[postgis-devel] Validity flag

[Hugo Mercier]

On 06/03/2016 22:46, Oliver Courtin wrote:
> Le 5 mars 2016 à 23:14, Daniel Baston a écrit :
> 
> 
> Hi Dan,
> 
>> Here's an example where GEOS and SFCGAL report a different result for ST_IsValid:
>>
>> SELECT ST_IsValid('POLYGON ((0 0 0, 1 0 0, 1 0 0, 1 1 0, 0 1 0, 0 0 1))');
>>
>> This returns true with GEOS, but false with SFCGAL (on Hugo's branch, where ST_IsValid is implemented with SFCGAL).  So, we wouldn't want a situation where the flag is set with a GEOS backend and read with a SFCGAL backend.
> 
> 
> Yeap that's a really good point !
> 
> 
> 
> Indeed as GEOS is 2D only, it won't be able to handle TIN and PS validity check
> (not that a big deal as an unknown valid would 'only' impact performances but won't crash PG process), 

TIN and PS can be in 2D as well if I am correct. GEOS raises an
exception to say it is not supported which is fine.

Returning "valid" on an invalid 3D geometry is more of a problem indeed.


> Few ideas about it:
> 
> - Don't really like the idea to have validity several flags for each backend 
>   (idea is to allow new backend to be added later, for example and maybe one day: GGL)
> 
> - Quick way to workaround would be to not allow GEOS to set validity flags on 3D geometries (HASZ), or on TIN/PS  

+1