[mkgmap-dev] Flooding in Germany

Wed Jan 20 19:41:48 GMT 2010

>
>
> On 20.01.2010 11:12, Clinton Gladstone wrote:
>> 2010/1/20 Felix Hartmann <extremecarver at googlemail.com
>> <mailto:extremecarver at googlemail.com>>
>>
>>
>>     Just downloaded new data for Germany, problem persists:
>>
>>     Is this maybe not solvable with current code?
>>     I'll retry with different max-nodes to see if it then maybe works.
>>
>>
>> I also noticed this with the Geofabrik extract of Germany: The tile
>> around Bremen always gets flooded. My tiles are different from yours,
>> so I assume we have different max-nodes parameters.
>>
>> I did also compile Geofabrik's complete Europe extract: here the
>> problem did not occur. There were a couple of other landlocked tiles
>> in France and Poland which were flooded though (caused by, I assume,
>> some bad data in the tiles).
>>
>> This may mean, therefore, that the problem stems from the way
>> Geofabrik extracts Germany. You could try making your own extract
>> (using a bounding box) for Germany out of the Europe extract. Perhaps
>> this would work better.
>>
>> Cheers.
> -- I reduced maxnodes to 800.000 and then the flooding became a lot
> smaller (and not the whole tile anymore). The problem seems to be that
> there is sea in the North, then a section with land until the boarder,
> and then further south again sea.
> See below (or to the right) a screenshot of Garmin (Mapsource) Topo
> Deutschland v2. One can nicely see the problem of the country boundary
> going seperated through the sea. It is really strange that there is a
> sea section without exit on dutch territory. But well.
>
> I don't know whether this can be fixable in code, or whether we should
> simply take it out from the main ocean and make a separate sea section
> in OSM data to make it easier to work with country extracts.
>
 From my experience the Geofabrik extracts are the problem. Our code 
will not be able to fix that 100%. From my point of view our code can 
work only if the coastline ways are complete.

The boundaries used by Geofabrik are sometimes too short. I analysed 
that for belgium. A good example is the land nose at Zeebrugge 
(http://www.openstreetmap.org/?lat=51.3465&lon=3.2097&zoom=13&layers=B000FTF). 
It is completely cut away in the Geofabrik dump.

So what has to be done to solve the problem?
1. Inform the geofabrik people that they may increase their boundaries. 
maybe they could include the three or twelf-mile-zone around a country?

2. The format of an OSM dump should be extended by the possibility to 
define the exact borders of the OSM dump. The osmosis tool could then 
add the boundary used to extract the OSM dump to the dump. This solves 
99% of the problems originated by inexact dumps and unknown boundaries.

WanMil