Hi Alister, Thanks for the response, and the link back into the history of the issue.
> I'm not even sure if a fix would involve work on QGIS itself, or gdal, or > perhaps both. I'd be a little surprised if it were GDAL doing something unexpected - one would have to jump through a couple of extra hoops to get GDAL to resample the raw, rotated data to north-aligned. However, I can't say I've ever looked into any of the details of how QGIS uses it to read rasters, and whether it's a simple read or a far more complex pipeline (perhaps this will be a prompt to, although illiteracy in C++ is a minor hurdle!). Cheers, Daniel On Sat, 11 Mar 2023 at 07:30, Alister Hood via QGIS-User <qgis-user@lists.osgeo.org> wrote: >> >> Date: Fri, 10 Mar 2023 13:52:42 +0000 >> From: Daniel Evans <daniel.fred.ev...@gmail.com> >> To: qgis-user@lists.osgeo.org >> Subject: [Qgis-user] Display of non-axis-aligned pixels >> Message-ID: >> <cannaqay0-e_hio8dww88zo-ahi4gsjsmterlbe0dth_xqps...@mail.gmail.com> >> Content-Type: text/plain; charset="UTF-8" >> >> Hello, >> >> I have some raster data where the pixels are not >> coordinate-system-aligned - i.e. the geotransform has significant >> diagonal components. `gdalinfo` reports: >> >> GeoTransform = >> 444048.6420808117, 6.302162394202463, 6.152691784443768 >> 5417729.777950762, 4.143808265940849, -3.26376570161891 >> >> When viewing the raster in QGIS, I am surprised to find that it >> displays the pixels as north-aligned. An example is here: >> https://i.imgur.com/i6y1gtM.png >> >> If I make nodata visible, it seems that QGIS is displaying an >> axis-aligned image corresponding to the bounding box of my original >> image (data in white, nodata in black). Screenshot here: >> https://i.imgur.com/ZQJ6Mi5.png >> >> This behaviour surprised me, as QGIS is capable of showing pixels at a >> slant in some circumstances. For example, if I set QGIS to render >> using a different UTM zone, the pixels are slanted - although in this >> case, it's applying a second rotation on top of the north-aligning >> rotation it's already applying: https://i.imgur.com/LoC7jyk.png >> >> 1. Is it possible to have QGIS display a raster without resampling the >> pixels to axis-aligned? > > > I don't believe so. > >> >> 2. Is there a reason for making this the default (or only) behaviour? >> It caused quite some confusion when trying to diagnose a >> geotransform-related issue elsewhere. > > > Several bug reports have been filed about this over the years, (e.g. > https://github.com/qgis/QGIS/issues/23760, which should really be reopened, > unless someone files a new ticket instead), and no one has ever tried to say > it "should" be this way. I'm no expert, but I presume the problem is simply > that no one has been both motivated and able to do the work to fix it, or to > fund someone to do it. > I'm not even sure if a fix would involve work on QGIS itself, or gdal, or > perhaps both. > > Regards, > Alister > _______________________________________________ > QGIS-User mailing list > QGIS-User@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user _______________________________________________ QGIS-User mailing list QGIS-User@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user