Can Leafless Trees Affect Accuracy?

[Sugar Daddy]

We were on a hunt tonight on a local trail and found the first cache. But the eTrex Legend told me the cache was much deeper into a thicket of bamboo that it actually was. we found the cache nonetheless, but with not too much help from the GPS.

 

We continued on the trail to the next cache and the GPS could only get about 50 ft. accuracy. I went back and forth along the path to try to find what spot on the path was closest to the cache. Sometimes I would turn around and head south, but the indicator (map view) on the GPS said I was still headed north. It was totally unreliable.

 

I just got this unit for Christmas and I've been very happy with it so far. We did a night cache in the woods (that were just as thick as today's woods) the other day and it had no problem at all.

 

On today's hike, we were on our way back to the car and the unit could not even get a fix at all. It was getting dark and we could have really used the assurance that we were getting close to where we parked the car (since we hadn't been on this trail before). We didn't have any flashlights and the sun had set. we only had 2 satellites that were showing up, and they were mostly above us. Any satellites that were 45 degrees or more off zenith were not giving us a useable signal. Is this typical?

 

Yesterday, we were on a cache, which was in a patch of woods as well, and it was near sundown. The readings at that point were unreliable. it would tell me the cache was within 2 ft and then I'd walk around and come back to the same spot and it would say it was 30 ft away.

 

?? What's going on here? If the woods are the issue, then when the leaves start to grow in, the thing will be totally useless!

[+Ocean Archer]

First thing I'd do was to check my batteries - sounds like yours were getting kinda "flat". Second thing, would be to check with other GeoCachers locally and compare machines - unlikely but possible you've got one that is not up to par.

 

With only two satellites in view, most GPS's will be unreliable - need a minimum of three for a proper fix

[+flannelman]

Occasionally my etrex legend will weird out on me like that but not very often. I think that the sats are in bad locations when it does that. I havent had too much trouble with it in the woods even in the summer. The leaves have to be really thick for it to loose signal. I think that the problem is just odd sat alignment or something like that.

[+TotemLake]

I just responded to a similar post in this thread...

 

Through anecdotal observation, I found the taller the trees the more the interference. The thickness of the foliage doesn't really seem to matter much. We assume it does because that's the first thing we decide upon when we look up... and not around at how the horizon has been affected by all the trunks creating a shadow, thus blocking the signal.

 

Leaves don't hold much water. No matter how thick the foliage, you're only talking a miniscule amount of water that's held by the leaves. You'll have more interference from an average rainfall. An average Elm tree with a trunk diameter of 24 inches (that's about a 60 foot height) has the capacity of taking in an additional 20-25 gallons of water in 2-4 hours when injected directly into the root system. That's 25 gallons of water in addition to what is already in the tree. When you want to talk about a water barrier, that's where you want to look.

 

The height and thickness of the tree's trunk and branches are what effects your ability to gain a good signal. Density of the forest can play into this if the trees are smaller in diameter. I'll add here that standing closer to a large tree or a large stand of trees will affect your EPE than when you stand away from it.

 

Bamboo probably will effect you the same way as it is probably similar in water content.

 

You will also find from hour to hour the number of visible satellites will vary, from the very minium to more than you'll ever need. If your horizon is affected at all by anything around you, this will narrow down that number available to you.

[+Torry]

Take a deep breath and don't panic.

 

Make sure you're not "hovering" over your unit.

Fresh batteries have already been mentioned.

Don't wander about in hurried circles when you're getting a bad signal. Try to set up a few steady, straightline walks and see if you can at least get a bearing on the cache. I'll sometimes get a decent bearing on my little yelller feller and triangulate the cache from that.

If all else fails, use other clues... a slight trail, and obvious hiding spot... use the Force if necessary.

 

... and welcome to the game.

[+briansnat]

it would tell me the cache was within 2 ft and then I'd walk around and come back to the same spot and it would say it was 30 ft away.

 

This is totally normal. You'd see this with any unit.

 

In general, your unit is going to put you from 0 to about 50 or 60 feet from the actual cache under good conditions. If there are other factors that can cause signal bounce (buildings, cliff walls, tall hills) you might see more variation.

 

Some things you can do to help. First, turn your unit on well before heading into the woods. It needs to figure out where all the available sats are and its much harder for it to do it cold in the woods. I turn mine on when I leave the house and keep it on my dashboard.

 

Second, make sure your unit is always held flat, face up to the sky. The Legend has a patch antenna, which works best in this position. The older eTrex units tend to be more

sensitive to position, so if you stick it in your shirt pocket, clip it vertically to your belt, hang it upside down from around your neck or just hold it in your hand dangling at your side you may have reception issues. You should it hold out in front of you almost like a waiter would hold a tray of beer.

Edited January 9, 2006 by briansnat

[+wandererrob]

There are days I swear a stiff breeze and a nearby chipmunk with an attitude problem will effect my GPSr accuracy. It's just one of those things sometimes.

 

If the problem persists I'd be more concerned about the GPSr itself, but try the stuff already mentioned. Beyond that all you can do is shrug, put away your GPSr and start a grid or spiral search pattern.

[+Hula Bum]

LOL, living in the redwoods we're generally happy if it gets us within 50 ft! We often jump from 2 to 75 ft!

Sometimes if it gets you in the area the best thing to do is take the eyes off the unit (kealia has a hard time remembering this) and start looking for the obvious signs that so often accompany the hiding spot.

Good luck!

[+canpaddle]

Hello and welcome to this great adventure! Im just going to try to relate to you some of my experiences. Im very new to the sport also received the Legend for Christmas 05 also. I knew nothing at all about these units. First try to keep your Gps Legend warm in your hand or in out of the cold. I dont think the tree cover is much to worry about. When arriving closer to the location zoom in closer to your location on the map. Come in closer not to close though. Use the goto feature that should allready be going by this time. Keep the LEGEND LEVEL in front you protected from the cold. Use the nav. arrow on the nav. page for your bearing readings. Dont rely on just this arrow though. When the arrow isnt going in the correct direction maybe its telling you that your somewhat past the area. Sometimes if you turm quickly around and go back it may get confussed. Try to turn slowly and keep moving keeping Gps in front. I feel sometimes just finding correct bearing from position is a matter of maybe averaging out between what the nav. arrow wants to do. Sort of taking an average between swings. Also when nearing the position use more so the map arrow showing the correct cordinates and the GOTO feature that is allready on. When the pointer and the waypoint meet you know that this should be the area and its close to here. Remember to have the map close in with the zoom but not to close. Circle the position from where your think the closest is. Ten feet twenty and back. Keep the GPS handy but mostly knowing the position is here. Make sure to be zoomed in but not to tight. My jackets have covered my Legend and had no trouble with mine . I searched for five caches in my area and did not find any of them. The reliabity fo the Legend had crossed my mind. Trust the GPS. A frind of mine had the similar unit and once compared readings from several differant locatoins. All the readings were so close mostly off just a few didgets at the end after the decimal point? Thousands?? Place. Anyway we figured they were accurate readings. What really helped me find my very first cashe after five other failures was the Gps is telling me where to go. It is very close to this point in this area. Coming into the area from another angle may be helpful also. Im not an expert and claim no advice that makes any sense. Try this first. Try to locate a known position that you know for sure is the correct waypoint spot. Then put in those cordinates of the known position. Make sure to mark ok . Third make a waypoint position of your location press ok and now enable the GOTO option. Now go and find the spot the map says to go. Dont zoom in to close. For example if you know the city park is the position at least the GPS will now bring you to the city park. This can be done several times all didderent locations and is a good way to learn about your GPS and to trust that is accurate By allowing it to bring you to KNOWN positions 2,3,4,5 times and then is it leading you someplace three blocks away?? Tyr this please dont get discouraged. Dont give up. Keep trying you have many options. Circle your position. Its here. Make sure to enter correct #. Mark current location. Make sure its actually not missing or something. Enable the GOTO. Hopefully itll lead you to the position. Remember I couldnt find any of my first five that I tried to find. I tried everything circling looking even wondering if the GPS was accurate or not. But I trusted the Legend. I tried going to KNOWN locations to prove it was leading me true. Try doing this three or four times going to KNOWIN locations. Is it now accurate? Use combination of nav. arrow and map pointer together but when getting close the map featue more. Circle the position and keep looking. I hope you get advice that will help you. Emale let me know what happening. Good luck.

[+Night Stalker]

I don't know about moisture in leaves, but I know that when I cache in the woods in Texas especially Houston I find that my satellite lock is not nearly as good as when I am caching back home in Idaho.

[+canpaddle]

Also if your nav. arrow is saying North and you are heading South perhaps the arrow is in the wrong mode. It probably needs to be in the mode when the GOTO or track back feature is used. The other mode is maybe the direction of travel?? Just something to check out if its in the correct mode. GOTO mode.

[survey609]

I use a Magellan hand held for caching and $60K Ashtech dual frequency system at work. If I step 10 feet into the woods with the Ashtech the accuracy degrades from 1" to 30' instantly. The satelite signal needs an unobstructed clear line of site to the antenna. The slightest twig, leaf or bug in the way deflects signal. Even high humidity can distorte the signal. You will also notice this effect walking next to a building. For instance, a signal coming from a satelite to your left may be reflecting off the building and your GPS thinks it coming from the right. Thats just the way it is.

[Sugar Daddy]

Thanks for everyone's replys. I now feel better about my unit. I was expecting a little too much from it. I'm getting very good with it, just not in the woods.

 

For trips into the woods, I guess I just can't rely on it to get a good fix every time. We went in today to try again to find a cache that eluded us before. The GPS was very inconsistent and maybe got us within 60 ft. But the hint was so vague that we left empty-handed, even though we searched for a while.

 

Do other models than the eTrex Legend get better results? What do you get when you upgrade to a higher priced model? Better reception? Better accuracy? More features?

[+TurLee]

Hi. A newbie lurker uncloaking here. I’ve been reading the forums for a couple weeks. Bought a yellow eTrex and went on my first hunt a few days ago.

 

My first and second finds were both in patches of dense leafless trees. As we got close to the location the GPSr would jump around, reading like 9 feet straight ahead, take one step and it said 45 feet to the left, one more step and it was 60 feet behind me. We searched and searched and couldn’t find a big black bucket that we thought should be pretty easy to spot.

 

We backed away a little until the unit was giving a clear and consistent reading. At that point, I aimed myself in the direction it was pointing and handed the receiver to my hunting partner. She walked about 100 feet away and got a consistent reading. We both walked a straight line from our positions til our lines intersected. From there, it only took a minute to find the bucket ... which was, of course, hidden, not just sitting on the ground like two newbies had expected.

 

Our third find was in a clear open field and the eTrex took us directly to it with no problems at all.

[+Renegade Knight]

I would imagine tree trunks and limbs could impact a GPS the same way as a bridges superstructure.

 

As for the leaves and the water I'm not sure how thick the water needs to be to block a signal but water does block a signal. Leaves are mostly water and in a thick canopy that's 100% under water after a fashon.

[+TotemLake]

I would imagine tree trunks and limbs could impact a GPS the same way as a bridges superstructure.

 

As for the leaves and the water I'm not sure how thick the water needs to be to block a signal but water does block a signal. Leaves are mostly water and in a thick canopy that's 100% under water after a fashon.

I'm sure (unscientifically speaking) it isn't much, both blockage and what a canopy contains. There is a significant difference between immersion in water and having water overhead. If it isn't a consitent and continuos bubble film, you're not really that blocked. The signal gets through. As I indicated before, you'll have more interference from a rain storm. Next time you're in the woods, watch the size and height and density of the trees versus the thickness of the canopy. There is a direct correlation.

[+Henki]

We started with an Etrex Legend and now have a Vista C. The Vista C has more features, but they'll both get us to where we want to be.

 

Definitely check the batteries. The times I've had the most trouble with readings, changing batteries always helped.

 

The other thing is to use the GO TO feature and keep your eye on the # of feet. Sometimes mine will only get down to 23 feet before it starts climbing up again. Wherever I get the lowest # of feet showing, I use as my main starting point. Then I step back from another angle and try to zero in on the area again. Sometimes just changing positions helps to get a better lock.

[boogie bear]

I have two units that I take with me all the time...my first unit was a Magellan 320 and the second was a Garmin fortrex...I found that both need a bit of time to figure out where they are at times...so what workes for me is to find a place where I've got a pretty good view of the sky and let the gps do it's thing (this usually takes a little longer with the Magellan due to age I think) this also allows me to look around and and zoom in on any clues posted by the hider...not to mention a short rest stop is a good thing...take some time and injoy the sport and the area your in..happy hunting

[Sugar Daddy]

I discovered on a recent hunt that I had better luck with the Map view when I was in amongst the trees. And I had better luck if I kept moving, than if I stopped and doubled back quickly.

 

I went by the arrow and turned around, and the arrow never reversed! It seems like the updating was happening so infrequently becuase of the tree cover, that it didn't catch up with me till I was down the trail 100-150 more feet.

 

Also, I don't think the stop and wait method works too well in the trees. The thing forgets where you are.

 

What ended up giving me the best tip to the location of the cache -- on this one at least -- was looking at my GPS trail as I was coming in, and finding the cache point in relation to that.

[+BilboB]

No one said it was going to be easy. If it was, everyone would be doing it.

[RhettB]

I've got a Legend too and one thing I've noticed is it seems to respond a little bit slower when I have the fancy detailed maps loaded. I still keep them on there because they're very handy to have while driving (especially in new cities) but it does seem to slow my GPS down just a bit.

[+yorelken]

If you have a Garmin GPS map 76Cs make sure you check out the calibrating the compass feature, especially after changing or re-charging batteries. Fairly often the compass arrow on the "go to" screen is pointing 180 degrees in the wrong direction.

[+Alan2]

I don't agree that it's the trunks and not the foliage. If that is true, why do the signals suddenly get better in the fall after the leaves fall off?

[+K0BKL]

A lot of good points were given in this discussion.

I turn on my Yellow Etrex when I leave the house,

then as I arrive, I take sightings coming in with a magnetic compass,

if the terrain is difficult. Coming into the apparent area

from several directions seems to narrow it down.

Again, it helps to sight with the magnetic compass to narrow it down.

[+TotemLake]

I don't agree that it's the trunks and not the foliage. If that is true, why do the signals suddenly get better in the fall after the leaves fall off?

As I said in my first post... it is an anecdotal observation.

 

My observation is based entirely for the area I'm in... mostly evergreen. Obviously with such unscientific observations ymwv. I have been in a few areas where there were leaves instead of needles, but the density of the brush and trees was thin enough to make the correlation.

[+Alan2]

Oh. Pine trees-that explains it. Actually it's because your trees being pointed on top concentrate the signals that then get dispersed through the limbs and thicker trunk as the signals go down the from the top.

 

OK. I just made that up!

[+fishingdude720]

it would tell me the cache was within 2 ft and then I'd walk around and come back to the same spot and it would say it was 30 ft away.

 

This is totally normal. You'd see this with any unit.

 

In general, your unit is going to put you from 0 to about 50 or 60 feet from the actual cache under good conditions. If there are other factors that can cause signal bounce (buildings, cliff walls, tall hills) you might see more variation.

happends to me too. Just stand still for a good minute or two while the GPS adjusts. And again, try new batteries. Always works for me. Good luck!

[+Poidawg]

You put down in your query that you had two sats showing up. You need 6 for better accuracy. If Im not getting a good read from where I am, I back away to the closest clearing as far away from anything as I can get. I double check my bearings and then head towards where I know the cache should be. I also found that using different pages on my unit helped alot recently. I did not just stick with one. Welcome to caching, make sure your WAAS is on and the datum information is correct.

[+kelly83686]

I use the eTrex Legend and have been very happy with it. Accurate and easy to use. (I bought mine used so got a good deal on it. If I were to buy new I'd probably go for the eTrex Vista or Vista C with the built-in electronic compass. But that's another discussion.)

 

I've found, IN GENERAL, my Legend gets me pretty darn close. I use the NAV page with the arrow to get me close. I notice that when I'm 10-15 feet away from the destination the arrow begins to jump around and the distance readings do too. At this point I usually switch to the satellite page, which has the Lat-Long reading at the bottom and try to zero in using Lat-Long. Again, IN GENERAL, I'm usually only a hundreth or less (and usually 2-4 thousandths) of a decimal minute away (i.e very close). If I can't find the cache it's usually because of the human not being smart enough to find it, not the reciever. (Those of you that have gone back a second time to find a cache you missed the first time know what I'm saying.)

 

Oh, also check your WAAS accuracy. If your WAAS is on and you're not getting a good WAAS signal, that might mess you up too. I normally operate with WAAS off. For some reason I don't get a good WAAS signal.

 

Garmin (and the other GPS manufacturers) make really good products. 99 times out of a 100 it's operator error.

 

Kelly83686

[+SAWDUST123]

Torry made a good point about triangulation. With any handheld gps, any cover, buildings, cars, etc. you are going to have to work for it. Not saying you will never get an exact point but don't get discouraged if you have to look around. Thats part of the fun!!! I navigate with bigger units everyday with an external ant. and it still jumps around once and a while.

Etrex models seem to be the way to go for handhelds. I have had pretty good luck with my vista.

[+JDandDD]

Lots of things can make the GPS act weirdly including the arrangement of the satellites. On Friday I had 6 active satellites that almost in a complete line from horizon to zenith. My area is at about 240m above sea level but my GPS had me at 2986 to 3200m above sea level about 2km south of where I was. About 25 minutes later when the constellation spread out a bit the GPS snapped right in perfectly to the correct altitude and place.

 

I've had that happen a couple of times over the last 3 years when the satellites get in straight line orientations.

 

JDandDD