[postgis-users] Problems with ST_OffsetCurve

[Sandro Santilli]

On Mon, Feb 03, 2014 at 11:29:13AM +0100, Rémi Cura wrote:
> By the way Sandro,
> 
> don't you think that Geos should automatically translate the whole input
> using a pivot point ?
> It would of course be difficult when getting data pieces by pieces (like in
> aggregates),
> but when the whole data is available, why not?

Isn't that what I just said in my previous mail ? :)

If you meant "always" you must be aware that the translation is not always
safe as when you translate back you can introduce collapses. This is a real
case if you search the GEOS bug tracker. So BinaryOp does it only if direct
computation fails with a TopologyException (if it still does it, as new
versions directly switch to a FixedPrecisionModel, IIRC).

Again: this is best discussed in a GEOS ticket.

--strk;

> It would considerably help toward reducing the precision issue, and would
> not be so costly (a read of all coordinates to get min/max, then
> subtraction/addition for every coordinate).
> 
> 
> Maybe it could be add at the geos input/ouput level, thus not necessitating
> to change all code?
> 
> Cheers,
> 
> Rémi-C
> 
> 
> 
> 
> 2014-02-03 Sandro Santilli <strk at keybit.net>:
> 
> > On Mon, Feb 03, 2014 at 10:54:13AM +0100, Rémi Cura wrote:
> > > Hey,
> > > you use far too big coordinates.
> > > Please consider using st translate on your data, then curve offset, then
> > > inverse translate.
> >
> > Speaking of which, this treatment is one of those performed on catching
> > an exception in binary operations, maybe the GEOSOffsetCurve method should
> > be changed to _use_ the BinaryOp class (detail more useful in a GEOS
> > ticket,
> > btw).
> >
> > --strk;
> > _______________________________________________
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> > postgis-users at lists.osgeo.org
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> >

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