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- World Coordinate System (`astropy.wcs`) »
- Reference/API

# Reference/API

## astropy.wcs Package

`astropy.wcs` contains utilities for managing World Coordinate System (WCS) transformations in FITS files. These transformations map the pixel locations in an image to their real-world units, such as their position on the sky sphere.

It performs three separate classes of WCS transformations:

- Core WCS, as defined in the FITS WCS standard, based on Mark Calabretta’s wcslib. See `Wcsprm`.

- Simple Imaging Polynomial (SIP) convention. See `Sip`.

- table lookup distortions as defined in WCS distortion paper. See `DistortionLookupTable`.

Each of these transformations can be used independently or together in a standard pipeline.

### Functions

`find_all_wcs`(header[, relax, keysel, fix, ...]) | Find all the WCS transformations in the given header.
`get_include`() | Get the path to astropy.wcs's C header files.
`validate`(source) | Prints a WCS validation report for the given FITS file.

### Classes

`Auxprm`() | Class that contains auxiliary coordinate system information of a specialist nature.
`Celprm` | Class that contains information required to transform celestial coordinates.
`DistortionLookupTable`(*table*, *crpix*, ...) | Represents a single lookup table for a distortion paper transformation.
`FITSFixedWarning` | The warning raised when the contents of the FITS header have been modified to be standards compliant.
`InconsistentAxisTypesError`() | The WCS header inconsistent or unrecognized coordinate axis type(s).
`InvalidCoordinateError`() | One or more of the world coordinates is invalid.
`InvalidPrjParametersError`() | The given projection parameters are invalid.
`InvalidSubimageSpecificationError`() | The subimage specification is invalid.
`InvalidTabularParametersError`() | The given tabular parameters are invalid.
`InvalidTransformError`() | The WCS transformation is invalid, or the transformation parameters are invalid.
`NoConvergence`(*args[, best_solution, ...]) | An error class used to report non-convergence and/or divergence of numerical methods.
`NoSolutionError`() | No solution can be found in the given interval.
`NoWcsKeywordsFoundError`() | No WCS keywords were found in the given header.
`NonseparableSubimageCoordinateSystemError`() | Non-separable subimage coordinate system.
`Prjprm` | Class that contains information needed to project or deproject native spherical coordinates.
`SingularMatrixError`() | The linear transformation matrix is singular.
`Sip`(*a, b, ap, bp, crpix*) | The `Sip` class performs polynomial distortion correction using the SIP convention in both directions.
`Tabprm`() | A class to store the information related to tabular coordinates, i.e., coordinates that are defined via a lookup table.
`WCS`([header, fobj, key, minerr, relax, ...]) | WCS objects perform standard WCS transformations, and correct for SIP and distortion paper table-lookup transformations, based on the WCS keywords and supplementary data read from a FITS file.
`WCSBase`(*sip, cpdis, wcsprm, det2im*) | Wcs objects amalgamate basic WCS (as provided by wcslib), with SIP and distortion paper operations.
`WcsError` | Base class of all invalid WCS errors.
`Wcsprm`([header, key, relax, naxis, keysel, ...]) | `Wcsprm` performs the core WCS transformations.
`Wtbarr`() | Classes to construct coordinate lookup tables from a binary table extension (BINTABLE).

### Class Inheritance Diagram

## astropy.wcs.utils Module

### Functions

`obsgeo_to_frame`(obsgeo, obstime) | Convert a WCS obsgeo property into an ITRS coordinate frame.
`add_stokes_axis_to_wcs`(wcs, add_before_ind) | Add a new Stokes axis that is uncorrelated with any other axes.
`celestial_frame_to_wcs`(frame[, projection]) | For a given coordinate frame, return the corresponding WCS object.
`wcs_to_celestial_frame`(wcs) | For a given WCS, return the coordinate frame that matches the celestial component of the WCS.
`proj_plane_pixel_scales`(wcs) | For a WCS returns pixel scales along each axis of the image pixel at the `CRPIX` location once it is projected onto the "plane of intermediate world coordinates" as defined in Greisen & Calabretta 2002, A&A, 395, 1061.
`proj_plane_pixel_area`(wcs) | For a celestial WCS (see `astropy.wcs.WCS.celestial`) returns pixel area of the image pixel at the `CRPIX` location once it is projected onto the "plane of intermediate world coordinates" as defined in Greisen & Calabretta 2002, A&A, 395, 1061.
`is_proj_plane_distorted`(wcs[, maxerr]) | For a WCS returns `False` if square image (detector) pixels stay square when projected onto the "plane of intermediate world coordinates" as defined in Greisen & Calabretta 2002, A&A, 395, 1061.
`non_celestial_pixel_scales`(inwcs) | Calculate the pixel scale along each axis of a non-celestial WCS, for example one with mixed spectral and spatial axes.
`skycoord_to_pixel`(coords, wcs[, origin, mode]) | Convert a set of SkyCoord coordinates into pixels.
`pixel_to_skycoord`(xp, yp, wcs[, origin, ...]) | Convert a set of pixel coordinates into a `SkyCoord` coordinate.
`pixel_to_pixel`(wcs_in, wcs_out, *inputs) | Transform pixel coordinates in a dataset with a WCS to pixel coordinates in another dataset with a different WCS.
`local_partial_pixel_derivatives`(wcs, *pixel) | Return a matrix of shape `(world_n_dim, pixel_n_dim)` where each entry `[i, j]` is the partial derivative d(world_i)/d(pixel_j) at the requested pixel position.
`fit_wcs_from_points`(xy, world_coords[, ...]) | Given two matching sets of coordinates on detector and sky, compute the WCS.

### Classes

`custom_wcs_to_frame_mappings`([mappings]) |
`custom_frame_to_wcs_mappings`([mappings]) |

### Class Inheritance Diagram

## astropy.wcs.wcsapi Package

### Functions

`deserialize_class`(tpl[, construct]) | Deserialize classes recursively.
`sanitize_slices`(slices, ndim) | Given a slice as input sanitise it to an easier to parse format.format
`validate_physical_types`(physical_types) | Validate a list of physical types against the UCD1+ standard
`wcs_info_str`(wcs) |

### Classes

`BaseHighLevelWCS`() | Abstract base class for the high-level WCS interface.
`BaseLowLevelWCS`() | Abstract base class for the low-level WCS interface.
`BaseWCSWrapper`(wcs, *args, **kwargs) | A base wrapper class for things that modify Low Level WCSes.
`HighLevelWCSMixin`() | Mix-in class that automatically provides the high-level WCS API for the low-level WCS object given by the `low_level_wcs` property.
`HighLevelWCSWrapper`(low_level_wcs) | Wrapper class that can take any `BaseLowLevelWCS` object and expose the high-level WCS API.
`SlicedLowLevelWCS`(wcs, slices) | A Low Level WCS wrapper which applies an array slice to a WCS.

### Class Inheritance Diagram