[OSM-dev] coastline error checker and crossing ways

Ben Supnik bsupnik at xsquawkbox.net
Wed Aug 12 23:37:57 BST 2009


Hi Y'all,

The coastline error checker is alive again!  Awesome! :-)

Can anyone tell me what the black line means, e.g. why do some 
continents have it and not others?

Also two quality q's:

1. Pyramid Rock off of the coast of SF flags an error...I'm not sure 
what's going on here.

Way 32289185 is a CCW square island -

http://www.openstreetmap.org/browse/way/32289185

It looks okay to me but renders as a triangle, not a square, on the map. 
(Is it possible the base tiles haven't been updated in a while?)

Way 32289186 is a closed CCW triangle, that doesn't show on the map at all.

Does anyone know why the coastline error checker dots this or the map 
tiles are wrong?

2. The coastline has self-intersecting ways, e.g. way 38667961 
intersects itself (node 243393524 shows the problem).

My comment is: isn't this an error?  The coastline is defined by 
direction (e..g. land=left), so self-intersections hose the land-water 
definition.

The polygon coastline processor appears to use sort of a winding rule 
and somehow figures out which contour is correct and which is hosed.

Perhaps one of the existing error checkers that finds intersecting ways 
could catch this.

If the coastline processor source code is available, I could at least 
take a look at it...depending on what toolset it's written on top of, I 
don't know if I am qualified to fix these problems.

(I found the self-intersecting coastline using my own proprietary tool 
chain, which uses CGAL for polygon processing..the source is available, 
but it's not really suitable for a continuous check system.)

cheers
ben


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