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      Inverse bilinear interpolation.


Calling Sequence

      ibilin, x, y, xe, ye, a, b


      x = array of 4 corner x values. in
      y = array of 4 corner y values. in
      xe = x value of desired point. in
      ye = y value of desired point. in

Keyword Parameters


      a = rectangular image x fraction. out
      b = rectangular image y fraction. out
        Fractions not clipped to 0-1.
      flag = flag for point (xe,ye). out
        1=ok, 0=no point.

Common Blocks


      Notes: For a rectangular image, if values of some
        field are known at the corners then values at any
        point inside the image may be estimated by bilinear
        interpolation. The inverse problem, knowing the
        corner values and the value at a desired point, and
        finding the image point is not so straight forward.
        In general, for a single scalar, there may be many
        such image points. This routine is not that general,
        it is intended for 2-d coordinate conversion.
        Algorithm by Rick Chapman, JHU/APL.

Modification History

      R. Sterner, 1994 Sep 27
  Copyright (C) 1994, Johns Hopkins University/Applied Physics Laboratory
  This software may be used, copied, or redistributed as long as it is not
  sold and this copyright notice is reproduced on each copy made. This
  routine is provided as is without any express or implied warranties
  whatsoever. Other limitations apply as described in the file disclaimer.txt.

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