8 6           world x and y dims
4 3 7         viewpoint (x, y, z)

9             projecting plane
12 12 12      intensity

0   0    1    normal
2   1.5  3    point
1   0    0    x direction
4 3           size

sky.ppm
1
3


11                sphere
0 0 0            r g b ambient
11 11 11              r g b diffuse
0 0 0            r g b specular

4 3 -9           center
6                radius