What To Do When The Gps Just Isn't Good Enough

August 17, 2005

Folks,

I was recently out on a geocache expedition with the kids and the family dog. The cache page said that the cache should be about a hundered feet off the trail, but my gps never showed us closer than about 193 feet. I'm using a Garmin etrex, and I have a handicap that while it doesn't keep me in a wheelchair, it can slow me down pretty good at times. I was wondering two things.

1) are there other tools or techniques we can use when the GPS gets confused?

2) is there another gps I should look at that isn't as sensetive to my speed?

Thanks

Kurt

4.1k · August 17, 2005

Kurt,

Your GPSr should give an accurate reading whether you are moving slow, fast, or standing still.

If your GPSr was showing that far off perhaps you might check the logs for that cache and see if others have had the same problem. Also, check the "expected position error" to see how much error the unit thinks it has in it's calculations.

We have only had problems with our GPSr when there were heavy electrical storms nearby. So you may want to try again and see if the GPSr does better.

Good luck,

John

3.8k · August 17, 2005

The cache page said that the cache should be about a hundered feet off the trail, but my gps never showed us closer than about 193 feet.

If the GPSr is off by this amount, I immediately suspect that you may not have the datum set properly. Take a look at your manual, and be sure that the datum is set to WGS84. If it is set to something else (like NAD 27), you'll be off by a few hundred feet most of the time. Also, be sure that your format is set to hddd mm.mmm (hemisphere degrees, minutes.decimal minutes) and not dd mm.ss (minutes and seconds).

3.3k · August 17, 2005

Also consider the terrain around you: tall trees, high canyon walls, etc...

Also check placement of the the GPS, if too close to your body, it will block out signals.

Good luck.

38.2k · August 17, 2005

The compass in the eTrex will be affected by your speed, but the accuracy shouldn't be. Because it doesn't have a magnetic compass you must be moving at a brisk pace for it to determine your direction of travel.

One thing to help with the eTrex is to make sure it's always held flat, face up to the sky. If you hold it any other way you may have reception problems under trees.

August 17, 2005

Get a Lowrance iFinder PRO or above, and get an external powered antenna with a long cable for it.

The basic iFinders and iFinder GO/GO2 have single processors, the GO/GO2 have no external antenna connection processors The Pro and above have dual processors for update speed and you won't have to worry about them speed wise unless you can move over 40 MPH, and even then it catches up in one second.

Carry velcro cable ties with the unit and the antenna. When you get under canopy or in thick brush attach the antenna to the unit and then velcro it to a long stick and hoist it as high up as you have cable and stick to reach. Do remember that the antenna position and not the GPS position is what will determine position shown on the GPSr when you use an external antenna. Sometimes sixteen feet can make a big difference.

If you can't do a cache with that help, DNF it and be happy.

August 17, 2005

Don't know if this will help your situation, but what I do sometimes is stand still, read off the bearing (notthe heading), set my magnetic compass to it and then start walking in that direction.

Mostly though, it sounds like a datum issue. According to the eTrex manual:

The default datum in the eTrex is WGS 84

( http://www.garmin.com/manuals/eTrex_Owners...00andabove_.pdf )

So one thing you could try is leaving the batteries out of the unit for like a week. This should clear out all settings. Or if you can get to the System page (press the page button until you get to the Menu page, then select Setup, then select System) you should see a Defaults button that will do the same thing.

1k · August 17, 2005

If reception is so bad that you are 193 feet off, then the indicated position and bearing and distance to the cache will probably be "jumpy." If this is not the case--if your readings are fairly steady, then you should have confidence in the readings.

A couple of things to consider:

"Good" performance may still only get you within 15-20 feet of the cache.
Reported cache locations are not always accurate.
Caches sometimes get moved.

August 17, 2005

Try a PC Mobile reradiating antenna.

I have a Legend and it enhances the signal considerably.

Just Google pcmobile.com and they have all the specs and prices.

1.7k · August 17, 2005

The cache page said that the cache should be about a hundered feet off the trail, but my gps never showed us closer than about 193 feet.

I judge you didn't find the cache, so what were you 193 feet from?

If you're saying you never left the trail and took the cache descriptions statement "that the cache should be about a hundred feet off the trail" to mean almost exactly 100 feet and so you should have gotten a minimum distance reading of 100 on your GPSr, well . . .

It did say "about" so he may not have checked it. And, if this is heavy tree cover his coordinates could have been off quite a bit, then there's your GPSr error.

I'm not entirely sure what you mean.

Edited August 17, 2005 by Thot

9.5k · August 17, 2005

Get a Lowrance iFinder PRO or above, and get an external powered antenna with a long cable for it.

The basic iFinders and iFinder GO/GO2 have single processors, the GO/GO2 have no external antenna connection processors The Pro and above have dual processors for update speed and you won't have to worry about them speed wise unless you can move over 40 MPH, and even then it catches up in one second.

Carry velcro cable ties with the unit and the antenna. When you get under canopy or in thick brush attach the antenna to the unit and then velcro it to a long stick and hoist it as high up as you have cable and stick to reach. Do remember that the antenna position and not the GPS position is what will determine position shown on the GPSr when you use an external antenna. Sometimes sixteen feet can make a big difference.

If you can't do a cache with that help, DNF it and be happy.

Be real. That's no help and doesn't offer anything with the tools he already has in place.

TheMagnificent7AndSamson: Most of the above advice is good. You should indicate which cache you were looking for so it can be refined a little better for you. Not knowing the difficulty/terrain rating or the area that is in will produce a lot of guesses that may miss the mark.

Things to consider:

1. Make sure your datum is set correctly. Not knowing which GPS you have, you'll need to indicate here or use the manual.

2. Dependent upon your GPS model, you'll need to ensure you're orienting the antenna correctly for the best read. Quad-helix needs to be near vertical to vertical. Patch needs to be near horizontal to horizontal.

3. You have 6 caches found. It may be that you went after a cache that was just a bit over your skill set. Stick with the 1/1 - 2/2's until you have a better feel for hunting for caches.

Edited August 17, 2005 by TotemLake

August 17, 2005

Be real. That's no help and doesn't offer anything with the tools he already has in place.

OP has found half a dozen caches.

His post indicates a probable canopy problem(poor losignal/lock), something etrexes just happen to be known for.

His post coupled with his stats indicate he's got the right datum or he'd not likely have found the 6+locations he has found.

Unless you have a better idea, you might oughta try what I offered him and see does that expand your horizon some. As an Engineer of some thirty odd years, I still find the first cure for poor RF signal problems is still today get the antennas up higher. The darn etrexes are hard to read though when you get them fifteen feet up.

August 18, 2005

Wow thanks to all for the great response. There is a lot of good information here.

The cache was a 1/1.5 (I took 4 of my five kids on this one, ages 4 - 11). The datum and units are correct on my GPS. There were several suggestions involving antennas. As an engineer and an ametuer radio operator I can understand the need for something better than the little patch antenna in my etrex legend and I may try to find something practicle to help with Late spring and summer caching, but It sounds like there are serveral things that we can try without having to add to my techie stock pile.

Thot brought up a point that I've been thinking about all week. The cache listing said that the cache was "about" 100 feet off the trail. On the trail we never got closer than 193 feet. We did go bushwacking and got closer readings but never spotted anything that jived with any of the other clues. When I do the math, that puts my GPS off by almost 100 feet. At the time, that seemed more than an about would account for, but maybe I just don't have enough experience with geospeek yet. We didn't check to see how many sattalites were locked or what the tolerance was on the distance while we were on the trail. That's something that I'll remember to check from now on.

If I can trust the bearing and distance readings no matter how fast I'm moving (assuming I've locked enough sattalites). Then using a magnetic compass to get a heading, and the GPS for distance sounds like a good idea to try as well. I have cerebral paulsy which in my case isn't really too bad considering some of the cases I've seen. I can walk without crutches or braces and as long as the terrain doesn't require any balancing act or slopes that allow gravity to pull harder than I can compensate for with my own legs (ie I can walk up or down the hill) then I'm willing to try almost anything. I have to go real slow sometimes if there are obstacles to step over or around. The compass on the legend is almost worthless when I've got to slow down so I need some sort of replacement, either a magnetic compass or a GPS with a compass that doesn't care how fast I'm moving.

BTW the cache we were after was GCDDD1 if anyone is interested in Missouri caches, the park this is in (St. Francois State Park) is really nice for hiking and hence caching as well. There are a total of five that are on our list to conquer and I think most of them are easy enough for the whole family, at least based on the d/t scores.

August 18, 2005

You can hold your etrex face to the sky and that's about as good as it gets for that unit. They are known for having problems under leaf cover and that's just life.

When a GPSr has a poor signal and particularly when it is getting multipathed signal it has a tendency to be pretty jumpy. You see high EPE and if you wach the position it just doesn't want to stabilize. Under those conditions the best you can do is pick the closest area with the least canopy and hold the unit still and face up for maybe ten minutes to let it settle as best it can. If you turn on tracking it tends to make a plot that is elliptical and off to one side of where it thinks it is. Sometimes you can use this to your advantage. If all else fails back out into the open and take two good bearing from at least 90 degrees apart and use the intersection as a starting point. With four kids to use as markers, then searchers it should be a piece of cake.

A decent magnetic compass can be had for <$10 it beats the dickens out of the electronic versions.

9.5k · August 18, 2005

Unless you have a better idea,

TotemLake Posted on Aug 17 2005, 12:38 PM
2. Dependent upon your GPS model, you'll need to ensure you're orienting the antenna correctly for the best read. Quad-helix needs to be near vertical to vertical. Patch needs to be near horizontal to horizontal.

All without having to buy extra equipment or without having to replace the GPS unit. Imagine that. Most beginners don't know that and most beginners go out and buy stuff they don't really need without knowing what to try first before making a wasted purchase.

At any rate, based on the maps and satellite pics of the cache location, multi-pathing doesn't look like it's going to be a big problem. It's pretty open country. Based on the logs from all walks of experience it is likely the path gets closer.

August 18, 2005

A post by SprocketStL on August 7, 2004:

August 7, 2004 by SprocketStL (206 found)

[Had to do some bushwacking off the trail to get to it.

The hint may be somewhat misleading:] I think the "100 feet off the trail" is actually 100 feet off the dry creek bed, not the trail.

Descriptions (or "facts" given) on cache pages are not always correct for various reasons.

August 18, 2005

We found a cache yesterday under very heavy canopy, so our GPS was absoluteluy useless. In fact, it was worse than useless, it was a hindrance, since it never told us we were any closer to the cache than about 400'. We used the clue and our spidey sense to find the cache. :blink:

1.1k · August 18, 2005

I was recently out on a geocache expedition with the kids and the family dog. The cache page said that the cache should be about a hundered feet off the trail, but my gps never showed us closer than about 193 feet.

Are you saying that from where the cache was to the trail was 193 feet or your GPSr said the cache was 193ft from where you found the cache?

If the former then it was probable a guess to the owner made. If the latter then it could be many problmes. The only factor that your GPSr may have problme with are the way the pointer points as it need to be moving at a certian rate of speed to allow it to function correctly, about 10ft/sec I think. But what I do is have the distanct to waypoint and bearing to waypoint on my pointer page so that even if I am standing still I can use my compass to find the direction to the cache. This helps a lot if the terrain does not facilitate a constant speed. Email me if you need some moer clarification.

cheers

August 18, 2005

Another lesson learned from Phoenix2001.... Read all of the logs that are available. I hadn't gone back as far as a year. :blink:

2.6k · August 18, 2005

Something else that can help, Try Google Earth or usaphotomaps. They're both free progams you can download sat pics, google is in color usa is black and white mostly but they're slowly going to color,

but I think usa is clearer when you zoom in close. Plus I'm not sure if you can change the lat lon format in google, you can in usa and you can also go to topo maps with it.

It sure helps when your trying to find a close trailhead for a cache.

Hope this helps you out a little

August 18, 2005

Also, be sure it's set to magnetic north and not true north.

-Jeff

Edited August 18, 2005 by gpsjeep

August 21, 2005

I only have 29 finds, but I have found a standard compass a great help. Get the best reading possible from your GPSr- take that bearing and use a compass to site it. Cross check the bearing from 50 feet either direction. Read up and learn to use a basic, standard compass. They are $10 or less, and have helped me greatly.

Standard search patterns help to. I also suggest reading several of the books out there. I learned a lot from them.

August 21, 2005

BTW, a rule of thumb that's held over from my backpacking days is if you're on a trail and don't know the area COLD, make sure you've got a magnetic compass as a back up and know how to use it. :laughing:

Good luck!

-Leanne

August 22, 2005

Ha, The magnetic compass pays off big time. Using the bearing off the GPS and a magnetic compass was a great help. we found what looks like the place the cache is hidden, based on the distance and description of the area I'm sure we can go back next week and finnaly log this find. Why didn't we do it this afternoon? Good question.

1) we started to late in the afternoon and ran out of time

2) my silly old grey cells forgot the most important thing about this cache. I've got a white jeep travel bug that I have to place, and this is the place we picked. we decided to go back to the van and get the jeep. By the time we found it. we had to leave.

Any way, I learned a lot from all of the suggestions on this thread, and all I can say is keep on huntin'. As a sport this sure has changed my mind about taking a walk. I just wish I could do it every day and not just on weekends.

Thanks

Kurt

Edited August 22, 2005 by TheMagnificent7AndSamson

August 22, 2005

Post back & let us know how it went. Happy caching!

Dave

August 23, 2005

Could it also be that cheap G.P.S. are not as accurate as the dearer one, so when a person with a dear G.P.S. tries to find the Geocache it is not where it indicates......( because of this)

1.1k · August 23, 2005

Could it also be that cheap G.P.S. are not as accurate as the dearer one, so when a person with a dear G.P.S. tries to find the Geocache it is not where it indicates......( because of this)

NO. Just more bells and whisles but the underlying software is pretty much the same. My caching partiner with almost 4k finds uses the yellow etrex still.

cheers

2.2k · August 24, 2005

happy with my gps map 60c but always have back up of non electrical good old fashioned magnetic compass not matter how familiar i am with the area or terrain. better safe than sorry and in tree cover it doesn't have a little fit and start getting all huffy about which way to go. :laughing:

9.5k · August 24, 2005

About 3 years back, there was an issue with the early production Etrex patch antenna which has since been handled by better quality control. That's the only issue I'm aware of that would affect his accuracy as long as he holds it in the appropriate position for best reception.

August 24, 2005

Could it also be that cheap G.P.S. are not as accurate as the dearer one, so when a person with a dear G.P.S. tries to find the Geocache it is not where it indicates......( because of this)

NO. Just more bells and whisles but the underlying software is pretty much the same. My caching partiner with almost 4k finds uses the yellow etrex still.

cheers

I agree, I have an Etrex Vista and a Legend, and I swear that the cheaper gps settles down more quickly than the Vista.

August 24, 2005

To all who are interested (especially if you're in the St. Louis area.check out GCQ0CZ. First try it without any maps. It's up around I170 and St. Charles Rock Road in St. Louis County. I mention it here because we got very interesting GPS behavior even with a good open sky with the etrex legend on the dash, in the front window of our van. We finally found it, but if I hadn't checked a map and aerial photos, we'd still be looking. I'm going back this afternoon to drop off a TB and check things out with the good Ol' Silva

August 27, 2005

Always look at at least one map!

August 29, 2005

Unless you have a better idea,

TotemLake Posted on Aug 17 2005, 12:38 PM
2. Dependent upon your GPS model, you'll need to ensure you're orienting the antenna correctly for the best read. Quad-helix needs to be near vertical to vertical. Patch needs to be near horizontal to horizontal.

Totem Lake

Thanks for the tip about a quad-helix antenna needing to be vertical for optimal reads.............I did not know that.

August 29, 2005

Hm... I must have forgotten to click the last submit on my previous post. Anyway we wont have to move to Jamaica and wash cats for a living. We put JPERGY Jeep TB in the Missouri trail cache Saturday. That by the way is the cache that started this thread. Thanks again for all the good advice. We can keep it going as long as folks are finding it useful I guess

Kurt for TM7AS

What To Do When The Gps Just Isn't Good Enough

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