this helped as a user of QGIS Bialowieza LTR.

This helped me as the computed area using $area in Field Calculator was overestimated by about seven hectares compared to GroupStats result.

Thanks @NoelGorelick, I think this the reproject is just applicable for a single image? I'll edit my response.

I use Linux. Yes I'll try doing it manually.

Hello, I did your suggestion. I'm thinking, is it possible that I have problems with numpy? Installed it recently and nothing happens.

Hello, I'm having these errors: 0 .. evaluation of calculation A*logical_or(A<=85, B=2001) failed Traceback (most recent call last): File "/usr/bin/gdal_calc.py", line 401, in <module> main() File "/usr/bin/gdal_calc.py", line 394, in main doit(opts, args) File "/usr/bin/gdal_calc.py", line 288, in doit myResult = eval(opts.calc, global_namespace, local_namespace) File "<string>", line 1, in <module> ValueError: invalid number of arguments