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Show 71 are not as good as they should be. Of the two algorithms, only the fast version has been implemented. A possible implementation of the accurate version will be sketched out first, however, as it is simpler to und e r s tand . The mechanisms which are common to both versions will bE' introduced in the description of the accurate version. The final section of the chapter discusses potential visible errors and the tradeoffs between the two algorithms in eliminating them. Accurat ih Both algorithms function by tracking the position of the level curves in the u,v parameter space of the intersection of the Y(u,v) definition function with the constant Yscan plane. The accurate algorithm represents these curves by tracking only the boundary edges and silhouette edges in. u,v from scan line to scan line. The regions between these points are filled in during the X SC2n. Since the process of tracking the position of a edge intersection point is performed by Newton-Raphson iteration, these points are sometimes referred to as "iteration points". Loc£_l axima To provide for the creation of new iteration points when a local maximum is passed, a pre-scan of all the patches is performed to make a list of local maxima. This |
