Practical Algorithms for 3D Computer Graphics, 2nd Edition

10.10. Metaball modeling and marching cubes 435

33

3 7 8 6 2

8 9 7 3

2 6 6 1

3

1

1 12 20

1 42

Figure 10.60: A square grid with potential field values (of some nominal unit) at each

grid point. A contour with the value of 5 is shown after interpolation. The sh a d ed area

equates to the area where the p o tential field’s value is greater than 5.

A

A

InsideOutside

Figure 10.61: The 16 combinations o f grid squ a r e cr o s s in g s tha t depend on the values

of the field at the corner vertices relative to the contour.

(b)(a)

Outside

Inside

Figure 10.62: In the amb ig u o u s cases the contours co u ld be connected in two different

ways for th e same pattern of vertex ...