[postgis-devel] sfcgal && extensions

[Oliver Courtin]

Le 1 oct. 2013 à 04:34, Paragon Corporation a écrit :

Regina,

>  >  So if i hear you, there's a need to something like postgis_sfcgal extension,
>  >  in the next 2.2 that's it ? 
> Correct. I think its too early to demand people compile with sfcgal (heck I haven't yet and I don't think anyone except you and Bborie on core PostGIS dev team have). 
> Perhaps in a later release after others have done it we can fold the 2 into one extension again.

Ok i will create the related ticket 

>  > There's something somehow related in this specific use case:
> 
>  > - You compile PostGIS with SFCGAL
>  > - You don't load sfcgal.sql
>  > - You choose to force PostGIS backend to sfcgal
>  > - You call a function related to PostGIS backend
> 
> > And the result will be something like 'undefined function'
> 
> So are you saying you can't use SFCGAL functionality unless you load the sfcgal.sql since that contains the backend call to switch the backend?

Yes new SFCGAL functions (at least in 2.1) need sfcgal.sql load

>  What about the scenario where you 
> 1) compile with PostGIS with SFCGAL
> 2) you just do regular CREATE EXTENSION?
>  
> I presume that will just use GEOS and sfcgal will stay dormant.

Indeed there's 2 kinds of SFCGAL functions: 
the ones switched by postgis.backend and so common with GEOS (e.g ST_Intersects) 
and the brand new ones (e.g ST_Extrude)

If you don't load sfcgal.sql and don't do anything to switch 
postgis.backend, commons functions will still use GEOS backend,
and you won't have any extra SFCGAL functions available


> That would suggest that the 
>  
> CREATE EXTENSION postgis_sfcgal;
>  
> should load the functions and switch the backend.  Though not sure how doable that is.

Load the function, obviously yes.
switch the backend i would say : why so ?
it's looks like something the user should do by itself if he want/need to...

>  On a separate note Sandro was saying we should have a section in the docs that describes these GUCS.  I believe raster has one as well in 2.2
> and Sandro and Paul were threatening to create more for things like ST_Simplify behavior and some other thing like curve output behavior. 


Ok do you have something in mind to do so ?


O.





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