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GPS Receiver recommendations (1 Viewer)

L

Leif

Well-known member
I'm hoping someone can recommend a suitable GPS receiver to replace my current one.

I have a basic etrex from some years ago, which I use when recording fungi. Unfortunately it is often useless in woods due to tree cover. Is this usual, or are there more powerful units which can operate in for example Beech woods?
 
Leif you going for a all in one gps or a PDA and seperate bluetooth receiver? If the latter the new generation of SiRF III receivers are very powerful and work in buildings and forests apparently!

Stewart
 
The new range of eTrex HcX units claim for example Deep foliage, nor canyons faze the rugged eTrex Legend HCx. Its high-sensitivity receiver holds a GPS signal in the toughest environments./I]
Ideally you need something with a SIRFstar III receiver which the top of the range units have installed. Garmin are a bit shy of saying what is int the HCxs.

I am still using an old Legend and/or a PDA loaded with OS maps linked by Bluetooth with a TomTom SIRF receiver which works very well but is not so convenient.

I am looking someone with one of the new eTrexes to confirm their advertising before risking my cash, however, my guess is that they are a lot better (not difficult), but how much? Thats the question.
J
 
Thanks for the replies. I'm looking for a one piece unit not a PDA add on. The Garmin does look interesting.
 
The Garmin 60CSx is an excellent unit for use in the backwoods. It has the SIRF III receiver and I've had no problem with it on backpacking trips in all types of tree cover conditions. Very easy to use as well. One issue is that it only comes with a base street map that has limited detail. Probably beasue it is intended to be a backwood unit. But you can add any of Garmin's mapping software to it. I installed City Navigator and use the unit for trip navigation all the time. It's worth your consideration.
 
I'll toss in another recommendation for the Garmin 60CSx. Combined with the City Select maps I get street routing in the car and excellent reception in the woods.
 
Also 60csx
I have Topo mapping on mine which is excellent for offroad walking, it will autoroute on some pretty obscure country lanes.
I wouldn't be without it especially in winter with the short days.
 
I've never lost lock with my 60csx. Head-to-head, the previous generation GPSmap 76 struggled to get 3 satellites when my GPSmap 60csx had 8, so they've improved a LOT in the last few years.
 
In case anyone is interested, I bought a Garmin Etrex H, which is the base unit, with a B&W screen, and a high sensitivity receiver. £70 including P&P, and it can even pick up a signal indoors.
 
Leif said:
In case anyone is interested, I bought a Garmin Etrex H, which is the base unit, with a B&W screen, and a high sensitivity receiver. £70 including P&P, and it can even pick up a signal indoors.
Click to expand...

I use this in forests, and get a signal down to 5-7 m usually (though it can sometimes take a few minutes). No amateur hand-held unit can do better than that, without a base station.
 
KnockerNorton said:
I use this in forests, and get a signal down to 5-7 m usually (though it can sometimes take a few minutes). No amateur hand-held unit can do better than that, without a base station.
Click to expand...

To be honest I would not believe that accuracy. It might even be out by 10 times that amount. Still good, but not as good as quoted.

GPS was found to be not sufficiently accurate for use in automated plane landing systems, or for shipping use near the coast. The US is creating WAAS, which is basically a way of using sites at well determined positions to work out the errors in GPS measurements. Once you know the errors, you can broadcast corrections, and get very very accurate readings. These errors come from various factors including transit delays in the ionosphere, and orbital errors.

Anyway, I'm glad to hear that the unit is effective! I am certainly impressed by it. My old one was bought 6 or 7 years ago.
 
You can get accuracy down to about 3m, as judged by plotting the track on OS MasterMap at work (what used to be 1:1250 when it was paper). I'd say the actual accuracy is within 10m for about 80% of the time.
The reported accuracy isn't a measured accuracy, but just an estimate. The problem with GPS for autolanding was that it wasn't certain in real time whether the GPS location was accurate or not.

WAAS corrections are an average correction covering a wide area (such as the whole of Europe and North Africa), and don't improve the best case accuracy all that much. High accuracy (10cm or so) requires local corrections direct from local(ish) base stations. The OS maintain about 10-15 of these across the UK, IIRC.
 
Leif said:
To be honest I would not believe that accuracy. It might even be out by 10 times that amount. Still good, but not as good as quoted.
Click to expand...

it doesn't seem to bad, to be honest. I can compare it with LiDAR data for the area I'm in, and it seems pretty accurate to those distances. 7m is still 20ft, but it's a lot better than 200ft!
 
KnockerNorton said:
it doesn't seem to bad, to be honest. I can compare it with LiDAR data for the area I'm in, and it seems pretty accurate to those distances. 7m is still 20ft, but it's a lot better than 200ft!
Click to expand...

It's bloody amazing! I was going by some books I have recently been reading, having just started work for a company working in the geophysical survey market. My boss also thinks that GPS units are often quite far out, compared to the quoted accuracies.

The Wikipedia GPS article quotes about 15m as the reliable accuracy. Take that as you wish!

It could also be that equipment has improved since the books I read were written. I'll have a try with a map this evening, and see how well the unit agrees.

Regarding WAAS, I thought it was essentially a US system, and there it does give quite a lot of improvement.
 
I discount any on-screen accuracies of >12m. And some of the better registrations have been out by 15m or so, but not many at all. I've found that it takes the unit a while to 'settle down' and get a good accuracy at each data point - there seems to be a lag between what it tells you and what it actually does. So you could find a spot, record it as soon as you stop walking, and it will say 5m. But 30 secs later it will be 15m, and then will gradually get back down to 5m. So I tend to wait a while until it 'stabilises' for at least a minute at each data point.

This is all under canopy cover too, but in a flat area.
 
It's worth remembering that GPS devices may have a preferred orientation depending on how the antenna is aligned within the device. My Garmin Vista Cx is most accurate when held horizontally, but there are other models that read most accurately when held vertical (which is less then helpful for recording waypoints imo).

Because the GPS is normally vertical when stowed in my pocket, it may take a short while to get a stable reading when held horizontal for the first time. More importantly it won’t record the most accurate track record if attached to a belt etc and is best stowed flat in the top pocket of my rucksack for this purpose, especially when in woods.

Interestingly, the apparent sensitivity of my now superceded model has improved in the last year or so. It now works in my (granite) house, which it never did before. I'm not sure if this reflects a firmware update, improvement to the satellites or something else entirely...

Regarding WAAS - this is not available in Europe. We have the similar EGNOS system. I've played with it and it does often improve estimated accuracy to around 6ft. It seems very difficult to download the almanacs in NE Scotland (have to leave the GPS on and stationary all day in a place with a good sky view) and using it thereafter munches batteries on my device. Possibly it will work better further south and east.
 
Leif said:
It's bloody amazing! I was going by some books I have recently been reading, having just started work for a company working in the geophysical survey market. My boss also thinks that GPS units are often quite far out, compared to the quoted accuracies.

The Wikipedia GPS article quotes about 15m as the reliable accuracy. Take that as you wish!

It could also be that equipment has improved since the books I read were written. I'll have a try with a map this evening, and see how well the unit agrees.

Regarding WAAS, I thought it was essentially a US system, and there it does give quite a lot of improvement.
Click to expand...
I think the main reason for the difference is that there's more than one way of looking at what accuracy is.

You can go to a point and put down the GPS, and log a position every second for an hour or two, then analyse the results and say that 97% of the logged positions fall within a 15m radius circle centred at XY. Or take a reading that gives an XY answer, and then say that there is a 97% chance that the true position of the point XY is within 15m of where you are.

Alternatively, you can go to a known point X1Y1, take a position reading X2Y2, and then observe that X1Y1 and X2Y2 are only 2m apart.
 
I have a Mitec Mio 168 pda with built in GPS ariel.I use tom tom for road nav i also have OS maps for all GB plus bird songs on sd card.It seems to me that mine is about within 3-6m on OS maps showing my position only thing it seems to get wrong is altitude its always about 50m out being on the high side hope this may help.It also pics up satallites in doors and in woods.You also get an extension ariel but ive never had to use it.
 
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