[mkgmap-dev] More on Routing

Fri Jul 17 12:34:10 BST 2009

Mark Burton wrote:
> Hi Paul,
>
>   
>> Bury to CHester however starts along the M66, goes straight through
>> junction 18 to the next junction where you go all the way round the
>> roundabout, come back on yourself to junction 18 and then turn left onto
>> the M60 where the route is then as expected.This odd behaviour then
>> continues if routing to places further afield that require the same
>> initial route.
>>
>> http://www.openstreetmap.org/?lat=53.5497&lon=-2.261&zoom=14&layers=B000FTF
>> shows the junctions involved but I can't see how it can be data errors
>> as some routes go M66, M62 westbound without problem and all 3
>> destinations mentioned above are on the same tile
>>     
>
> Can't explain why
> you're seeing badness there.
>
>   

I might.

If Paul used XAPI to extract a part of the country in order to build his 
Garmin map then it's possible that his XAPI excerpt isn't complete. I've 
been seeing more and more of this happening in South Wales where I'm 
doing exactly that.

It seems (from other comments here) that there's a known problem with 
the various XAPI servers occasionally dropping a minute-diff and never 
recovering. I've seen this happening since the switch to the 0.6 API: I 
had never noticed it before that.

I've been sent on bogus routes around Swansea (my home town) due to 
small bits of roads going missing. I've got a partially missing 
westbound carriageway on a dual carriageway in one particular case, I've 
also spotted a missing urban one-way street and a few other cases.

If Paul looks carefully, does he spot (on the Garmin) a missing 
slip-road on a roundabout, responsible for there being no valid route 
from one side of a dual carriageway? Worse is an apparently present 
slip-road on a dual carriageway where the 'oneway' once pointed the 
wrong way, but has been fixed on OSM at some point, but where the fix 
was part of a minute-diff that the XAPI server dropped?

Steve

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