[silas_xue]

lz 极坐标和直角坐标系的变换方法你可以从数学书上查到的吧。
suppose A(i,j) is based on the rectangular coordinates, B(m,n) is based on its polar coordinates,then
m is the radius, with m = (i^2 + j^2)^(1/2)
n is the angle, with n = arc tg(i/y)
当然，这要考虑离散情况下的近似问题。

你也可以查一下，matlab的库函数。