| OCR Text |
Show 88 desired normal direction it is to follow. A=22.5 has been for termination divide by the normallizing factor used for most of the pictures here. This divides a circle into 16 segments. In the lteration which finds where G=O it will be necessary to compute dG/du and dG/dv. For the function as it stands this is rather complicated since Xn and Zn are both functions of u,v. We therefore adopt the following hybrid scheme. Use the function G'= Xn sin& - Zn cos& for iteration and computation of derivatives. Then for testing sqrt(Xn2+Zn2). This works because for G f/g we have G U f 9 - 9 f U U, g2 Near the roots of f, Gufu/g and the Newton iteration scheme can be approximated by G Uo - U f Uo - r- U Note that there are two normal vector directions which might be serviced by the same G function, e.g. the 0° and 1800 directions. In practice these two types of iteration point are quite distinct. If they both satisfy the same function there is danger that a point of one type might converge, during a scan line update, to the location of one |
