[pct-l] GPS, distance and speed.

[msaenz at mve-architects.com (Mike Saenz)]

Interesting info Adrian!
Where did you get this from?

I'm trying to learn as much as possible about this expensive and controversial piece of trail electronics I bought.

I've read articles, attended REI clinics and actually read most of the manual!

But what I've always heard is that with WAAS capable GPS units, the accuracy (theoretical, optimum conditions) is down to 3 meters. And that this accuracy limitation is imposed by the US government, not due to any lack of capabilities of the technology.

I also have been told that the newer (last three or four years) models have MUCH better reception than the older, clunky units (smaller & better!).

Specifically addressing your comment, my understanding is that the satellites emit signals in the form of continuous frequency. In other words, the GPS unit is receiving and measuring these signals on a constant, continuous basis. Even the lowest frequencies, which are the slowest, (now, I'm going way out on a limb on this as I am not a radio enthusiast) are still measured in MHz (million cycles per second) and couldn't possibly be affected by any speed in which we could transport the unit itself.
And GPS frequencies were selected by the military to penetrate water, both clouds and oceans, which would require a particularly high frequency. (I'll go check my manual for the frequency spec when I get home tonight)

So I would have to believe that, in good conditions (WAAS capable and hitting on at least 6 satellites), most newer GPS units would hit the 3 meter restriction before any technological limitations on the GPS electronics itself.

I have my Rhino set to good ol' feet, not meters. I've seen my accuracy read off as 3 and 4 feet for a second or two. In Joshua Tree, my accuracy report hit and stayed at 9 feet several times, though I have to admit it was reporting 10-12 feet more often than not. And I was hitting on all 12 satellites, though some were not being received as strongly as others.

I also dabbled in Geocaching, just to learn how to play with my new toy. Now, THAT's an activity that requires an accurate GPS! Even if you're standing right on top of the geocache, they're usually hidden so well you can't find it. Two things are working against you on this: how accurate was the long/lat coords reported by the person who placed the geocache, and how accurate is yours when you go looking for it. If you're 9 feet off, you may not find it. Most of the time, I'm staring at the bearing and accuracy when I'm looking for a geocache, and I've seen my accuracy jump around from 4 to 16 feet while I was standing still.

M i c h a e l   S a e n z
McLarand Vasquez Emsiek & Partners, Inc.
A r c h i t e c t u r e    P l a n n i n g    I n t e r i o r s
w  w  w  .  m  v  e  -  a  r  c  h  i  t  e  c  t  s  .  c  o  m

 -----Original Message-----
From: 	adrian.borner@ch.abb.com [mailto:adrian.borner@ch.abb.com] 
Sent:	Tuesday, April 13, 2004 8:05 AM
To:	pct-l@mailman.backcountry.net
Subject:	[pct-l] GPS, distance and speed.


The accuracy of the GPS is in the range of 20 to 30ft horizontally and even
less vertically depending on reception. The misreading is not always in the
same direction and as a result the distance covered between two readings
could even be negative when walking. As a result from this random error the
accumulation i.e. distance covered and max speed are not accurate when you
move slowly.
Doing the same thing in a car cruising down a highway with 60mph, the
random error is much smaller in relation to the distance covered.
Adrian

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