  In this paper a new efficient algorithm for computation of radio wave ray
trajectories is described. The algorithm is based on an original second-order
difference scheme with a specific "length-conservation" property, which allows
to resolve the ray shape even in the regions where its curvature is high.
Besides the scheme, the algorithm includes a number of mechanisms ensuring its
correctness and stability. The algorithm is intended for obtaining multi-pixel
solar images in wide range of radio frequencies, and it is designed to be used
in studies of the solar environment with modern high-resolution radio
interferometers and radio telescopes such as the Murchison Widefield Array
