compute_triang_interp.sci

function M = compute_triang_interp(face,vertex,v,n, options)

// compute_triang_interp - perform interpolation of a triangulation on a regular grid
//
//   M = compute_triang_interp(face,vertex,v,n);
//
//   n is the size of the image
//   vertex is a (2,n) list of points, they
//       are assumed to lie in [1,n]^2.
//   face is a (3,p) list of triangular faces.
//
//   If options.remove_nan==1, remove NaN non interpolated values using a
//   heat diffusion.
//   
//   Copyright (c) 2004 Gabriel PeyrŽe

options.null = 0;
verb = getoptions(options, 'verb', 0);
remove_nan = getoptions(options, 'remove_nan', 1);

if argn(2)<4
    error('4 arguments required.');
end
if size(face,2)==3 & size(face,1)~=3
    face = face';
end
if size(face,1)~=3
    error('Works only with triangulations.');
end
if size(vertex,2)==2 & size(vertex,1)~=2
    vertex = vertex';
end
if size(vertex,1)~=2
    error('Works only with 2D triangulations.');
end

if min(vertex(:))>=0 & max(vertex(:))<=1
    // date in [0,1], makes conversion
    vertex = vertex*(n-1)+1;
end

nface = size(face,2);
face_sampling = 0;
if length(v)==nface
    face_sampling = 1;
end

epsi = 1e-9;

M = zeros(n,n);
Mnb = zeros(n,n);
for i=1:nface
    T = face(:,i);          // current triangles
    P = vertex(:,T);        // current points
    V = v(T);               // current values
    // range
    selx = min(floor(P(1,:))):max(ceil(P(1,:)));
    sely = min(floor(P(2,:))):max(ceil(P(2,:)));
    // grid locations
    [Y,X] = meshgrid(sely,selx);
    pos = [X(:)'; Y(:)'];
    p = size(pos,2);    // number of poitns
    // solve barycentric coords
//    warning off;
    c = [1 1 1; P]\[ones(1,p);pos];
//    warning on;
    // find points inside the triangle
    I = find( c(1,:)>=-10*epsi & c(2,:)>=-10*epsi & c(3,:)>=-10*epsi );
    pos = pos(:,I);
    c = c(:,I);
    // restrict to point inside the image
    I = find( pos(1,:)<=n & pos(1,:)>0 & pos(2,:)<=n & pos(2,:)>0 );
    pos = pos(:,I);
    c = c(:,I);
    // convert sampling location to index in the array
    J = sub2ind(size(M), pos(1,:),pos(2,:) );
    // assign values
    if ~isempty(J)
        if face_sampling
            M(J) = v(i);
        else
//           disp(size(M(J)));
//            disp(size(J));
//            disp(size(c(2,:)));
            M(J) = M(J) + V(1)*c(1,:)' + V(2)*c(2,:)' + V(3)*c(3,:)';
        end
        Mnb(J) = Mnb(J)+1;
    end
end
I = find(Mnb>0);
M(I) = M(I)./Mnb(I);
I = find(Mnb==0);
M(I) = -1e9;

return;

if remove_nan
    Mask = (M<=-1e8);
    M(Mask==1) = mean(M(Mask==0));
    M0 = M;
    h = ones(3)/9;
    niter = 20;
    for i=1:niter
        M = perform_convolution(M,h);
        M(Mask==0) = M0(Mask==0);
    end
end

endfunction