According to the GADF definition (https://gamma-astro-data-formats.readthedocs.io/en/latest/general/coordinates.html#coords-fov), "FOV LON should increase with decreasing OTHER LON". As this is the coordinate system in which a background model has to be stored, it is mandatory to switch the sign of longitude angle when creating a background model.
In Gammapy, this is not solved consistent up to now (see: gammapy/gammapy#3510) for ALTAZ and RADEC alignment of the FoV coordinates. If it will be changed in Gammapy, it will also have to be changed in the creation of the background files.
According to the GADF definition (https://gamma-astro-data-formats.readthedocs.io/en/latest/general/coordinates.html#coords-fov), "FOV LON should increase with decreasing OTHER LON". As this is the coordinate system in which a background model has to be stored, it is mandatory to switch the sign of longitude angle when creating a background model.
In Gammapy, this is not solved consistent up to now (see: gammapy/gammapy#3510) for ALTAZ and RADEC alignment of the FoV coordinates. If it will be changed in Gammapy, it will also have to be changed in the creation of the background files.