Jaime Vives Piqueres wrote:

>     color LightColor*7*pow((DX+DZ)/2,2)
>     fade_distance 1
> 
>   and you will see they give the same scene!'

Now scale the whole scene by 0.00001 and keep fade_distance 1 :)
Use one source.

> So, what this means?

It means the the difference in in the far field is not visible. Even
for X and sqrt(X) :)

> > http://www.pp.htv.fi/kkivisal/relative_error.gif
> 
>   Sorry, I'm not that mathematically minded: I do not see what the graphic
> is suposed to show... :( I really prefer to test things with pov! :)

It's the relative error of axial intensity between distances 1-25, when using
fade_distance 1 and fade_distance 5 to estimate 25x25 square source. Just to
demonstrate fade_distance 1 produces higher error. The error decreases with
distance so in the far field the error becomes insignificant for both cases.
The blue curve is fade_distance 1. 

The equation used in pov clearly tries to estimate the combined axial near
field of multiple point sources on planar surface. fade_distance tells the
size of the source.


_____________
Kari Kivisalo

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