[QGIS-Developer] QGIS standalone script examples

[Richard Duivenvoorde]

Hi Paul,

Can you come up with a little info about your actual use-case? Because maybe people then have some alternative ideas. QGIS-Application/Canvas off course does a lot of extra stuff when you load data (like for example using some default crs or styling etc etc...) not sure if you would want to redo that all in your scripts (IF it would be doable at all).

But maybe we could come up with another solution? (like maybe create 'qlr(?)' QGIS Layer files, or projects which point to other (small) projects (a project can be part of another project).
Or maybe you could re-use some excisting project by using some naming scheme in your data or so?

Regards,

Richard Duivenvoorde

On 5/23/21 12:59 PM, Paul Wittle wrote:
> Hi folks,
> 
>  
> 
> I’m trying to do a simple script to open an existing project, add a layer and then save the result but finding it hard to piece together the information I can find online.
> 
>  
> 
> I’ve found various posts suggesting that you need to connect up the canvas or all the GUI information gets lost when you do a project.write() command but for some reason I can only find answers that contain snippets which usually seem to reference iface or canvas without showing how to initiate those in a standalone way.
> 
>  
> 
> Particularly, if you look at https://docs.qgis.org/3.16/en/docs/pyqgis_developer_cookbook/loadproject.html <https://docs.qgis.org/3.16/en/docs/pyqgis_developer_cookbook/loadproject.html> you have a note about needing to set a bridge but that references canvas which if you copy/paste as per the details in that section alone will of course result in a ‘canvas undefined’ error.
> 
>  
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> Is there a simple full example anywhere that shows how you can open a project file using a standalone python script, add one layer and save it without losing half the information in the project file?
> 
>  
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> My best effort so far added the layer but resulted in existing layers being invalid when I opened the project in QGIS and my “improved” version…at the moment…seems to be almost halving the size of the project so I assume it is still deleting all the canvas information. Any hints would be appreciated 😊
> 
>  
> 
> Thanks
> 
> Paul
> 
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