Replicated from the GGA EZBoard:

lmoseley
BigDoggie
(8/21/01 9:46:48 am)
Question about GPS reception at "Exit the Reagan"

A question:

Searching for "Exit the Reagan" was a real GPS nightmare. Even though the tree cover was fairly light, and good sat locks were shown, the GPS wandered all over the place.

Here's the question: Not far away were the ball fields with large chain link fences. Could these fences be what was messing up the GPS?


~~~~~~~~~~~~~~~
erik88l r
Registered User
(8/21/01 3:01:29 pm)
Re: Question about GPS reception at "Exit the Reagan&qu

Lewis - What coordinates did you use? On the first day the latitude ended in .004. That put the cache about 600+ ft. outside the park. I gave up, and went home. I e-mailed Brian, he doublechecked and corrected the coordinates the next day such that the latitude now ends in .084. Using that coordinate I walked down the trail on the other side of the wooded strip from the ball field and had good reception. The GPS counted down to 2 ft. I stopped, the distance changed to 4 ft, the needle moved around a bit, but all in all it was as trouble free as it could be. I'm using a Mighty Mouse 2 antenna in my hat, which may help. I didn't try approaching from other directions to see what would happen. When actually at the cache the GPS read 28 ft., but that's still right on it as far as I'm concerned. Maybe the geocache gods liked me that day. I've had other times when I spent an hour wandering around before I find what's supposed to be an easy cache.


~~~~~~~~~~~~~~~
lmoseley
BigDoggie
(8/21/01 4:44:33 pm)
Re: Question about GPS reception at "Exit the Reagan&qu

NOTE: This message has spoilers for the Exit the Reagan. Don't read this unless you are willing to see them.

I had the 084, the revised coords, thank goodness. I noticed that the Mapquest map placed the cache outside the park... and still does. I wonder if the mapquest link is updated when someone updates the cache co-ords? Since the Mapquest works on degrees and ten-thousandths of degrees, it is hard to tell without going to the hassle of converting.

We went down the aisle between the fences from the concession stand, then hung a right down the trail you mention. At this point, the cache was ahead and to the right, but the GPS showed ahead and significantly to the left, down in the briars jungle. We spent close to a half hour down in there, getting no where, then said to hell with it and went back to the trail. As we passed what we eventually found to be the location of the cache (on our right), the arrow (and compass bearing) were showing it to be 60 feet to the left, back down in the briars. A bit farther down the trail, I recognized the open area that Wonko mentioned in his log, went there, took a bearing and distance as he recommended, and then just paced it off and looked around.

We met Bugboy there, and his GPS had led him off into the briars as well. And, from the trail near the cache, was pointing him off into the briars, too.

And, all the while, I was checking the satellite screen and it showed that there were 5 or 6 satellites (not necessarily always the same ones) in the black at all times.

I guess maybe I have too great expectations of these gadgets... but we could have spent DAYS down in the briars and never found anything but bugs and thorns.


~~~~~~~~~~~~~~~
erik88l r
Registered User
(8/22/01 7:23:05 am)
Re: Question about GPS reception at "Exit the Reagan&qu

Well......, maybe you had 5 or 6 bad satellites and I had good satellites Seriously - the triangulation is best if the satellites are low in the sky, vs. right over head. If you're between two hedges you might only get the over-the-head ones, unless you luck out and there are satellites in front and behind (where the hedges aren't).
If you really want to delve into something you probably can't control - go here:
sirius.chinalake.navy.mil...ery.cgi?dl
Enter the cache coordinates and the date and time you hunted for it. I was there the same day, probably a couple of hours later, see if I had better satellites.
Have fun!


~~~~~~~~~~~~~~~
Ramness570
Registered Geocacher
(11/2/01 3:47:52 am)
cool

Wow I'm sorry so many of you had trouble with this one! Since I have just recently figured out the averaging function on my GPS, this cache is on my list to back and average. Each time I have gone to check on this one I haven't taken the GPS with me so I had no idea y'all were getting such wierd readings other than what I have read in the logs.


~~~~~~~~~~~~~~~
lmoseley
BigDog
(2/11/02 12:59:35 am)
Re: cool

WARNING - MESSAGE CONTAINS SPOILERS

The real funny thing about this one was that, when you actually sit down at the cache box location and let the GPS settle (not a good idea, as Frogger found... chiggers!!), it showed close to 0' separation. But, when you went back to the trail 10 feet away, it again showed the location on the other side of the trail, way down in the briars.

That is strange. The first time I took a run at this cache the darn GPSR sent me down the hill too. After walking around the brush for a little while I back tracked to the pathway and started over. After coming at it from three different directions (both directions on the pathway and along the fence) I determined that I was NOT suppose to be down the hill. Found the real location eventually.

I have also had problems with Exit the Reagan Part 2 and Are You in the Loop. The Loop coordinates tried to send me down a steep, steep hill towards a sewer cap. But having done Sidewalk Ends I knew what I was looking for and just concentrated in the logical area. I have made two runs at Exit the Reagan Part 2 and not found the cache yet. Originally, I chalked that up to dense overhead cover and a REALLY well hidden cache box, but after talking to Charlotte Ford she never found it either.

Did anybody else have problems with Part 2? Or am I just a blind old man? I can take it. My wife says that I am a blind old man.

That one gave me trouble too. I walked all through the swamp because I'd left my printout with its cheat in the car.

I have a theory about satellites and a GPS.

It goes like this:
If a geocache is hidden in the afternoon and you hunt for it in the morning you will have a harder time than if you had hunted for it in the afternoon because different satellites are in view. And vice versa - a cache hidden early in the day would be harder to find late in the day.

Now my next trick is to figure out which geocachers are morning people, and which stay up late, so I can match my find times with their hide times.

So far I've figured out through forum postings that mtn-man is a night owl so I won't bother to hunt his caches early in the morning. I still have to build a probability profile on the rest of you.

So now that you know my secret it should never take you longer than 5 minutes to find a cache.
Yeah sure!

~erik~

LostNfound's profile for erik's compilation:

1) Old Blind Man
2) Night Owl
3) Never hunts caches before serious coffee or sometimes before having Lunch.
4) Uses Magellan equipment while trying to hunt Garmin placed geocaches
5) Stupid enough to place his compass on a fiberglass post holding two LARGE metallic trash cans and then wonders why he ended up about 30 degrees off from your first waypoint on Field Sobriety Test
6) Still out there trying!

I have noticed that it is fairly common for GPS units to indicate the cache is at two separate locations. Sometimes the wrong location is 60 to 100 feet or more away from the right location. Problem is that wrong and right are defined by what the GPS of the person who placed the cache indicated at the time it was placed. I agree with Erik, I think that this is probably caused by the GPS using different satellites, either because of terrain, trees, time of day, or some combination of these factors. The Cache the Hooch cache is one where this bipolar thing happens, and several cachers, including me, searched in an area about 100 feet from the cache location. At the time I did that cache I noticed that while my GPS was getting 5 sats it indicated the wrong place, but when it picked up a 6th sat it indicated the correct location. Steep terrain seems to be a common element in these bipolar locations.

FWIW,
CharlieP

You may be onto something there CharlieP. I remember the cache at Morgan Falls Dam fell into a Bermuda Triangle of sorts. The same for a cache Ramness570 and I hunted together on a hillside along the Hooch. I can't remember the name (Muddy Creek maybe?) but we were led all over that hill by our GPS. Signals bouncing off the terrain maybe?

I'll update my profile of LostNFound too!

~erik~

I think *maybe* the signal bounce thing is a separate phenomenon, but it seems to happen in some of the same kinds of places as the bipolar thing. I think bounce is what causes the GPS to sometimes just refuse to settle on any position at all, and you end up wandering all over the place. I have had that problem at your Cat cache beloe Buford Dam, the Etowah Chief cache, the Jones Bridge Rock and Roll, Johnnie's Halloween cache at Allatoona Pass, and Rocktown, to name a few. All of these locations are on or near large rocks or rocky slopes. I had such bad signal bounce problems at Rocktown with my old GPS that I had to climb one of the big rocks just to get any position at all.

FWIW,
CharlieP

at 12:30 p.m. to see what all the fuss is about. GPSR took me right to it with no weird reactions. Exit the Reagan, Part 2 was another matter entirely... see my tale of woe here.

quote:

---

Originally posted by ~erik~:
I have a theory about satellites and a GPS.

It goes like this:
If a geocache is hidden in the afternoon and you hunt for it in the morning you will have a harder time than if you had hunted for it in the afternoon because different satellites are in view. And vice versa - a cache hidden early in the day would be harder to find late in the day.

---

Interesting theory, but most likely wrong. In the absolute sense GPS satellites are never in the same place twice. However they are almost in the same place every 12 siderial hours (that is 11 hours 58 minutes and 2 seconds. So they are also almost in the same spot in 23 hours 56 minutes and 4 seconds. So the chance a cache hunter will be there at the time when the satellites are almost in the same position is slim. Also two GPS of the same model at side by side at the same time will give different answers, sometimes just a few feet by rarely it can be 100+ plus feet. That is because by the way they work there is always errors. The accuracy of the GARMIN V is rated at 15 meters (45 ft), 95% typical. Which means for each reading it gives there is a 95% chance that the actual cooridinates are within 45 feet and a 5% chance that it is further than 45 ft. The accuracy reading it displays while working is the 50% reading. That is if it says 19 feet that means there is a 50% chance it is 19 feet or closer and 50% chance that it is further than 19 feet. The more satellites it picks up the smaller the number but there it is still a chance it is further than that. A gps that does averaging helps in that more of the reading will be close to the "real" answer and will bring the average closer, in fact if you were to average for 12 hours which will allow all the satellites to go overhead then it will get a fairly accurate reading.

As for "bipolar" readings I think that is caused by different satellites being picked up by the GPS in the two different locations. I have seen this while driving in the mountains, go around a curve and the "location" on the screen jumps, then go around a curve in the other direction and the "location" jumps back. Also in dense forest and/or mountain valleys, the total number of satellites is reduced and that reduce the absolute accuracy of a GPS, making the effect worse.

"inherent error budget" - I think I'll try to work that into my 2003 objectives somehow!

"Alright Boys, I'm a formin' a Posse." We're gunna hunt down that lily-livered cross-eyed snake of a critter who hid that box on November 14th. If Brian had trouble finding it . . . . just dang! I know exact where the box is now based upon Brian's new clue. I poked a hole in every piece of ground south of the base of that tree. I was even contemplating buying that $29 metal detector at Radio Shack. Guess that I can save my $29. Or maybe not. I still have not done any of the caches at the Yellow River Park. Second thought . . . anybody know where a good Radio Shack is? Ha, ha.

Just out of curiosity because I don't see it mentioned, but did anyone try pulling out a compass and triangulating the location using the bearing on the GPS? I'm still figuring this system out and don't even claim to know what I'm doing. I was wondering what other's success rate is doing this when all else fails. I've tried this when tree cover around the cache area makes the GPS act crazy. I'll back out to a couple places where I can get better reception and wait for the GPS to settle down and then shoot a bearing and distance. After I triangulate the general area, the GPS goes in my pocket and I just
try to find the cache without the GPS. Sometimes it works and sometimes it doesn't

Got skunked yesterday and went back this morning for more before Brian had updated the coordinates. I posted the coordinates that I read at the cache in my log, and they are nearly right on Brian's latest ones.

All of that said, when I was there yesterday afternoon I experienced erratic GPSR behavior. I seem to recall that all of the locked satellites were nearly directly overhead, and I believe that you get better accuracy when you can lock on to satellites that are lower in the sky. I also experimented with power cycling the GPSR (hey, it works with Windows PCs!) and found that the GPSR "thought" I had moved when it powered back up. Maybe there is a previously unrecognized Reagan Triangle out there.

Glad to hear that others have had trouble with this one. Part 1 was no problem. My first cache. I've been to number 2 twice without success. Will try again now that the mosquitos are gone.

I just did Part 1 and Part 2 this last weekend. Part 1 was no problem and was led straight to it with my Vista. Part 2 was another story. Somehow I stumbled onto a 'back door' and had very little walking before I got to the hidey spot. My Vista was literally spinning in circles, so I fired up my old yellow ETrex and it led me to it steadily. Curiously, I had them both on side by side and they were pointing in the opposite directions. Go figure! I too could not find it without the cheat. I left it in the van, so I had to call my wife and had her read it to me. With the cheat info, it was a snap. It is right where it says it is, aggressively hidden, but it is there. At the spot, you will be very visible to passersby, so I pretended to be taking pictures.
Good Luck

'Oink' - A Pig

quote:

---

I pretended to be taking pictures.

---

omg, I've done that! At my very first cache, even!