How to select a good GPS receiver?
What should one look for in the specifications to determine whether a handheld purpose-built GPS receiver provides good navigational consistency under reasonably normal, low-speed conditions? Highly preferably both in open areas as well as potentially dense woodland.
I am looking primarily for something that will work well for walking and bicycling (hence low-speed; good accuracy while travelling by car is less of a concern because then even a 15 meters error may translate to about half a second of travelling time).
Are marine units as a general rule better in this regard than (for want of a better word) "personal" GPS receivers, in the absence of an external antenna? Or are they simply more rugged, and certified for marine use, while providing little potential benefit to non-maritime users?
My current (admittedly somewhat dated) GPS receiver, even after having had plenty of time to download a full GPS almanac, with a clear view of the sky and half a dozen satellites to work with, often reports navigational accuracy to be in the range 10-20 meters. What's more, that number tends to vary quite wildly. That certainly is good enough to e.g. find one's way back to a known location such as getting back to the car or campsite, but as soon as you need more accuracy than that, it falls way short.
I will be using the receiver primarily within Scandinavia, and Sweden in particular, generally outside of cities and often in forested areas.
To clarify, it doesn't have to provide pin-point position accuracy (for that, 10-20 meters is very often quite sufficient), but consistency in readings in the same area is much more useful. As an example, if I lay down a track and then have the dog follow that track, I am very interested in how closely the dog actually follows the track but I am not particularly interested in the exact location of the track. So, if the readings are off by some reasonable distance that isn't a major concern (as has been pointed out, it's not like being 20 meters off means you are hopelessly lost; if it is, it's not like a GPS receiver is likely to help much); as long as that within a reasonably short time frame (more than minutes, less than hours) two readings taken in the same physical location match well in terms of the reported location, that's good enough for me.
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I haven't seen any evidence that one brand or model of handheld GPS unit differs from any other model in its random or systematic errors. As far as I understand, the errors are determined by (1) the geometry of the satellites currently in the visible part of the sky from your location, and (2) the physics of the propagation of the radio waves (including effects such as multipath, ionospheric refraction, attenuation through forest canopy, ...). These effects can be reduced with techniques like dual-frequency GPS and differential GPS, but those features aren't available in hand-held GPS units, only in units such as those intended for use by surveyors.
What differentiates one hand-held GPS from another is other factors such as size, weight, screen resolution, color screen, ease of use, and mapping features.
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I live in Sweden and I hike a lot in the wild. My personal top three properties to look for in a handheld GPS receiver for The Great Outdoors:
- Battery life
- Battery life
- Battery life
I honestly don't care if the measurement is 20 metre off. In the Swedish mountains, it usually isn't, there are no deep canyons, and if there are you can only go in one direction anyway (well, two). I don't need and I don't want a colour display, nor any map information. In Sweden, you really don't need a barometric altimetre. A compass takes battery life but you can get directional information by walking a bit in a certain direction, and in the Swedish mountains, this is almost always possible. The best way to maximise battery life is to get rid of all the useless stuff. I still want a GPS receiver that doesn't have a screen that's always on.
All I want a handheld GPS-receiver to do is to tell me where I am (all models do) and keep a tracklog (all models do?). But when I'm in the wild for ten days, I don't want to have to carry 20 batteries. Therefore, my only consideration is: battery life.
Did I mention battery life?
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If you really do need exceptional accuracy, you could use the solution many Ingress players use - a good Android phone with a battery pack.
In the game you often need accuracy of 2 or 3 metres - so the Galaxy S3 or a phone paired with the Nexus 7 (which has an excellend GPS) are the tools of choice. The game uses google maps and wireless navigation, as well as the inbuilt compass and accelerometers.
My battery pack (a 12000mAh one I picked up for about £25) is only slightly larger than my S3 so the pair are easy to fit in my trouser or jacket pocket.
To be honest though, even my Garmin eTrek has accuracy better than 10m, which for walking and cycling should be far more than enough. Can you describe what your specific need is that requires this sort of accuracy. I can't think of any time I would need it when hiking, cycling or exploring...
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