GPS discussion

CaptCaper · Jun 4, 2006

Paradox said:
I checked that out, Thank you. Wandering seems to be a frequent complaint. I just set my 60CSx on the ground in my backyard for 10 minutes. The reading wandered NE in a straight line about 50 feet horizontally in the first minute and the altitude dropped 20 feet. Over the next 9 minutes it did not wander horizontally from that location by more than 10 feet. Altitude dropped another 25 feet. Maybe I just got a good unit, kind of like not getting a car made on a Monday.

I had heard of the WAAS problem before I bought the unit and have never enabled it. The only time I have ever enabled the WAAS was on my eTrex Vista when on a trip Annapolis to Marblehead. WAAS worked great for out on the Atlantic. At the dock, I could follow the pointer fore and aft on the 42' boat we were on. Pretty cool, but to rely on technology for that type of repeatable accuracy, might get you into trouble. For hiking it seems like overkill. In geocaching you are also depending on the accuracy of the unit that placed the cache in addition to your own unit so it seems like it is not useful there either.

I am having alot of fun with this unit, due in part because I can hang it from my belt and it always gets a signal.

I have an 60cs and as with the other gps's also I've owned I leave the WAAS on all the time. The WAAS signal corrections carry for a while so if one loses it it will still give good accuracy. Remember not only positional but data,Speed,altitude,etc. are all better with WAAS.
I've had situations where I loaded a track from a hike during good weather again when I went back with so much fresh snow from a bizzard I couldn't tell the trail from anything else around. The accurate track recorded with WAAS on put me right down the trail safely and kept me on it as it wandered around along the side and in and out of the trees. I would have struggled to find the trail with out a good track.
I believe they might (Garmin) have fixed the wandering with the last software and unit updates. I always leave mine running all day as it get's better accuracy after running for an hour or so with good signals.

So I don't think it's over kill, for me anyway and the way I use it. 10ft. here or there makes a difference sometimes. I'll keep my WAAS thank you.

DougPaul · Jun 4, 2006

Paradox said:
I checked that out, Thank you. Wandering seems to be a frequent complaint. I just set my 60CSx on the ground in my backyard for 10 minutes. The reading wandered NE in a straight line about 50 feet horizontally in the first minute and the altitude dropped 20 feet. Over the next 9 minutes it did not wander horizontally from that location by more than 10 feet. Altitude dropped another 25 feet. Maybe I just got a good unit, kind of like not getting a car made on a Monday.

All GPSes wander. Your first fix is likely to be inaccurate. After a few fixes, it settles down and then typically wanders around, mostly in the error circle (see below).

As for GPS altitude, the typical errors are about 1.5--2 times the horizontal error. If you are talking about the barometric altitude (which is what the Garmin S models show), it acts differently depending upon how you calibrate it (auto (from the GPS) vs manual). Manual is limited by the accuracy of your calibration altutude and auto can take a half hour or longer to settle down.

I had heard of the WAAS problem before I bought the unit and have never enabled it. The only time I have ever enabled the WAAS was on my eTrex Vista when on a trip Annapolis to Marblehead. WAAS worked great for out on the Atlantic. At the dock, I could follow the pointer fore and aft on the 42' boat we were on. Pretty cool, but to rely on technology for that type of repeatable accuracy, might get you into trouble. For hiking it seems like overkill. In geocaching you are also depending on the accuracy of the unit that placed the cache in addition to your own unit so it seems like it is not useful there either.

WASS reduces the EPE from about 10m to about 5m. (An EPE of 10m means that the error is expected to be less than 10m 95% of the time.) A 10m error is good enough for my hiking and boating. Most likely yours too.

Lots of info at http://www.gpsinformation.net.

Many of the experts hang out at news://sci.geo.satellite-nav. Can also be accessed though http://groups.google.com/group/sci.geo.satellite-nav?lnk=gschg&hl=en

Doug

arghman · Jun 4, 2006

another anecdotal reason to listen to people who say don't depend on a GPS for primary navigation (which is not why I use it):

I just had the extremely aggravating experience of losing lock w/ my GPS

, in conditions of cloud cover, light misty rain (probably what did it), and nearly full tree cover. This is about the only thing worse than running out of batteries (which is human error, preventable if you have sufficient backup cells).

It happened at a spot where I knew exactly where I was, but I was trying to re-find some nearby plants that I'd marked 3 wks earlier... I did eventually find them, & then followed a skid road back to my car instead of taking a more meandering bushwhack through the woods. Had a compass but just used it to verify the skid road was heading west. The @#$#@ GPS would not re-gain lock despite open sky above the skid road & occasional clearings, and repeated attempts to power down/up and force it to search for satellites, holding it up high (and despite/because of my repeated audible comparisons of it to porcine excrement). Finally when I got to an open field with a full view of open sky, it acquired "lock" on an incorrect point about 1km away, which it didn't correct for another 10 minutes, right about the time I got back to my car.

BTW this is a Lowrance iFinder PhD which seems slightly worse than my Garmin Legend for re-acquiring lock in questionable situations. There have been a few times (once on a clear day!), like today, that it just gives up & screams "Ha! Doubt me!" & I can't trust it at all.

DougPaul · Jun 5, 2006

arghman said:
another anecdotal reason to listen to people who say don't depend on a GPS for primary navigation (which is not why I use it):

I just had the extremely aggravating experience of losing lock w/ my GPS , in conditions of cloud cover, light misty rain (probably what did it), and nearly full tree cover. This is about the only thing worse than running out of batteries (which is human error, preventable if you have sufficient backup cells).

GPS signals are basically unaffected by weather. (The frequencies were chosen to minimize this problem. The wavelength is ~19cm -- anything less that ~1cm (ie water drops) will have negligible effect on the radio signals. Bulk water or sheets of water are the trouble makers.) It is more likely is that the GPS was in a wet case or that the electronics of the GPS were wet. A film of water on the case might also cause problems.

GPS has been qualified as a primary navigation system for aircraft in Alaska (and I think in the continental US also). WAAS was added by the FAA as part of a GPS bad weather and limited visibility landing guidance system. It does work in bad weather...

Doug

CaptCaper · Jun 5, 2006

Paradox said:
In geocaching you are also depending on the accuracy of the unit that placed the cache in addition to your own unit so it seems like it is not useful there either.
QUOTE]

Actually Paradox, most of them use WAAS and external antennas for consistent accuracy so I'd do what they'd do to find the cache.
Also if your accuracy is showing 10ft. that's 10 ft. to each side of you for an overall error of ft. that makes a huge difference in finding trails,caches,shipwrecks, plus keeping the data steady.
This fall will WAAS will much better for us here in the NEast. They've added more birds and moved them for better reception. I wouldn't give it up.That would be a waste of performance.
No offense guys but I'd follow my track in a snow squall,night,etc. or my son's for that matter than yours period.

Good luck

jrichard · Jun 5, 2006

Paradox said:
Does anyone out there use GPS differently?

I don't own a GPS, but I have borrowed a couple. I mainly use them for mapping out paths that don't have trailmaps. I've done this two ways: 1) using an older GPS I wrote down coordinates in a notebook every view minutes and 2) using the route function in newer a GPS.

Lest someone think I'm a cartographer, these maps are only for myself.

I'd be curious what kind of software people use to superimpose GPS coords on a topo map for printing. I'm using a very old version of TOPO! (It so old it says "Wildflower Productions" instead of National Geographic.)

CaptCaper · Jun 5, 2006

jrichard said:
I don't own a GPSS, but I have borrowed a couple. I mainly use them for mapping out paths that don't have trail maps. I've done this two ways: 1) using an older GPSS I wrote down coordinates in a notebook every view minutes and 2) using the route function in newer a GPS.

Lest someone think I'm a cartographer, these maps are only for myself.

I'd be curious what kind of software people use to superimpose GPS coords on a topo map for printing. I'm using a very old version of TOPO! (It so old it says "Wildflower Productions" instead of National Geographic.)

NGTopo has a new version that came out this spring that you might want to look into.
You can print the map out with different options as to labeling with coordinates,email sending,etc. a

DougPaul · Jun 5, 2006

jrichard said:
I'd be curious what kind of software people use to superimpose GPS coords on a topo map for printing. I'm using a very old version of TOPO! (It so old it says "Wildflower Productions" instead of National Geographic.)

That will work (I have a later version). Many (most?) consumer GPSes can record a track (and wapyoints) which can be transferred to the computer. Maptech Terrain Navigator is also popular. Most GPS suppliers also offer software with maps (eg Garmin Mapsource). There are also a number of freeware and shareware programs.

If you wish to load maps into a mapping GPS, you will need software and maps from the manufacturerer.

Doug

skidoc22 · Jun 5, 2006

DougPaul said:
GPS signals are basically unaffected by weather. (The frequencies were chosen to minimize this problem. The wavelength is ~19cm -- anything less that ~1cm (ie water drops) will have negligible effect on the radio signals. Bulk water or sheets of water are the trouble makers.) It is more likely is that the GPS was in a wet case or that the electronics of the GPS were wet. A film of water on the case might also cause problems.
Doug

I have experienced a significant difference in the reception of my Magellan Platinum (now defunct) on overcast days versus clear days. I do not know the technical explanation for this circumstance but I know it has happened with regularity. I am not talking about rain or fog which might get the outside of the unit wet but just solid cloud cover. The unit is waterproof so I doubt there is much likelihood of the electronics being wet aside from condensation. As I said the unit had its share of problems so I guess it may have had some unusual or unique issue.

Paradox · Jun 6, 2006

I have a Garmin 2720 street pilot that mounts on my car dashboard. The satillite reception is very poor when the weather is cloudy or raining, makes no difference. (I still love these things, I turn it on to drive two miles home and I've had it fo almost a year.)

DougPaul · Jun 6, 2006

Paradox said:
I have a Garmin 2720 street pilot that mounts on my car dashboard. The satillite reception is very poor when the weather is cloudy or raining, makes no difference.

Neither rain nor clouds has had any noticeable effect on my Garmin eTrex Vista or 60CS when mounted on my car dash.

The dash adds the possibility of winshield wipers interrupting the signals.

I have also read reports of a kayaker using one of the eTrex line attached to the deck of his boat. Plenty wet, but kept on working.

Doug

dougb · Jun 7, 2006

For kayaking, I like the Garmin Foreunner and now the Foretrex. Having the screen on my arm, instead of on the deck, is pretty handy. I can take a quick look at the direction arrow as I paddle. That doesn't work so well when hiking.

To reiterate what someone else said, though, you still should bring the ol' compass and know how to use it. Last year on Marshall, in pouring rain, the GPS got one too many mud-baths and decided to croak (the Forerunner).

One last use for the GPS, that I don't think I've seen, is as a record. I turn the unit on at the trailhead, lunch, peaks, etc. and when I get back, I save the track. In addition to notes and photos, I have the time stamped track & map as a record. One more thing to look at on those long days away from the trail!

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