Light-weight GPS tracking

I lied sorry about that here are all the prices AUST $ Legend H $229 Legend Hcx $369 Vista h $272 Vista hcx $412 and the one pmcke has is around $500

How is the Vista HCx izoqi? Have you put any topo maps on it?

I'm finding the Vista HCx to be excellent, though I'm using it in Aussie coastal heath, with little tree cover and zero interference from terrain as there isn't much in the way of contours! Quick to pick up satellites and the screen seems easy enough to read in both daylight and night-time with a good adjustable backlight. Works well with both mac and windows, though some Topos have required a bit of poking to work with Garmin's mac software. Using the windows mapconverter software works well in that regard. Looking forward to testing out Gary's GTmaps in Northland next month.

Yep, it's working wonderfully, and so far I can't really fault it. Personally I'm finding the screen size to be fine, and also the controls, so the two biggest concerns I had are resolved. I haven't been pre-conditioned on anything else before it, though, so perhaps that helps. I downloaded Joel Thomas's free NZ set of topo maps from http://mapcenter2.cgpsmapper.com/catalogue.php?country=165&region= (converted from LINZ data), though I had to compile a few of them since the source was too large for the online compiler to work -- having gotten them working I suspect they might be all I need at present. Getting the Windows software to work in 64-bit linux was a challenge, but I managed to get it to run satisfactorily in Wine with some effort. (If you've never had any intention of using Linux, don't worry about any of this.) I haven't used it much for mapping apart from curiosities, though, and I think I've spent more time tinkering with autorouting around streets than in the back-country. I've used it for tracking on several occasions, though, which is the main reason I wanted it. I bought some 2500 mAh NiMH rechargeable batteries, and so far 2 of them have reliably lasted the 25 hours advertised guideline, which in both weekends so far has been more than enough for me to track everything as I wanted to, so I still haven't needed to replace them with the second set I've been carrying. (After the first time, I left it switched on to run them down as a rough check.) I haven't tested the batteries in freezing conditions (aside from when we woke up at Dundas Hut with frozen socks and boots 2 weeks ago, but it warmed quickly) and they probably wouldn't perform as well. I've spent the last few weeks experimenting with GPX files, Javascript and Google Maps. Fun fun fun.

I should have added that I haven't (seriously) used the electronic compass for navigation, but I've found it very handy for keeping the map display oriented when I'm standing still. I do have one set of questions about the reliability of GPS and barometric altimeters with my Vista HCx. Late on Saturday afternoon I went on a short walk around nearby hills for a couple of hours, which was a subset of the Skyline Walkway for anyone who knows Wellington. The previous couple of times I'd switched off the auto-calibration. This time I didn't have anything to calibrate on, and decided to leave the auto-calibration on. When I plugged the resulting GPX file into my little javascript program, it somehow decided that in 3 hours I'd climbed 1710 metres and dropped 1722 metres. I know there was some undulation, but the route never went over 430 metres, it was a 3 hour walk for which I spent an hour on streets and in a supermarket, and I don't believe those figures for a second. Half of them might've been barely believable. It's very different from the last couple of weekend tramps where my program came up with total ascents/descents that I found believable. The GPX file is at http://www.windy.gen.nz/wp-content/uploads/2009/10/20091003-skyline-chartwell.gpx and GPS Visualiser drew me a nice elevation profile (at http://www.gpsvisualizer.com/display/1254725911-18885-P-118.93.46.228.png until they delete it) which shows rapid elevation fluctuations at higher altitude. Given my program's really simple, those fluctuations more or less explain how it's gotten so confused. But... is there some obvious way I can reduce the fluctuations, or am I better off changing my program to use a moving average of recent elevations when it calculates total ascent and descent? I can think of a couple of possible reasons why the altimeter might have been confused, but I'm not sure what's most significant. ie. * When higher up, I was walking through some strong wind (the hard-to-stand-up variety), in and out of sheltered places. This seems to correlate with the fluctuations on that elevation profile. Would this have resulted in sufficient changes in air pressure to screw up the barometer? * Maybe the auto-calibration is messing up the elevation profile, which is why I've tried to avoid using it in the past, but I didn't think it'd cause fluctuations quite so rapidly as what's in that graph. Oh, and one further question since I'm on a roll -- would a barometric altimeter (being used to track elevation in real time) be significantly affected by leaving it inside an air-tight bag? I had it inside a small dry-sack in the lid of my pack initially, but then realised I wasn't sure if this'd have an effect on its readings. Thanks for any thoughts.

Having it inside your pocket makes it less accurate so I tend to have it attached to my pack strap unless I am bush bashing! Possibly could have occurred inside the supermarket!

Yeah, well it was inside the front pocket of my daypack the whole time. Definitely not the supermarket. From the elevation profile, all the rapid fluctuations occurred when I was up-hill exposed to wind. I guess it shouldn't be too surprising given that barometers measure air pressure and when air's moving quickly (ie wind), the pressure's lower.

Just some points izoqi. GPS will work best with lots of sky visible and probably better when you are moving the faster the better. I would suggest leaving the autocalibration for the altimeter on and leave the compass off. The GPS and altimeter will work together to get you the best position. This is probably less relevant with the more sensitive antennas but inthe old days when you would loose lock under the canopy and say you were descending a hill, the altimeter would keep track of your altitude while you had lost lock. This would mean that when you did pick up lock again the GPS would be more accurate. In the old days of the Garmin 12, you had to get 4 satellites before you got a fix on altitude. A common problem was to drive to some place, switch on the GPS and only get 2D lock (3 satellites). If you had driven from sea level to 1500m then your 2D lock would be 100s of m out. I once used my GPS when it has previously been used in an aeroplane. My initial lock was several kms out. It is also a good idea when starting a trip to switch on the GPS early, say while packing next to the car. GPS likes to be still and in open ground when it is aquiring lock. Once you have a good lock you can move into the bush. It is hopeless trying to get lock while moving in the bush. Leave the compass off because it uses a lot of battery power. As you say, it is only really for orientating when you are stationary. Don't worry about the odd spike on your track. These things happen, you get used to it. I once had one that took me into a different hemisphere for a few seconds No, your plastic bag or dry sack will make no difference. Wise to keep it in there, despite the claims of water proofness, I have drowned one. Last weekend it was raining so I tucked my GPS into the map pocket on my parka. I got a really broken and erratic track. I usually carry it in a little water bottle carrier velcrod to the outside of my pack shoulder strap, it works fine there. so freewebs is right on that point. As for accuracy. I wouldn't claim anything better that 20-30m horizontal and double that vertical. It is probably better than that but you can't be sure.

It hadn't crossed my mind that the electronic compass would be draining power, and it's a good point. The fact that a couple of rechargeables lasted the benchmark 25 hours (only anecdotally) mekes me wonder if it's switching the compass off automatically whenever it's not flat. I might try to find out about this. It's getting the track nicely from the main lid pocket in my pack, but probably not perfectly. That's good enough for me at least, since I really just want to track where I've been. I haven't been watching what's going on with the satellites it's finding, but I did notice I can walk for a while with it switched on and it'll never get a fix when I'm moving, but after a point as soon as I stop for 5 seconds it'll get the lock, quickly zero in on a small point, and will happily track all day from inside my pack after that. Regarding altimeters, does it actually use the data somehow from the altimeter as a factor in calculating the horizontal position more accurately? That's how I read what you wrote, anyway. I did some quick googling a few weeks ago, and found a few people suggesting it was a good idea to leave the altimeter auto-calibration off, as long as you remember to calibrate the barometric one (and stay in consistent weather), since it's much more accurate and with auto-calibration switched on the GPS one can come and interfere. Perhaps that advice is more appropriate for places with more stable weather, though. It'd be nice to know what sorts of thresholds it uses to decide when it's time to re-calibrate given GPS elevation is only supposed to be accurate within about 30 metres. The experience I mentioned above was just one I found interesting though, more because of the total inconsistency of the inaccuracy. I think it was the barometric altimeter going bizarre from rapid air pressure fluctuations in high wind. Is this something that happens often with barometric altimeters, or is there something I could do better? Maybe it's something completely different that caused it. That first link to the graph's expired, but I made another one here: http://www.gpsvisualizer.com/display/1254986794-31975-P-118.93.46.55.png Thanks for all the ideas. It's all very helpful and interesting, and I'm enjoying my new toy.

Hey all, Im new here im just posting to say Yo. How is everyone?