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# Validation and Bounds checking

## Validating the WCS keywords in a FITS file

`astropy` includes a command-line tool, `wcslint`, to check the WCS keywords in a FITS file. The example below shows it reporting back results for a problematic file named `invalid.fits`:

    > wcslint invalid.fits
    HDU 1:
      WCS key ' ':
        - RADECSYS= 'ICRS ' / Astrometric system
          RADECSYS is non-standard, use RADESYSa.
        - The WCS transformation has more axes (2) than the image it is
          associated with (0)
        - 'celfix' made the change 'PV1_5 : Unrecognized coordinate
          transformation parameter'.

    HDU 2:
      WCS key ' ':
        - The WCS transformation has more axes (3) than the image it is
          associated with (0)
        - 'celfix' made the change 'In CUNIT2 : Mismatched units type
          'length': have 'Hz', want 'm''.
        - 'unitfix' made the change 'Changed units: 'HZ      ' -> 'Hz''.

## Bounds checking

Bounds checking is enabled by default, and any computed world coordinates outside of [-180°, 180°] for longitude and [-90°, 90°] in latitude are marked as invalid. To disable this behavior, use `astropy.wcs.Wcsprm.bounds_check`.