MATLAB: Polar to cartesian conversion problem

Question

Hey,

I need to convert two vectors in polar coordinates (rho,phi) to cartesian coordinates, but something goes wrong because if I convert it back (from cartesian to polar) I don't get the same results ().

phi=linspace(0,2*pi,N);
rho=linspace(0,R_a,N);
[x,y] = pol2cart(phi,ro);
[theta2,rho2] = cart2pol(x,y);

Thanks in advance.

Answer 1

"but something goes wrong because if I convert it back (from cartesian to polar) I don't get the same results"

Nothing goes wrong, you just have two different representations of the same angle.

Your input angles are given over the range 0 .. 2*pi, but cart2pol documentation clearly states that its ouput "...value of the angle is in the range [-pi pi]", so we would certainly not expect to have the same values.

You can convert to 0..2*pi using mod:

theta2 = mod(theta2,2*pi);

Note that due to floating point error we would still not expect those values to be exactly the same, but close enough.