People new to GPS will sometimes ask some variation of the question "What GPS Receiver Should I Purchase?". Below is a newsgroup posting, and selected responses, providing both specific technical information, and some general advice that applies to any purchase of a GPS receiver. ============================================================================ ---------------------------------------------------------------------------- Subject: Tree Canopy From: collegechas@yahoo.com (Bob) Newsgroups: sci.geo.satellite-nav Date: 13 Feb 2003 19:32:53 -0800 Looking for a good GPS that will capture a signal through thick tree canopy. I have recently gained access to a large tract of land but it is mostly populated with tall pines and oak trees. Looking at the Etrex Vista. Any thoughts? ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Subject: Re: Tree Canopy From: kf6vyh@aol.com (Kf6vyh) Newsgroups: sci.geo.satellite-nav Date: 14 Feb 2003 06:37:29 GMT The E-trex series of GPSR have patch antennas which are not very good. Face it, a GPS is a radio, ,the most important part of a radio is the antenna. Go with any other Garmin or a Magellan GPS. ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Subject: Re: Tree Canopy From: "Searching_Ut" Newsgroups: sci.geo.satellite-nav Date: Fri, 14 Feb 2003 15:52:40 GMT You often hear people express the opinion that Patch antennas are inferior, but then in the same thread the suggestion for tough terrain is often an external antenna. Of course the external antennas recommended are almost always patch antennas. Anyone except me find that to be somewhat odd? ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Subject: Re: Tree Canopy From: "Eric Fairbank" Newsgroups: sci.geo.satellite-nav Date: Fri, 14 Feb 2003 17:23:01 GMT Nothing odd about it at all. People who don't have a clue what they are talking about post misinformation in newsgroups and forums all the time. ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Subject: Re: Tree Canopy From: cam@holyrood.ed.ac.uk (Chris Malcolm) Newsgroups: sci.geo.satellite-nav Date: Fri, 14 Feb 2003 14:56:04 +0000 (UTC) Lots of folk will tell you where to get the units which track best under tree canopy, and many of them will tell you that under trees the Vista is somewhere between not the best and completely useless. A handheld GPS is a compromise between size, battery consumption, performance, etc.. You have to decide on how much weight to give the competing factors. For example, I like to carry some tools around so I can do local fixing. But size and weight is *very* important. So I carry a Swiss Army knife despite agreeing that every single one of its tools is probably inferior to the cheapest tool you could buy. But the point is the Swiss Army knife is good enough for me, and size matters. So try out a Vista in practice. Maybe it's inferior to a Cortez in tracking under canopy, but is that worth the extra size and weight of the Cortez? Perhaps, although compared to a Cortez the Vista often loses lock, you can always get lock when you want it (e.g to set a waypoint or get a bearing on your destination) simply by stopping for a minute or two, and in extremely difficult conditions, maybe moving a few yards to a better place. Or maybe while the Cortez will track fine inside your trouser pocket, the Vista needs to be up on a shoulder strap to achieve the same performance. The question is, how much do these things matter? There's a tendency for technogeeks to lust after the most highly featured whizzbang model, and end up buying a pen which will write upside down under 60 feet of water when all they actually needed was a pencil. If it so happens that your tree canopy is so heavy that it is often impossible to get a signal, remember that units (like the Vista) which also have an electronic compass and a barometric altimeter have two navigational aids which still work under the most impenetrable cover; which of course you could buy separately. Question of convenience. In sum, you don't need the best, you simply need the good enough, and you need to take into account *all*features, battery life, size, available maps (if you want maps -- it's a lot cheaper if you can put up with paper maps, which are also much more detailed), display options, etc.. And you need to decide the relative importance of things. For example, do you want the unit which gives the most accurate tracks, or which give the most accurate waypoints, or which finds out where it is the fastest after switching on? If you'll be doing a lot of work back home with computer-based mapping utilities, with the GPS being basically a data capture and "get home" device, you may not need to have so many facilities built in to the unit, because they're all, and more, in the computer software. Take your time deciding. Remember, all the fun of deciding what to buy *stops* at the moment of purchase. After that there are only regrets and rationalisations :-) If you take long enough deciding, there'll be a new even better unit comes along. You wouldn't want to buy a Cortez III just a month before the much improved Cortez IV was announced, would you? ---------------------------------------------------------------------------- ---------------------------------------------------------------------------- Subject: Re: Tree Canopy From: "Searching_Ut" Newsgroups: sci.geo.satellite-nav Date: Fri, 14 Feb 2003 15:48:14 GMT You didn't say what exactly you were going to try and do with your gps, or if mountainous terrain is involved as well. Often what works good in flat tree cover might not be as good in canyons. My experience in owning both an eTrex Legend, and a sportrak map is that the sportrak will be a little more accurate in heavy tree cover if you can allow it at least 10 minutes to autoaverage. The Magellan meridian series seem to behave virtually the same way. In moderate to heavy tree cover however, the sportrak doesn't do a very good job of recording tracks if you're trying to map out trails etc. The sportraks wanderings and positional lag will often provide you tracklogs that don't even come close to resembling your actual travels. The eTrex series are quite a bit more sensitive to how they are held, but in my experience are pretty close in reception if held in the correct manner and given a couple of minutes to sort themselves out while stationary. They don't average however, and tend not to be quite as accurate at providing a stationary location fix under many conditions. While moving, I have found the eTrex to be considerably more accurate in recording tracks in tree cover or other reception problem areas. They also record far more detailed tracks. As to which works better, there are a lot of variable based on terrain, moisture content of trees etc. As an example, in my house with aluminum siding, but no metal on the insulation in the roof my Legend always locks onto more satellites than my sportraks do, and can often get a lock when the sportraks can't. In my girlfriend house with metal lined insulation in the ceiling, but brick walls the sportraks generally work better. I've found it varies in similar manners in canyons, different types of tree cover etc. I personally use both receivers most of the time, generally relying on my Legend to guide me while hiking, or geocaching. The legend is also easier to use one handed while on the move. I use the sportrak when I'm stationary and prefer it while in my vehicle as the front mounted keypad is easier to use, and it works better in a vertical position which is how I use it in my truck. If I'm only going to take one unit with me however, the Legend is virtually always the one I choose. Right now I don't think the perfect GPS unit is out there. They all seem to have there fair share of strengths and weaknesses. Whichever receiver you choose, one of the most important aspects to getting good results will be the manner in which you hold it for stationary readings, or the way you carry it to record tracks. ----------------------------------------------------------------------------