[mkgmap-dev] [PATCH] Correct longitude distance while finding nearest border

Fri Jan 22 21:48:09 GMT 2010

Hi Felix,

if you created the map with the extend-sea-sectors option this may help 
you. Previously I ignored that a distance in longitude drection depends 
on the latitude. One degree on equator is same for longitude and 
latitude, while one degree at a pole is zero. The attached patch does 
this correction.

So if using the data you posted in your first mail, the additional point 
is drawn on western border of tile instead of going to north and cutting 
the real coastline.

Nevertheless this behaviour may occur again if the size of the tile 
changes. Like WanMil wrote the only possibility to get rid of this is to 
have the exact borders of the extract stored in the osm data and move 
them to the generated maps.

Am 20.01.2010 11:55, schrieb Felix Hartmann:
>
>
> 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.
>
>

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