[postgis-devel] A letter to the Postgis Developers and Packagers

[Sebastiaan Couwenberg]

On 05-02-16 18:54, Sandro Santilli wrote:
> On Fri, Feb 05, 2016 at 02:48:17PM +0100, Sebastiaan Couwenberg wrote:
>> On 18-10-15 20:52, Andrea Peri wrote:
>>> The new topological library of Tuscany Region will be deposited on a
>>> distinct GIT repository, with an open license similar to that of
>>> liblwgeom and of course we will be pleased and honored if in the future,
>>> when it will be more robust and reliable, the Community of PostGIS
>>> Developers and Packagers will decide to link it as a shared library for the
>>> topological component functions.
>>
>> Is there any news on the new topological library?
> 
> Current state is here:
> https://gitlab.com/rttopo/rttopo

Thanks for the link. I'll start packaging a git snapshot shortly.

> It is basically liblwgeom with symbols renamed to have an RT
> prefix, the API reworked to be fully re-entrant and the SFCGAL
> dependency removed.
>
>> I'd like to drop the liblwgeom dependency from the spatialite Debian
>> package, because it introduces a circular dependency that is
>> complicating updates of GEOS, GDAL and related packages [0].
> 
> Wow, my head spins, the circularity is:
> 
>  liblwgeom -> sfcgal -> openscenegraph -> gdal -> spatialite ->
>  liblwgeom
> 
> So rttopo should fix that, by cutting the "sfcgal" out.

This is a recent additional circular dependency caused by the
introduction of sfcgal. The initial circular dependency is
spatialite->postgis/liblwgeom->gdal->spatialite. It was worked around
for the transition to GEOS 3.5.0, but with sfcgal the situation got worse.

>> I'm seriously considering dropping the liblwgeom dependency from
>> spatialite already to get rid of the circular dependency, but this will
>> introduce an ABI break which I'd like to avoid. Resolving this situation
>> will be painful either way, so we might as well get it over with now.
> 
> I feel your pain. Wouldn't it be wonderful if GDAL could use
> runtime plugins for drivers ?

That sounds good, but GDAL drivers are not very problematic so far. The
GDAL <-> GRASS dependency is resolved by building the grass plugin
separately.

GDAL not having a direct dependency on SpatiaLite will help with this
specific issue. As will replacing liblwgeom with librttopo in spatialite.

>> If the new topological library will be available soon, and spatialite is
>> updated to use it, the reduced functionality in spatialite will be a
>> short lived issue. If not, we'll just have to live with the reduced
>> functionality.
> 
> The first release should be available before the end of 2016, but
> I dont' really have a date. It's mostly up to Alessandro Furieri
> to do the spatialite side of it.

That will be too late for upcoming Ubuntu xenial (import freeze on Feb
18) and Debian stretch releases (expected freeze on Nov 5), but we'll
have plenty of time to get it into the next releases.

For now I've dealt with the circular dependency by dropping the
liblwgeom dependency from spatialite.

Kind Regards,

Bas

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