[OSM-talk] How to fix wonky coastline?
reviews at pacific-rim.net
Wed Feb 28 20:49:09 GMT 2007
----- Original Message -----
From: "Artem Pavlenko" <artem at pavlenko.uklinux.net>
To: <talk at openstreetmap.org>
Sent: Wednesday, February 28, 2007 8:34 PM
Subject: Re: [OSM-talk] How to fix wonky coastline?
>> As I think I've said before, I think the easiest way deal with coastlines
>> efficiently is to define that the sea is on one specific side. That way
>> renderers can determine where the sea is based on purely the bit of the
>> that falls within the area they are trying to render.
>> It would mean correcting coastlines already present.
>> I think it should be possible to do make heuristic decisions about which
>> side is sea presently: for example finding a near (non-bridge) highway to
>> coastline way (on the assumption that non-bridge highways are always on
>> land!) and determining which side they are on relative to that bit of
>> (construct a line from one of the highway nodes to one of the nodes of
>> coastal way, counting intersections with any coastal ways between -
>> essentially a point in polygon test, eve though it isn't really a
> This will never work reliably.
>> While this could be done by a renderer it is not very helpful for tiles
>> where the nearest road is a long way off the tile, but it could also be
>> used to automate the correction of coastline direction for ones which are
>> currently against the rule I am proposing, so a one-off task.
>> The renderer merely needs to close up the sea area by adding pseudo
>> segments between the ends of the coastline where they intersect with the
>> edges of the tile (or use the nodes off the edge of the tile) around the
>> tile edges in the direction indicated by the rule.
>> This allows all rendering of sea decisions to take place locally to the
> What?? Honestly, are you serious? All we need to do is to use *POLYGONS* ,
> full stop. What is the problem?
as I understood it, you did some work on this a few weeks back along the
south coast of the United Kingdom, and I've been regularly looking at the
mapnik layer in the slippy map to notice a change, but haven't seen one.
a) was there any conclusion you came to about putting the results of your
work back into the OSM database?
More information about the talk