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[mkgmap-dev] Configurable flood blocker

From WanMil wmgcnfg at web.de on Sat Dec 18 12:57:13 GMT 2010

Am 17.12.2010 16:49, schrieb Felix Hartmann:
> On 17.12.2010 16:45, WanMil wrote:
>>>> 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
> Well can you check why it does not work when giving "polygons" or
> "no-mp" as command? Multipolygon mode is not really the best solution....


there is nothing to check. The flood blocker works only in multipolygon 
mode. It is not possible to implement that for the polygon mode.

Where do you think is the advantage of the polygon mode?


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