Author Topic: Routes on Garmin eTrex 20/30  (Read 896 times)

Bianchi Boy

  • Cycling is my doctor
  • Is it possible for a ride to be too long?
    • Reading Cycling Club
Routes on Garmin eTrex 20/30
« on: April 20, 2014, 08:24:17 am »
Hi,

I have an eTrex 30 and was a track user on my old (now dead) eTrex Vista HCx. The old eTrex had a facility to beep when you were off track and I used this at night so I did not go off track. Now after a long email exchange with Garmin support the beep when off track only applies to direct navigation between points. I think this is meant for walking and sailing, but completly useless when cycling on road. So I have tried routes with mixed success. My Easter Arrow was perfect example. Some worked and other just sit there for ages and fail to calculate. I have looked for logic or a pattern, but can see none that makes any sense. I had one this weekend for Sandy to March where the track was 62 km and the route 145 as calculated.

I have open source maps from a few months back have some routs that work perfectly. I can see no pattern to the success or failure of the routes and have about a 70% success rate for the routes I plan.

Thanks in advance to the collective.

BB
Set a fire for a man and he will be warm for a day, set a man on fire and he is warm for the rest of his life.

frankly frankie

  • I kid you not
    • Fuchsiaphile
Re: Routes on Garmin eTrex 20/30
« Reply #1 on: April 20, 2014, 09:22:23 am »
I'm not a routing expert - because, contrary to the above, some of us do cycle using a preferred mode of direct navigation between points.  'Compelely useless' it is not.

But 70% success using OSM sounds quite plausible to me.  And there would be no logic to the failures, because it would be mostly down to the Wiki- nature of OSM, the completely variable nature of the contributions.
The most obvious type of problem would be roads that haven't been joined correctly in the map, so that routing cannot flow from one to the other.  Sometimes 1-way sections of road are incorrectly tagged.  Very often there is no consistency about the status of a road - primary, secondary, tertiary, other, bridleway, etc - a long load will often have been mapped by a combination of 2 or more people, who might each have tagged their section differently.  (This shouldn't happen, but anything is possible if there's minimal quality control.)  Depending on the routing mode you have set the GPS to (car, cycle etc), these inconsistencies will affect it in different ways.

This is not to say that OSM isn't a good map - it is, but it does have these characteristics.  When a problem is found, why doesn't someone go in and fix it?  Well in some ways I think refining the map is a far more difficult proposition than constructing it in the first place (which is now mostly done).  It may involve treading on toes, or invading an area that someone regards as 'their patch', etc etc.
It's not dark yet but it's getting there.

Bianchi Boy

  • Cycling is my doctor
  • Is it possible for a ride to be too long?
    • Reading Cycling Club
Re: Routes on Garmin eTrex 20/30
« Reply #2 on: April 20, 2014, 10:00:04 am »
I'm not a routing expert - because, contrary to the above, some of us do cycle using a preferred mode of direct navigation between points.  'Compelely useless' it is not.

But 70% success using OSM sounds quite plausible to me.  And there would be no logic to the failures, because it would be mostly down to the Wiki- nature of OSM, the completely variable nature of the contributions.
The most obvious type of problem would be roads that haven't been joined correctly in the map, so that routing cannot flow from one to the other.  Sometimes 1-way sections of road are incorrectly tagged.  Very often there is no consistency about the status of a road - primary, secondary, tertiary, other, bridleway, etc - a long load will often have been mapped by a combination of 2 or more people, who might each have tagged their section differently.  (This shouldn't happen, but anything is possible if there's minimal quality control.)  Depending on the routing mode you have set the GPS to (car, cycle etc), these inconsistencies will affect it in different ways.

This is not to say that OSM isn't a good map - it is, but it does have these characteristics.  When a problem is found, why doesn't someone go in and fix it?  Well in some ways I think refining the map is a far more difficult proposition than constructing it in the first place (which is now mostly done).  It may involve treading on toes, or invading an area that someone regards as 'their patch', etc etc.
Is this all an argument for splashing out on Garmin maps?

I had those before and they were OK - but I never routed on them.

BB
Set a fire for a man and he will be warm for a day, set a man on fire and he is warm for the rest of his life.

Kim

  • Timelord
Re: Routes on Garmin eTrex 20/30
« Reply #3 on: April 20, 2014, 01:04:56 pm »
Garmin's City Navigator maps are my preferred option for autorouting.  They're not always 100% accurate with what's on the ground (no map is perfect, but OSM is awesome at keeping up to date with new developments), but they are internally consistent, and the routing algorithm always finds a route from A to B, if not necessarily a sensible one for cycling (you have to use extra routepoints to persuade it away from main roads at times).

I also find the level of detail is about right for road cycling.  It shows the roads, major terrain features (water, woods etc) and an assortment of POIs.  It doesn't map every footpath and snicket in the way that OSM does, which means a lot less clutter in urban areas.  I like combining City Navigator with the SMC contour overlay, so you have an idea of upcoming gradients.

My experience with OSM and routing is variable.  It seems to work pretty well in some (mostly urban) areas, and go horribly wrong in others.  And of course it will lead you down cyclepaths when you want to stay on the road, or lead you back to the road when you want to follow a Sustrans route.
Careful, Kim. Your sarcasm's showing...

Euan Uzami

Re: Routes on Garmin eTrex 20/30
« Reply #4 on: April 20, 2014, 01:52:18 pm »
Up-to-date, sensible route, turn by turn beeps - choose any two!

Personally I choose 1 & 2 and do without 3.

Autorouting with City Navigator probably give you something approaching 2 and 3, autorouting with OSM probably gives you something approaching 1 and 3 - but there is the question of what use is 1 is without 2...

It is frustrating, the false hope when it does produce a sensible route with OSM to think "that's great - so why the bloody hell can't it do that all the time?" and I've spent hours debugging the data and tweaking and retesting only to come to the conclusion that OSM is, like ff says, far too variable for there to be any rhyme nor reason to it.

Bianchi Boy

  • Cycling is my doctor
  • Is it possible for a ride to be too long?
    • Reading Cycling Club
Re: Routes on Garmin eTrex 20/30
« Reply #5 on: April 21, 2014, 09:11:15 am »
Thanks for the advice. It looks like I prefer reliable routing over the most 100% up to date maps. The only reason I have got into this pickle is because eTrex 20/30 does not beep when off course. As a bit of a day dreamer I found this most useful.

Will I but look and see how much the Garmin maps are. Been a bit of a poor bloke I may want to avoid spending money.

BB
Set a fire for a man and he will be warm for a day, set a man on fire and he is warm for the rest of his life.

frankly frankie

  • I kid you not
    • Fuchsiaphile
Re: Routes on Garmin eTrex 20/30
« Reply #6 on: April 21, 2014, 11:57:15 am »
Maybe look in the usual places for someone selling a copy of Metroguide v9.  v9 was the final version before Garmin discontinued it, and dates from about 2009 as I recall.  Say £30 would be an OK price, IMO.  I still use it** and it's quite unusual for any out-of-dateness to actually be problematic.***
It has to be hacked to enable the autorouting (that Garmin disabled, to differentiate it from City Nav) - but that's easy and cheap.  It has the huge advantage (for multi-GPS households) that it isn't locked in any way, you can use it on multiple GPSs.

** with overlaid SMC contours, like Kim does, and with contours from another source for France/Switz/Italy.
*** last year I (and a group) was badly caught out by a (very) new construction 'cutting' the lane we wanted to use - but then so were several cars, at least we were able to climb an embankment and over a railing, the cars for all I know are still milling around ...
It's not dark yet but it's getting there.

Bianchi Boy

  • Cycling is my doctor
  • Is it possible for a ride to be too long?
    • Reading Cycling Club
Re: Routes on Garmin eTrex 20/30
« Reply #7 on: April 21, 2014, 05:51:34 pm »
Hi,

I have just paid £31 for garmin maps that covers the UK and north France. I really was getting sick of the routing failures and could just about part with the cash for the maps. I hope my expectations are not dashed on the first ride with full route support.

BB
Set a fire for a man and he will be warm for a day, set a man on fire and he is warm for the rest of his life.