[OSM-talk] Routing on OSM maps on a Garmin device

[Apollinaris Schoell]

On 15 Jun 2010, at 6:45 , Maarten Deen wrote:

> On Tue, 15 Jun 2010 15:20:07 +0200, Lambertus <osm at na1400.info> wrote:
>> On 2010-06-15 01:53, Liz wrote:
>>> On Mon, 14 Jun 2010, Maarten Deen wrote:
>>>> Does anyone have similar experiences, and maybe an explanation why
> this
>>>> happenes? Are the OSM maps too detailed for a simple device like this
> to
>>>> calculate?
>>> Using a separate *set* of maps for Australia, I have had trouble with
>>> calculating a route that crossed a border from one map in the set to
>>> another.
>>> The distance involved is not the problem in this case, but the
> existence
>>> of the border.
>> 
>> That could be a result of the method used to split the data. If you use 
>> the Mkgmap Splitter tool then crossing borders should be possible, but 
>> using Osmosis et al won't.
> 
> And it would explain it only partly. I know the Garmin map does extend
> some distance into Germany in detail, but it also covers Europe in low
> detail. So you would expect to get some form of route, albeit not very
> accurate, and the device would not show you on the road.
> 
> But it does not explain why I got a route to my first waypoint from the
> start (likely to be outside of the Garmin map, but I'll have to check that)
> and not when, after I was well and truly in Germany and on the OSM map, I
> chose not to follow the route and it could not recalculate the route. Nor
> does it explain why I got a route in "economic route" mode and not in
> "fastest route" mode.
> 
> And the maps from All in one Garmin Map are also made with Mkgmap, so the
> problem shouldn't occur anyway.
> 

this is a known problem but unknown reason and solution. sometimes garmin devices can't find a route adding additional through points help. did a route recently from south of germany to north. one trough point on the first route was sufficient. then I planned a different version and it did not work even that I had an additional through point after both routes where supposed to merge already. so calculating the first portion of the route influenced how the rest was calculated. My guess is that garmin devices have either not enough memory or they use a recursive algorithm and the stack size or number of recursions is limited. 

btw mkgmap mailing list is the better place to discuss these topics

> Regards,
> Maarten
> 
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