[mkgmap-dev] Flooding of sea - this time inside the middle of the Alps, not related to geofabrik cutting

Fri Feb 26 17:20:21 GMT 2010

>
>
> On 26.02.2010 11:49, Mark Burton wrote:
>> Felix,
>>
>>
>>> I looked for an anti-lake, but could not find one...
>>> I think ultimately we would need some check against flooding. Easiest
>>> maybe would be if there are more than 30 forest polygons inside water
>>> (without natural=land) and if so, then assume tile is flooded and put
>>> land into the whole tile. Much better to miss some sea, then to have
>>> flooding.
>>>
>> Agreed, sanity checking the sea areas (do they contain roads/cities)
>> would make sense because at the moment it only needs a tile to contain
>> a single way tagged natural=coastline and it is likely to get flooded.
>>
>> Mark
>>
> Couldn't there be some sanity checking using the multipolygon code?
> Maybe remove sea polygon once more than 1000 polygons want to cut inside
> the sea, and no more than 5% are natural=land (so that regions with many
> islands are still having sea, though I doubt that any single tile can
> contain more than 500 islands). It should be possible somehow to check
> for something that is so easily detectable by human mind...

It would be possible to add some checks to the multipolygon code. But I 
think it would make more sense to add it to the generate-sea code?! I 
also think that the generate-sea code needs some comments and maybe it 
is worthy to move it to a separate class. This new class could share 
some code with the multipolygon class.

But first we have to think about a good rule for error detection.
* more than 500 islands? => if you split finland to three tiles I think 
I remember that each of these tiles contain > 3000 islands.
* > 5% natural=land? Then it will be hard to create a map of Hawaii 
(http://www.openstreetmap.org/?lat=22.1&lon=-163.7&zoom=5&layers=B000FTF)
* Number (or length) of streets in the water: yeah, this could work. But 
I have no idea how much performance this will cost.
* Any other ideas?

WanMil