How to check if QGIS is using RPC or not or on my image?

Question

I have an image with RPC file near it, but there is also geo-referencing information within the image itself.

How do I check if the image is georeferenced using the RPC file or not?

Answer 1

I don't believe you can check that directly with QGIS. One option is to read the documentation https://gdal.org/drivers/raster/gtiff.html and trust that the .RPB file is used

GDAL can read and write the RPCCoefficientTag as described in the RPCs in GeoTIFF proposed extension. The tag is written only for files created with the default profile GDALGeoTIFF. For other profiles, a .RPB file is created. In GDAL data model, the RPC coefficients are stored into the RPC metadata domain. For more details, see the RFC 22: RPC Georeferencing. If .RPB or _RPC.TXT files are found, they will be used to read the RPCs, even if the RPCCoefficientTag tag is set.

Or then you can use gdalinfo. It is listing the files that it read, and the RPC metadata. If there is a mismatch with the internal and external metadata then you should see different RPC metadata if you delete or rename the .RPB file.

gdalinfo md_dg.tif
Driver: GTiff/GeoTIFF
Files: md_dg.tif
       md_dg.RPB
...
RPC Metadata:
  ERR_BIAS=1.49
  ERR_RAND=0.58
  HEIGHT_OFF=95
  HEIGHT_SCALE=501
  LAT_OFF=41.8791
  LAT_SCALE=0.0150
  LINE_DEN_COEFF=+1.000000E+00 +4.696998E-05 -3.057960E-03 -8.778793E-05 -3.454986E-07 +1.971646E-08 +1.083809E-06 -1.723920E-06 +9.397055E-06 +1.371016E-06 +1.647007E-08 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 -3.685579E-08 +0.000000E+00 -2.476523E-07 +0.000000E+00
  LINE_NUM_COEFF=-6.181087E-03 +3.510113E-02 -1.109763E+00 -8.245546E-02 -1.574358E-04 -1.151270E-05 +3.785618E-04 -1.617343E-04 +3.392421E-03 +1.557476E-05 +2.094558E-07 -6.314112E-08 +7.033553E-07 +5.121700E-08 +2.389848E-06 -1.042301E-05 -1.402098E-06 +6.953425E-08 -5.038526E-07 -9.876127E-08
  LINE_OFF=812
  LINE_SCALE=938
  LONG_OFF=12.5798
  LONG_SCALE=0.0225
  SAMP_DEN_COEFF=+1.000000E+00 +9.641438E-04 +1.340215E-04 -4.371442E-04 +4.849114E-08 +0.000000E+00 -6.403717E-08 +9.014668E-07 +0.000000E+00 -2.387648E-07 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00 +0.000000E+00
  SAMP_NUM_COEFF=-1.941040E-03 +1.012973E+00 +2.549412E-02 +3.146281E-02 -7.701827E-05 +4.973536E-04 -2.130061E-04 +9.757313E-04 +7.164101E-06 -5.137094E-06 -3.021765E-07 +9.135275E-07 -5.816734E-08 +1.078116E-07 -1.534883E-07 +0.000000E+00 -1.318700E-07 +9.196606E-07 -3.705506E-07 +0.000000E+00
  SAMP_OFF=850
  SAMP_SCALE=1152