website a few times, and one of the
interesting
features is that it will tell you the exact coordinates of a point
you
select in the crosshairs. I'd been curious about how accurate that
was
compared to my GPS, so yesterday I checked it. I selected an
intersection
about a mile from my house, and plugged the TopoZone coordinates
into the
GPS. On my next errand run, I drove through that intersection to
see how
close the coordinates would correspond. The result, almost dead on.
Pretty
cool.

I've done the same thing with DeLorme's "Street Atlas" software.
Generally, the results have been very good, but I've noticed some
errors of ten to twenty yards. Certainly close enough for most
applications, I think, but it might make a significant difference in
some. Even without the GPS it quickly becomes apparent that some
features on the software maps are not exactly in the right place.
I've found a few businesses, for example, a block or so away from
where they are shown.

Wolfgang

"Wolfgang" wrote...
snip
Even without the GPS it quickly becomes apparent that some
features on the software maps are not exactly in the right place.
I've found a few businesses, for example, a block or so away from
where they are shown.

I've found a LOT of that type of problem. Microsoft Streets & Trips 2000
software has Coburn, PA seventy miles west of its true location.
--
TL,
Tim
------------------------
http://css.sbcma.com/timj

"Tim J." wrote in message
I've found a LOT of that type of problem. Microsoft Streets & Trips 2000
software has Coburn, PA seventy miles west of its true location.

That's its true location. There are two Coburns in PA.

Joe F.

"rb608" wrote...
"Tim J." wrote:
I've found a LOT of that type of problem. Microsoft Streets & Trips 2000
software has Coburn, PA seventy miles west of its true location.

That's its true location. There are two Coburns in PA.

Then the software has a greater fault - the second one isn't listed.
--
TL,
Tim
------------------------
http://css.sbcma.com/timj

I've found a LOT of that type of problem. Microsoft Streets & Trips 2000
software has Coburn, PA seventy miles west of its true location.

That's its true location. There are two Coburns in PA.

Then the software has a greater fault - the second one isn't listed.

My guess is that the datum used on your GPS and in the software
isn't the same. The difference will lead to dramatic
differences between the actual location and the location your
GPS is displaying....

"Wolfgang" wrote in message
...
I've done the same thing with DeLorme's "Street Atlas" software.
Generally, the results have been very good, but I've noticed some
errors of ten to twenty yards.

Both my GPS and the map display accuracies of .01 minutes. How far is that
anyway? (I'm not in the mood to do the math.) BTW, I've wondered about
the actual coordinate memory of these things. Even though it displays to
hundredths of a minute, do they store a greater accuracy internally?

Certainly close enough for most
applications, I think, but it might make a significant difference in
some.

Like, the bridge over the river is at 39° 36.53'N, 76° 38.11'W , and there's
a 20" brown at 39° 36.35'N, 76° 38.43'W.


Joe F.

"rb608" wrote in message
...
Both my GPS and the map display accuracies of .01 minutes. How far is
that
anyway? (I'm not in the mood to do the math.)

One minute is approximately one nautical mile (6080 feet). I leave the
decimal point movement to the reader.

The GPS in my car is accurate to within 10 meters, which makes it somewhat
less accurate than current models with WAAS enabled. The very few times
I've matched it to map coordinates it's been bang on.

--
Stev Lenon 91B20 '68-'69
Drowning flies to Dark Star

http://web.tampabay.rr.com/stevglo/i...age92kword.htm

"rb608" wrote in message
...
"Wolfgang" wrote in message
...
I've done the same thing with DeLorme's "Street Atlas" software.
Generally, the results have been very good, but I've noticed some
errors of ten to twenty yards.

Both my GPS and the map display accuracies of .01 minutes. How far
is that
anyway? (I'm not in the mood to do the math.)

Hm......

Well, assuming the Earth's cirumference to be 24,000 miles, that would
make one degree of longitude at the equator equal to 66.67 miles. A
minute of arc is 1/60th of a degree or 1.11 miles. So, .01 mintue
equals .011 miles or roughly 58.67 feet.

BTW, I've wondered about
the actual coordinate memory of these things. Even though it
displays to
hundredths of a minute, do they store a greater accuracy internally?

No idea.

Certainly close enough for most
applications, I think, but it might make a significant difference
in
some.

Like, the bridge over the river is at 39° 36.53'N, 76° 38.11'W , and
there's
a 20" brown at 39° 36.35'N, 76° 38.43'W.

Zactly! Um.....then again, unless your casting is at least as precise
as your GPS it's probably moot.

Wolfgang
and, of course, if you're at 45° 12.42'N, 90° 8.33'W the whole thing
is just plain silly.