fredvanner
Well-known member
... missing from my workflow above. Before saving as FITS, delete the PV1_1 and PV1_2 keywords. I suspect (but I am open to correction) that the value of PV1_2 is wrong. Most applications will assume the default values for the selected projection type if these keywords are missing.
These keywords are defined in Representations of celestial coordinates in FITS, where it is noted that:
These keywords are defined in Representations of celestial coordinates in FITS, where it is noted that:
"zenithal projections all have (phi_0; theta_0) = (0; 90)"
Since the default TAN (gnomonic) projection is of zenithal type, I would expect PV1_2 = 90.