about inverted sphere parameterization

[bring728]

To do volume rendering, we need to get x', y', z'.

And in the paper, in order to find x', y', z', it is said to be obtained by rotating point a of the figure.

If you just divide x, y, z by r, isn't it x', y', z'? Why do I have to get it as hard as a picture? Am I misunderstanding something?

[Kai-46]

For distant points, (x, y, z) can be huge, leading to numeric issues.

[bring728]

Oh, we should also think about numeric issues! And,

looking at the code, when sampling the background, we don't know the coordinates of x,y,z, so you have to rotate point (a) to get x',y',z'! When sampling, only 1/r is known... I understood. Thank you!