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Show 85 point. The computation to follow these iteration points is somewhat more complicated than that for the accurate algorithm. The fast algorithm effectively trades some more lengthi computation at a few points along a scan line for a simpler computation at every point along a scan line. Iteration Point Definition The intersection of the scan plane with the patch will define a curved line as the cross section in X,Z. We have already defined two types of points on this curve, the boundary edge and silhouette edge trackers. This section defines how to choose the other points on the cross section curve to best approximate its shape, and how these points are defined mathematically for the Y iteration. scan bivariate We will first consider the case of an orthographic view of the objct. That is, the cross section curve in 3D space is viewed by parallel projection of its points onto the screen. For the cross section curve in figure 23, the boundary and silhouette points are as shown. Let us consider this as the two dimensional problem of drawing a curve with straight line segments. One good method for chosing points along the curve is to follow the vector normal to the curve. Place points on the curve .wherever this vector matches up with a set of equally spaced angular directions. Thus we might place points where th normal is at 00, 45°, 90°, 1350, etc. This would |
