[QGIS-Developer] R: GSoC 2021 QGIS On-the-fly Raster Calculator proposal draft review and feedback

[Francesco Bursi]

Hi Alister,

Thank you for the feedback.
Well, I imagine the new feature with some properties of the existing Raster Calculator but not exactly the same, e.g It won't be possible to set layer extent / output CRS, because this would be already pre-defined by the layer on which the renderer is applied, in the basic mockup you should not see these 2 field. The same can be said for choosing other layer. It should work like contours/hillshade renderer, where you can style only the layer you have currently selected but you can choose the band.
Besides, I think that the existing Raster Calculator in the processing toolbox (as well as the Gdal Raster Calculator) allows the creation of a temporary file, enable the addition of a layer to the project that you can style, but maybe here I misunderstood what you meant.
One of the advantage of the on-the-fly (styling) is to  avoid the need to create derived raster files and layers.

Let me know if I misunderstood something and thank you for the message.

Kind Regards,

Francesco Bursi

________________________________
Da: QGIS-Developer <qgis-developer-bounces at lists.osgeo.org> per conto di Alister Hood <alister.hood at gmail.com>
Inviato: martedì 13 aprile 2021 14:10
A: qgis-developer at lists.osgeo.org <qgis-developer at lists.osgeo.org>
Oggetto: Re: [QGIS-Developer] GSoC 2021 QGIS On-the-fly Raster Calculator proposal draft review and feedback

Hi,
This functionality would be great, but as a user, I can't help thinking the proposal is to implement it in the wrong way.

If implemented as a renderer, as described, you could conceivably use an expression that uses other layers but not the layer you are supposedly rendering.  What is displayed would not correspond in any way to the actual layer... Bizarre.

Would it not be possible to instead implement a "virtual raster" *provider*?  Add a checkbox in the raster calculator labelled "create as virtual raster".  Create a new layer that can be styled using the existing renderers and behaves in every way like a non-virtual layer - e.g. the right values would be shown using the identify tool and the "value tool" plugin, and you could use the layer as an input for other processing tools.

Regards, and best wishes with the proposal,
Alister

Date: Mon, 12 Apr 2021 12:20:53 +0000
From: Francesco Bursi <francesco.bursi at hotmail.it<mailto:francesco.bursi at hotmail.it>>
To: qgis-developer <qgis-developer at lists.osgeo.org<mailto:qgis-developer at lists.osgeo.org>>
Subject: [QGIS-Developer] GSoC 2021 QGIS On-the-fly Raster Calculator
        proposal draft review and feedback
Message-ID:
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Hello QGIS Dev,


I?m Francesco Bursi, an M.Sc. civil engineer from Italy currently enrolled in a Master of Advanced Studies (Level 8 EQF) in giscience and geoinformatics at the University of Padua.

I?m really interested in the QGIS (possible) new rendering feature that involves raster calculator capabilities, I've already discussed the project with mentors Martin Tobias and Peter Petrik and possible co-mentor Roberto Marzocchi,  they gave me a lot of feedback and advice for the project.
I would like to share my proposal with you before the final submission. Don't hesitate to give me feedback and ask me question/clarification or point me out what's missing.


proposal 2021<https://docs.google.com/document/d/1u8L_L1IJjGCZ3d8Vq8duxHbsHZeyzwqOe3tXa1JcKbs/edit?usp=sharing>


I'm open to advice, remarks and criticism in order to improve.

I am looking forward to a feedback, thank you for your time.


Best regards,

Francesco Bursi
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