function fp = gridResample3D(varargin)
%GRIDRESAMPLE3D 3-D interpolation
%  fp = gridResample3D(x,y,z,f,xp,yp,zp) resamples the values of the 
%  function fp at points on a 3-D rectilinear grid specified by the vectors
%  xp, yp, zp, based on the original function, f, which has points
%  specified by the vectors x, y, z.  The x, y, z vectors must be
%  monotonically increasing, but the vectors xp, yp, and zp do not.

%  fp = gridResample3D(...,mode) specifies an interpolation mode.  The
%  'mode' argument can be either 'linear' or 'nearest', which corresponds
%  to 3-D linear interpolation and nearest neighbor interpolation,
%  respectively.  The default interpolation mode is 'linear'.
%
%  For data defined on a simple Cartesian grid, this function is much
%  faster and more effective than interp3, which requires the user to input
%  a set of three 3D coordinate grids (one for each dimension), along with
%  the original data.  This wastes time and memory.
%  
%  Ryan T Flynn, 6-27-07

% convert data to single format
x = single(varargin{1});
y = single(varargin{2});
z = single(varargin{3});
f = single(varargin{4});
xp = single(varargin{5});
yp = single(varargin{6});
zp = single(varargin{7});

if length(varargin) == 8
    if ischar(varargin{8})
        mode = lower(varargin{8});
    else
        error('Mode argument must be a character string.');
    end
else
    mode = 'linear';
end

% do the interpolation
fp = gridResample3Dc(x,y,z,f,xp,yp,zp,mode);