Use the selected CRS as subsetting CRS

[jampukka]

Here's one solution to #8.
This is based on the assumption that the user would always select a CRS in the dialog that is equal to the current canvas CRS. This might not be the case.

[marcusmohr]

Unfortunately this solution leads to another problem. The crs of the SUBSET coordinates in the query (which are taken from the map canvas) will no longer match SUBSETTINGCRS. The user would have always to choose a crs that matches the one of the map canvas. Otherwise an error will occur ("Image extent does not intersect with desired region."). To prevent this you'll have to transform the coordinates if SUBSETTINGSCRS doesn't match the destination CRS (map canvas).

[jampukka]

Sorry for the inactivity. Your assessment is correct. Proper solution would be to find a crs string from wcs.getCRS() that matches the crs authid of the map canvas. For this I need to find or develop a function that can recognize and convert URL crs string to short authid format (e.g. http://www.opengis.net/def/crs/EPSG/0/3067 to EPSG:3067)

[kannes]

QGIS 3.30 added QgsCoordinateReferenceSystem.toOgcUri():

>>> crs = QgsProject.instance().crs()
>>> crs.toOgcUri()
'http://www.opengis.net/def/crs/EPSG/0/4326'

[kannes]

FYI I am working on this at the moment and will hopefully be able to present a nice solution soon-ish.

[kannes]

Oh dear, this is overly complicated...

Services might support more CRS for subsetting if they support the CRS extension I guess. But then you need to find out the axis labels for making subset requests somehow and that is so complicated it drained any motivation from me. For the native CRS of a coverage those labels are included in the DescribeCoverage response but it seems virtually impossible to get those of other CRS from the server without making three million requests including third-party servers.

https://gis.stackexchange.com/questions/377221/where-do-i-find-crs-axis-names

https://gis.stackexchange.com/questions/461135/axes-labels-names-of-qgscoordinatereferencesystem

It would be possible to query QGIS' Proj's proj.db SQLite to get the names but that feels super icky (and hey, the server might have a different DB...) so I stopped there.

I rewrote the getCovQueryStr method to still use map canvas CRS but with correct handling of CRS URIs, axes, transformations etc to match the native CRS of the coverage. Because I also changed many other things I'll see if @marcusmohr is fine with all of them instead of investing too much time in a clean PR.

[kannes]

It looks like it is fairly straightforward if we are ok with a subprocess run of projinfo. It can parse OGC URI strings and output nice PROJJSON which makes it easy to get the axis abbreviations. I'll see if I can get the time for writing something with that approach. Ref: https://gis.stackexchange.com/questions/461135/axes-labels-names-of-qgscoordinatereferencesystem/461311#461311

[kannes]

FYI I am still sitting on half-finished work for this, should receive funding to continue working on it and finally contribute it to the project in Q1/2024. I hope!