| OCR Text |
Show speed/accuracy-complexity spectrum. The slow-but-accurate CHAPTER 5 SCAN LINE PARAMETRIC SURFACE ALGORITHM For twenty terces I phrase the answer in concise and actionable language; for ten I use the language of cant, which occasionally admits of ambiguity; for five, I speak a parable which you must interpret as you will; and for one terce, I babble in an unknown tongue. Jack Vance, The t In any computer algorithm there is a trade-off between cost and performance. Accordingly, the scan line parametric surface algorithm can be implemented in many variations which differ primarily in speed, accuracy of the produced picture, and complexity of code. Two such variations will be described here which lie at opposite ends of the version explicitly finds the u and v parametric values for each patch visible in each picture element by performing a bivariate Newton iteration at each X value on the X sc?n. This is wasteful for very high r@solution images where the surface undulates only gradually. The faster version of the algorithm attempts to avoid much of this computation by approximating the intersection curve by straight line segments. This, unfortunately, leads to an increase in the complexity of the code and also can produce some visible errors in the picture when some of the approximations used |
