[QGIS-Developer] FME to QGIS functionality mapping

[Andreas Neumann]

Hi Nyall,

Thank you for sharing this interesting document.

I have questions and remarks:

1. One fundamental difference between FME and QGIS modeler, as far as I 
understand it, is the fact that FME data sources are much more tightly 
coupled with the model than in QGIS modeler. This has the advantage, 
that the data readers, transformers and writers always know what 
geometry types and attributes they have. The disadvantage is that it is 
harder to exchange data sources with sources that have other attributes. 
In my experience the FME approach is what most users prefer. They like 
the fact that they can always see at each transformer what attributes 
are available at this stage. Would you see an improvement - perhaps 
another modeler mode - where also QGIS modeler would be more tightly 
coupled with the data sources and that the model and algorithms would 
always know at any step what attributes are available at this stage? Or 
is this a fundamental difference between the two approaches that 
couldn't be bridged?

2. One aspect where FME shines is the ability to graphically debug 
models. One can at every step in the model get the view (map and table) 
of the intermediate step. One can also see at each branch in the model 
how many features take this route and how many the other route. I know 
this doesn't have anything to do with the transformer list you shared, 
but this an aspect that I think, many users like about FME.

I agree that there would a lot of "low hanging" fruits and I'm looking 
forward to more feature parity between the two. And to the discussion 
around it.

Greetings,

Andreas

Am 07.04.20 um 03:27 schrieb Nyall Dawson:
> Hi list,
>
> Just wanted to give a heads up on a document I've recently completed,
> which maps existing FME functionality across to the equivalent QGIS
> Processing or Expression equivalent:
>
> https://github.com/nyalldawson/qgis-processing-hitlist/blob/master/fme.md
>
> Since FME transformers are both algorithm-like and expression-like
> functionality, the document splits the QGIS equivalents into columns
> for both algorithms and expressions. Wherever the transformer
> functionality doesn't apply, a "N/A" is entered in the corresponding
> column (e.g. the "StringCaseChanger" transformer doesn't make sense
> the implement as a QGIS Processing algorithm -- it's equivalent is
> instead the expression functions "lower", "upper" and "title". And
> conversely the "DuplicateFilter" transformer maps to the Processing
> algorithms "Delete Duplicate Geometries" and "Delete duplicates by
> attribute", but doesn't make sense to have an expression function
> equivalent!)
>
> There's also Transformers in FME which really don't need an equivalent
> in QGIS -- e.g. those relating to styling features.
>
> Overall we have a good level of coverage of the most important
> functionality. There's a LOT of low-hanging fruit which could easily
> be addressed in small PRs (e.g. things like the
> "CharacterCodeExtractor" transformer would be a trivial task to
> implement as a new QGIS expression function ... a GREAT task for
> someone getting started with QGIS development!).
>
> (and just for completeness - QGIS offers hundreds of processing
> algorithms and expression functionality which **doesn't** have
> equivalents in FME. I suspect the reverse document would have just as
> many "missing" cells!)
>
> Feedback welcome! At some stage I think it would be nice to move this
> document across to the QGIS repo, and possibly pull into the QGIS
> documentation itself (along with similar documents for Arc/...
> functionality!)
>
> Nyall
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