[postgis-devel] force_sfs

[Olivier Courtin]

On May 10, 2013, at 3:56 PM, Sandro Santilli wrote:

Sandro,

>> ST_ForceSFS_11 sound better ?
> 
> Ugly :)

I agree :)

> What's the real use of this ? Is it only for GEOS ?

Well SFCGAL retrieve SFS 1.2 geometry.
And GEOS could only handle SFS 1.1

So when you want to nest a SFCGAL function with GEOS ones,
it could lead to problem (for instance GEOS stop as not 
able to deal with TRIANGLE...)


First real use case of such a thing was for ST_ConcaveHull,
when SFCGAL backend enabled, as concave hull
mix ST_Intersection (SFCGAL), with ST_IsValid (GEOS)

> Does it need to be exposed to SQL at all ?

Yeap i think so, except if we choose to silently convert
SFS 1.2 -> SFS 1.1 types directly before GEOS calls.


> Note that we have an st_force_collection already
> which could work for TIN and POLYHEDRALSURFACE
> (would need to be renamed as well) so it really
> only seems to be an issue for TRIANGLE.

Humm that's not exactly the same need,
as with st_force_collection on a MULTIPOLYGON you will
have a collection of POLYGON.
(rather that with ST_ForceSFS, aim is to have pure SFS 1.1
 geometry type)


O.