GetGradOri_vector.m

function [mag vect] = GetGradOri_vector(pix,r,c,s)

[rows cols slices] = size(pix);

if r < 1
    r = 1;
end
if c < 1
    c = 1;
end
if s < 1
    s = 1;
end
if r > rows
    r = rows;
end
if c > cols
    c = cols;
end
if s > slices
    s = slices;
end


if (c == 1)
    xgrad = 2.0 * (double(pix(r,c+1,s)) - double(pix(r,c,s)));
elseif (c == cols)
    xgrad = 2.0 * (double(pix(r,c,s)) - double(pix(r,c-1,s)));
else
    xgrad = double(pix(r,c+1,s)) - double(pix(r,c-1,s));
end
if (r == 1)
    ygrad = 2.0 * (double(pix(r,c,s)) - double(pix(r+1,c,s)));
elseif (r == rows)
    ygrad = 2.0 * (double(pix(r-1,c,s)) - double(pix(r,c,s)));
else
    ygrad = double(pix(r-1,c,s)) - double(pix(r+1,c,s));
end
if (s == 1)
    zgrad = 2.0 * (double(pix(r,c,s+1)) - double(pix(r,c,s)));
elseif (s == slices)
    zgrad = 2.0 * (double(pix(r,c,s)) - double(pix(r,c,s-1)));
else
    zgrad = double(pix(r,c,s+1)) - double(pix(r,c,s-1));
end

xgrad = double(xgrad);
ygrad = double(ygrad);
zgrad = double(zgrad);

mag = sqrt(xgrad * xgrad + ygrad * ygrad + zgrad * zgrad);

if mag ~=0
    vect = [xgrad ygrad zgrad] ./ mag;
else
    vect = [1 0 0];
end