Ground ambient level

Hello everyone,
I am not sure I got the meaning of Ground ambient level I get from gensky. In the definition of gensky it reads

In addition to the specification of a sky distribution function, gensky suggests an ambient value in a comment at the beginning of the description to use with the −av option of the RADIANCE rendering programs

Would this be what I am looking for?

The suggested ambient level produced by gensky equals the sky (indirect) horizontal irradiance times pi, and this is a suitable setting for -av (you just enter it three times for a gray RGB value). Do not use this -av setting for interior positions, only if you are rendering an outside view. Otherwise, you are liable to greatly over-estimate indirect contributions.

Also note that the importance of the -av setting decreases with increasing -ab bounces, but it never disappears from the calculation. Some would say that the safest setting for -av is 0 0 0, which biases the calculation on the low side, but will always converge to the correct value. If your -av setting is too high, then you will converge from a high value, but this can take longer if your setting is much too high, which is why you should not use gensky’s recommendation for indoor views.

Hi Greg, thank you for the explanation!