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astropy.wcs ⚬｜Documentation｜1st｜20251021001516-00-⌔
World Coordinate System (astropy.wcs) — Astropy v8.0.0.dev245+ge5da16967#introduction
Introduction
World Coordinate Systems (WCSs) describe the geometric transformations between one set of coordinates and another. A common application is to map the pixels in an image onto the celestial sphere. Another common application is to map pixels to wavelength in a spectrum.
astropy.wcscontains utilities for managing World Coordinate System (WCS) transformations defined in several elaborate FITS WCS standard conventions. These transformations work both forward (from pixel to world) and backward (from world to pixel).For historical reasons and to support legacy software,
astropy.wcsmaintains two separate application interfaces. TheHigh-Level APIshould be used by most applications. It abstracts out the underlying object and works transparently with other packages which support the Common Python Interface for WCS, allowing for a more flexible approach to the problem and avoiding the limitations of the FITS WCS standard.The
Low Level APIis the originalastropy.wcsAPI and originally developed aspywcs. It ties applications to theastropy.wcspackage and limits the transformations to the three distinct types supported by it:
- Core WCS, as defined in the FITS WCS standard, based on Mark Calabretta’s wcslib. (Also includes
TPVandTPDdistortion, but notSIP).- Simple Imaging Polynomial (SIP) convention. (See note about SIP in headers.)
- Table lookup distortions as defined in the FITS WCS distortion paper.
Printed 2026-06-28.
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