[mkgmap-dev] River flooding with r1955

Wed Jun 8 11:02:19 BST 2011

> On 2:59 PM, WanMil wrote:
>> please post the splitters areas.list file. The tile borders are
>> important for analyzing flooding problems.
> Attaching the areas list on this email.
>> Also important:
>> - Where did you download your data files (geofabric, cloudmade etc.)
> Data downloaded from geofabric, North Carolina extract:
> http://download.geofabrik.de/osm/north-america/us/north-carolina.osm.pbf
>> - Which splitter settings do you use?
> Splitter was used as follows:
>
> java -Xmx1792m -ea -jar %SPLITTER%/splitter.jar --no-trim
> --max-areas=150 --cache=cache --mapid=63240001 --max-nodes=1200000
> --write-kml=world.kml --geonames-file=cities15000.zip --pbf
> north-carolina.osm.pbf
>
>> - Which mkgmap parameters do you use?
>
> mkgmap settings:
>
> java -Xmx1792M -ea -jar %MKGMAP%/mkgmap.jar --road-name-pois
> --adjust-turn-headings --latin1
> --name-tag-list=name:en,int_name,name:zh_py,name:engels,name
> --remove-short-arcs --make-opposite-cycleways --route --description="NC
> Routable" --series-name="NC Routable" --country-name="UNITED STATES"
> --country-abbr="US" 6324*.osm.pbf
>
> REM MERGE
>
> java -Xmx2048M -jar %MKGMAP%/mkgmap.jar --index
> --overview-mapname=63240000 --series-name="NC Routable" --latin1
> --description="NC Routable" --product-id=4 --family-id=2053 --tdbfile
> --nsis --gmapsupp *324*.img M0000805.TYP
>
>

The flooding is caused by incomplete relation data in the tile. This is 
a well known splitter problem. In such a case mkgmap must do a best 
guess and in this case it does not produce the expected result.

I have uploaded all outer ways of the relation in the tile after joining 
(http://files.mkgmap.org.uk/detail/26). The GPX files can be openend 
with JOSM. That helps much for a better understanding of the mp processing.

1. MP joins all input ways. This creates three ways. One is a small part 
of the river but two ways cover most of the river bank. The ways are not 
closed because some little parts in the west are missing in the tile.
2. MP tries to close ways. All ways that can easily be closed outside 
the bounding box are now closed by mp. Most of the time this is the 
correct behaviour but in this case the two polygons of both river banks 
are closed to itself which causes the flooding.

At the moment I have no idea how to fix that. mkgmap has to guess here 
and that also means that sometimes its guesses are wrong.
In this case reducing the overlap of splitter might help or also 
increasing the overlap. If endpoints of the river banks are not directly 
closeable without touching the bounding box the mp algorithm first tries 
to connect outer ways. This was committed in r1953.

WanMil