[postgis-users] line simplication

Andy Turk andy at streetlight.com
Mon Jan 6 17:17:22 PST 2003

Douglas Peucker is a useful algorithm, but you need to be careful with
it in a mapping setting. The algorithm basically removes points from a
linestring that don't change it too much.

The problem is that the algorithm has no knowledge of the surrounding
environment. Intersections are a good example. If you have a normal
intersection of two street segments, moving the point of intersection a
little doesn't harm the map much.

However, D-P may take T-intersection and transform it either into two
disconnected lines or two lines that cross each other. Neither of these
looks correct visually and may cause other problems in interpretation.

Also, D-P operates in a cartesian space and applying it to raw lat/lon
data probably wouldn't work right.

On Mon, 2003-01-06 at 16:47, Paul Ramsey wrote:
> Precisely correct (I think). The best way to the desired result should 
> be to implement a Douglas simplification function, and then create a 
> view which (a) uses attributes to reduce to just the features of 
> interest (interstates, etc) and (b) uses the simplify() function to 
> remove unnecessary vertices from the features.
> P.

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