Using QGIS 3.26.1 Buenos Aires.

I am georeferencing orthophotos produced with an RTK drone and Reality Capture software. These are typically a few centimetres out of alignment with one another. Marking four points on the orthophoto shows the expected offsets to apply:GCP table However, once this is transformed I'm getting a correct-shaped result but the scaling and the position is way off:georeference result (some of this image is cropped for confidentiality). The tiny rectangle to the top left: that's earth. The lats and longs that this is producing have nonsense values like '21375.00N, 29301.56E'.

Everything is ESPG:4326 throughout. I get the same results whether I am manually entering co-ordinates, or whether I am picking from the map, and with multiple different orthophotos shot on different days. The transformation type and resampling method doesn't seem to make a difference.

  • Are you aware of this? gis.stackexchange.com/a/383437/88814
    – Babel
    Aug 22, 2022 at 10:03
  • Thanks for that, it's useful information but I don't think it fixes the problem. The original orthos were created as EPSG:4326, the QGIS project settings are ESPG:4326, when I georeference , QGIS asks for a target CRS, which I'm making ESPG:4326. One thing that seems unusual is the display at the bottom of the georeferencer window stating that Scale is (1.29426e-07, 1.30745 e-07), though that would imply that the resultant georeferenced tiff will be hugely smaller, not hugely bigger, than the original. Aug 22, 2022 at 12:16
  • And did you check this? gis.stackexchange.com/q/392546/88814 If you change your project CRS to EPSG:3857: does the problem persist?
    – Babel
    Aug 22, 2022 at 12:26
  • It very looks like a CRS error - wrong CRS definition for the layer. Are the orthophotos somehow already georeferenced and you set layer CRS? That would be typical for "lats and longs (..) have nonsense values like '21375.00N, 29301.56E'." Can you provide more details about your input data and exact (georeference) workflow - with screenshot of georeference window? Can you share your data (at least a sample)?
    – Babel
    Aug 22, 2022 at 12:32
  • Hi Babel, thanks for those detailed responses. My understanding is that EPSG 3857 web-mercator makes things look the 'right' shape and ESPG 4326 effectively 'squashes' things, which I'm used to.. I've shifted the project onto my home computer running QGIS Tisler, and it has just performed the transformation correctly - no change away from EPSG:4326 all the way. Aug 22, 2022 at 13:05


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