% interp2_fa ( x, y, Z, xi, yi, METHOD )
% -------------------------------------------------------------------------
%
%    Two-dimensional data interpolation using bin/brightness matching
%    (flat aperture resampling). Grids (x, y and xi, yi values) must be 
%    evenly spaced.
%
% USE:  Zi = interp2( x, y, Z, xi, yi, METHOD )
%       Zi = interp2( Z, xi, yi, METHOD )
%
% NOTE: Currently x's spacing must be 1, and go from 0:n.
%       Also, xi not restricted to x's range (Should be limited to +- 1/2).
%       
%
%    Same usage as Matlab's interp2.m, except for grid spacing requirements.
%    Zi = interp1(x, Y, xi) returns vector Zi containing elements 
%    corresponding to the elements of xi and determined by interpolation 
%    within vectors x and Y. The vector x specifies the points at which 
%    the data Y is given. If Y is a matrix, then the interpolation is 
%    performed for each column of Y and yi will be length(xi)-by-size(Y,2).
% 
%    Out of range values !!![should be]!!!! returned as NaNs.
%       
%   METHOD -  The default is linear interpolation.
%               'linear'        linear interpolation
%               'quadratic'     piecewise quadratic interpolation
%
%   FUNCTION CALLS:
%
%       interp2_fa.m
%
% Mark Dow, April 1999
% Mark Dow, modified March 2007, derived from interp1_bm
% Mark Dow, modified May 2007

function Zi = interp2_fa ( x, y, Z, xi, yi, METHOD )

   % First two argument can be ignored:  must be 1:N where n is number
   % of columns and number of rows of matrix.  Fix up arguments.
   if nargin == 4
   
      METHOD = xi;
      yi = Z;
      xi = y;
      Z = x;
      
      x = 1:size(Z,2);
      y = 1:size(Z,1);
   
   end

   Zfp = interp1_fa( y, Z, yi, METHOD );
   Zi  = ( interp1_fa( x', Zfp', xi, METHOD ) )';