The availability of a robust and efficient routine for calculating lightcurves of a finite source magnified due to bending its light by thegravitational field of an intervening binary lens is essential for determiningthe characteristics of planets in such microlensing events, as well as formodelling stellar lens binaries and resolving the brightness profile of thesource star. However, the presence of extended caustics and the fact that theimages of the source star cannot be determined analytically while their numberdepends on the source position (relative to the lens system), makes such a taskdifficult in general. Combining the advantages of several earlier approaches,an adaptive contouring algorithm is presented, which only relies on a smallnumber of simple rules and operations on the adaptive search grid. By using theparametric representation of critical curves and caustics found by Erdl &Schneider (1993), seed solutions to the adaptive grid are found, which ensuresthat no images or holes are missed.
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