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Metadata that apply to images |
FITS Images
The keywords listed below are required, recommended, or suggested for all FITS files that contain images. In simple FITS files, all keywords must appear in the primary (P) header, but for images inIMAGE extensions these keywords should appear in the relevant extension (E) header. (Note: WCS related keywords must only appear in the extension for which they apply.) Recommended keywords, if absent, will be computed and inserted prior to ingest; suggested keywords would be beneficial to archival users if present.
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Headers must also include the basic structural FITS keywords and the list of common keywords.
| Keyword | HDU | Notes | |
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APERTURE | P or E | Name of aperture used for exposure (if any) | |
BUNIT | P or E | Brightness unit for array values | |
CDi_j | P or E | Transformation matrix between pixel axis j and intermediate coordinate axis | |
CDELTi | P or E | Increment of the world coordinate at the reference point for axis i, in units of deg/pixel. Used in conjunction with PC notation for transformation matrix; ignored for CD notation. | |
CRPIXj | P or E | Location of the reference point in the image for axisj, in array pixel units. | |
CRVALi | P or E | World coordinate value at the reference location for axisi | |
CTYPEi | P or E | World coordinate type for axis i | |
CUNITi | P or E | Physical units of CRVAL for axis i. Note: units for celestial coordinate systems must be degrees. | |
DETECTOR | P or E | ID of detector used for exposure | |
FILTER | P or E | Name of filter used, or 'MULTI' if more than one defined the passband | |
FILTERnn | P or E | Name(s) of filter(s) used to define the passband, if more than one was used, with nn incrementing from 1 (and zero-pad if nn >9) | |
PCi_j | P or E | Alternative to CD notation for transforming pixel axis j to intermediate coordinate axisi. Must be used with CDELTiand must not be used with CDi_j. | |
DEC_TARG | P or E | Declination coordinate of the target or field, in degrees | |
PSFSIZE | P or E | Typical spatial extent of the point-spread function, in pix | |
RADESYS | P or E | Mnemonic for celestial coordinate reference system (typically 'FK5' or the preferred 'ICRS') | |
RA_TARG | P or E | Right Ascension coordinate of the target or field, in degrees | |
WCSAXES | P or E | Number of axes in WCS description, which may exceed the number of pixel array axes |