View Full Version : GPS receivers
The geocaching thread over at http://www.bushcraftuk.net/community/showthread.php?t=1101 has meant that I've had a few PMs relating to GPS receivers. As there seems to be a lot of interest, I thought I'd create this thread so that you can post your GPS related questions - I've been using GPS receivers for over 5 years extensively in recreation for a variety of applications and I'll do my best to answer your questions!
I look forward to your posts!
OK, I'll start with an obvious question, which is probably rather stupid, but as I know absolutely nothing about them, it seems logical to me. Which one is the best? Accuracy, reliability, robustness, price etc.
I might be persuaded.
Good idea Adi!
I've been using GPS in my work for the past seven years or more. I have tried several models but keep coming back to Garmin. For me they are the most compatible with other computer software (GIS etc) and equally relaible in the field. I like the way you can automatically update the software from the Garmin website without having to buy additional programs or send the unit off e.g Silva. I've recently got hold of the Geko 301 which has all the features of the Etrex Summit but is also EGNOS enabled - It's an excellent unit, very easy to use, small and compact. Garmin customer service is also excellent (unlike some others e.g. Silva)
There is also a thread on the OM forum regarding GPS:
http://www.outdoorsmagic.com/forum/forummessages/mps/dt/4/UTN/3682/srchdte/0/V/1/SP/
Good question Martyn!
As for accuracy, since the system is a military system and as such the signal processing code is all standard, accuracy between one unit and another will be the same. Under clear skies all units should give you a position fix accurate to about 8 - 10 m. Under tree cover or on the side of hill or mountains or in valleys where part of the sky is obscured or reflected signals received from the satellites (called SV - space vehicles), then accuracy can drop. Trees are a particular problem because the chlorophyll in the leaves absorb the microwave signal at the freq that the GPS system uses.
If you want more accuracy, you now have the option to go for a WAAS GPS receiver (Wide Area Augmentation System). this receives an additional signal from a European satellite in orbit and can give your position to about 1 - 3 m (I've had some good accuracy with this).
But for accuracy of a standard GPS receiver, 8 - 10 m can be expected from the cheapest to the dearest - I've never seen any significant variation in accuracy related to price.
Best brands for reliability and robustness are Garmin and Magellan - I've standardized on Garmin because I found that their customer service is excellent.
Price ... begins at about £80 but if you'd like the ability to connect to a PC or PDA, go for one with a port on them ... worth the extra tenner i think!
The eTrex series by Garmin offer a full spectrum of price and features ... with the higher end receivers having barometers and electronic compasses build in. Another good range (albeit with fewer features) is the Gecko range.
Best prices ... www.globalpositioningsystems.c o.uk
OK, I'll start with an obvious question, which is probably
rather stupid, but as I know absolutely nothing about them, it seems logical to me. Which one is the best? Accuracy, reliability, robustness, price etc.
I might be persuaded.
Good points there ... Garmin and Magellan units can have their software updated by the user (although I've heard of quite a few Magellan units being messed up by this while I've yet to come across a Garmin unit fried by the update).
My model of choice is the Garmin Vista ... It's a great unit! All I'd suggest as extras are a set of rechargeable NiMH 2100 mAh batteries ... feeding it on Duracells can be expensive!
I've used the Geko a bit at a Geocaching meet and thought it was a well featured unit ... but I still like the slightly bigger screen of the etrex ... although if size/weight is an issue, the Gecko is a good unit.
Good idea Adi!
I've been using GPS in my work for the past seven years or more. I have tried several models but keep coming back to Garmin. For me they are the most compatible with other computer software (GIS etc) and equally relaible in the field. I like the way you can automatically update the software from the Garmin website without having to buy additional programs or send the unit off e.g Silva. I've recently got hold of the Geko 301 which has all the features of the Etrex Summit but is also EGNOS enabled - It's an excellent unit, very easy to use, small and compact. Garmin customer service is also excellent (unlike some others e.g. Silva)
There is also a thread on the OM forum regarding GPS:
http://www.outdoorsmagic.com/forum/forummessages/mps/dt/4/UTN/3682/srchdte/0/V/1/SP/
I have been using GPS for about ten years and love it.
I started with a Magellan gps 2000, good bit of kit although as with all early products quite basic, it did however guide me through the gate to the farm we camp on some 300 miles away, the main thing to remember is that unless you are a map based gps the unit will always point directly at the target grid referance and give you a distance to be covered as the crow flys (in a straight line), ok if your travelling in a straght line to your target but can be very misleading if you are using it in your car, main draw back with this was the battery life, eight hours from 4 AA's.
I, a few years later upgraded to a Garmin Emap, and what a tool, map based, I now have world wide street level software, a 128meg memory card (got 95% of the UK street plan on it), power lead to run from the Lannys power supply and 17 hours from 2 AA's.
Because it is map based you can actually plan your journey street by street, route planning can be planned on you PC (easier than doing it on the GPS unit, but can be done if needs must) and uploaded to the unit.
One product that Garmin have in the States (but not here yet :-( ) is the Garmin Rino 120, a GPS and pmr radio all in one, the thing that I love about this is the fact that it will transmit you location to the other units in your group so that you can see each others locations on the screen of your unit, and they can see you on theirs, great for keeping an eye on your kids (and my Scouts). Unfortunatly the position sending fearure is not yet legal in the UK, and until the Radio communications agency realises the incredable safety featurs of this unit and gets the law changed we wont see it here, it is selling like hot cakes in the US and so it should, but dont be tempted to order them from over there as:
1, They are illegal to use in the UK.
2, The US pmr frequencies are not legel over here. US is on a different setup to the UK that will never be compatable with the UK, so your nice new Garmin Rino's will not be able to talk with any Uk spec pmr radios that you may already have.
3, If you do get tempted and get caught you wont like the fine of watching the judge using your nice new kit as a gavel block.
Be patient and play the waiting game and hopefully we may see them over here. :-D
It's worth adding is that these GPS SV (space vehicles) orbit the Earth at an altitude of about 14,500 miles and each orbits the planet twice a day.
There are always at least 24 active satellites with a minimum of at least 3 above the horizon at any one time. Usually there are at least 6 visible.
The GPS signal is not affected by adverse weather.
Here is more information on the GPS system and the constellation of GPS SVs.
http://www.trimble.com/gps/
If you plan on using your GPS in a car then you might also want one of these:
http://www.pocketgps.co.uk/reradiating.php
Depends on the car but I find that even if you don't have metalized windows in increases the signal strength dramatically and also make the GPS work better and be more accurate if you are driving along forest roads or valleys.
I bought a basic yellow garmin etrex last week and its amazing
It can keep sat loc in my car , in my pocket , I can connect it to my laptop and run it in my car
This weekend I'm taking the kids up to the North York moors to go walking and camping
The most exciting thing is the fact I can connect it to Autoroute, plot a course to the next continent and just follow the flashing icon
Brilliant
Oh and I use it for the geocaching malarky too
Great bit of kit ... and if you have figured out how to combine it with mapping, you're onto a winner!
:biggthump
Interesting to hear about the Garmin Rino. Shame it's not legal here.
As yet, it is not legal to transmit data on PMR 446 radios. You can transmit data (including position reporting data from a GPS) on amateur radio (with appropriate license)
APRS (Automatic Position Reporting System) was invented to allow Amateur Radio operators to utilize Packet Radio (AX25) to exchange data over a wide area network of stations. That information is then displayed in a graphical format, super-imposed onto maps using suitable software. The information could include:
Position
Speed
Course
Station Type
Weather
Objects
Messages & Email
One of the most popular uses of APRS is to incorporate a GPS receiver to a radio and frequently beacon a Mobile Station's position into the network allowing it to be tracked to a high degree of accuracy. Originally APRS users were connected by Amateur Radio, but as time has gone on, many people are also using Internet Gateways (Igates) allowing them to use the Internet as their medium.
The American hams are mad keen on this. Loads of stuff about it on the net.
Yeah, now that Garmin have ironed the bugs out of the Rino it sounds like a good bit of kit that could save lives.
I have used Garmin Gps in Canada, U.K., Kenya and other places, but I have also used Trimble, Magellan(trailblazer and GPS2000) and can honestly say they are a usefull aide to navigation.
But we should never forget that they are just that an aide to navigation and no substitute for standard skills using map and compass.
I will echo the fact that of all the GPS that I have used, the best have been made by Garmin and I have had good customer service from Garmin (when the internal lithium battery died they replaced the unit there and then).
I will echo the fact that of all the GPS that I have used, the best have been made by Garmin and I have had good customer service from Garmin (when the internal lithium battery died they replaced the unit there and then).
They did the same for me too at no cost for a unit that was well outside of the warranty period. Excellent company to deal with!
ORIGINAL CONTENT REMOVED AS I DONT WANT LOADS OF PEOPLE TRYING TO GET FREE KIT
Lets just say that having both Garmin and Magellen GPS units and having delt with both companies customer services.
Garmin is very good, but Magellan is 500 times better.
:-D :-D :-D :-D :-D :-D :-D :-D :-D :-D :-D :-D :-D :-D :-D :-D
Might have to try that wioth my old (now useless) Magellen 310!
Hey Adi have you ever shopped at Gaynor Sports, I know it is a bit up country from you, but they do have some good kit at cheap prices (Lowe Alpine Flash Jackets £100 cheaper).
Well currently they are having offers on GPS http://www.gaynors.co.uk/acatalog/Catalogue_Contents_Navigation_ Equipment___GPS_4.html have a look.
Also one of the guys mentioned memory map they appear to be selling that as well.
Good prices! Thanks for posting that!
With all this talk of GPS and connectionn ports to the PC I thought I'd add that one of the dearest parts to a GPS is the communication cable ... you'll pay between £20 and £30 for the geniune article. However, here is a place that sell good quality cables for connecting GPS to PC and iPAQ:
www.lynks.co.uk
No probs. Check out the whole site. I was up there a few years ago when they had a delivery arrive, about £3,000,000 worth it lasted for about a week and then they had to re-stock.
Edited
Thanks for the link Adi, I have been after a a cable for an old GPS12XL for a time and most of the time they have been a lot more expensive then the ones on the above site.
I had a Garmin GPS12 and upgraded last year to an ETREX Vista - great bit of kit and has had a rough ride in the past year or so.
My only problem has been that I changed laptops late last year and my new one doesn't have a serial port - only USB ports. I have asked around and no-one seems to know but do Garmin do a USB cable at all? At the moment, I have a quality laptop and excellent GPS which can't talk to each other!
ADI posted a link earlier on in this thread for cables that link a GPS to your PC, I think they were actually called links
I had a Garmin GPS12 and upgraded last year to an ETREX Vista - great bit of kit and has had a rough ride in the past year or so.
My only problem has been that I changed laptops late last year and my new one doesn't have a serial port - only USB ports. I have asked around and no-one seems to know but do Garmin do a USB cable at all? At the moment, I have a quality laptop and excellent GPS which can't talk to each other!
Mike
You can get USB to serial adaptors quite easily, I had the same problem until i got an adapter from maplin.co.uk.
ADI posted a link earlier on in this thread for cables that link a GPS to your PC, I think they were actually called links
http://www.lynks.co.uk/
I had a Garmin GPS12 and upgraded last year to an ETREX Vista - great bit of kit and has had a rough ride in the past year or so.
My only problem has been that I changed laptops late last year and my new one doesn't have a serial port - only USB ports. I have asked around and no-one seems to know but do Garmin do a USB cable at all? At the moment, I have a quality laptop and excellent GPS which can't talk to each other!
Mike
You can get USB to serial adaptors quite easily, I had the same problem until i got an adapter from maplin.co.uk.
Here's another ... http://www.lynks.co.uk/usb.html
Mike
You can get USB to serial adaptors quite easily, I had the same problem until i got an adapter from maplin.co.uk.
Brilliant - which one did you get and you can confirm it works fine? The reason I ask is because I know someone who bought an adaptor and it didn't work!
Brilliant - which one did you get and you can confirm it works fine? The reason I ask is because I know someone who bought an adaptor and it didn't work!
I got this one:
http://img61.photobucket.com/albums/v185/fraserM/34449i0.jpg
It's the A86AN USB to Serial Adaptor. Works fine for me!
Well currently they are having offers on GPS http://www.gaynors.co.uk/acatalog/Catalogue_Contents_Navigation_ Equipment___GPS_4.html have a look.
Also one of the guys mentioned memory map they appear to be selling that as well.
Mikey the link above was put up before, they have usb cables for the new gps :-D
I've got to stop reading BCUK - I only end up buying things!
Just ordered a plain vanilla yellow Garmin Etrex. £75.35 including VAT and post from Expansys. I note that in the US these things cost $100 - say £54. I was quite tempted to import one from the US from one of the ebay dealers but when you add carriage, and the possibility of a £13 customs bill, I decided not to.
Of course, our local outdoor shop has them for £118.......
I had thought that these things just gave you your position in Grid or Lat/Long. Obviously they do rather more than that.
I did wonder how well they work in forest, and whether interfacing with a computer is straightforward?
I've got to stop reading BCUK - I only end up buying things!
Just ordered a plain vanilla yellow Garmin Etrex. £75.35 including VAT and post from Expansys. I note that in the US these things cost $100 - say £54. I was quite tempted to import one from the US from one of the ebay dealers but when you add carriage, and the possibility of a £13 customs bill, I decided not to.
Of course, our local outdoor shop has them for £118.......
I had thought that these things just gave you your position in Grid or Lat/Long. Obviously they do rather more than that.
I did wonder how well they work in forest, and whether interfacing with a computer is straightforward?
Interface ... easy, you need a cable. For that, don't buy Garmin because it is mega pricy but try www.lynks.co.uk (http://www.lynks.co.uk) where you can get a ready-made cable or bits. Connecting is easy!
In tree cover - it's OK. The problem is that leaves are moist and wanter absorbes the microwave signal. However, patchy cover will still allow the signal through. Hold the GPS receiver horizontal for the best reception.
The yellow eTrex is a good gadget ... you'll enjoy it! :super:
Tree cover + large metal box is a bit of a problem for those antenna, however.
I ought to fit a suitable one to the 110...
In those situations I find re-radiating antennas a big help ...
http://www.globalpositioningsystems.c o.uk/viewprod.php?product_id=1393&category_id=46&pp_id=217&PHPSESSID=71c6b48f51efb2e42d1a 1a40edb8f5a6
http://www.globalpositioningsystems.c o.uk/viewprod.php?product_id=1394&category_id=46&pp_id=217&PHPSESSID=71c6b48f51efb2e42d1a 1a40edb8f5a6
BorderReiver
07-07-2004, 19:31
I bought a basic yellow garmin etrex last week and its amazing
It can keep sat loc in my car , in my pocket , I can connect it to my laptop and run it in my car
This weekend I'm taking the kids up to the North York moors to go walking and camping
The most exciting thing is the fact I can connect it to Autoroute, plot a course to the next continent and just follow the flashing icon
Brilliant
Oh and I use it for the geocaching malarky too
You forgot to mention that it is fully submersible too :ylsuper:
You forgot to mention that it is fully submersible too :ylsuper:
Yep - to IPX9 spec. The battery compartment might get wet/damp but it won't harm the GPS itself.
I've had a Garmin 72 for about a year now. Very capable and configurable but not the most user freandly beast. Whoever organised the menu system needs a slap.
Linking your gps to a computer makes route planning a piece of cake. No more entering grid referances with the up/down buttons. Just point and click.
Jon
Well, I received the yellow Etrex yesterday.
I like!
Almost uncanny how it knows where it is. Also gives Maidenhead locators - much used in Amateur Radio.
Does anyone know: should I leave the map datum on the default setting, or change to the Ordnance Survey option (when using OS maps)?
Any other hints appreciated as it is a bit of culture shock using GPS for the first time after 30 years of good old Silva compass and OS map.
On a similar theme, any views on Harveys walkers maps versus OS? I have so far resisted them as being different, but users opinions would be of value.
In those situations I find re-radiating antennas a big help ...
Cute... But the EMap has a socket on the back, so re-radiating is not strictly neccessary. Nice, though.
Cute... But the EMap has a socket on the back, so re-radiating is not strictly neccessary. Nice, though.
External antennas really clobber the batteries tho ... but useful when you need it!
Well, I received the yellow Etrex yesterday.
Does anyone know: should I leave the map datum on the default setting, or change to the Ordnance Survey option (when using OS maps)?
If you are using the OS grid co-ords then the datum has to be set to OSGB otherwise you'll get a positional error of about 30 m. The Garmin eTrex are good though because they usually go this automatically. If you are using Deg, Deg, Min or Deg, Min, Sec then you will need to use WGS84 datum or, again, you'll get errors.
On a similar theme, any views on Harveys walkers maps versus OS? I have so far resisted them as being different, but users opinions would be of value.
I'm too set in my ways to change! I can read OS like a book and I'm comfortable with it so I'm not going to change - especially as I have the whole of the UK on CDs in OS format!
Thanks for that Adi.
I see there are a few geocaching caches near me.
As I have no PC cable yet, I guess I need to enter the cache location as a waypoint manually: Am I right in thinking that cache co-ordinates use the WGS84 datum? So should I select WGS84 and enter the coordinates as lat long?
Also, does it use more power when its 'working hard' eg, plotting speed and location of a fast car, compared to just sitting there switched on?
Also, how can you check the position fix accuracy - Using OS 1:25000 maps I doubt I could resolve to much more than 25m anyway.
I'm also pleased to see it calculates sunrise sunset times. Nice feature.
Do you find its estimated accuracy to be reliable?
I'm told the altitude data is not particularly reliable - any comments?
Sorry - the persistent questioning of a man with a new toy!
Thanks for that Adi.
I see there are a few geocaching caches near me.
As I have no PC cable yet, I guess I need to enter the cache location as a waypoint manually: Am I right in thinking that cache co-ordinates use the WGS84 datum? So should I select WGS84 and enter the coordinates as lat long?
Yes. Cables are easy to get or even make ... if you go over to www.lynks.co.uk you can find the Pfranc connector - make a pledge for one and they'll send them out to you. Chop up an old COM port cable and away you go! Really cheap and effective. This makes life easier and you can move co-ords to the unit a lot easier.
Also, does it use more power when its 'working hard' eg, plotting speed and location of a fast car, compared to just sitting there switched on?
No, the receiver is a 12 channel receiver and updates the screen and data every 1 sec, irrespective of whether you are moving or not.
Also, how can you check the position fix accuracy - Using OS 1:25000 maps I doubt I could resolve to much more than 25m anyway.
Not needed, but if you want you can always use a trig point - go to www.trigpointing.co.uk for info.
I'm also pleased to see it calculates sunrise sunset times. Nice feature.
Cool feature, innit!
Do you find its estimated accuracy to be reliable?
Reliable enough. You can expect 10 m accuracy under good conditions. It's just an estimate but it's normally quite good.
I'm told the altitude data is not particularly reliable - any comments?
True. Altitude data is a bit flaky simply because most of the sats are above you - the clearer the horizon the better the altitude data, but even then it's always going to be less accurate than a positional fix.
Sorry - the persistent questioning of a man with a new toy!
Enjoy your toy!!!!! :biggthump
External antennas really clobber the batteries tho ... but useful when you need it!
Yeah but.. It'll be on the dash. Right about the lighter socket? ;)
Yeah but.. It'll be on the dash. Right about the lighter socket? ;)
:biggthump
Thanks for all the info Adi.
Good bit of kit, the etrex.
MartiniDave
12-07-2004, 10:17
I've just ordered an etrex. Checking on lynks they do several different cables. Anyone know which one I need?
Cheers,
Dave
I've just ordered an etrex. Checking on lynks they do several different cables. Anyone know which one I need?
Cheers,
Dave
Cables are on this page ... http://www.lynks.co.uk/cables.html
If you want a data cable only, you need the eD1 (http://www.lynks.co.uk/ed1.html), while if you want a combo data/car cord, go for the eCombo (http://www.lynks.co.uk/ecombo.html) or eMax (http://www.lynks.co.uk/emax.html) - the difference between the eCombo and the eMax is that with the emax you can choose whether you want to have the data and power or data alone or power alone connectors.
Or, if you've got an old COM port cable lying around, you can get just the plug. The plug you need is the ePlug on this page (http://www.lynks.co.uk/pplugs.html).
Hope that helps!
Just bought Garmin Summit with Memory Map. PC Data cable. All is so far fine (having fun playing..) but for some reason, when downloading waypoints/routes/tracks from GPS to PC (Memory Map) a new waypoint is being created off the map area (sometimes it says I've been in the middle of the north sea, but I haven't - I know 'cos my socks aren't damp :wink: ). Any idea what causes this and how to stop it?
Thanks in advance
Just bought Garmin Summit with Memory Map. PC Data cable. All is so far fine (having fun playing..) but for some reason, when downloading waypoints/routes/tracks from GPS to PC (Memory Map) a new waypoint is being created off the map area (sometimes it says I've been in the middle of the north sea, but I haven't - I know 'cos my socks aren't damp :wink: ). Any idea what causes this and how to stop it?
Thanks in advance
First off I'd suggest that you check for updates to Memory Map ... I seem to recall that this was a bug with certain versions.
Failing that, check the cable connector in the back of the PC.
Oh, one more thing. If you go into setup on the GPS and check out the coordinate system used ... it should be OSGB and the datum British Grid or WGS84 and a datum of WGS84.
First off I'd suggest that you check for updates to Memory Map ... I seem to recall that this was a bug with certain versions.
Failing that, check the cable connector in the back of the PC.
Oh, one more thing. If you go into setup on the GPS and check out the coordinate system used ... it should be OSGB and the datum British Grid or WGS84 and a datum of WGS84.
Version checked, and it is the lastest one available.
Checked cable - seems OK :-?
Confirmed OSGB / British Grid settings.
Have now done all the above, (thanks for the advice). Will be out and about tomorrow and try again. Although if I do end up in the middle of the North Sea, I will be blaming you.. :wink:
Again thanks for the help,
Regards
Squidders
26-09-2004, 20:31
I love the Garmin range, I have a streetmap III in my car and it's brilliant.
On the subject of cables for the etrex, I got mine from Maplins, I think it cost £15 and there was no messing about.
I have found the accuracy of my little etrex to be ok, nothing special and turning the backlight off gives me ages of battery life. It's been used for a lot of things, including checking speed when snowboarding and on this may I offer the following advice: Don't look at the screen whilst snowboarding as it's liable to turn you into a human snowball :yikes:
Can anyone help? Have tried searching (but GPS is too short a word) to find a link to a site which was titled something along the lines of "anyone thinking about buying a GPS unit should read this first!". It gave a lot of technical info and highlighted the drawbacks of buying GPS without having even basic map & compass skills etc. A real eye opener, but I can't find it now.
I must have seen it here (I don't subscribe to any other similar forums) and forgot to 'waypoint' it (favourites) when I last came across it. :naughty:
As always, thanks in advance...
Squidders
09-10-2004, 22:13
Hogan,
I had a little poke around and found this with google: http://www.travelbygps.com
There are some nice tutorials and helpful information. I hope this is what you're after... if not, you may publicly flog me :o):
Hogan - what's the problem you are getting? I'm not sure I understand ...
I hope this is what you're after... if not, you may publicly flog me :o):
http://myweb.tiscali.co.uk/xhogan/pix/whip1.gif
Great site, which I'm sure I will use a lot, but not the one I was asking about.
Thanks though
Regards,
Hogan - what's the problem you are getting? I'm not sure I understand ...
Not one specific problem, but lots of little ones..
Like : My GPS lost signal and as a result, I have two saved tracks (one going up the hills, and the other coming down. I'd like to know how, using memory map, I can join the two together. I tried, but it kept reversing the second track, which made it look as if I started from the hill, went home, then back up the hill again :?:
The site I was asking about was simply one that remembered as being very interesting, but as happens so many times, I put it down, and can't remember where I left it :cry:
I was certain I had seen it from a link on this forum, but as I said, a search didn't turn it up - I'll know it when I see it though :-)
Regards
mojofilter
07-12-2004, 00:56
Ive had a yellow etrex for about 3 years as a standalone, but now I want to link to the PC. What is the best software to use?
cheers
stuarty
Not one specific problem, but lots of little ones..
Like : My GPS lost signal and as a result, I have two saved tracks (one going up the hills, and the other coming down. I'd like to know how, using memory map, I can join the two together. I tried, but it kept reversing the second track, which made it look as if I started from the hill, went home, then back up the hill again :?:
The site I was asking about was simply one that remembered as being very interesting, but as happens so many times, I put it down, and can't remember where I left it :cry:
I was certain I had seen it from a link on this forum, but as I said, a search didn't turn it up - I'll know it when I see it though :-)
Regards
If you want to work with routes and waypoints then the tool I'd suggest you use is called G7toWin - http://www.gpsinformation.org/ronh/ - it looks basic but it is in fact very powerful and what you can do with this is take the waypoints that make the track you have and combine them. Much more powerful then Memory Map for data management.