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Kake

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GPS devices? [Feb. 28th, 2007|03:29 pm]
Kake
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Hello. I'm looking for a GPS device, as inexpensive as possible. I asked martling and he said my best bet was probably a Garmin eTrex, which costs around £60. (Presumably the cable for connecting it to my iBook will cost extra.)

So I was wondering (a) if anyone here has any experience with this device — is it definitely happy talking to an iBook? What does the data look like when it comes out? — and (b) if anyone has one (or something equally suited to my requirements) lying about that they want to sell on.

The main thing I want is to be able to stand somewhere and tell it to record the location of that point and let me put in a label for it, then when I get home pull out all the points I recorded as CSV or something like that, and do Sums on them to turn them into OSGB coordinates and other useful things. It needs to be able to talk to my iBook, and I'd prefer if it had a rechargeable battery rather than me having to keep buying new batteries for it. I don't want to have to carry my laptop around with me, so it needs to be independent.

I'd also quite like it if I could occasionally tell it to record points every minute or so until I tell it to stop (this is called a GPS trace, yes?), but that's less important.

Edited to add: This is mainly for use within London, i.e. a city with many tall buildings. If that makes a difference.
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Comments:
[User Picture]From: land_girl
2007-02-28 03:47 pm (UTC)
bisonfish has both things, but I'm afraid I have no idea how they talk to each other! If nobody else can help I'll send him your way ...
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[User Picture]From: nou
2007-02-28 04:00 pm (UTC)
That would be very useful, thank you, regardless of whether anyone else replies — all opinions will help!
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[User Picture]From: sammoore
2007-02-28 04:10 pm (UTC)
If you are talking about on the move, most data exchange between GPS and navigation units (Autopilots, In Car navigation systems, realtime display panels) is done by NMEA (http://www.nmea.org/pub/0183/)

Otherwise I would image it would export a CSV file. You should be able go get it to write OSGB data straight off, certainly you can on mine.

Sam
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[User Picture]From: nou
2007-02-28 04:18 pm (UTC)
I don't need it to do anything beyond gather data when I'm actually out and about. I'll plug it into my laptop when I get home.
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[User Picture]From: crazyscot
2007-02-28 04:14 pm (UTC)
It certainly used to be the case (a few years ago) that GPSs had an RS232 serial port on the back of them, which (with the correct cable, which are not cheap) you could connect to a standard PC. Down this line would normally come, every second, an NMEA string giving time and location - and they were configurable to store and replay traces like you describe. Alas, RS232 is no good for talking to an iBook, but I wouldn't be too surprised if they could do USB these days.
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[User Picture]From: nou
2007-02-28 04:19 pm (UTC)
Thanks — yes, I should look for USB support, shouldn't I.
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[User Picture]From: lovingboth
2007-02-28 04:24 pm (UTC)
The other place to ask would be the bunch that's trying to do a map of London (and various other places) without infringing the OS's copyrights. They wander around the place doing this.

If you can't find their website from this stunning description :) I'll have a hunt.
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[User Picture]From: nou
2007-02-28 04:29 pm (UTC)
Openstreetmap? I looked at the GPS reviews on their wiki, but I don't really have enough background knowledge to properly understand what I'm reading.
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[User Picture]From: pozorvlak
2007-02-28 04:35 pm (UTC)
I've got one of those. I haven't tried using it in a place with tall buildings, but it's fine in places with lots of tall mountains :-) It doesn't work indoors, though, so YMMV. You need to supply batteries, and a pair of rechargeable ones is a very good investment (though for me, a run-down battery at the wrong time is potentially more serious than it would be for your usage scenario). You can get GPS-to-USB cables for it, though I don't think they're especially cheap (can't remember how much). I haven't tried talking to it at a low level, so can't speak as to the output format, but it's certainly possible to get waypoint and path data out of it (there exists proprietary software for doing this - Googling, this bit of freeware might meet your needs).

Other things: the altimeter seems OK, but the compass is laughably inaccurate - don't try to rely on your GPS as your sole navigation aid. Waypoint names are limited to six characters, which doesn't exactly do justice to the beauty of the Gaelic tongue (or the English tongue, for that matter). The buttons are uncomfortable to push, particularly with RSI-ridden/cold hands. The user interface is, in general, not great - entering names/data is slow and somewhat frustrating, rather like entering your name into the high score table of an arcade machine. Upsides are that it speaks OSGB/km natively (along with about fifty million other map conventions), it can mark where you are and trace your path very easily (and records distance travelled, average speed, etc, if you're interested), it has no dependence on a computer (if you don't want to lug your laptop around London, think how I would feel about lugging one up Sgurr na-h'Ulaidh), it's waterproof, and battery life seems pretty decent (though I usually turn mine off when not in use, as I really don't want it to be dead if I actually need it).
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[User Picture]From: nou
2007-02-28 04:46 pm (UTC)
It does sound as though the etrex will meet my needs as well as anything. I don't need it to work indoors, and I don't plan to use it for navigation. Thank you!

martling also warned me about the user interface, and suggested it might be simpler just to number them sequentially and keep a separate record of locations on a piece of paper.
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[User Picture]From: blech
2007-02-28 05:09 pm (UTC)
I have an older Bluetooth data logging GPS which, annoyingly, doesn't output NMEA tracks (as someone else said, NMEA is a common (TSV-based, iirc) standard), but does prove that you don't need a cable (although if your iBook is old enough you would need a dongle instead).

It's worth looking for the SiRF III chipset, as I've heard this is much better than previous GPS chips for tall buildings. On the other hand, I've never got properly into the hang of GPS so maybe other advice is more useful anyway.
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[User Picture]From: nou
2007-02-28 05:30 pm (UTC)
Hm. It looks like SiRF III units start around 180 quid, which is rather more expensive than I'd like. I'm wondering if it might work out cheaper overall to get the eTrex now, and use that until the better units come down in price. If that's likely.
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[User Picture]From: pfig
2007-02-28 07:29 pm (UTC)
i had a garmin etrex which talked happily to the mac using the keyspan serial-to-usb thingie. i quite liked the garmin, at the time (4 or 5 years ago). now i have a nokia bluetooth one (£50), which i use with my e61, have yet to try it with the mac. both spit out the standard formats for gps data (emea something i can't remember) and there are things on cpan which handle that well.

p.s. the garmin etrex does everything you say, and then some. the nokia does, too.
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[User Picture]From: peshwengi
2007-02-28 10:06 pm (UTC)
I have a USB one which only works when plugged into a computer... you can have it for free if you like, which is pretty good value ;)

I used to use it on my linux laptop with some freeware which downloaded maps and worked pretty well. I made it work with my powerbook but couldn't find any decent software and didn't have time to write any. It provides raw NMEA data which means that it should be easy to find software for or write code for.
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[User Picture]From: nou
2007-02-28 10:41 pm (UTC)
Thank you for the offer, but I don't think I'd be able to use it; I don't really fancy standing about in the street with my laptop out :)
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[User Picture]From: hatter
2007-02-28 11:20 pm (UTC)
I've got a etrex (summit rather than the basic yellow one). As many people have covered, they're serial, but you can convert to usb in-cable or use an existing usb-serial adapter. I'd point at http://www.gpsw.co.uk/ as a decent place to buy from, though ebay may well also suit you. The garmin geko units are smaller/cheaper/newer but slightly more restricted in what they allow (so as to avoid killing the market for both older and newer etrex models).

I've never used the garmin software, but there are perl modules for both NMEA and Garmin format, and iirc the garmin module also allows you to up/download tracks and traces. The raw data over serial isn't too complex, NMEA is open and Garmin's is reverse engineered fairly widely. There are also a load of other unixy utils for processing the data that may well compile. When you're recording a track, you'll be able to download it later and look at that data to sample it every minute.

Some bits of london are tricky or impossible to get a GPS lock on, because of the limited sky view and reflections, you'll have more luck getting lock further away and then moving into them, but some times (literally, depending on the position at that time of the gps constellation) you won't be able to see the 3-4 satellites that you need to fix a position. Standing at junctions improves the amount of sky visible; standing in the middle of roads too, but that's less practical. But that's only a small part of the city you'll really struggle.

I use mine with NiMH AA batteries, I carry spares for several things anyhow, and the units themselves are solid, mine's been kicking around for a good number of years - I did manage to scratch the screen when it was in my bag with some PCI cards though so either take a very small amount of care, or consider a screen protector


the hatter
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[User Picture]From: wintrmute
2007-03-01 01:02 am (UTC)
Some bits of london are tricky or impossible to get a GPS lock on
You'd be surprised how much better non-Garmin units (inc. sirfstar3 chipsets) manage in London. We've wandered around with one of each and compared the tracks later, and in central london the garmins were nearly useless - dropping out frequently, taking ages to relock, and tracks that jumped all over the place - vs very accurate, continuous, tracks from some of the others. SS3ftw though.
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[User Picture]From: wintrmute
2007-03-01 01:00 am (UTC)
Garmin GPS receivers (at least the lower end ones, eg. eTrex) are really, really poor, especially in urban environments.

Get something with a SiRFStar III chipset instead.

My work has collectively had a reasonable amount of experience with GPS devices, plus I have personal experience, and I found the Garmin's to be useless in London.

The Globalsat BT338 works great though; gets about 20 hours battery life from a single charge of the rechargeable battery. (vs the garmin etrex that runs off AAs boo)
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[User Picture]From: nou
2007-03-01 01:09 am (UTC)
Is the Globalsat BT338 standalone for data collection, or does it need to be plugged into a PDA or something? (The reviews I can find on the interweb seem to assume that you know this kind of thing already, and I don't.)
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From: ewtikins
2007-03-01 06:34 pm (UTC)
I have a Garmin eTrex you could borrow for a bit to try out if you like - I don't really use it a lot, I was planning to use it for a foraging database but shortage of Round Tuits has interfered.

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[User Picture]From: nou
2007-03-01 11:31 pm (UTC)
Yes please!

Are you in tomorrow (Friday)? I'm free all day, can pop round and collect it any time that suits you; afternoon probably best though. I'll try and find your bracelet to bring too (I put it somewhere safe and forgot where).
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