[postgis-devel] filter by m-value and effective area

[Nicklas Avén]

The ST_SimplifyVW does that filtering, but I didn't open any way to do
the filtering on already computed m-values. But I also added
ST_SetEffectiveArea, which is kind of ST_SimplifyVWPrepare()
but not ST_SimplifyVWPrepared() in the meaning that it works on already
prepared VW.

ST_SimplifyVW shortcits when the requested effective area is found so
it is a little slower to run ST_Seteffectivearea.

That is an interesting difference between ST_Simplify and
ST_SimplifyVW, that ST_Simplify gets faster the fewer points it shall
filter away, and ST_SimplifyVW is faster the fewer points it shall
return.

They attack the problem from different ends.

/Nicklas


On Sat, 2017-09-23 at 13:05 +0200, Sandro Santilli wrote:
> On Sat, Sep 23, 2017 at 12:39:16AM +0200, Nicklas Avén wrote:
> 
> > Today we have no function doing this "removing of vertecies". But
> > it
> > would be quite simple to write a function that just filters by the
> > m-
> > value, and the simplification will be very fast.
> > 
> > It will be a 2.5 function, but what do you think?
> > 
> > Is this worth another function in the crowd?
> 
> Of course !
> Actually, I thought you already added that function
> as part of the Visvalingam-Whyatt algorithm work.
> Should it be a ST_SimplifyVWPrepared() or are you
> thinking of a more general "filter by M" one ?
> 
> --strk;
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