The following suggestions are based on my interest in hiking and canoeing. The list of considerations does not cover everything that you might want but it does give you some basic ideas. There is a lot more information on the GPS Receiver Information WWW page and the associated GPS forum.
The first thing that you should realize is all recreational GPS receivers provide the same basic accuracy and position information (e.g. a rough comparison of GSP 60 and iFinder Pro tracks, another comparison under more difficult conditions, or GPS60, GPS76, iFinder Pro). The difference between companies and models (high & low end) is in software, updated hardware (chip sets) and additional features. Some of these features may give you better accuracy, aquisition times, and reception under some specific conditions - many of the same features can give you worse or misleading information under other conditions.
Before you go off to buy that shiny new GPS receiver make a check list based on your needs (e.g.: price range, color preference, changeable face plates to match wardrobe, plays MP3 tunes, take pictures, surf the web, etc...). When you go to look at units start with your check list then ask the sales person for additional suggestions. Even though the sales person is there to sell you stuff and make money they generally don't want to sell you something that will not meet your needs. See if you can 'rent' or try out the GPSr and if it does not meet your needs make sure it can be returned. If you are buying software or maps try to get a live demonstration since you may not be able to return opened software. Some mapping software will only load on a single GPSr - is that all you need? After looking at the available options go for a walk and ask yourself is this a good idea?
When looking at buying a GPSr check the manufacturer's WWW site to see if the unit is still in current production. A few years ago one of the retailers here in Winnipeg was selling 'end-of-run' receivers at a good price - there is nothing wrong with this and the receivers were (and still are) useful and work well. The concern I had was the retailer assured me that the units were still being produced and fully supported - hmmm - I was glad I did my own homework.
Most hiking and canoeing applications don't require a GPSr. Even when you take one you should travel with alternative navigation aids. A GPSr can quickly become an expensive toy that rarely gets used, gets left at the bottom of a pack, and then broken/lost, or just left in a drawer at home. They cost a lot, even the cheap ones; can you spend your money on something better?
How upset will you be when you drop it off a cliff, leave it on top of your car when you drive home (you will at least once - everyone does), crash with it on your bike, or see it sinking slowly to the bottom of the lake when you dump your canoe.
Before you buy a GPSr borrow, rent, or go with a friend who has one. Try things out and see if it is worth the time and money. There are a number of very active forums on the web that provide reviews - take a look, read the reviews.
Like many things in life a GPSr can't do everything. Consider the primary purpose when picking features.
Built-in software ranges from simple to very complex. Less expensive units often have more basic software and are easier to use but there are limited options and functions. Some units have an 'easy mode' and an 'advanced mode' - I personally skip the easy mode as it is generally too limited. Built in software is the most important reason to try out a GPSr before you buy. Spend some time with the GPSr and see if the software works for you and your needs. There are a few special purpose GPS receivers on the market now (e.g. geocaching, in car routing), is that all you need?
Some things that I consider
Unfortunately your GPSr requires power. Check the number and type of batteries (AA, AAA) you require. A few of the newer units use a built in rechargeable battery - not very useful when you are in the middle of a 2 week trip and you run out of power. Can you use rechargeable batteries (e.g. NiMH)? Does it have an external power connection. At least then you can use the roll up solar cells that you bought last summer.
When I am on a road trip I use my DC external power supply. This is not helpful when I am on the water canoeing but it means that I don't burn my batteries getting to the launching point.
If you are out in the field for a month, or even a day, can it last for the time you need. Generally I only use my GPSr intermittently so batteries last a very long time. If the product literature says 30 hours see if that is under normal conditions or up to 30 hours in power save mode. Does it have a 'power save' mode?
Some of the things that use up batteries quickly: backlighting, electronic compass, WAAS. See if these can be put on a timer or shut off completely. The one sure thing that will use up batteries quickly is leaving the GPSr powered on (in any mode). This might be great for doing a 'track-back' but if you run out of power on the way back it is not that much fun. Power up the GPSr periodically and throw in a waypoint instead. Use the GPSr periodically to get a bearing for using with your compass on the way out.
If you are going to use your GPSr in the winter then consider lithium batteries. In this case make sure you check the specifications for the temperature range appropriate for the unit. Most units range from -15 to +60°C but some should not be used below 0°C. I have found the screen update gets very sluggish below 0°C on both my Garmin 12 & 76; my Dakota and eTrex Vista remain active all the way down to -15 °C.
You will be hard pressed to find a new GPSr that doesn't have 12 parallel channels Remember you often will not 'see' more than six to nine satellites anyway so 16 or more parallel channels is a little over kill. On the other hand the more parallel channels the greater the number of satellite options, the greater the chance of getting and maintaining a fix. In some cases if you are using WAAS correction one (or two) of your channels will be taken up by the WAAS satellite(s). This is OK and even benificial if the GPS is using the satellite as part of the determined solution (e.g. on Garmins look for a solid black bar).
I have one unit with a touch screen that I quite like - until I have to change anything in the winter. To use the touch screen I have to take my gloves off (mitts). I am also a little leary of touch screens right now - how long will they last, are they robust enough? I figure that PDAs and other things with touch screens have been around for some time now so the technology must have settled down a little. Remember to go back and consider how you are going to use the unit.
The additional accuracy provided by WAAS is not generally an important consideration for me except when geocaching. Unless you have a good sky view you may not even see the geo-stationary satellite(s) when you are further north or in an east/west running canyon. With a good sky view basic GPS often gives you <10m accuracy anyway; WAAS will only take you down to ~3m range. If you are out hiking or canoeing and can not find yourself with a 100m error then you have other more important navigation problems. On the other hand you can hardly find a GPSr without WAAS capabilities these days.
A number of units will allow you to turn off WAAS when you are out of the appropriate correction area or to save power. Apparently the antenna needs to be powered continuously or at least for longer periods to collect WAAS signals - if you don't need it turn it off. On a related note most of my units are DGPS capable. This is not a selling feature for me as it requires additional hardware and like WAAS the additional resolution is not necessary for my needs.
For those of you that like that little bit of extra information many Garmin units send Pseudorange and Carrier Data through the serial port. If this information is captured it can be used in post processing corrections.
Is it really waterproof or can it just be splashed? Look for at least the IEC 60529 IPX7 standard (submersed 1m for 30 minutes). When canoeing it is useful to have a waterproof GPSr but remember that seals can break so you might want it in another container anyway. If you do put it in a waterproof container consider putting in a desiccant packet as well - some people have reported issues with fog or damage due to condensation. Most GPS receivers don't float. If you think you will be in the drink ask if it also floats. The 'waterproof' designation may not include the battery compartment; be sure to check.
Don't bother with these extras unless they come with other things you want. This is, of course, my personal opinion there are many people that believe that these are useful extras.
I have found GPSr magnetic compasses helpful on a few rare occasions. I have also found them too sensitive to my movements and slight direction changes. The electronic compass in my Vista takes longer than I expect to settle down before taking a reading; unlike my liquid filled Silva. Electronic compasses also use up batteries very quickly.
Even though the barometric altimeter should provide better accuracy than the GPS altitude but it must be calibrated. Barometers are good for change in weather if you are not changing altitude and change in altitude if the weather is not changing. Remember for altitude measures they must be calibrated regularly. Most have an auto-calibrate setting that will calibrate to the GPS altitude. I have found it alittle funny the my Vista Cx altimiter has more problems with drift than the GPS alone in my GPS60 when paddling across a large lake.
I found the thermometer really sluggish on the one unit I had with this option - I was out skiing at -10°C and the GPSr thermometer didn't read below 0°C in over 30minutes. This is likely due to the location of the sensor inside the GPSr case. It still tended to read significantly 'warmer' than my other thermometers after more than an hour. I don't know how it would work in warmer weather since I returned the unit.
Patch or Quad-Helix (quadrifilar) antenna? Under good conditions both work equally well. Patch picks up overhead satellites well but may miss those on horizon. Patch may also work better than the quad-helix when used next to your body such as when it is carried in a shirt pocket. Quad-Helix will often pick up satellites lower on horizon so theoretically you have more options in the bush - remember those low satellites may also have a poorer signal quality therefore possibly more error.
External Antenna connection. I don't often use my external antenna but it is really handy when I need it - usually driving with my family and the kids want to use the GPSr. I personally don't use use this feature in the field but I know several people that attach the external to a pole on their backpack. Just a more recent update - I have now used the external antenna when hiking and skiing where I had to leave the GPS in a pack or pocket and was loosing signals. I either put the external antenna under my hat or in the top pocket of my backpack.
I was recently given a USB GPS Receiver with no screen. It is the diameter of a loonie, plugs into my computer, and is powered through the USB port with long cable. It is magnetic and weather proof so it can be mounted outside (on the roof). Now my hand held can be left off on the road but I can still capture necessary information and get real-time mapping to/from/between field locations. I didn't think I would find one of these units that usefull.
The ability to connect to a PC is very helpful for saving routes, points, etc... It is usually easier to enter/edit routes and points on a PC then upload the information. A lot of what I do also involves downloading tracks and waypoints created in the field. If you want to use maps on your GPSr you must have a computer connection.
Updates to GPSr software are often available on the WWW. It is a good idea to periodically check the manufacturers site and then apply the updates if they contain features/patches that you use or that might affect the use of the GPS.
Get a demo or find a way to try out bundled software first. Remember many retailers will not take back software that has been opened. If you use a Macintosh or Linux based system is there software at all? Usually the answer is yes but it is good to check. There is also lots of PD or shareware software out there - give it a try before spending more money. I like GPS Utility; many geocachers like GSAK. If you are into mapping then you probably want to look at OziExploer.
An important consideration with power and PC connections are the cost of the cables. Expect to pay a premium for the proprietary connectors used by most manufacturers. More recently standard USB connections have started to appear and many units will take MMC/SD cards. Using a card to load or save settings is great because of the almost unlimited expansion they provide. Unfortunately the slots are sometimes in an annoying spot like under the batteries.
Memory is really important if you have maps and then you will want lots of memory (20MB as a minimum). If you are transferring large amounts of data make sure you get a unit with a high speed connection like USB and a MMC/SD card expansion.
I use maps when I am on a road trip but in the bush I carry a hard copy map. Even on road trips I generally use my computer with a 'live' connection for positions as the GPSr screen on my units are not large enough for longer distance planning. There is a trade-off between my hiking needs and car routing needs.
While I have not done extensive testing of accuracy of the topographic maps I have noticed that they can be quite variable in Manitoba and NW Ontario. Paddling lakes and rivers (even driving roads) the maps can be 50-100m or more off. The error is easiest to see when paddling along a lake shore or down a narrow river and the track line is actually on the shore. At this point in time I would use the built in maps as a suggestion.
On my garmin mapping unit auto-routing is possible using the topographic maps but you have to be careful since the topographic roads don't appear to know about over/under passes. When auto-routing make sure that your road map is showing - you can then turn it off.
If possible I turn off the built in base maps that come pre-loaded into many GPSr units. Don't buy a GPSr because of the built in map; you must be able to load maps specific to your needs. The background maps that come with many units these days are usually little better than useless and sometimes are very inaccurate.
When buying maps find out the licencing limitations before you open the package. Some companies tie their CD/DVD distributed maps to a single GPSr which means if you buy another GPSr you need to buy another map licence. I don't see this as a major failing but if you have multiple GPS receivers it can be annoying.
If you do want to use maps then there are some additional considerations:
There has been a lot of discussion about the additional sensitivity of receivers with newer chipsets (e.g. Garmin GPS60cx with SiRF III). No doubt these units are fast and do acquire and keep satellites locked under very trying conditions. There is still a premium on these units but the price has come down a lot and the higher sensitivity receivers are appearing on many entry level units. When I compare my first GPSr (GPS12) to newer units there are lots of additional bells and whistles, and the new units do keep a better lock but that original unit still tells me where I am within my tolerance.
The accuracy of these units is no better than other units given the same input information. There are the same limitations such as signal multipathing, ionospheric interference, poor satellite geometery, etc... The inhanced speed, time to fix, and ability to maintain lock on a weaker signal are the advantages.
Becareful with units with higher sensitivity antennas. I have one GPSr that is quite sensitive to weak signals which is great as long as I remember that the error can be higher.
Over a number of years a variety of people have written similar lists and suggestions. See the links on the GPS Receiver Information WWW page.
Back to my GPS page
Email: burc...@cc.umanitoba.ca Last modified: Sat Oct 23 07:10:13 2010