WFPC2_READ

   Read WFPC2 images in either FITS or STSDAS format into IDL variables.

   This a versatile procedure for reading Wide Field Planetary Camera 2
   (WFPC2) images.   One can read either FITS or STSDAS format, and specific
   chip or chips.    One can also read all four chips into a "batwing" mosaic--
   so-called because the PC chip (chip 1) has a plate scale of 0.045", while
   the other three WF chips have a plate scale of 0.1"

    WFPC2_READ,filename,chip1,hdr1,chip2,hdr2,chip3,hdr3,chip4,hdr4
                   or
    WFPC2_READ,filename,chip,hdr, NUM_CHIP = [1,2,3,4], [/TRIM, PATH = ]
                   or
    WFPC2_READ,filename,image,hdr,/BATWING

    filename - Name of FITS or STSDAS file with a stack of images from
            the four WF/PC-2 chips, followed by a FITS ASCII
            table with header parameters for each chip.    If the file
            name extension ends in 'h' then it is assumed to be an
            STSDAS file.   If no extension is supplied, and the file is
            is not found, then WFPC2_READ first tries appending a '.fits'
            extension, and then tries appending a '.c0h' extension.
            The file may als be gzip compressed (with a .gz extension)

    NUM_CHIP - Integer scalar or vector, subset of 1, 2, 3, 4, specifying
               particular chip numbers to read.    Outputs will be in same
               order as specification of subset.   (See Example 2.)
    /TRIM   - If set, trim off areas with no image and re-orient so that
              all  the chips have a common orientation suitable for insertion
               into "bat-wing" mosaic (no image distortion removal, however).
    PATH   -   scalar string specifying a !PATH-like list of directories
               in which to search for the file.   Default is to look only
               in the current directory.
    /BATWING -  Return a 1600 x 1600 array containing all four chips in a
               "bat wing" mosaic formation.     This image is mainly for
               display  purposes, since the PC chip is compressed to match the plate
               scale of the WF chips.    In addition, a small astrometry error
               is introduced since chips do not have the same rotation, nor
               are they aligned at the integer pixel level.

    chipN    - 800 X 800 image from chip N.   If /TRIM is set then the output
               size is somewhat smaller (e.g. 756 x 757)
    headerN  - Individual FITS header for chip N with correct astrometry.

     For FITS I/O: FITS_CLOSE, FITS_OPEN, FITS_READ
     For STSDAS I/O: EXTGRP, FTGET(), SXOPEN, SXREAD()
     Other procedures:  CHECK_FITS, FDECOMP, FIND_WITH_DEF(), FREBIN, HEXTRACT,
           HROTATE, SXADDHIST, SXADDPAR, SXPAR()

    (1) Read all four chips of the FITS file u2ou0201t_c0f.fits
    IDL> wfpc2_read,'u2ou0201t_c0f',c1,h1,c2,h2,c3,h3,c4,h4
     (2) Note that supplying the .fits extension is optional.   Now read only
     chips 1 (the PC chip) and 3.   Trim off portions of the arrays where
     there is no image.
    IDL> wfpc2_read,'u2ou0201t_c0f',c1,h1,c3,h3,num=[1,3],/trim
      (3) Note that with the /TRIM option the output chip sizes are no longer
          800 x 800 but odd sizes such as 770 by 753.    Now read all 4 chips
          into a 1600 x 1600 "batwing" mosaic
    IDL> wfpc2_read,'u2ou0201t_c0f',im,h,/batwing

     Written by W. Landsman, Raytheon STX, for IDL V5.0     June 1998
     Based on code by Robert Hill, Raytheon STX
     Better astrometry of PC image in "batwing" configuration, W. Landsman
                August 1999
     Use vector call to SXADDHIST  W. Landsman   March 2003

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