[Qgis-psc] outstanding issues

[Giovanni Manghi]

Hi,


> Ftools dissolve would be a good candidate to be replaced by OGR dissolve
> which we already have in processing.

if we want all the tools in ftools>geoprocessing can be replaced with
ogr2ogr+SQL tools, in fact I already started a while ago (see
https://github.com/qgis/QGIS/pull/1905) and added a few operations in
processing. A few of them are faster than the ftools counterpart
(dissolve for example, that also does statistics on dissolved fields)
others not really (clip on large vectors).

I plan do add also the other operations, the ones that involve the use
of two inputs since Luigi in Denmark added a first implementation to
create on the fly virtual vectors (in ogr2ogr+sql you cannot specify
directly two inputs, you must have them into one virtual vector and
then refer to layers in it).

Said that this approach has a few problems:

* the "use only selected fectures" Processing option does not seems to
work with ogr tools
* this approach work only for layers with a proper geometry column,
but  in processing we don't have a way to show for inputs only
datasources that are compatible with a certain tool, at least as far
as I know.
* ogr+sql fails if input geometries have errors, not sure if is
possible to do something about that (maybe I'm missing something
simple), or for example adding an option to add makevalid to the
queries. Ii'm not even sure makevalid is available out of the box when
we do ogr+sql.
* it would be nice to have in processing an easy way (a dropdown with
multiple selection) to allow users to choose what columns they want to
keep along the operations, right now is either "select *" or just give
them a space where to create a comma separated list with column names


cheers

-- g --