# 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

Note

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.