[postgis-devel] Snap-Rounding based overlay operations

[Sandro Santilli]

On Wed, Sep 20, 2017 at 10:57:59AM -0400, Daniel Baston wrote:
> Would a GUC really be needed for enabling / disabling fixed-precision mode?

There's a bit of confusion here.

Martin plan is not about "fixed-precision mode" but about "snap-rounding mode".
Such new mode basically creates 2 possible handling of "fixed precision"
geometries: "current" and "snaprounding".

> 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

Indeed my current idea was for GEOS to always implement "snaprounding"
when fed a "fixed precision" geometry, discarding the "current" mode
completely (as one that was never used before by PostGIS).

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

One idea of martin was to also use "snaprounding" mode for floating
precision geometries, by computing a "safe" precision up-front.

But I still think the idea of making precision model the discriminant
is a good one, for its simplicity and linearity.

--strk;