Author Topic: Barimetric altimeter and electronic compass - worth bothering with? (Read 5608 times)

GrahamG · « **on:** 22 February, 2011, 10:16:38 am »

Right after mining the knowledge resources of everyone on two different threads, I've decided to go for a Garmin Dakota. After getting permission from the better half for buying one as a wedding gift to myself (great excuse, eh?!), I thought I'd keep it cheap. This does leave the final question as per thread title - is it worth £50+ extra just to have a barimetric altimeter and electronic compass?

The geek in me would kind of like more altitude info but I gather the GPS still does this to a reasonable accuracy. £5 would buy me a little compass if I'm that bothered (and the phone has one too).

mrcharly-YHT · « **Reply #1 on:** 22 February, 2011, 10:18:52 am »

If you are moving, the GPS acts as a compass.

I'd save your money and get a nice compass - something you can use to take bearings.

GrahamG · « **Reply #2 on:** 22 February, 2011, 10:21:06 am »

Didn't realise that, thanks.

Ah, just noticed the other cost saver... no internal memory card option. However it does have 850mb of internal memory. I would be wanting to load OSM into it.

mrcharly-YHT · « **Reply #3 on:** 22 February, 2011, 10:24:40 am »

I maybe should clarify that. All GPSs' that I've used can display a compass. However this doesn't show which way the GPS is pointing, it shows your heading.

It also updates slowly, so you can end up in a mess if you stare at the GPS and try to follow it (yes, when helming at night for the first time, I did end up doing 360's a couple of times).

Personally, I think a compass is only of use on a bike to triple check you are facing the right way on a road. You need maps, and a GPS is handy to check where you are. If it has maps as well, fantastic.

GrahamG · « **Reply #4 on:** 22 February, 2011, 10:27:30 am »

Good point - it'll have maps. In fact, whilst I consider a compass essential for touring when following (paper) maps etc. for my intended GPS usage (following pre-planned routes), it's really not going to be worth it.

Just checked and the UK & Eire OSM maps are only 320mb odd so 850mb internal memory should be more than sufficient.

Greenbank · « **Reply #5 on:** 22 February, 2011, 10:34:45 am »

Quote from: GrahamG on 22 February, 2011, 10:16:38 am

This does leave the final question as per thread title - is it worth £50+ extra just to have a barimetric altimeter and electronic compass?

Simply put, no, not £50.

Quote from: GrahamG on 22 February, 2011, 10:16:38 am

The geek in me would kind of like more altitude info but I gather the GPS still does this to a reasonable accuracy.

I'm not entirely sure the barometric altimeter makes it more accurate over long distance rides.

Jo has more stuff on his page: Accuracy of Elevation Measurement Using GPS

It's all to do with the way GPSes determine altitude (which is derived from the position information and the model of the oblate spheroid that is Earth). Google for 'GPS geode accuracy' for more...

I've certainly got some tracklogs of my commute that, for some reason, puts London at 200m ASL, despite having 7 miles to sort itself out. (This is an Edge 705 with barometric altimeter.)

It's much better when it calibrates itself against a known position/height. The unit only does this some times outside my house, I need to investigate how to trigger it so that it does it all of the time.

In practice, the tracklogs of rides I've done using a basic yellow Etrex (no altimeter) and my Edge 705 (with barometric altimeter) don't look that much different at all. Neither seems consistently better than the other.

However, not having the altimeter means you don't get the elevation profile pages, which can be useful if you've uploaded a tracklog with elevations in it as you can see what is coming (I think).

I've never found a use for an electronic compass (none of my GPSes have one). If you're on a road you just need to look at the map page to work out which way is North, if it's tricky then start moving and it'll become obvious.

GrahamG · « **Reply #6 on:** 22 February, 2011, 10:39:39 am »

Balls, it would appear that the final cost saver is a 'beep'/alarm clock. So no audible alert for waypoints. Hmmm, now it's getting to be a case of if I have to spend as much as £190 for the Dakota 20, do I just go for the Oregon at £230 odd.

Just when I thought I was ready to buy!

Ham · « **Reply #7 on:** 22 February, 2011, 10:40:02 am »

If you are going to use it for walking, then yes it is worth having. Remembering always that you have to calibrate the darn thing, otherwise it is useless. Main purpose for altitude is for plotting exactly against paper map, plus the compass means that you don't always have to get the real one out (because you would never be without a traditional compass, yes?). All in all, very useful indeed for mountain walking where getting the right path can be essential for your corporeal wellbeing. If I were using it for cycling alone, I'd agree it is of very limited use.

Manotea · « **Reply #8 on:** 22 February, 2011, 10:43:45 am »

Quote from: Ham on 22 February, 2011, 10:40:02 am

If you are going to use it for walking, then yes it is worth having. Remembering always that you have to calibrate the darn thing, otherwise it is useless. Main purpose for altitude is for plotting exactly against paper map, plus the compass means that you don't always have to get the real one out (because you would never be without a traditional compass, yes?). All in all, very useful indeed for mountain walking where getting the right path can be essential for your corporeal wellbeing. If I were using it for cycling alone, I'd agree it is of very limited use.

If out in the wilds being aware of changing air pressure, i.e., approaching weather fronts, could be very useful indeed. Not really a consideration for cycling in Surrey though.

GrahamG · « **Reply #9 on:** 22 February, 2011, 11:17:27 am »

Thanks chaps, I'm just trying to confirm the 'beep' option - can't believe something like that would be omitted and the info comes from a random online blog so fingers crossed Garmin can answer me!

Greenbank · « **Reply #10 on:** 22 February, 2011, 11:21:31 am »

The 'beep' thing would be useless for me as I often ride with headphones on.

A screen that lights up as a turn indicator is ok, but I've still missed it (even riding on unlit roads at night).

The one that works for me is having the 'distance to next turn' data point displayed on the screen. That way I can glance down, see it says "7.23km" and think (right, that's at least 15 minutes I don't have to think about it).

And you only need to look at it for a few seconds to spot whether it is going up (which signifies you've probably missed a turn unless the road is doubling back on itself).

Kim · « **Reply #11 on:** 22 February, 2011, 11:22:34 am »

Pretty much echoing what's already been said:

On a bike, the compass is largely useless due to proximity to metal, but that doesn't matter because a bike moves in such a way that the GPS-derived direction is nearly always accurate. The compass is a power drain, but you can turn it off. The barometric altimeter helps to smooth out some of the elevation noise caused by GPS glitches, but may of course introduce its own artefacts in the process. Pragmatically, it's the least-worst way to obtain a realistic elevation plot when moving near steep inclines (where GPS tends to suffer from multipath interference and interpolation after the event using 2D position and a contour map is going to be highly error-prone). How much that matters for cycling is up to you. I don't know the Dakota, but on the eTrex the models with barometric altimeter also gain you a rather nifty elevation profile screen.

On foot, the compass becomes much more useful, especially if you're using the GPS in a dig-it-out-occasionally-for-a-quick-check manner. It's not as precise as a real compass for taking bearings with, but you've got a GPS receiver so probably won't be doing a lot of that. I find it particularly useful for orienting myself when emerging from railway stations in unfamiliar built-up areas, as working out which way you want to be heading using GPS alone can be about as effective as simply wandering around until you find some road names.

frankly frankie · « **Reply #12 on:** 22 February, 2011, 11:29:49 am »

It's that 'stop at a crossroads and look at the map' moment. Using a GPS without inbuilt compass, this is a disaster, and you soon learn not to do it. That's why travelling with a GPS is quicker - because you can't stop! With the inbuilt compass, it stabilises the map and that's OK. At the cost of some battery runtime.

I had a Dakota for a while and the beep/light for upcoming turn works OK - though it's not at all customisable - no volume control, no choice of beep tone (you get lots of choice on the Etrex C) though you can adjust how far in advance it beeps.

I would suggest that the card is the main thing though - especially if you might be into 'alternative' maps.

Biggsy · « **Reply #13 on:** 22 February, 2011, 11:39:00 am »

I use a compass a lot while cycling - as often I'm content just to head in the right general direction without following a planned route all the time - but a Recta Clipper on my mitt is fine for that. So I chose an Edge 605 instead of 705.

GrahamG · « **Reply #14 on:** 22 February, 2011, 11:44:07 am »

Quote from: frankly frankie on 22 February, 2011, 11:29:49 am

It's that 'stop at a crossroads and look at the map' moment. Using a GPS without inbuilt compass, this is a disaster, and you soon learn not to do it. That's why travelling with a GPS is quicker - because you can't stop! With the inbuilt compass, it stabilises the map and that's OK. At the cost of some battery runtime.

I had a Dakota for a while and the beep/light for upcoming turn works OK - though it's not at all customisable - no volume control, no choice of beep tone (you get lots of choice on the Etrex C) though you can adjust how far in advance it beeps.

I would suggest that the card is the main thing though - especially if you might be into 'alternative' maps.

Was yours the Dakota 10 or 20? I take Greenbank's point about distance to next turn - is that something that is easily displayed on the dakota?
The online manual really is pants.

frankly frankie · « **Reply #15 on:** 22 February, 2011, 11:52:02 am »

Quote from: GrahamG on 22 February, 2011, 11:44:07 am

Was yours the Dakota 10 or 20? I take Greenbank's point about distance to next turn - is that something that is easily displayed on the dakota?

I had the 20. I wouldn't buy a new GPS without a (micro)SD card, FWIW.

Yes 'distance to next' is the killer feature of GPS IMO. This is a Dakota screenshot -

GrahamG · « **Reply #16 on:** 22 February, 2011, 11:56:07 am »

Superb. Sounds like it would be a bit daft not to put the extra £60 in for the 20.

GrahamG · « **Reply #17 on:** 22 February, 2011, 12:04:41 pm »

of course, with bike mount and delivery that's still £208 from Handtec and a 705 with mount, cadence and HR is £230 odd,.. God I'm going to have just toss a coin at this rate. Or just accept lack of audible beep and SD card and get a cheapie Dakota 10...
Garmin, I hate you.

Biggsy · « **Reply #18 on:** 22 February, 2011, 12:07:03 pm »

Oh, lack of audible beep? That's no good. A beep is very very useful. Don't even need the "distance to next" display when you have a beep.

frankly frankie · « **Reply #19 on:** 22 February, 2011, 12:11:16 pm »

Where did you see this 'no beep' information? It's the first I've heard of it.

GrahamG · « **Reply #20 on:** 22 February, 2011, 12:26:22 pm »

Two separate blogs giving a detailed review of the Dakota 10 - one described it a useless without a waypoint alert and the other just said it has no alarm or audible beep feature.

BTW, I forgot to ask - what are you using now?

tom_e · « **Reply #21 on:** 22 February, 2011, 12:29:02 pm »

I can confirm the bottom-end Oregon, the 200, doesn't have a beep. So they have form for it, even if it must be one of the stingiest feature gradings ever.

FWIW, I manage perfectly happily without beep on my Oregon. I wouldn't want to be without an SD card slot personally, but I like to muck around with different maps.

frankly frankie · « **Reply #22 on:** 22 February, 2011, 12:35:52 pm »

That's a remarkable thing to omit - it's not as though there isn't enough product difference anyway, with the card, barometer (and associated displays) and compass.

Quote from: GrahamG on 22 February, 2011, 12:26:22 pm

BTW, I forgot to ask - what are you using now?

Well I had the Etrex Legend Cx before that, and to be honest I simply don't like the Dakota (they are very different) so I'm back with the Etrex again, and very happy with it. The Dakota menus are just too simplified for my taste. My review here:
http://www.aukadia.net/gps/dakota20.pdf

Manotea · « **Reply #23 on:** 22 February, 2011, 12:45:00 pm »

I don't bother with beeps. Apart from anything else I cannot hear the beep when I have my mp3 on. Actually my hearing is pretty duff anyway; riding with swiss hat last year he asked me to turn off the beep on my Polar HRM because it was annoying him. I didn't know it was on (and I wasn't using an MP3 at the time).

GrahamG · « **Reply #24 on:** 22 February, 2011, 12:47:34 pm »

Well at £120 for an etrex legend HCx, I'm tempted just to go that route. Will consult with the little lady when I meet her for lunch shortly; she'll put the money vs. features stuff in perspective.