how is it possible to correspond negative coordinates to matrix indices?

I was working on a piece of code which take a cartesian image and change it to polar demonstration (rho , phi).

using "interp2" negative non-integer numbers correspond to indices of an image (which are positive integers).

in part of the code we see:

x = Pixel_spacing* (-(nrad-0.5):(nrad-0.5));

[x,y] = meshgrid(x,x);

polar_image = interp2(x, y, double(image), xi, yi);

here x and y are expanded on something like (-9.5 , 9.5) and through this these negative coordinates work as indices of matrix. note that x ,y and image are the same size.

having this example in mind, how can correspond indices of a matrix to negative and non-integer contents of another matrix, like the function 'interp2' does?

thanks

Answer 1

[chicken vector]

You can normalise the coordiante to transorm them into indeces:

x = -9.5 : 9.5;           % -9.5 -8.5 ... 8.5 9.5
xIdx = x - x(1) + 1;      %   1    2  ...  19  20

[Babak]

you're right. thanks :)