Purpose

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  This function creates a blank image and fits header, based on input
  parameters describing the desired image size and orientation.

Keyword Parameters

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  center: A 2 element array specifying the sky location of the center
          pixel. The coordinate system can be specified with
          COORDSYS. This keyword is required.
  width: The width of the image in DEGREES. A one or two element
        vector. If width is not specified, both pixwidth and
        pixscale must be.
  pixwidth: The width of the image in PIXELS. A one or two element
            vector. If pixwidth is not specified, both width and
            pixscale must be.
  pixscale: The size of an individual pixel in DEGREES. A one or two
            element vector. If not specified, both width and pixwidth
            must be.
  coordsys: An optional string indicating which coordinate system to
            use. Options are FK5 and GAL. Default is FK5
  type: The data type to use for the image. Default is 'FLOAT'.
  extra: Any other keywords will be added to the header with the
        appropriate names.

Output

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  A structure with two fields. result.map is the blank array, and
  result.head is the header

Modification History

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  March 2010: Written by Chris Beaumont
  December 2010: Fixed a big when checking type of coordsys