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-Abstract

   MTK_SETREGION_BY_LATLON_EXTENT creates a region structure that defines an approximate region of
   interest given a center latitude/longitude coordinate and a latitudinal/longitudinal full extent
   in specified units of degrees, meters, kilometers, or pixels. This structure is used as input to
   other MTK routines, Mtk_ReadData in particular.

-Copyright

   Copyright (2005), California Institute of Technology.
   U.S. Government sponsorship acknowledged.

-I/O
   
   Given:
   
      center_lat     center latitude of region
      center_lon     center longitude of region
      lat_extent     latitudinal extent (in extent_units)
      lon_extent     longitudinal extent (in extent_units)
      extent_units   units of extent

   Where:

      extent_units is a case insensitive string that defines the units of lat_extent and lon_extent.

      Acceptable values are:
        1) "degrees", "deg", "dd" for degrees;
        2) "meters", "m" for meters;
        3) "kilometers", "km" for kilometers; and
        4) "275m", "275 meters", "1.1km", "1.1 kilometers" for number of pixels of the specified resolution per pixel.

   the call:
   
      status = MTK_SETREGION_BY_LATLON_EXTENT( center_lat, center_lon, lat_extent, lon_extent, extent_units, region )
   
   returns:
   
      status         0 on success; otherwise failure
      region         MTK region structure

-Examples

      ;;
      ;; Set up input parameters
      ;;
      lat          = 66.0
      lon          = -89.0
      lat_extent   = 111000.0
      lon_extent   = 111000.0
      extent_units = 'meters'
      status       = MTK_SETREGION_BY_LATLON_EXTENT( lat, lon, lat_extent, lon_extent, extent_units, region )
      
      ;;
      ;; Output...
      ;;
      print, 'center latitude       : ', lat
      print, 'center longitude      : ', lon
      print, 'latitudinal extent    : ', lat_extent
      print, 'longitudinal extent   : ', lon_extent
      print, 'extent_units          : ', extent_units
      print, '================================================='
      FOR i=0,N_TAGS(region)-1 DO $
         PRINT, STRTRIM((TAG_NAMES(region))[i],2),': ', $
         STRTRIM(region.(i),2),FORMAT='(A-22,A2,A)'

   IDL outputs:
   
      center latitude       : 66.000
      center longitude      : -89.000
      latitudinal extent    : 111000.0
      longitudinal extent   : 111000.0
      extent_units          : meters
    =================================================
      GEO_CTR_LAT           : 66.000000
      GEO_CTR_LON           : -89.000000
      HEXTENT_XLAT          : 55500.000
      HEXTENT_YLON          : 55500.000

-Particulars
   None.

-Required Reading
   For important details concerning this module's function, please refer to
   the MTK routine MtkSetRegionByLatLonExtent.c.

-Version
   -IDL-MTK Version 1.2.0