[mkgmap-dev] Configurable flood blocker

Fri Dec 17 15:45:12 GMT 2010

>> Thanks Felix,
>> I tested it now with:
>> extend-sea-sectors,close-gaps=6000,floodblocker,fbgap=60,fbthres=200,fbratio=0.6,land-tag=natural=background
>>
>> No errors and sea polygons came back, but the floodblocker blocks still too much.
>> I've tried it with other fb numbers but it still gives the same picture:
>>
>> http://img404.imageshack.us/img404/3702/nogroningen.jpg
>>
>> The tested tile you can download at http://mijndev.openstreetmap.nl/~ligfietser/diverse/Test.zip
>
> Minko,
>
> I will download your test data and give it a try.
>
> If you want to get detailed information what the flood blocker is doing,
> you should enable an appropriate logging.
> See
> http://www.mail-archive.com/mkgmap-dev@lists.mkgmap.org.uk/msg02381.html
> how the logging.properties file can be configured and add the line
> uk.me.parabola.mkgmap.reader.osm.SeaPolygonRelation.level=INFO
> to the logging.properties file.
>
> You might also add the parameter fbdebug to the sea-generation options.
> In this case the flood blocker creates GPX files for each checked
> polygon and the pro blocking (highways) and the contra blocking (ferry
> routes) points. Opening these files with JOSM makes it easier to
> understand why the flood blocker fails.
>
> WanMil

Ok, I have tested the tile with your parameters.
The sea generator created one big sea polygon (sea_polygon.png). As you 
can see the polygon is erroneous because it intersects itself. This is 
caused by the incomplete coast data in the tile which squeezes the sea 
generator to guess how the real sea polygon looks like.
I must admit that a check could be added if the polygon intersects 
itself and in this case the sea sector extension could try some other 
completion strategies. (But that's not a task of the flood blocker and I 
guess it would be a performance problem.)

Without the flood blocker large areas near the german border would be 
flooded. The flood blocker detects that (see sea_polygon_contra.png) by 
checking how many blocking points are contained in the polygon. In this 
case there were 26602 points within the sea polygon and therefore the 
polygon was converted from sea to land polygon. As a result the flood 
blocker worked perfectly!

You can see the result of the flood blocker in the logfile:
Flood blocker for sea polygon 4611686018427390756
area 476449303,0000
sea 125
land 26602
ratio 5,5571
Polygon 4611686018427390756 type sea seems to be wrong. Changing it to land

So from my point of view this was a good test case for the flood blocker 
and it worked as expected.

Have fun!
WanMil
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