Definition of "corral" value in the ambient cache

radiance-general
1

Hi community,

can somebody explain what the “corral value” represents for points in the ambient cache file?

for a simple rpict, the points in the ambient file with a corral value greater than zero looked like these in the attached image, while the points with a zero corral value where spread all over the model surfaces.

points_corral_greater_zero
points_corral_greater_zero.jpg608×526 130 KB

thanks!

2

It tells the code where to watch out for nearby geometry to avoid light leaks. Explained in https://radiance-online.org/community/workshops/2014-london/presentations/day1/Ward_WhatIsNew.pdf

3

Thanks Greg,

i thought it was related to the points shown on edges of objects in Figure 5b of your paper “A raytracing solution for diffuse interreflection”. I wanted to visualize which points were calculated (rays sampled from them) and which points had their values found through interpolation. Any way i can do that?

Iason

4

Well, any points that had their values interpolated did not result in a new calculation, so you could say that every pixel in an image where there is no ambient value was interpolated. Does that help?

5

Yes it helps! So, is it correct to say that all points stored in the ambient file (*.amb) were calculated, and all other points (pixels) were inter or extrapolated?

6

Yes, with the addition that there are “levels” in the ambient values that correspond to which bounce they correspond to in the calculation. Only the “0” level ambient values are finally applied to pixels.

By the way, you can use the “genambpos” utility to visualize many aspects of the ambient values in the scene.

1 Like
7

This is very useful for teaching and learning.
genampos is not cross-platform (using windows here…), that is why i was using lookamb
i see now that sarith has re-written genampos in py, i will check that. Thank you!