[postgis-users] Topology: Simplifying Coastlines with Islands

[Sandro Santilli]

On Mon, May 28, 2012 at 02:50:43PM +0200, Michiel J. van Heek wrote:
> Quoting Sandro Santilli <strk at keybit.net>:
...
> >How do your country boundaries look now ? :)
> 
> They look pretty good. Most remaining trouble edges are relatively
> short. Three long coastlines remain problematic: arctic Canada,
> southern/eastern USA, and Brazil. (Red color in attached
> screenshot.) Probably because they have some quite large islands
> very close to the coastline.

"Probably" ? Dissipate any dubt, take a closer look !
Pick the Brazil coast, looks interesting.
Zoom in, see the edge which was colliding in the ST_ChangeEdgeGeom
error message.

> If we want to handle these kind of
> cases automatically, the easiest way would be to removed the
> islands, but I don't like that idea, because some islands may be
> very big, like the arctic islands of Canada. It is like removing
> Great Britain from the map. :-)

One way would be to split the edge introducing nodes making it
harder for each sub-edge to collide to anything. I wonder how
finding such new nodes could be automated. But we're running too
much. Zoom on the Brazil coast first, and extrapolate the actual
error message. Oh, note that running a second time might give you
more successes, so worth reaching a "stable state" before going
on. 

--strk;

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