# Simulating light ray movement inside swimming pool water. Light sources not in the water

Hello Lars,

It would be great to run the simulations with moving water surface but since
i want to compare the simulations with the measurements it would be
difficult to create similar conditions in the real pool. Your suggestions
were very useful though and i will start working immediately with a simple
model to understand how it works and eliminate possible problems that may
come up.

Thanks again

Sotiris

[mailto:[email protected]] On Behalf Of Lars O.
Grobe

ยทยทยท

-----Original Message-----
From: [email protected]
Sent: 23 July 2009 03:23
Subject: Re: [Radiance-general] Simulating light ray movement inside
swimming pool water. Light sources not in the water

Hi!

Lars, my concern in the dissertation is the glare effect created in
the swimming pool and do not allow a lifeguard to search the bottom of
the pool. According to the theory found till now, I am interesting in
the amount of light reflecting from the surface and the amount that is
travelling through the water till it hits the bottom and all the way
up. The ratio of the intensities will show me how much glare I have in
the swimming pool.

Wow, this sounds like a not so trivial problem... I think you need
first to study on what surface shapes to expect. On a perfectly even
surface, you could easily look through to the ground, as long as you do
not hit the total reflection by very low angles. But as the lifeguard
will usually be interested in the pool when there are occupants, the
surface will not be a plane any more, but wavy. And now everything
depends on the shape - having big, smooth waves will allow good view,
but small wrinkly waves (ok, here I hit the limits of my English
language skills) would cause a lot of reflections by total reflection,
and at the same time caustics resulting in uneven illuminances on the
ground. If you are able to model the water surface geometries which you
need to consider, it will be possible to make some estimates on
visibility of anything below the surface. There are two ways afaik, one
being rtcontrib, the other one pmap. rtcontrib comes with recent
distributions, but is not really documented. pmap comes with a nice
documentation, but is currently supported only with radiance 3.7.

By the way, I think there are two effects to consider. One is glare.
Even more important may be the total-reflection that simply does not
permit you to look through a water-air interface (aka the water surface)
under narrow angles, with or without glare. Glare alone might render the
task of the lifeguard tiring, but non-visibility renders it impossible...

Cheers, Lars.

_______________________________________________
[email protected]

Hi!

It would be great to run the simulations with moving water surface but since

I did not want to propose an animation. I was just wondering whether you
know the shape of the surface. I do not know how even how to describe
the wave patterns, it is about frequencies, amplitudes, interference and
all that over the surface of limited dimensions, which means including
edges reflecting back. So the geometrical description seams to be not
trivial, and I have no clue whether there are any standard models to use
when simulating certain "wavyness" conditions of a pool.

I think that this geometry topic is much more difficult then the
rendering stuff once the model is generated.

Cheers, Lars.