%MIRT3D_MEXINTERP Fast 3D linear interpolation
%
% Output_image = mirt3D_mexinterp(Input_image, XI,YI,ZI) interpolates the 3D image 'Input_image' at
% the points with coordinates X,Y,Z. Input_image is assumed to be defined at a regular grid 1:N, 1:M, 1:K,
% where [M,N,K]=size(Input_images). Points outside the boudary return NaNs.
% This is equivalent (but much faster) to Matlab's:
% Output_image = interp3(Input_image,XI,YI,ZI,'linear',NaN);
%
% Output_images = mirt3D_mexinterp(Input_images, XI,YI,ZI). Input_images can be a stack of many 3D images (4D).
% The function interpolates each of the 3D images at X,Y,Z coordinates and return a stack of corresponding
% interpolated images. This is equivalent to Matlab's
%
% Input_images(:,:,:,1)=Input_image1;
% Input_images(:,:,:,2)=Input_image2;
% Input_images(:,:,:,3)=Input_image3;
% Input_images(:,:,:,4)=Input_image4;
%
% Output_images(:,:,:,1) = interp3(Input_image1,XI,YI,ZI,'linear',NaN);
% Output_images(:,:,:,2) = interp3(Input_image2,XI,YI,ZI,'linear',NaN);
% Output_images(:,:,:,3) = interp3(Input_image3,XI,YI,ZI,'linear',NaN);
% Output_images(:,:,:,4) = interp3(Input_image4,XI,YI,ZI,'linear',NaN);
%
% This is especially usefull fpr vector valued 3D images, RGB images, to interpolate the whole 3D video at the same coordinates
% or to interpolate image and its gradients at the same time (in image registration).
% The speed gain is also from the precomputation of nearest points for interpolation, which are the same for all images in a stack.
%
% Andriy Myronenko, Feb 2008, email: myron@csee.ogi.edu,
% homepage: http://www.bme.ogi.edu/~myron/
% The function below compiles the mirt3D_mexinterp.cpp file if you haven't done it yet.
% It will be executed only once at the very first run.
function Output_images = mirt3D_mexinterp(Input_images, XI,YI,ZI)
pathtofile=which('mirt3D_mexinterp.cpp');
pathstr = fileparts(pathtofile);
mex(pathtofile,'-outdir',pathstr);
Output_images = mirt3D_mexinterp(Input_images, XI,YI,ZI);
end
