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[mkgmap-dev] River flooding with r1955

From Marko Mäkelä marko.makela at iki.fi on Tue Jun 7 22:15:53 BST 2011

On Tue, Jun 07, 2011 at 02:02:03PM -0400, Francisco Moraes wrote:
>Well, I found this:
>2011/06/07 13:51:35 WARNING (MultiPolygonRelation): 63240017.osm.gz: 
>Multipolygon http://www.openstreetmap.org/browse/relation/169902 
>contains errors.

>Not very informative but it seems like the relation is indeed broken.
>Any thoughts? I will take a look but I am not yet exactly sure of what I
>am looking for.

I fired up JOSM, hit ctrl-l, typed
and invoked the JOSM Validator on it. No errors found. Then I fired up 
the relation editor and noticed that all ways forms nice loops. I 
selected all the inner ways, and hit '3' (zoom to selection) and then 
zoomed in to one inner way at a time, checking that the inner way does 
not reside outside the outer way. I deselected each inner way, hit '3' 
again and zoomed in again, until I had reviewed and deselected every 
island. The map data looks correct but very detailed.

The problem seems to be insufficient Garmin precision. Many islands are 
closer than 5 meters to the riverbank. I guess that the coordinates get 
rounded or truncated so that the islands will sometimes overlap with the 
riverbank. There are some multipolygons like that in Finland, for some 
golf course and maybe buildings. I am filtering out warnings for such 
multipolygons on a case-by-case basis.

WanMil is our multipolygon expert. Could the code be made smarter in 
some way? When rounding the coordinates of inner ways, try to move them 
inside the outer way. If the inner way polygon gets too small, drop it 
entirely. Something like that?


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