Gps Waaaaay Off

[+penguin44]

Hi there, I just waypointed a potential location on my laptop Garmin GPS18USB. I have never had this problem. I marked the location, my unit was accurate to within 2.3 meters. I had a friend of mine with a new i5 and we discovered that my laptop marked us 58meters away from the location. We got out his trusty vista and that was correct. How can my gps18 be so off? They are all from the same satelites. I can accept 3 meters, not 58. That's almost 200 feet.

 

When I plotted my house there weren't any differences in the 3 units. Just this location. Anything would be helpful.

[+Sputnik 57]

Except for your last sentence, I would suspect that you have the datum set to something other than WGS84. You might want to check that.

 

Edit: I'm not sure how the GPS18 interface works, but you also might want to check that you don't have it set to "lock on roads".

Edited January 13, 2006 by Sputnik 57

[+StarBrand]

I have seen that type of erratic behavior on one of my Garmin's when the batteries were quite low. Kept giving me readings about 600 foot off of one of my own caches until I dropped a new set of AA's in it.

[+Renegade Knight]

Using a different datum (NAD 27 for example) can put you 200-300 feet off when everthing else looks identical.

[+ZingerHead]

It's weird that it's correct some of the time and wrong some of the time. That doesn't give you much to work with, since any settings you change will screw up the "good" readings. Any chance it was just bad reception, so that you would have poor accuracy?

[+Thrak]

It's the last sentence in your post that gives me problems. If not for that sentence I'd just figure you weren't using the correct map datum on the one unit. Any chance that accidentally got changed?

[+penguin44]

Sorry to confuse you all. Maps are all the same, lock roads is off on the laptop. I am using WGS84 on all. What I meant to say in the last sentence was, for kicks, we plotted my house as if it were a cache. We did this on all 3 units no problems. Kinda strange.

[+penguin44]

Well my cache was approved and thankfully people have found it. I didn't make it too hard considering the area doesn't lend itself to great spots.

[+Renegade Knight]

General things.

 

Maps are off. You can be shown across the street etc. IT's a limitation of maps.

 

Power lines, trees, vertical surfaces (cliffs/buildings) bridge trusses can all throw a GPS off.

[+HaLiJuSaPa]

With many GPSr's, that actually happens when the batteries get low. Did you try new batteries?

 

In rarer occasions, it can happen if your GPSr's satellite almanac got corrupted, particularly in a situation where it's locking on only 3-4 satellites anyway at the time. Most units have a "cold start" function or something similar where it rebuilds the almanac to correct this, something that you're usually supposed to do as well if either you've had the unit turned off a long time (like a month or more I believe but not sure) or if you've travelled more than a few hundred miles with the unit off.

 

Recently I had my unit on on a very foggy day and thought the fog caused this same kind of problem (even asked in a forum post here) and I am now pretty sure it was low batteries.

 

As Renegade Knight says, it can also be just how buildings and power lines are situated as well. For some reason, I am always "off" when I'm near my day job, and it turned out to be that factor (lots of power lines there because it's very near a major power plant).

Edited January 15, 2006 by hairymon

[+The Cheese Eaters]

Hi there, I just waypointed a potential location on my laptop Garmin GPS18USB

What do you mean ?

[+Sputnik 57]

I'm guessing that s/he used a Garmin 18 and City Select on a laptop to mark a location for a possible new cache.