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 perspectiveSZP
: slant zenithal perspectiveTAN
: gnomonicSTG
: stereographicSIN
: orthographic/synthesisARC
: zenithal/azimuthal equidistantZPN
: zenithal/azimuthal polynomialZEA
: zenithal/azimuthal equal areaAIR
: Airy’s projectionCYP
: cylindrical perspectiveCEA
: cylindrical equal areaCAR
: plate carréeMER
: Mercator’s projectionCOP
: conic perspectiveCOE
: conic equal areaCOD
: conic equidistantCOO
: conic orthomorphicSFL
: Sanson-Flamsteed (“global sinusoid”)PAR
: parabolicMOL
: Mollweide’s projectionAIT
: Hammer-AitoffBON
: Bonne’s projectionPCO
: polyconicTSC
: tangential spherical cubeCSC
: COBE quadrilateralized spherical cubeQSC
: quadrilateralized spherical cubeHPX
: HEALPixXPH
: HEALPix polar, aka “butterfly”
And, if built with wcslib 5.0 or later, the following polynomial distortions are supported:
TPV
: Polynomial distortionTUV
: 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.