Exposing Processing algorithms with py-qgis-wps and docker-compose

[maborroto]

Hello,
I'm trying to expose the processing algorithms with py-qgis-wps to be used with Lizmap. I'm using the docker-compose variant because it is easy to install and use. Everything went well until I decided to expose the "native" algorithms.
In the docker-compose.yml file, I set the provider property in this way:
QGSWPS_PROCESSING_EXPOSED_PROVIDERS: native,qgis

When executing docker compose up I'm getting the error reported below:

This error occurs just when using the "native" provider; if I use just the qgis (QGSWPS_PROCESSING_EXPOSED_PROVIDERS: qgis) provider, everything works well but I can't see the "native" algorithms, e.g. native:buffer

PD: I'm using the docker image: 3liz/qgis-wps:3.30, but I also used 3liz/qgis-wps:release-rc and 3liz/qgis-wps:ltr-rc, but i got the same error.

Can you give me some hints on how to solve this problem?

Thanks!!

[dmarteau]

The answer is simple: you cannot expose the native provider .

Neither you should expose the qgis provider: theses algorithms have never been designed to work with WPS marshalling (remember that the input/output parameter's set in Qgis processing is much larger that what's possible to expose in WPS).

But you may wrap call to native/qgis algorithm into your own algorithm to fit specialized needs, which is more suited to be used as WPS service.

[maborroto]

I got it, thank you a lot. I have written a custom algorithm wrapping the native:buffer, and it works perfectly.

[dmarteau]

👍

[cBevilaqua]

I got it, thank you a lot. I have written a custom algorithm wrapping the native:buffer, and it works perfectly.

@maborroto , can you please send me the wrapper you made with the buffer algorithm? I need to do the same but have no idea how to do it. Thanks.

[Gustry]

If I were you, I would go for a processing model, easier as it seems you are not familiar with PyQGIS (which is what the wrapper is about)

• https://docs.qgis.org/latest/en/docs/user_manual/processing/scripts.html
• https://docs.qgis.org/latest/en/docs/pyqgis_developer_cookbook/processing.html

@cBevilaqua In your processing toolbox, you have a Python button at the top, "Create script from template" which is doing the wrapper more or less with the example provided.

[cBevilaqua]

If I were you, I would go for a processing model, easier as it seems you are not familiar with PyQGIS (which is what the wrapper is about)

• https://docs.qgis.org/latest/en/docs/user_manual/processing/scripts.html
• https://docs.qgis.org/latest/en/docs/pyqgis_developer_cookbook/processing.html

@cBevilaqua In your processing toolbox, you have a Python button at the top, "Create script from template" which is doing the wrapper more or less with the example provided.

Thanks!

I made a small example here: https://github.com/cBevilaqua/qgis-sample-processing, following the example here (https://docs.qgis.org/3.28/en/docs/user_manual/processing/scripts.html) and got it working.
Thanks!