TITLE: Waterfall
NAME: Sascha Ledinsky
COUNTRY: Austria
EMAIL: sascha.l@teleweb.at
WEBPAGE: http://aart.home.ml.org
TOPIC: Water
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
JPGFILE: waterfa1.jpg
ZIPFILE: waterfa1.zip
RENDERER USED: 
    Pov-Ray 3.1 (Win32)

TOOLS USED: 
    Pov-Ray 3.1 for Windows for Editing/Rendering
            Paintshop Pro 4.14 for adding text and for JPEG-Compression

RENDER TIME: 
    about 22 hours

HARDWARE USED: 
    Intel Pentium Pro 200, 256KB L2 Cache, 64MB DRAM


IMAGE DESCRIPTION: 


This is a raytraced version of M.C.Escher's (1898-1972) famous lithography
'Waterfall' (1961), which again is based on a spatial illusion drawen by the
mathematician Roger Penrose. Escher used Penrose' impossible triangle three
times in his picture. Water falls down a waterfall, drives a mill, and then
slowly flows down a ramp between two towers, until it reaches the point where
the waterfall starts again. The two towers are equally high, but the right one
is one level below the left one.
If you're interested, visit the World of Escher on the internet (
http://www.worldofescher.com ), where you can take a look on the original
picture.


DESCRIPTION OF HOW THIS IMAGE WAS CREATED: 


Modles:
All Models are Primitives or CSG-Objects, modeled in POV's Scene Description
Language. I first started with a brick-texture, but it didn't look very
realistic. So I wrote a short include file (bricks.inc) which is used to create
a superellipsoid for every single brick in this scene. The clouds below, in the
background, are just a white plane with a bumpy, turbulent normal pattern.
For the waterfall itself I used the new 'Media'- and 'Interior'-features of POV
3.1. They replace the old 'Halos' and provide much more flexibility. The
waterfall consits of three parts:
1) A bumpy, transparent surface with a specular-finish for the highlights.
2) The interior of the waterfall, a 'media' with a marble density pattern.
3) A smaller, transparent object with a bumpy normal pattern for the refractions
and the caustics.
 
Lights:
The sun is a 3x3 area light for smooth shadows. It has a yellow or orange color,
because it's late afternoon.
The standard ambient light didn't look good, because 500f the objects are in
shadow. I first tried radiosity to add a bit more realizm, but it didn't
produce the effect I was looking for. For the final rendering, ambient light is
globally turned off, and the scene is surrounded by blue area lights, to
simulate the light coming from the sky - takes awfully long to render (It only
sayd '0 Pixel per Second' on my Pentium 133, but fortunately I had access to a
Pentium Pro 200, otherwise the scene would still render...)

The Camera and the Trick:
To produce the illusion of this impossible building, I used a parallel
projection (orthographic camera). Each ramp appears actually two times in the
scene, and the 'unwanted' parts are simply clipped away by a plane which stands
normal to the projection plane. That was the easy part...
The problem starts with the shadows. POV-Ray isn't very flexible in handling
shadows (what would be very usefull here is a feature which allows things like:
Object A will cast a shadow on itself, on object B but not on object C, or,
another example, object A will not recieve shadows from object B, but from
itself and from all other objects...), so I had to clip away more parts and
move them along the projection rays to cast all unwanted shadows into the
emtyness.
There is still one 'bug' with the clipping and I had no time to fix it. For that
reason, rendering has to be stopped at scanline 450, the line #declare
Clipping_offset=Upper_Half has to be replaced by #declare
Clipping_offset=Lower_Half, and rendering continued (don't forget to turn on
the continue trace option +C !!!). I know, this isn't very smart, but I think
it doesn't violate the 'no post-processing' rule, since the final image is
still pure render output.

Files:
All files for rendering this scene are included in the Zip-File, but the
source-code isn't documented, a little bit chaotic and most of the
object/texture-names are in german...
If you have any questions please e-mail to sascha.l@teleweb.at

Rendering parameters:
800 x 600 x 24bpp
Quality 9
Anti-aliasing on, threshold 0.2, method 1, depht 3
Split unions on (worked a bit faster on my machine, don't know why)
End Row 450 for the first part,
Continue trace on for the second part.

This is my first picture I sent to the IRTC, I hope you like it. I experimented
with some other Escher-like images erlier, you can see them on my homepage (
http://aart.home.ml.org ) and on http://www.worldofescher.com too. The
'Water'-Topic of this round finally was the motivation for me to start working
on 'Waterfall'.
Thanks to the POV-Team for POV-Ray and to the IRTC-Admin Team for running the
contest!
And sorry for my english :)

regards,
-Sascha Ledinsky