vertex simplification

thomas bonfort thomas.bonfort at GMAIL.COM
Sat Oct 27 08:26:53 EDT 2007

hi all,

I'm looking into adding some vertex simplification at the image level,
for the time being limited to the agg renderer. I've got two questions
I'd like to have feedback on:

* it's very easy to add a local simplification, by removing vertexes
in a linestring that are closer than some threshold to their preceding
vertex. I'm getting nice speedups by mimicking what's currently (more
or less implicitely) done with gd, by removing vertexes that fall in
the same pixel than its predecessor (of course these speedups would
only happen for complex line layers. I'm currently testing with the
canadian road data mentionned in I
know agg is all about subpixel accuracy and such, but I'd think this
behaviour could be enabled by default ( as in this case the maximum
error for a vertex is less than a pixel)

* is anyone interested in having a global and tunable vertex
simplification functionality. I don't think it would be too much work
work to implement a douglas-peuker line generalisation algorithm, that
could be turned on and tunable with a new mapfile keyword. That's
basically doing what postgis' SIMPLIFY can already do, except this
would be done in pixel coordinates, and therefore would not have to be
tuned w.r.t. scale.


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