Weird GPS behavior... any ideas?

[W]

Calling all you GPS gurus out there! ;-)

Took the ol' GPS out for a first spin on Monday on my hike up to Wind Cave in Logan Canyon (Garmin eTrex Vista Cx, just FYI). Wanted to keep track of how far up I'd hiked, so I reset the Trip Odometer at the bottom of the trail & started off.

All the way up the trail it was doing a great job of keeping track of where I was, how far I'd hiked, etc. (Although the recorded distance to the cave didn't quite match what the trail marker said -- was supposed to be 1.3 mi. to the cave, but I was just a shade over 1.5 mi. when I got there.)

However, while I was getting ready to head back down after digging the camera out of my pack & taking in the great views up there, I looked down at the Trip Odometer only to be shocked that it thought I'd hiked close to another 7 miles in those few minutes... and even while I was standing still, it was clicking off a couple tenths of a mile!

Now, either Wind Cave is also a rift in the fabric of space-time, or something monumentally screwy happened to my GPS signal (or even possibly -- and likely being a noob -- user error).

Anybody ever seen anything like this before, have any idea what went wrong?


Thanks!
-Josh

[Win]

First thing you should do is try it at home and see if it's the unit acting up. The government may have temporarily degraded the signal. I've not seen them do it with GPS but they would occasionaly do it with an earlier navigation system called LORAN.

Win

[Cirrus2000]

I find that if I'm in a narrow area with poor reception, my GPS will act up, thinking I'm about 80 feet this way, then 50 feet the other... It kind of flips all around, and the track ends up looking like a scribble. That happened to me, for example, in the Alcove Site at Horseshoe Canyon a couple of weeks ago. If that went on for a while, it would certainly add up, distance-wise.

Just a thought...

[Udink]

I find that if I'm in a narrow area with poor reception, my GPS will act up

Yeah, being in a narrow canyon, up against cliffs, under very heavy tree cover, etc., will throw your signal off and cause your "location" to bounce around a lot, which in turn causes you to rack up distance on the odometer. However, 7 miles seems very excessive, so it could possibly have been something else causing the problem.

[vamedtech]

I own an e-trex vista and I've had similar occurances. I remember a couple of times hiking and my max speed reading is 30 mph. Now that ain't right. I do believe it has to do with satalite reception andd signal bounce in canyons. My gps freaks out way to much for my taste which makes me want to try a Magellan next.

[Udink]

My gps freaks out way to much for my taste which makes me want to try a Magellan next.

I'm not sure a Magellan would be much better, unless it has a better antenna than the eTrex. I used to have an eTrex Legend, but my newer GPS 60 with an external antenna gets decent reception in areas where the Legend would lose satellite signals altogether. And actually, my sister's Magellan (I believe it's a Meridian Platinum) consistently got better reception than my Legend. I think it's more a matter of model/form factor, than brand name.

Any GPS is bound to have issues when satellite reception is poor. Basically, the unit will receive good signals one second, while the next second it's got poor reception and will immediately update your position using those bad signals, which can sometimes show a jump of dozens of feet in one second, so your mileage begins to add up and your max speed will also be affected. I don't think there's a GPS unit out there that won't experience this problem.

[W]

Thanks guys -- I kinda suspect you're probably right about it being a signal issue. I was, for several minutes, either under the roof of the cave or alongside the cliff face at the entrance to the cave, so I can see how the signal would have been pretty severely hampered.

Guess I just thought that if it lost signal it would have stayed put 'til it got a new signal to work off of. Maybe instead of completely losing the signal it was just getting weak, intermittent and/or reflected signals, hence the problem.

On the plus side, I guess I can say I hiked 9 miles in under two hours!

Have to see how well she does in Adams Canyon tomorrow.

Thanks!
-Josh

[RugerShooter]

I think My Vista CX got my Max MPH wrong this weekend, going to Wendover it shows I got going 199 MPH. WOW I never knew that I could go that fast in my Corolla