All content copyright © 2010-2024 Frank Revelo, www.frankrevelo.com, United States copyright office registration number TX-7931345
Primary purpose of GPS receiver is to receive signals sent by GPS satellites and use these to determine current position via triangulation. Positions can optionally be saved in GPS receiver memory, either as single waypoints or as series of points forming a track. Both waypoints and tracks can be later uploaded to computer. Alternatively, waypoints and tracks can be downloaded to GPS receiver, to allow displaying distance and direction of waypoint/track from current position. Trailblazer can thus record trail using GPS receiver, then publish track as a GPX file, then other people can download and follow this track using their GPS receivers. GPS thus makes navigation by compass obsolete.
Mapping GPS's additionally display digital topo map, along with track and current position, thus making paper topo maps obsolete. In practice, carrying compass and paper map is often still advisable, since GPS, like all electronics, can fail in the field. Also, mapping GPS's have very small screens and low-resolution, and thus are cumbersome to use for route planning and getting an overview of area compared to paper maps.
GPS loaded with GPX track file can be very useful for following poorly marked trails (snow-covered, flooded swamp), or for situations where it is necessary to deviate from trail then find one's way back to trail further on, or for situations where where there is no paper map available with trail marked. It is not necessary to have mapping GPS loaded with topo maps to use track files, though of course such maps help (at least if they are accurate). All that is required is for GPS to display current position versus track, so that you can see when you are deviating significantly from track and which direction to move to get back to track.
Another handy use of GPS is to mark waypoint so as to return to location after wandering around off-trail. For example, I sometimes make camp in featureless desert sagebrush terrain, then wander off to explore. GPS plus waypoint allows me to confidently find my way back to my gear later.
GPX track files can be edited with GPX_Editor (works best, though has some bugs) or GPS Track Editor (doesn't work so well). Editing means getting rid of off-trail trackpoints (due to bad GPS reception or to deviations off trail to eat lunch, explore, etc), consolidating trackpoints along straight segments, merging and splitting GPX files, etc.
GPS Visualizer and ITN Converter allow converting between GPX and other formats (such as KML and PLT).
To merge IMG map files (such as those available from Open Street Map), use GMapTool.
Many paper maps lack a GPS grid, but this doesn't mean GPS can't be used with these maps. Just obtain GPS positional fix at a known location on map, such as intersection of trail with a road. Later, compare GPS coordinates at this known location with current GPS coordinates to find current location on map. It helps to use UTM format when doing this, since calculating distances with UTM much easier than with latitude and longitude.
Sources of GPX tracks: Waymarked Trails, WikiLoc, .
gpsinformation.net is huge source of GPS links.
Graph showing positioning error due to using wrong datum. Using WGS84 (effectively equivalent to NAD83 in United States and ETRS89 in Europe) instead of NAD27 or ED50 gives up to 200 meters error. This about what I have noticed in the field when I used wrong datum with large-scale maps.
gpsfiledepot.com is a source of free maps in Garmin format.
gpstracklog.com has lots of good info about GPS.
Etrex 20, purchased from REI. 100g for GPS receiver, 20g for carrying case, 30g for 2 x AA lithium batteries. Bicycle handlebar mount accessory weighs 20g.
Can be used with 2 AA non-rechargeable lithium, alkaline batteries, or rechargeable NiMH batteries. Either alkaline or fully charged 2300 mAh NiMH batteries will typically power Etrex 20 GPS for about 24 hours, or 3 days assuming 8 hours/day of usage, moderate weather conditions. I am not sure about hours of usage with lithium batteries. Based on spec sheet at data.energizer.com, should last at least as long as alkaline or NiMH.
Standard-A to mini-B USB cable allows attachment to computer, for downloading firmware updates, downloading maps, and uploading/downloading GPX files.
Etrex 20 comes belt hook, which I used for while to hook GPS to neckpurse strap. However, belt hook not very secure and allowed GPS to fall off, almost causing me to lose it. So I threw belt hook away and stored GPS inside neckpurse thereafter. Once I got into habit of always putting GPS in same place in neckpurse, it became as easy to retrieve as when using belt hook to attach to neckpurse strap. Belt hook might provide secure attachment with thick leather belts, versus thin webbing strap on neckpurse. Bicycle handlebar mount accessory is very secure. Carrying case is important when carrying GPS in neckpurse,to protect easily scratched screen, though it does make screen somewhat more difficult to read, especially in wet conditions when plastic screen cover fogs up. When carrying GPS attached to bicycle handlebars, less danger of screen being scratched, so I don't use carrying case.
Additional cost of Etrex 30 versus Etrex 20 not justifiable for most people, in my opinion. Better to spend money buying good digital topo maps to load onto GPS. Etrex 30 has barometer/altimeter, but this is unnecessary if GPS is loaded with topo maps, since these show exact altitude as part of topo information. Also, altitude given by GPS satellite triangulation is probably adequate for most people. Etrex 30 also has electronic compass, which I see as being of marginal value. Avoid Etrex 10, which does not support adding maps.
To create GPX files, to allow other people to follow trails for which there is no paper map available, set GPS to record automatically and save track files daily. Etrex 20 allows up to 10,000 points per track, but my tracks tend to average about 2500, or about 5 times/minute assuming 8 hours of recording . I have GPS set to automatically adjust recording rate based on trajectory, so that it records less frequently when walking in straight line, and more frequently when making lots of direction changes. I doubt I would ever walk longer enough in one day to exceed 10,000 point limit. If that limit did pose a problem, I could set GPS to record less frequently. Etrex 20 is capable of storing up to 200 track files with 10,000 trackpoints per track file, which is plenty capacity for my 90 days or shorter trips to Europe, which is when I might want to create GPX files.
Etrex 20 is rugged if not abused, but accidental abuse is always a possibility outdoors. For example, dropping GPS onto rock so that screen cracks. Given my dependency on GPS these days, and difficulty of replacing broken or lost GPS in small towns, some sort of backup plan is necessary. Either carry spare GPS unit, preloaded with GPX tracks, or use smartphone as replacement for a dedicated GPS unit (more on this below).
[Update as of 2014: Sure enough, Etrex 20 failed after several years of usage: two long hiking trips in Spain plus seven long bicycle tours, for a total of about 150 days hiking and 400 days bicycle touring. Failure actually occurred at home, while I was playing around with adding maps, but it might have failed on tour. Device was beyond 1-year warranty and repair cost was $90 plus shipping to Garmin, versus buying new for $180. so I just bought a new unit.]
Problem with Etrex 20 during Spain 2013 hiking trip, in that it appeared to lose track data if I let it freeze at night with track data unsaved. GPS was set to record and save tracks automatically. There were also some cases where GPS did not show Spain maps when I turned it on initially. If I turned it off and then back on, it did show maps. There were some firmware updates when I got back from this trip. During my 2014 Spain Hiking trip, I saved and archived track data each evening just before turning GPS off. Either because of this or because of firmware updates, I had no problems with data loss on this trip. Saving track data daily also organizes track information by day, which is helpful when later editing GPX files, so is good idea I've decided, regardless of whether it helps avoid data loss or not.
Micro-SD card with 1:100K USGS Topo maps for lower-48 United States was included in Etrex 20 bundle. These maps have numerous errors with respect to dirt road network. Supposedly, these Garmin 100K topo maps are based on US Census TIGER road database, whereas Garmin licenses Navteq road database for use with its 25K maps.
Possible to purchase microSD cards from Garmin loaded with topo maps. I purchased such cards for Spain and Bulgaria, and was satisfied with quality of maps.
Possible to convert free Open Mapping Project topo and road maps to Garmin format and then download to either 2GB built-in memory of Etrex 20, or to separate micro-SD card inserted in Etrex 20 card slot. I tested this capability at home, using topo maps for Greece, and it worked well enough, however I never tried using these maps in the field. Do internet search for more info.
Standard 1.6V non-rechargeable lithium batteries (30g for 2 AA) work better than alkaline batteries (50g for 2 AA) in sub-freezing weather, have longer shelf-life and do not leak. Leakage is strongest argument for avoiding alkaline in favor of lithium. Avoid 3.6V rechargeable lithium, which will overload GPS electronics. Rechargeable NiMH batteries (50g for 2 AA @ 2000mAh, plus 55g for Apple compact charger) work better than alkaline in cold conditions, though not so well as lithium, but supposedly don't work well in very hot conditions. I'm not sure what is meant by very hot. I experienced no problems with NiMH batteries in temperatures of 30°C/86°F.
When using lithium batteries, charge level shown on GPS device will remain at full level until right before batteries die, whereas charge level is shown more accurately with alkaline and rechargeable NiMH batteries. When using GPS to record GPX tracks, it is important to keep tabs on charge level, so that GPS doesn't die unnoticed while recording. Rechargeable NiMH batteries would thus be better for track recording.
I tested using Android smartphone plus GPS app plus offline maps during 2017 (GaiaGPS app) and 2018 (Locus and OruxMaps apps) hikes in Spain and Bulgaria. System worked well enough that this is now my primary GPS system for hiking. However, I might continue to carry Etrex 20 for use in rainy/snowy weather or where I want to record tracks.
Of apps I tested, Locus was best for my purposes, mainly because better interface. Note that neither Locus nor OruxMaps is available on IPhone, whereas GaiaGPS is. See pages for Spain and Bulgaria for details of maps I used with these apps.
First problem with smartphones is that track recording tends to run down smartphone battery. Be sure to bring along external batteries (described on Smartphone page) if you plan to use smartphone for recording GPX tracks. During my 2017 Spain hike, without recording GPX tracks but using GaiaGPS constantly to check position, and keeping screen lit 2 or more hours daily for reading ebooks and editing text files, and playing music and other audio files via bluetooth to an external speaker 2 or more hours per day, and doing small amount of cellular usage (checking email, several phone calls), I almost completely drained 10000 mAh external battery but still had 65% charge on smartphone after 4 days hiking and 3 nights camping, using Moto X 3rd Gen smartphone running Android Marshmallow. It would thus be possible to go over a week between hotel stops with two 10000 mAh external batteries, at this rate of usage. I am not sure exactly how much power GaiaGPS consumes when recording GPX tracks, but it is obviously more than when not recording. Locus app appears at least as efficient as GaiaGPS in terms of power consumption. Not sure about OruxMaps.
Second problem is that smartphone capacitive touch screens tend to act flaky when wet, so even if phone is water-resistant, as it should be for use as hiking GPS, you will need some way to dry screen each time you need to touch it to zoom, pan or perform other operations. I was able to get by wiping screen against my shirt few times I encountered rain/snow (most of my hiking is in dry conditions).
Third issue is that electronics can fail. Since I no longer carry paper maps when hiking in Europe, some sort of GPS is critical. So if using smartphone as GPX, bring along backup smartphone, loaded in advance with GPS app, offline topo maps and GPX tracks, and with fully charged battery.
Fourth issue is that, GPS signal reception on older or lower quality smartphones might not be as good as with dedicated GPS receivers like Etrex 20, especially in difficult situations, such as deep canyons, under heavy tree cover, etc. GPS signal reception on Moto G Power 2022 version smartphone appears to be equal to that of Etrex 20, so this is no longer an issue for me.
