[QGIS-Developer] Processing 3.0: Possible change to the Singlepart to Multipart algorithm

[Nyall Dawson]

On 27 June 2017 at 09:28, Nyall Dawson <nyall.dawson at gmail.com> wrote:
> Hi all,
>
> As you may be aware, I've been working on rebuilding the backend of
> Processing in c++ and refining how it operates.
>
> As part of this I'd like to clear up the list of existing algorithms
> and also refine how they behave. This list of "QGIS" algorithms has
> grown organically during the 2.x cycle, and there's now numerous
> oddities in the selection of available algorithms and their options.
>
> This discussion relates to the "Singlepart to Multipart" algorithm. I'd like to:
>
> 1. drop the option for "unique ID field". This option is used to
> 'collect' the geometries from features with matching ID  together into
> a single output geometry. I'd like to remove this option and make the
> "Singlepart to Multipart" algorithm purely upgrade geometry types from
> single part to multipart, without adding any extra parts or collecting
> geometries. So basically the algorithm would upgrade single parts to
> collections containing just a single part - the equivalent of PostGIS'
> ST_Multi function.
>
> 2. Add a new algorithm "Collect parts" which does what the option in
> Singlepart to Multipart used to do. This would collect all features
> with matching fields (you could select more than one field - unlike
> the current Singlepart to Multipart option) and output collection
> features containing these geometries. Just like dissolve, but without
> the dissolving of overlapping parts.
>

This proposal is now implemented in https://github.com/qgis/QGIS/pull/5129

Nyall