Hi all,

Not much of an idea about GPS but looking forward to buying one and learning the basics. Drawn between eTrex 20 and 30... My question being, today I played around with them in the shop and noticed that as I moved around in a circle, the blue waypoint marker on the eTrex 30 moved in real-time, but on the 20, it just remained static - in fact it didn`t really seem to move at all, so I`m wondering how you`d use it? That and the `compass` on the 20 didn`t seem accurate at all, not much use... maybe the eTrex 20 showroom model wasn't properly configured? I note that the 30 has a 3axis compass, could this perhaps explain the difference? Any ideas?

:confused1:

EDIT; I also read about a "sticking issue" with some of the lower end Garmins, that if you move under a certain speed (ie slowly) it will not update... could this have been the issue with the eTrex 20 in the showroom, i.e. it was just not updating itself and hence the waypointer was left static? They were tied down to the counter so could not walk around with them...

PS... does anyone know if either unit power from USB?

You need to realize that there are different levels of 'GPS' units ..

A base GPS only tells you where you are, no compass, no sun/moon rise set, no track of where you have been .. just the basic where you are. The next level will tell you the time and date and height (roughly).

Then you get optional extras ...
A 'track' of where you have been - from this it can calculate a direction to give you a compass of sorts.
A 'destination' .. and from a track can calculate a rough time of arival base on your present rate of travel.
Sun and moon rise and set.
A flux gate compass - real time compass. Think this is you difference between the 20 and 30.

Maps .. with and without routing.

Personally I'd get one with mapping .. and routing. It makes life so much easier to see immediately where you are on a map particularly in a strange city. And the maps usually have things like hotels...

You can get all this on some smart phones .. I find the dedicated GPS is better in poor reception areas compared to the phone .. and has a better battery life.
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I have a Garmin GPS Map60Cx (obsolete .. years, probably a Montana now) and a phone - Galaxy miniS4 with OSMAnd for off line maps.

Thanks for getting back to me Warin, but still feel none the wiser. Both the 20 and 30 have mapping abilities... I want a GPS for remote regions in the Atacama, featureless places like deserts, salt flats, etc and for when I get lost. Nothing else at the moment. I suppose my question put in a more succinct way would be why didn`t the blue waypointer rotate as I moved the unit around on the spot (for the eTrex 20)? If you were moving around, that blue waymarker should, in theory, move around to as one changes on direction? Is it just slower to update, and is that therefore the use of a real-time compass?

Cheers,
Rtw

RTW:

I'm going to try and expand on Warin's answer above. In the first sentence of your post, you wrote: "Not much of an idea about GPS...", so, I'll try to cover things starting from first principles. Please don't interpret this as me talking down to you.

A "GPS device" consists of a number of components that provide different capabilities or functions. Not all devices have all possible components. So, let's look at what these are:

1) The satellite reception system. This enables the device to determine where you are. Not all systems update at the same speed. A smartphone might only update the position once per second. A dedicated GPS navigator typically updates 5 times The difference between update rates is not important to a pedestrian or hiker, but is very significant to a person navigating a vehicle that might be moving at 90 feet per second (60 MPH, 100 km/h).

2) Cartography. By this I mean whatever maps exist within the unit to display your position on. The Garmin eTrex 20 and 30 that you mentioned come loaded with a 'basemap', which is only a very low detail map. You would need to buy additional maps (either topographic or road, depending on whether your interest is on-road or off-road) and load those maps into the device before it would be of much use to you.

3) A navigation engine (a processor that calculates and shows you routes). This is a hardware component. Like anything else in the world, a processor that is fully dedicated to GPS navigation will be more efficient than a processor that is handling navigation as a sideline task (for example, a smartphone processor). Be aware that there is a rough correlation between the price of the device and the power of the processor.

4) Navigation software. (the program that the processor uses to generate the route, operate the device, etc.) Small hand-held devices such as the Garmin eTrex line are designed for pedestrian use (hiking, geocaching, etc.) They are not designed to support vehicle navigation, although some will generate routes on roads if the appropriate cartography has been loaded.

5) A display. That might sound obvious, but there are HUGE differences between displays. Consider, for example, the difference between the 1.4" x 1.7", 176 x 220 pixel display on the eTrex and the 4.25" x 2.55", 800 x 480 pixel display on the Zumo 590. The little display is fine if you are on foot and can pause to look at it or zoom in or out, pan around, then keep walking. For vehicle use, you generally need a physically larger display that shows you everything you need to know in one quick glance.

Before you can make a wise decision about what kind of GPS device you should purchase, you will need to define what you intend to use it for. If you plan to use the device for on-road navigation, then an eTrex would be a poor choice for you. For the same price as the device and the additional maps needed, you could purchase a device that is specifically designed to support road navigation (including big screen, pre-installed maps with free future updates, stuff like that).

If you intend to spend most of your time off-road but in a fairly small area (say, within an hour or so riding time from your home), the eTrex might do the job for you, but keep in mind it is optimized for pedestrian / hiker use, not motorcycle use.

If you intend to travel long distances (to other countries, for example) and spend time off-road on the way or once you arrive (considerable on-road use is implied by that, otherwise, how would you get your bike there?), then you should think about buying an automotive or motorcycle specific GPS that has sufficient memory to hold both road maps (which support automatic route generation) and topographic maps with high levels of detail (that means more than just the basemap).

I hope this information helps you with your shopping.

As for the question you asked about compass behaviour, ANY GPS will work as a pseudo-compass once you start moving. It does this just by figuring out what direction you are going in, then orienting the map (or a compass rose) to show you how the direction you are moving in correlates with north.

If you want a GPS device that has a true, stand-alone compass in it (the flux valve that Warin referred to), then you will probably have to buy a device that is primarily designed for hikers. Such a device is less than optimal for motorcycle riders. Personally, I think the 'pseudo-compass' inherent in all GPS navigators designed for cars or motos is more than sufficient, even for riding way off-road. All you have to do is move forward (in any direction) for about 5 feet, and the device will know which way you are moving, then orient the map display correctly... hence you will know which way you are pointed.

Michael

The eTrex 20 doesn't have a true compass inside it. Hence, it can only determine direction by observing lateral movement... movement between two different places (that creates a vector), rather than simple rotational movement (if you just rotate the thing in the same location, it's not moving in relation to the GPS satellite constellation).

The eTrex 30 does have a stand-alone compass mechanism (a flux valve) in it. Hence it does not rely on the satellite constellation to calculate a vector when you move the device laterally (i.e. 5 feet in any direction away from your starting position). The compass would work even if the entire satellite constellation was turned off.

But... having said all that, I still don't think that the eTrex series would be the best choice for off-road motorcycle riding (primarily due to the small screen), unless you were doing most of your riding pretty close to home, and had no need at all for any navigational guidance on the road.

Michael

Have a read of the Smartphone thread. There is a mass of choice and different functions, but personally I doubt I will ever buy another separate GPS handheld.


Andy

Michael,

This answered my question, everything makes perfect sense now! Many thanks!