Best GPS for Off trail

1:45 a.m. on November 11, 2008 (EST)
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Hi,

What's the best GPS for off trail hiking?

The most popular one seems to be the garmin 60 csx, but the garmin oregon 400t is the newest. I plan to start using this in the states, but my intent is to take a long off trail hike in central america with it. I guess the main issues would be accuracy, reception and battery life.

Are there GPS accesories (antenna, amplifier?) you can buy to increase reception if needed?

Thnx

11:35 a.m. on November 11, 2008 (EST)
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almills said

I guess the main issues would be accuracy, reception and battery life.


and, if you intend to use it outside the US, availability of maps.

The 60CSx is popular because it is still, after 3 or 4 years on the market, the best suited for most people for off-trail use. The Oregon (and Colorado) are a bit dumbed down, and are geared more to the geocaching crowd.

However, there are some problems with the 60CSx. First and foremost is the "S" in the model number. It has a barometric altimeter that you cannot shut off and it has a fluxgate compass. These might seem like good things except (1) they are battery hogs and (2) they both require constant recalibration. For the altimeter, you cannot set the CSx (or any of Garmin's other units with a barometric altimeter) to display the GPS-derived altitude. Yes, you can temporarily display it, but when setting the displays in the various windows, GPS-derived altitude is not a choice with any of Garmin's "sensor" units (including the 76, eTrex series, and the ones in the Oregon and Colorado series). So you are at the mercy of weather changes or frequent recalibrations. A flaw in the algorithm is also that if the absolute pressure would give a barometric altitude more than a critical amount higher than the GPS-derived altitude, any calibration you make is overridden. This is not important for most travellers, but does come into play if you go to high altitudes, especially in polar regions.

The flux gate compass, like all flux gate compasses, is easily subject to decalibration by many RF fields, such as cell phone transmissions, handheld radio transmissions, and even (as I have found) the leakage from automotive electronics (engine controllers). Plus you have to recalibrate when you change batteries. Add to that the huge battery drain, the answer is to never turn the compass on.

Given both of these, you are better off getting the 60Cx or one of the non-sensor eTrex units. Be sure, in the eTrex series, you get one of the "H" units (high sensitivity chip set) - the older chipset was completely blind under trees. The Magellan eXplorist series performs as well, and in many cases better, than the Magellan 60 series. The GPS-derived altitude is more accurate than any barometric altimeter (+/- 20 ft consistently with a good 3D fix vs up to several hundred feet drift during an 8 hour period or when changing altitude by more than a couple thousand feet on very warm or very cold days).

The Magellan Triton series has a lot of promise, but, using a Microsoft operating system, it has had a lot of development problems. The great thing about it is that you can download maps from National Geographic's Topo! program. Garmin has 1:24,000 maps as well, but their own proprietary software.

You might also look at the Delorme PN-40 (just being released as a major upgrade to the PN-20). Delorme's TopoUSA can be used to upload scanned USGS maps, as well as satellite and aerial photos.

Be aware that topographic maps to load into GPS receivers are pretty much limited to the US. You can get road maps for the US, Canada, Europe, Australia, and a few other places to upload. The maps for places like Central and South America and most of Asia are limited to major roads, and not very accurate at that.

Back to you "issues" - accuracy is the same for all consumer GPSRs. The limitation is the information provided for the "non-authorized user" from the satellite navigation message. Reception for the newest receivers with the high sensitivity chipsets is pretty good under most canopy, though redwoods and some tropical vegetation will block signals and/or cause distortions in position even for the newest chipsets. The amplified antennas don't help significantly in those conditions. The canyon problem affects all receivers (can't get a signal through rock), as does multipath (reflected signals that are traveling a longer path). Consumer units handle multipath very poorly at present.

As for the accessories, external antennas are only available for a few consumer units (the Garmin 60 series is one of the few). But these are amplified units and are battery hogs, shortening battery life by often half. They do help, but for your Central American trek, you would need a very long cable and a method of raising the antenna pretty high in the jungle areas. They are of most use in vehicles where you can plug into the car's power.

3:09 p.m. on November 11, 2008 (EST)
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Thanks for the very generous and useful answer.

So as I understand it electronic topographic maps for areas in central america (and generally outside the US) are difficult to obtain.

So then an alternative I see is using a GPS system with a paper topographical map - find your coordinates using GPS and then find that location on the paper map.

How difficult is this in practice though?

Is the format the coordinates are provded in on the GPS compatible with most paper topographical maps?

How difficult is it to find a set coordinates on a paper topo. map anyway?

I assume there would have to be a pretty high resolution coordinate grid overlaid on the map (or you would have to be pretty good with a ruler) to find out exactlly where you are.

What about satellite maps, like the kind from google maps, can you get paper versions of those that come with an overlaid coordinate system that you can use with GPS?

Lastly is there a central web repository for topo. maps both paper and electronic?

Thnx

6:08 p.m. on November 11, 2008 (EST)
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almills asked a bunch of questions, starting with

So then an alternative I see is using a GPS system with a paper topographical map - find your coordinates using GPS and then find that location on the paper map.


It is required to use a GPSR as secondary to map and compass, at least if you are sane and don't intend to get thoroughly lost. This is primary, not an alternative. GPSRs run out of battery in the most difficult situations and the most inconvenient moments. The compass need only be a basic baseplate compass. You definitely do not need one of the mirror compasses or pocket transits (unless you are making maps and doing surveys).

How difficult is this in practice though?


Can you use a ruler? Provided you have a basic understanding of maps and have a maps with the coordinates marked on them, it is very simple. Most topographic maps produced by national map service offices in most countries are marked with some form of georeferenced coordinates - lat/lon, UTM, national grid systems that can be related to UTM. One problem is that some countries still consider such maps a matter of national security, making them difficult to obtain (Israel, Iran, many of the former Soviet republics, including Russia, are examples).

Trail maps generally do not have any sort of georeference, and often are not even to a uniform scale over the whole map. In many countries (especially 3rd World, but even some "advanced" countries), it is next to impossible to get topographic map locally, even though the country's government makes and distributes them.

You can buy templates for marking the coordinates, or on metric maps, just use a millimeter ruler with UTM or local national grids, which are usually just offset UTM coordinates with the zero point at the national capitol rather than 180 deg longitude. But at worst, almost all countries have lat/lon and UTM both marked on them.

Your GPSR will have a large number of possible datums available, and will give you lat/lon or UTM (MGRS is just the same as UTM), or at worst allow you to set in a local grid for those very few countries that refuse to modernize (or for old maps if that's all that's available). Just look at the marginal information to see what datum is used (most US and Mexico topo maps use NAD27, a few use NAD83. Many other countries use WGS84). The tricky maps are old maps of former Soviet satellites, which use an obscure datum that is in the lists of most GPSRs.

Is the format the coordinates are provded in on the GPS compatible with most paper topographical maps?


Yes. Just go into the setup and pick the appropriate datum and coordinate system as listed on the map.

How difficult is it to find a set coordinates on a paper topo. map anyway?


If you mean, which system is used for the map, it is in the marginal information, somewhere near the scales and compass diagram. If you mean, how hard is it to measure the coordinates on the paper map and put them into the GPSR or vice versa, if you can use a ruler, you can easily do it.

I assume there would have to be a pretty high resolution coordinate grid overlaid on the map (or you would have to be pretty good with a ruler) to find out exactlly where you are.

No, it's pretty easy with a little practice to eyeball close enough to find your location and go between map and GPSR (both ways). One of the nice things about NatGeo's Topo is that you can print grids of whatever resolution you want in lat/lon or UTM, NAD27 or NAD83/WGS84 (these two differ in the position of their origins by less than a meter, and if you can't tell where you are when the GPSR gets you within a meter, you have much bigger problems than reading the map).

What about satellite maps, like the kind from google maps, can you get paper versions of those that come with an overlaid coordinate system that you can use with GPS?


Well, yes, sort of, for a price. You can readily read lat/lon from the Google Earth images and maps, print the map yourself (free), then mark a few well-chosen locations. You can also download tracks and waypoints from your GPSR and show them on Google Earth, then print the map or sat view.

Lastly is there a central web repository for topo. maps both paper and electronic?


Not really. USGS maps can be found on the USGS web site. But most countries are very restrictive about electronic maps (some charge huge prices for electronic copies). There are several online shops you can get all the available topo maps. Omni Resources http://www.omnimap.com/ has topo maps for most countries for which they exist. In some cases, Guy can get maps to you faster than you can get them by going to the government map service in the country for which they were made (I sometimes get Mexico maps for a friend who runs an adventure travel service in Mexico, which is much easier than him getting them locally in Mexico City).

You can search on the web and find companies that have a few topo maps of other countries, but in most cases, the only thing available from any one dealer is road maps, many of which are mediocre at best.

9:33 a.m. on November 15, 2008 (EST)
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Most of the maps I have (USGS 7.5 quads of TN & NC ) are Nad 27.
Many of the maps state (bottom left) that they have NAD 83 corner ticks and have a 1000m UTM grid.
I use both Lat/Lon & UTM and have never really had a problem changing formats.

I've noticed that a lot of people seem to prefer UTM just because they can quickly count off meters on the map using the UTM grid marks whether by estimating by eye between lines, or by measuring with a UTM ruler.
I have a ruler but usually just guess because it's pretty easy to work in multiples of ten. I find that if I get within 100m I can just look at the terrain and find my location on the map provided I am headed to a prominent landmark, usually a stream or rim for me. Or if I pull bearings off a fire tower and a known mountain and the lines cross halfway between grid marks, I know I'm at say 334500mE and then I check with the altimeter to see which contour line I should be on.

If I pull my coords. from my GPSR I usually get out the ruler and pin it down on the map and be done with it, but I don't always have a signal with my Etrex and I just don't trust it to always work properly.

Just my thoughts after being out & using both yesterday.

12:42 p.m. on November 15, 2008 (EST)
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And if you are using a baseplate compass, you have the ruler and protractor combined in one compact device, for about $10. For a little more, you can get a baseplate compass with scales to match most maps - 1:24,000, 1:25,000, 1:50,000, etc.

2:11 p.m. on November 15, 2008 (EST)
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Yes you do, My Suunto has a 1:24,000 scale on the compass marked off in tenths of a mile. I also use of of those square plastic pocket grid overlay tools marked off with 100m ticks.

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