[Qgis-developer] Merging of incompatible changes

[Martin Dobias]

On Sat, Oct 27, 2012 at 11:16 AM, Sandro Santilli <strk at keybit.net> wrote:
> On Sat, Oct 27, 2012 at 01:41:49AM +0200, Tim Sutton wrote:
>
>> * One of the major limitations I and the many people that contact me
>> about QGIS experience is lack of performance. Just yesterday I got an
>> email from someone in Sudan trying to use QGIS to work with ~300 000
>> point records and it taking 4 hours to do some simple operations on
>> the dataset.
>
> I think such cases should be handled by only fetching a sample of the
> data for visualization purpose, rather than the full set. And similarly
> only a subset of vertices could be fetched when facing dense vectors.
>
> This is something that might need an API change too, as you would need
> the providers to be told when the data has to be fetched only for
> visualization (thus generalization is possible) or for editing (thus
> you want all the data, possibly forcing a restriction on extent).

The changes on the branch make adding such improvement possible:
requests are encapsulated into QgsFeatureRequest class, so the
generalization could be implemented with a new flag within that class
- some providers could support it, some would just ignore it (or fetch
all vertices and let GEOS simplify the geometry before rendering).

Martin