Supported projections#

As astropy.wcs is based on wcslib, it supports the standard projections defined in the FITS WCS standard. These projection codes are three letter strings specified in the second part of the CTYPEn keywords (accessible through Wcsprm.ctype). For example, a tangent projection with RA, DEC coordinates is defined by CTYPE1 = RA---TAN and CTYPE2 = DEC--TAN. If a SIP distortion is present the keywords become CTYPE1 = RA---TAN-SIP and CTYPE2 = DEC--TAN-SIP.

The supported projection codes are:

  • AZP: zenithal/azimuthal perspective

  • SZP: slant zenithal perspective

  • TAN: gnomonic

  • STG: stereographic

  • SIN: orthographic/synthesis

  • ARC: zenithal/azimuthal equidistant

  • ZPN: zenithal/azimuthal polynomial

  • ZEA: zenithal/azimuthal equal area

  • AIR: Airy’s projection

  • CYP: cylindrical perspective

  • CEA: cylindrical equal area

  • CAR: plate carrée

  • MER: Mercator’s projection

  • COP: conic perspective

  • COE: conic equal area

  • COD: conic equidistant

  • COO: conic orthomorphic

  • SFL: Sanson-Flamsteed (“global sinusoid”)

  • PAR: parabolic

  • MOL: Mollweide’s projection

  • AIT: Hammer-Aitoff

  • BON: Bonne’s projection

  • PCO: polyconic

  • TSC: tangential spherical cube

  • CSC: COBE quadrilateralized spherical cube

  • QSC: quadrilateralized spherical cube

  • HPX: HEALPix

  • XPH: HEALPix polar, aka “butterfly”

And, if built with wcslib 5.0 or later, the following polynomial distortions are supported:

  • TPV: Polynomial distortion

  • TUV: Polynomial distortion


Though wcslib 5.4 and later handles SIP polynomial distortion, for backward compatibility, SIP is handled by astropy itself and methods exist to handle it specially.