1. A method for transforming a first image given in polar coordinates r i , φ i into a second image given in Cartesian coordinates x i , y i , or vice versa, the method comprising: a. dividing at least part of the first or second image, into at least one triangular shaped area, having three vertices; b. determining for the vertices polar coordinates r k , φ k of the first image and respective Cartesian coordinates x k , y k of the second image; c. allocating first and second attributes A k and B k to the vertices x k , y k , wherein the first attribute A k is the product of φ k and r k and wherein the second attribute B k equals r k ; d. calculating attributes A i and B i for at least one current coordinate pair x i , y i of the second image from the attributes A k , B k of the vertices x k , y k of a triangular shaped area by an interpolation with respect to the position of the current coordinate pair x i , y i relative to the vertices of the triangular shaped area; and e. calculating the angle φ i of a current coordinate pair r i , φ i of the first image, corresponding to the current coordinate pair x i , y i of the second image by dividing the first attribute A i by the second attribute B i .