Garmin etrex 20 Off Road v On Road for Time/Distance

[Vitara]

I'm off on a tour at the weekend and have been supplied with GPX files which have more than 50 route points so I need to select off road for navigation as opposed to On Road for Time which I usually use with my own routes. Can anyone enlighten me as to how these modes vary beyond the vague information supplied in the manual. Will I still get turn by turn instructions etc. I'm confident enough that the files work as they come from a reliable source and have already been used by others, I'm mainly just wanting a better understanding of how the modes differ.

[monxton]

Probably too late to be of use, but here goes. Garmin's terms "Off Road" and "On Road" for routing are highly confusing. Francis Cooke's very helpful articles http://www.aukadia.net/gps/ translate them to "Direct" and "Auto" routing.

So for "Off Road" or Direct routing, you can have a maximum of 250 route points, and the Garmin will show you a route between them without regard to the map. I don't think you will get turn-by-turn directions in this mode, though Cooke implies that you do. Perhaps it depends on the device and/or the map. You will get a pop-up when you reach a route point, which may contain some helpful information depending on how carefully the route point was created. In my opinion this kind of route is less useful than navigating a track, which on your eTrex can have 10,000 track points, more than you could need for a day's cycling.

With "On Road" or Auto routing, you are limited to 50 route points. Between these points, the Garmin uses the map you've got loaded to give you a route, based on the parameters you've defined in your Routing setup. It will pass through all the points you have specified, but the way you get between them may not be exactly what you intended. You definitely get very clear turn-by-turn signals, the ones with the thick white arrow showing you a path through the junction, and (if you've configured it) a bar at the top of the screen giving you details of the next turn. Another issue is that the Garmin takes quite a long time when you load the route to do this route calculation, or to re-calculate if you go off-route.

The belt-and-braces approach is to use both a fully-detailed track (with up to 10,000 track points), which you just show passively on the map, AND a 50-point autoroute. That way you get both the turn-by-turn directions and the reliability of the track. It's not too much effort to do this because whatever you're using to create the route will probably let you save the same data in two different ways.

HTH

[bryce]

If you're going with both a track (the exact route with up to 10,000 points) and a route (auto navigation with a 50 point limit), it's often nice to limit the number of points on the route. The track provides a line to follow that's precisely what was planned, the route provides live planning and will fill in if you go off the planned route either by missing a turn or because another road looked better. The fewer points the more flexibility when replanning.

On leisure loops I've both going and mostly end up following the planned route. When going somewhere unusual in London, I just use the track and improvise with a vague idea of a good route from looking at maps. Neither the track nor the route is an absolute, it's a tool that can make route planning more flexible by choosing to both follow it and ignore it as seems best.

[sjs]

If you're going with both a track (the exact route with up to 10,000 points) and a route (auto navigation with a 50 point limit), it's often nice to limit the number of points on the route. The track provides a line to follow that's precisely what was planned, the route provides live planning and will fill in if you go off the planned route either by missing a turn or because another road looked better. The fewer points the more flexibility when replanning.

On leisure loops I've both going and mostly end up following the planned route. When going somewhere unusual in London, I just use the track and improvise with a vague idea of a good route from looking at maps. Neither the track nor the route is an absolute, it's a tool that can make route planning more flexible by choosing to both follow it and ignore it as seems best.

The trouble I have with routes is that you need a lot of points to get the device to route the way you intended, but then it's not useful if you deviate from the plan, because it tends to want to go to the next route point however obvious it is (to you) that it's better to bypass it. I've come to the cnclusion that it's better just to follow a passive track. Then, if for some reason you deviate, you could either

a) just use you map to get back on track (like you would with a paper map) or
b) ask the device to navigate you back to a specific point on the track

So, I'd convert the route to a track, and go with that.

[bryce]

sjs, what maps do you use? I've only used velomaps and they've been good overall.Though on the Dunwich Dynamo they didn't like some sections that were fine during the (night) ride, during the day I'd avoid as they were.

[sjs]

sjs, what maps do you use? I've only used velomaps and they've been good overall.Though on the Dunwich Dynamo they didn't like some sections that were fine during the (night) ride, during the day I'd avoid as they were.

I generally use talkytoaster. I've used velomaps, but find them just too clever with their road classification, and can't tune my routing to stop them taking me down tracks that are too rough for my road-oriented bike. In fact, I usually plan my routes in advance using OS maps (on Bikehike, for instance). Never found anything automatic that really works for me.

[bryce]

I've only used "by distance" not "by time" (extra nice or quiet routes with velomaps). They've been fairly close to my preferences but I do avoid roads that look wrong to my tastes. So far I've been impressed with them, they do about as well as the better online planners overall.

[al_yrpal]

Garmins manual is pants! Tells you practically nothing, and explains nothing.

Al

[sjs]

Garmins manual is pants! Tells you practically nothing, and explains nothing.

Al

True. Seems to be the same with everything gadgety these days. There is a lot of material available online though.

[CREPELLO]

Good thread.

Can I add a couple of quick Q's?

What effect do the different functions of "off road transitions" and "lock on road" have?

Thanks.

[sjs]

Good thread.

Can I add a couple of quick Q's?

What effect do the different functions of "off road transitions" and "lock on road" have?

Thanks.

Not sure I have off road transitions on my Oregon. I think "lock on road" means it indicates your position as being on the nearest bit of road even if it thinks you're off road. Only useful of course if you're always going to be on a road that's on your map.

[monxton]

What effect do the different functions of "off road transitions" and "lock on road" have?

I think "lock on road" means it indicates your position as being on the nearest bit of road even if it thinks you're off road. Only useful of course if you're always going to be on a road that's on your map.

Yes that's right, "lock on road" tells it to make its best guess as to which road you're on. IMO this just leads to confusion. Sometimes it gets it wrong and then when it "realises" (sorry for the anthropomorphism) it jumps disturbingly to the correct road. If the road that you're on is missing from the map all bets are off. "Lock on road" is best turned off.

"Off road transitions" - who thought up that name? - is about how close to a waypoint you have to get (in off-road routing mode) for it to decide you have reached it. If set to Auto, it decides when you've got there and bleeps, but you can override the distance by setting this value. Well that's the theory, I don't think I've ever had it set to anything but Auto.

[CREPELLO]

Thanks for that chaps

[andrew_s]

With "On Road" or Auto routing, you are limited to 50 route points. Between these points, the Garmin uses the map you've got loaded to give you a route, based on the parameters you've defined in your Routing setup. It will pass through all the points you have specified, but the way you get between them may not be exactly what you intended.

This works well, and you can go 2-300 miles on 50 points, but it's only any good if the GPX file was prepared with this type of routing in mind.
It it's a general use GPX from BikeHike or whatever, you are likely to have too many points (eg every junction), and any automatic simplification is likely to discard the point that stops you getting routed onto the motorway.

"lock on road" is a function that got added to GPS units way back when the GPS signal was deliberately mucked about with to make it less useful to THE ENEMY, and your position was only good to 100 feet or so, which often wasn't good enough to reliably get the right street in towns and made routing difficult. Then WAAS came along to make things more accurate, and the deliberate error finally got turned off for the first Gulf War when the US troops were using civilian GPS units. Positions are good enough now that it's a pointless function. WAAS/EGNOS is also not really of a great benefit any more - I keep it turned off on mine to save battery life, and still get 3m accuracy most of the time.