[postgis-devel] Snap-Rounding based overlay operations

[Daniel Baston]

Would a GUC really be needed for enabling / disabling fixed-precision mode?
I'd think the mode could be inferred by the fact that we're calling an
overlay function either with or without a specified precision..

ST_Intersection(a.geom, b.geom, op_precision := 1e-6) would use a fixed
precision algorithm, however that is implemented by the installed GEOS
version

ST_Intersection(a.geom, b.geom) would use the current double precision
algorithm

Dan

On Wed, Sep 20, 2017 at 10:18 AM, Darafei "Komяpa" Praliaskouski <
me at komzpa.net> wrote:

>
>
> ср, 20 сент. 2017 г. в 17:08, Sandro Santilli <strk at kbt.io>:
>
>> On Tue, Sep 19, 2017 at 05:18:51AM -0700, Paul Ramsey wrote:
>> > I'm generally in favor of the GUC, and to some extent in favor of
>> having it
>> > turned on by default, though I could stand a release cycle with it off
>> for
>> > testing purposes. I don't think we want the granularity of declaring
>> > precision by table or by feature.
>>
>> A GUC for enabling it and GUC for specifying a precision GRID ?
>> Or letting precision GRID being figured out by GEOS internally ?
>>
>
> I am strongly against a GUC that will change precision.
> We already have a switch for GEOS/CGAL backend, so a similar one for
> enabling (or disabling) FIXED mode is fine.
>
>
>> I generally think that precision would be a characteristic of
>> a data rather than session.
>>
>
> There is a PR on validity flag for CGAL. This is a similar algorithm input
> characteristic, that should be stored in geometry, if cannot be effeciently
> calculated each time. And in general it can't - ST_SnapToGrid(geom, pi())
> will make it a 3.14... meter grid, with all the last bits mostly set.
>
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