GPS down loading onto Google maps or NZ Topo

There's a thought. Maybe we never hear from anyone backtracking to their tent at night because all those who have done it before GPS died doing it.

Sounds like something wrong here. You had better start by telling us what GPS unit you have and what software you use to download the tracks to. Keep in mind that if you are using Google Earth, it is more likely that Google Earth is wrong rather than your track, that is a known fact. Your last comment seems to suggest that when you load the track back into the GPS then it is in a different place from when you first recorded it. Is that the case?

I am using a Garmin gps 60.The problem is i was hunting the Landsborough valley this year and travelling over a low pass into the headwaters of the Clarke valley,i had my gps on so i could hit back track and get back at night as we had very heavy rain,snow and thick fog for most of the 15 days.It wasn't to bad because i know the area very well,but i was not spot on.When i got home and down loaded the gps on to the computer i found that the down load on to topo maps and onto google earth in places were a long way off and in some cases i had not even been in that gully.I have checked the the gps and topo and google are all using the same reference and this seems to be ok,so i am surprised and stumped.

How often does this happen? Does it appear out by the same amount every time you download a track, or is it out inconsistently? If the latter, is it always out in certain places? The mapping software's unlikely to change, so if some locations are correct sometimes but not other times, it's probably a problem with the GPS. I'd suggest it could be just inaccuracy from my limited experience, but 500 metres out is a lot!

The jumps appear to be all the same size 4-500m going from right to left and then back.Who would be the best person to see about this as i will use my backtracker until i get this settled.

I note that the Garmin 60 does not have the high sensitivity antenna so I wonder where you are carrying your GPS. It should be in the vertical position and high up so that it can see losts of sky. I carry mine up on my pack strap on my shoulder. If you had it on your belt or in a pocket then the shadow from your body would effect the signal. Bush cover will effect it as well, but the open flats of the Landsborough should be OK, except high hills around will effect the number of satellites you see and if it was a bad satellite day then that might be an issue. Does the 60 have a plug for an external antenna? If so you will notice an improvement if you use one of those. You can get one for about $60. Other than that I would keep using it and try carrying it in different places on your body, in differnt environments and see if you find out where it works best. From what you say it sounds consistent with a degraded signal.

At a guess I'd go with with what pmcke has suggested, although I have limited experience. Have you considered asking in the forums at somewhere like the Recreational GPS Society? http://forums.gps.org.nz/ The left and right jumps you've described sound similar to what I occasionally see with my eTrex Vista HCx. If I'm in a shadowed area like a gorge, it might suddenly decide I'm walking 30-40 metres inconsistently from wherever I was a few hours before walking in the other direction, but the tracks will stay parallel some distance apart with similar kinks for a while, before one of them suddenly hops back to the other. I figured it's just because it's lost a satellite or something and therefore lost some resolution in a particular direction. 500 metres sounds like a lot, but pmcke's point about the antenna could possibly explain that. The only GPS I've played with that had a low sensitive antenna was the el-cheapo eTrex, and that simply either had reception or lost it completely. The GPS60 range has a tubular antenna design, which apparently makes it more resilient and less discriminatory about orientation than flat antennas.

The error you talk about izogi is probably a multipath error, ie. reflections from walls of the gorge trees or whatever. Unfortunately the more sensitive antenna is also more sensitive to the multipath errors as well. Yes, 500m is huge and I notice the 60 also does not have an altimeter which brings up another possibility. Without an altimeter a GPS needs lock on at least 4 satellites to calculate altiude. It will work out a 2D fix with lock on 3 satellites and assume the altitude is the same as what it was when last used. If the senario that the GPS was last used in the valley and then switched on when on the tops but can only lock on 3 satellites it will produce a very significant error until it can fix on that 4th satellite, or the altitude is entered manually (which you could on the Garmin 12, not sure about the 60). I once had the situation where I was using my GPS in a plane at 30,000ft. When I got back to the ground and switched on the GPS it's initial fix was about 3km out until it caught that 4th satellite and then streaked back to the right spot at the speed of light.