Meshgrid

Hi,

I have 3 vectors x,y,z; with x and y representing co-ordinates and z their values. Picture this as an image matrix that has been decomposed into vectors of x & y and pixel intensity z. Now I want to get back my picture. Here is what I did and where I got stuck:

[x1 y1] = meshgrid(-a:a) % -a:a defining the square image.

Now the problem is how to assign values (z) at the appropriate co-ordinates. Suggestions would be appreciated.

Charles

Answer 1

[Andrew Newell]

I assume that x and y have the same values as x1 and y1, but in a different order. You could do a search for each pair (x1,y1), but it's faster to sort the coordinates and then reshape Z. Here is an example with an actual image to give you the idea:

%%Set up the problem

load mandrill
Z = X; %rename image
nrows = size(Z,1); ncols = size(Z,2);
[x1,y1] = meshgrid(1:nrows,1:ncols);
x = x1(:); y = y1(:); Z = Z(:);

% Scramble the elements.
index = randperm(numel(Z));
x = x(index); y = y(index); Z = Z(index);

%%Now the problem is set up, unscramble x and y and then reshape Z.
xy = [x y];
[~,index] = sortrows(xy,[1 2]);
x = x(index); y = y(index); Z = Z(index);

Z = reshape(Z,nrows,ncols);
image(Z)

Of course, if x and y were originally obtained from a process like that in the previous cell, you won't need to sort.

Answer 2

[Ashish Uthama]

Either use interp2, griddata or if you have a newer version, triscatteredinterpclass. The doc pages have examples to get you started.