[postgis-devel] Autofix and retry for GEOS overlay ops

[Sandro Santilli]

On Sun, Feb 04, 2018 at 03:00:37PM +0000, Darafei "Komяpa" Praliaskouski wrote:

> which boils down to "try intersecting, if failed, MakeValid the inputs, try
> intersecting, fail if failed".

I'd say "if failed *and* input is invalid".
GEOS already checks the input upon hitting a topology exception,
and reports that with something like this:

    ERROR:  Error performing intersection: TopologyException:
    Input geom 0 is invalid:
    Self-intersection at or near point 5 5 at 5 5

So maybe you could parse that exception message to tell if
it's worth running a MakeValid.

You still want to emit a WARNING because the caller might prefer
to fix the inputs earlier in the process, for speed benefits
(for example I think ClipByBox is documented for possibly returning
invalid geometries, so a user would need to MakeValid those outputs)

A GUC to control whether or not to activate some behavior would
be useful (although painful to use/maintain). I'd also like to be
able to request a NULL in preference to an exception, for example,
as that's an easiest way to find out _which_ inputs are problematic
when dealing with big tables with lots of data...


--strk;