[pct-l] GPS, distance and speed.

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

Guy, Steve & Dude (and of course all you out there in PCT e-mail land...)

I'm surprised that your GPS experiences include such bad reception, accuracy and mileage reporting.
And it may be that the newer models are more reliable (though Steve's Geko couldn't be more than a couple years old), but I've found that my Rhino is about as accurate in all it's data reporting that I'd ever need.
I've participated in few postings of software/guidebook/actual mileage discussions here before. what I've found is:
1) the software mileage reports truly stink.
2) Guidebook mileage listings are derived from a wheeled odometer contraption.
3) The posted miles on the trail signposts are not EXACTLY accurate.
4) My GPS mileage reports match EXACTLY what my truck's odometer tells me (within 1/10 of a mile over 100 miles)

I use both Topo! And Delome software. Topo! Has very nice scans of USGS Topo maps, but (at least my version) have a TERRIBLE route marking/ distance estimating tool. Delome will highlight trail sections and map routes easily, but the trails are very low-resolution, and therefore do not accurately reflect all the twists and turns of the trail.
The guidebooks (as I've been told) list mileage as recorded by one of those wheeled odometer thingys (what is the correct name for these?). BUT, exactly how is this used? On a 2 foot wide trail, is the wheel rolled in the middle, hugging opposite turns (like a race car on a course) or by the wobbly, "path of least resistance" hand of a hiker (this would be my guess)?
Think about it. If you stepped 12" to the right or left of the trail for 1/2 the day, you could increase your mileage significantly.
My guess is that someone with a wheeled odometer (over, say, a 10 mile hike) would be trying to hold the wheel as best he could in the middle of the trail. But are his steps following this? I doubt it. I know MY steps are all over the place, considering best foot placement, anticipation of my next step and what is naturally the easiest footing along a trail.
All of the above, with the knowledge that my GPS reports extremely accurate mileage on the road would make me trust my GPS over any other mileage listings. I've seen a 20% error in my software (Cuyamaca to Warner Springs being the most spectacular error). The guidebook lists Barrel Springs to Warner as 8-1/2 miles (my GPS reported 8 miles). I don't remember exactly what the numbers were, but the posted miles from Morena Reservoir to the bridge at Buckman Springs Road was over estimated by something over 1/2 mile.
If you get a GPS with WAAS, you'll get elevation readings triangulated from satellite signals, instead of barometric altimeter (which need to be re-adjusted every day and will vary in accuracy to weather fronts coming and going.
GPS's don't "send" any signals. They only receive or "read" signals emitted from satellites. One satellite "read" gives you no usable data, two will give you a rough 2-dimensional location, three tightens up your long/lat location and will start triangulating your vertical position in 3 dimensions, and so on. All this "reading" is simply the GPS timing the signal interval from a particular satellite. Each satellite emits an ID and a pulse. The GPS then figures out how far away the satellite is by measuring how long a signal takes to get to it.  The more satellites you're "hitting", the more accurate your positioning. Theoretically, you can get accuracy down to 3-meters.(I've heard that this limit is imposed by the US military because they don't want anyone else to have the pin-point accuracy they can achieve that allows them the ability to drop bombs down vent shafts and through windows...) But that's only if you're hitting on all satellites possible (mine can track 12 satellites, if I remember correctly). I've only lit up all satellites twice. Once while above 14,000 in Colorado for a week and once in Joshua Tree.
Dropping into a canyon, HEAVY tree cover and weak batteries will impede satellite reception. My GPS sounds a beep when it loses reception, but it usually picks it back up again fairly quickly. But this loss could easily throw off all the pace/distance info by small percentage. Location data is more accurate than you can plot on a topo map in the field. And as soon as you re-acquire reception, this data is exact.
But exactly how accurate does your information need to be? I suppose that's the real question. It's really nice to know how fast you're hiking. It's also nice to know how far you've hiked. Be aware that if you're the only person with a GPS in a group, you'll be constantly pestered with silly questions of "how far have we hiked?" and "how much further do we need to go?". These questions will come from adults as much as from kids. And it's DAMN annoying. And if you're pre-planning tells you that your hike is 10 miles, and it turns out to be 13 miles, you'll never hear the end of it...
The April edition of Backpacker Mag has a good section on GPS's. REI has a couple clinics on the subject. Check these out before you drop $100+ on a GPS. Do the research like you would on any other piece of gear you're thinking of buying. Asking for opinions here on the e-list is a great way to learn about these things. Sooooooo....
IMHO, if you don't need the radio function of a Rhino, don't spend the extra $ and pack the extra weight. No matter what GPS you get, expect to pack extra batteries. Electronic devices will run out of power exactly when you need them most, Murphy's Law. For a thru hike, you may only need to turn a GPS on when you want to know your location, so the batteries should last quite a long time. The published battery life of a Rhino is measure with all the bells and whistles turned on. I only have my radio on when I'm with others with radios (not very often).
And don't depend on a GPS! Always carry a map/compass. (yeah, you can get around many places without a map and compass because trails are so well marked around Southern California, but good navigational skills get you to places off-trail that enrich any hike).
Oh, and you can get a Rhino 110 (mine) for around $170. You can spend anywhere between $100 to $500 on a unit. Downloadable maps, extra memory, color, etc. will affect the price.
Figure out exactly what you'll use it for and get the one that fits your needs.

See ya on the trail,
Mike



Additional posts pasted in for relevancy:
I am sure the GPS reports what I call flat miles. I think the guides also report flat miles too. The GPS just measures distances using lat/longs. Some GPS have altimeters, but they seem to be quite inaccurate. On long hikes I tend to reset mine 2-3 times a day. If the GPS tried to us the altitude gain in the equation you might get some surprising results.
I have looked at the pace and speed reported by my GPS. I agree that it can be inaccurate, but it seems to average most of the time. Except maybe the altitude change. What is interesting is that the maximum speed is also kept and sometimes reads 30 mph. Now that is fast walking!
Ken
----- Original Message ----- 
From:	"Steve Setzer" <steve_pct@hotmail.com>
To:	<pct-l@mailman.backcountry.net>
Sent:	Saturday, April 10, 2004 12:46 PM
Subject:	Re: [pct-l] GPS, distance and speed.


> The other problem is that GPS may not take into account the vertical
> component of your route. For example, if you travel a mile in the
horizontal
> plane, but also climb a mile vertically while doing so (I know that would
be
> really steep) your actual distance travelled is 1.4 miles (the equation
for
> the hypotenuse of a triangle) while the GPS may report your distance as a
> mile (just using the lat/long coordinates).
>
> I know that my GPS - the Garmin Geko 201 - consistantly under-reports
> mileage when I'm on steep, switchbacking terrain but is right on for
> straight, flat trails.  I'm not sure if its becuase of the vertical
distance
> or the reason that Dude mentioned in his emails.  Maybe both.  You could
> probably find this info from the GPS company.
>
> Steve
>
>
> >The short answer is "yes".  However, I would caution against relying on
> >any GPS for pace and distance because the way that they calculate both
* >makes them inherantly inaccurate.  The GPS is not in constant





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: 	Ilagan, Guy [mailto:IlaganG@cofc.edu] 
Sent:	Monday, April 12, 2004 6:02 AM
To:	Mike Saenz
Subject:	RE: [pct-l] GPS, distance and speed.

Thanks Mike,

How much $ does the Rhino 110 go for?  And, is 15 hrs of battery life adequate for thruhiking.  I thruhiked the AT w/o compass or GPS so thanks again for the info!

-Guy

-----Original Message-----
From: pct-l-bounces@mailman.backcountry.net
[mailto:pct-l-bounces@mailman.backcountry.net]On Behalf Of Mike Saenz
Sent: Friday, April 09, 2004 4:28 PM
To: Ilagan, Guy; pct-l@mailman.backcountry.net
Subject: RE: [pct-l] GPS, distance and speed.


Guy,
Most GPS models out there have standard features such as speed (current, average and max), distance traveled and elevation. Prices for these have fallen dramatically in the last couple years.

I carry a Garmin Rhino 110.
But pretty much all the time, I only use the distance, average speed, elevation and "go to" navigation features.
It does much, much more (more than I've learned how to use so far), but these three features get me from point A to point B in the most efficient manner.

With a USGS Topo map in hand, I can pinpoint my location by estimating distance traveled on the map and matching up the elevation the GPS is telling me. The average speed will tell me when I'll get to any particular destination at any given point.
And I always store waypoint coordinates at the trailhead, campsites and final destination, and any interesting points between by locating the coordinates on my mapping software.

So, my point is: If all you want are the basic features, might I suggest a Geko? At 3.1 oz (minus batteries), it's a compact, lightweight GPS.

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: 	Ilagan, Guy [mailto:IlaganG@cofc.edu] 
Sent:	Friday, April 09, 2004 1:09 PM
To:	pct-l@mailman.backcountry.net
Subject:	[pct-l] GPS, distance and speed.

Hey, 
 
I don't much about GPSs.  I want the pace and distance features as well as the GPS (and affordability).  There is a Garmin Forerunner 101 for $140.00 that does pace,and distance.  The (2) AAA batteries last 15 hours.  I do not want recharchable.  Do other affordable GPSs do pace and distance??
 

-Guy

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