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  This function warps a map projected image from one map projection to another, using
  Map_Proj_Image to do the warping. Useful in general, it is used specifically to
  warp map projected images into the Equirectangular map projection with a WGS 84 ellipsoid
  that is used by Google Earth. See the program `cgImage2KML` to see how it is used.


    Map Projections, Utilities


    An image warped into the output map projection is returned.


    image: in, required
      Any 2D or true-color image with or without an alpha channel. This image will
      be warped to the output map projection (`mapOut`).
    mapin: in, required, type=object
      A map coordinate object (cgMap) describing the map projection and coordinates of the
      input image that is to be warped.


    boundary: in, optional, type=dblarr
      A four-element array specifying the Cartesian (XY) coordinates of the input
      image range, in the form [xmin, ymin, xmax, ymax]. If this parameter is not
      present, the boundary will be obtained from the `MapIn` map coordinate object.
      On output, this variable will contain the Cartesian boundary of the warped image.
    bilinear: in, optional, type=boolean, default=0
      Set this keyword to warp the image with bilinear interpolation. The default is
      to do nearest neighbor interpolation.
    latlonbox: out, optional, type=fltarr
      A four-element float array containing the boundaries of the warped image in
      the [north, south, east, west] form preferred by Google Earth. Listed as degrees.
    mapout: in, optional, type=object
      A map coordinate object (cgMap) describing the map projection and coordinates of the
      warped image. This image will be warped into this map projection. The [XY]Range of
      this object will be set to the `XYRange` of the output image.
    mask: out, optional
      Set this keyword equal to a named variable that will contain a byte array of the same
      dimensions as the output image, containing a mask of the “good” values. Values in the output
      image that were set to `Missing` (that is, the values were off the map) will have a mask value
      of 0, while all other mask values will be 1.
    missing: in, optional, type=integer, default=0
      Set this keyword equal to an integer value to be used for pixels that fall outside of
      the valid map coordinates. The default value is 0.
    xyrange: out, optional, type=dblarr
      The Cartesian (XY) coordinates associated with the output image. These are the map image
      boundaries of the output image.


    To prepare a GeoTiff file for creating a KML overlay on Google Earth::
      netObject = Obj_New('IDLnetURL')
      url = 'http://www.idlcoyote.com/data/AF03sep15b.n16-VIg.tif'
      returnName = netObject -> Get(URL=url, FILENAME=AF03sep15b.n16-VIg.tif')
      Obj_Destroy, netObject
      map = cgGeoMap('AF03sep15b.n16-VIg.tif')
      googleMap = Obj_New('cgMap', 'Equirectangular', Ellipsoid='WGS 84')
      warpedImage = cgChangeMapProjection(image, map, MAPOUT=googleMap)


      David W. Fanning
      1645 Sheely Drive
      Fort Collins, CO 80526 USA
      Phone: 970-221-0438
      E-mail: david@idlcoyote.com
      Coyote's Guide to IDL Programming: http://www.idlcoyote.com


    Change History::
        Written, 30 October 2012 by David W. Fanning.
        Fixed a problem with a TRANSPOSE command for true-color images. Bad logic. 4 Jan 2012. DWF.
        Fixed a problem in which Map_Proj_Image was not handling true-color image warping correctly
          and also a problem with handling missing values passed from cgImage2KML correctly. 20 Feb 2013. DWF.
        Forgot to specify the default value for MISSING. 25 Feb 2014. DWF.


    Copyright (c) 2012, Fanning Software Consulting, Inc.

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