% REGRID  Change of rectangular grid in 1D, 2D or 3D
%
%    Interpolation of data between two rectangular grids. Basically
%    an interface to interp1, interp2 and interp3 ensuring that
%    interpolated data get expected size.
%
%    The data is assumed to have dimensions: A(x,y,z)
%    Grids for dimensions not used must be left out.
%
% FORMAT   B = regrid(A,x,xi,y,yi,z,zi[,iopt])
%        
% OUT   B      Interpolated data.
% IN    A      Data to be interpolated.
%       x      Original x-grid.
%       xi     New x-grid. 
%       y      Original y-grid. Only to be included if A has dimension >= 2.
%       yi     New y-grid. Only to be included if A has dimension >= 2.
%       z      Original z-grid. Only to be included if A has dimension >= 3.
%       zi     New z-grid. Only to be included if A has dimension >= 3.
% OPT   iopt   Interpolation option. See e.g. *interp2*. Default is 'linear'.

% 2006-08-22   Created by Patrick Eriksson.


function B = regrid(A,x,xi,y,yi,z,zi,iopt)


%- Check input
%
rqre_datatype( 'numeric', A );
%
rqre_datatype( 'vector', x );
rqre_datatype( 'vector', xi );
%
if length(x) ~= size(A,1)
  error('Mismatch in size between *x* and *A*.');
end
%
dim = dimens( A );
%
if nargin < 1+dim*2
  error( 'Too few input arguments.' );
elseif nargin > 2+dim*2
  error( 'Too many input arguments.' );
end
%
rqre_scalar( 'Dimensionality of A', dim, 1, 3 );

imethod = 'linear';


if dim == 1

  if nargin == 4
    imethod = y;
  end

  B = interp1( x, A, vec2col(xi), imethod );

elseif dim == 2

  rqre_datatype( 'vector', y );
  rqre_datatype( 'vector', yi );

  if length(y) ~= size(A,2)
    error('Mismatch in size between *y* and *A*.');
  end

  if nargin == 6
    imethod = z;
  end

  [xi,yi] = ndgrid( xi, yi );

  B = interp2( y, x, A, yi, xi, imethod ); 

elseif dim == 3

  rqre_datatype( 'vector', y );
  rqre_datatype( 'vector', yi );
  rqre_datatype( 'vector', z );
  rqre_datatype( 'vector', zi );

  if length(y) ~= size(A,2)
    error('Mismatch in size between *y* and *A*.');
  end
  if length(z) ~= size(A,3)
    error('Mismatch in size between *z* and *A*.');
  end

  if nargin == 8
    imethod = iopt;
  end
  
  [xi,yi,zi] = ndgrid( xi, yi, zi );

  B = interp3( y, x, z, A, yi, xi, zi, imethod ); 

end