Buying a GPS
Posted 07 December 2006 - 12:28 PM
Since I managed to score a big tax return (yay! to me for paying too much last year...) I have some money burning in my pocket. It might go to that digital video thing (tivo-like) that I have been thinking about for awhile, but another thing that I don't have is a GPS (which should be a must for a outdoorsy cartographer, shouldn't it?).
What I wonder, what would you recommend? I would love to have a reasonably rugged one with a decent display, memory for map data but also with Bluetooth, which I don't see in Garmin's devices, for instance (unless they have released something new?).
Why bluetooth? Because then I could use the PDA/phone (running windows mobile) that I currently have and install car navigation software on it, and use the GPS unit as an external thing. I don't own a car, so it would only mean occasional use (if I did own a car, I would consider buying a permanent unit).
An alternative there, though, is to buy one of those external GPS receivers (just for bluetooth), they are not too expensive.
Posted 07 December 2006 - 05:05 PM
A two additional things I'd consider are USB connectivity and the ability to attach an external antenna, if you may use the unit for cartographic work.
My personal unit (Garmin eTrex Vista) lacks both (USB and external antenna), but over the past year and a half I've begun to use non-professional grade GPS units (the new Garmin eTrex Vista [USB, but no external antenna] and Garmin Street Pilots [no USB, but external antenna capable]) for data capturing. Mainly this has been road data and building locations, but also reccies for 4WD trails and foot paths. To connect my GPS unit to my computer, for data transfer or for on-the-fly mapping, I need to use a proprietory Garmin plug which is then connected to a serial to USB adapter. I've run into the problem of those adapters being tempermental and producing flaws in the data transfer. Being able to use a standard (and common) USB cable to connect, which I've been able to use on my non-personal units, was great. Less stuff to worry about, easier to setup, etc.
Most units don't allow for an external antenna. I'm not refering to the little puddly antenna many units have built-in, but the big ones, which either allow you to place your GPS unit inside a car and the antenna on the roof, the farthest point away from you on the dashboard, or even stash the unit in your backpack and have the antenna attached to your shoulder harness. I've done some comparative testing, and the accuracy and signal strength had noticable differences without the external antenna, or if the unit was being operated at a position within the vehicle other than being in the nook where the windshield meets the dashboard. Having windows all around the vehicle's sides didn't help a whole lot, nor did strapping it to the dashboard so I could read it while driving. Many external antennas are not shaped like a fencing sabre (or a normal car antenna), which could be both limiting and annoying. The antennas I've primarily worked with (again, Garmin) are long cables with a very small receiver box on the end, with a removable magnet which would allow you to attach it to the roof or hood of your vehicle.
With this setup we've been able to create some very good base data for areas which previously had no data available (including commercial data). It is far cheaper than a Trimble, and for non-engineering work, the data was far better than adequate.
At first I was attracted to the external bluetooth GPS receivers. I typically believe that the less wires you have, the better. But my GPS use has typically been for extended periods of time, usually on long reccie trips, and I worry about battery life. The accuracy of GPS reads decrease as your battery strength decreases, so I'll do anything to minimize that. Unfortunately, few units come with an external DC/car charger. But, I am still very attracted to bluetooth receiver option because of its flexibility and similarity to the external antennas. I could put the receiver on the top of the vehicle, or the top of my backpack (or handlebars or panier), where it could have a clear view, and still use my laptop while driving or stash my laptop in my backpack if hiking. It has been almost a year since I looked into the bluetooth receivers. What sort of battery life do they have? Can they be externally powered? Would they survive a drizzle of rain or a ton of dirt, dust, and bugs from driving?
Of course, it all depends on your usage. I've never used a GPS unit recreationally. Primarilly, I guess it's an inner goal of not having to go back home when out hiking or what not. Thus, if I get lost, all the better!
But, as for professional use and gathering data, a recreational-grade GPS unit can be an extremely powerful tool.
I hope some of these thoughts help..
Posted 14 December 2006 - 12:15 AM
We just recently obtained a Garmin GPS 60 for field work. It's our first use of a GPS device and it's primary purpose at this point will be for setting locations and annotations when doing field checks. Although its possible to use for recording tracks, I'm not sold on the accuracy/frequency of points for that purpose. But we are still experimenting with it. I will echo Brody's comments about an external antenna, it's a necessity if you will be using it at all for data collection. You can place the device where ever you want to make it more useable and you will improve the number of satellites it can see and lock onto, thereby its accuracy. A car power adaptor is also a necessity to keep from burning through batteries. This particular unit was under $200. It does have some limits as to the number of points and the amount of memory available. Memory is not removable at this price level, but it appears the Garmins only use removable memory for base maps, not for data recording.
Another issue for us was compatibility with our Macintoshes, generally there isn't much out there that is very Mac friendly. Garmin has been promising an OS X version of their software for a while, it still isn't available. GPS MacPro is a decent piece of software but for us so far has been glitchy when accessing the unit. We came across a great piece of software, GPSBabel+ that is phenomenal for downloading and uploading data from the device in over 80 different formats (including KML). We don't need software to plot out the data for us, I've got that covered in all my other tools, I just need to get the data into a usable format. The program is from open source and there is a version for any operating system you might come up with.
Posted 19 December 2006 - 03:56 PM
Posted 22 January 2007 - 06:21 AM
Handhelds (GPS's) should be good for +/- 10 metres (3-4 meters in good going) - theyre not meant for accurate work. That said I've compared my Garmin 12 and later versions with accurate surveyed measurements and sometimes I get about 300mm difference over 1-2 km - thats a fluke so I wouldn't say they are that good.
...and the GPS was off by 10 to 30% almost every leg of the trail. ...but don't depend on them if you really need to know the distance you travel within a tenth of a mile.
Measuring wheels are not necessarily accurate either - they also measure the surface distance whereas GPS measures a distance that could be considered a straight line (without getting bogged down in science).
Did you buy a unit? There are some Bluetooth GPS units that work well with handhelds - pocket PC's. You can run ARCpad on them and together make a very usefull little data collector. The pocket PC's arent very rugged though. I have 2 garmins and they are both rugged - I've dropped them several times without any issues surfacing.
Posted 22 January 2007 - 02:28 PM
No, I haven't bought any yet. Seems like we are spending the money on traveling instead, this year, and there are a number of Windows Mobile phones coming out now, that have built-in GPS, when it is time to phase out my current (a year maybe) I might get one of those!
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