[QGIS-Developer] Using memory layer in Processing with SAGA and GRASS

[Nyall Dawson]

On 26 April 2018 at 16:42, matteo <matteo.ghetta at gmail.com> wrote:
> Hi Nyall,
>
>> No - neither SAGA nor GRASS have any concept of QGIS memory layers.
>> You need to give them a disk-based file path to save their outputs to.
>
> ok, clear now why this was not working
>
>
>> If you use a memory layer as an input to these algs it will also have
>> to save it out to a disk based format, but this is done automatically
>> by saving to a file in the temp folder. We could potentially do the
>> same thing to allow SAGA/GRASS algs to output to a memory layer by
>> first saving the output to a shp in the temp folder, then loading that
>> file and copying the features to a memory layer. But it would be
>> rather inefficient and counter productive - you're still being forced
>> to loop over the disk-based format, so you're just adding extra
>> processing for little gain.
>
> so within a script (or a Processing plugin) both input layer and output
> one have to come from a disk saved file.

Not quite - the input layer doesn't *have* to, because processing will
automatically save it to a disk file if required.

Nyall