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Kai-46 / nerfplusplus

improves over nerf in 360 capture of unbounded scenes
BSD 2-Clause "Simplified" License
930 stars 102 forks source link

about inverted sphere parameterization #19

Closed bring728 closed 3 years ago

bring728 commented 3 years ago

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

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 commented 3 years ago

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

bring728 commented 3 years ago

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

image

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!