EMAIL: wbaltz@qwest.net
NAME: Warren Baltz
TOPIC: Decay
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
TITLE: Exponential Decay
COUNTRY: United States
WEBPAGE: N/A
RENDERER USED: POV-Ray 3.5
TOOLS USED: JPatch (bicubic patch editor), Gimp to create image-maps
RENDER TIME: 25 minutes
HARDWARE USED: Pentium 1.8 GHz  Linux ix86
IMAGE DESCRIPTION:

	Most obviously, this image shows the remains of a once large stone building falling apart in a murky swamp, on a dreary day.  But a closer look shows that the ruins of the building graph an exponential decay (like 1/x) on the screen.  The shape of the towers show an exponential decay as well, quite a bit steeper.  A little treat for the mathematically inclined.  I want different people to see different things the first time they look at this image.

DESCRIPTION OF HOW THIS IMAGE WAS CREATED:

	All the stone buildings were described mathematically using macros.  The basic structures were built using nested loops to place stones.  The towers for instance, were created by looping through a height position.  And for each height, calculating a radius and looping an angle through a 2*pi sweep.  So each stone would be placed at a given radius as a function of height and translated to the approriate height and radius, then rotated through the angle.  The stones were created using isosurfaces mapped using the same variables used for their position, so that they would neatly fit together as if they were cut to fit for structural strength.

	To add the aged and decrepid look, I created probability density functions to determine which stones should be missing.  I also hand selected several stones to be left out.  The holes in the wall are good examples of this.  I also wrote a macro to place individual stones.  I used it to draw stones that had fallen on the ground, but hadn't yet sunken into the mud.

	The walls between the towers were also created using nested loop macros that calculated an exponential curve.  The stones were offset to the side so as to overlap them instead of having stacks of stones next to each other.  I accomplished this with a simple toggle variable that flipped between 0 and 1 each time through the loop.  This did cause some problems with my loop algorithm though, so I had to rewrite it to be row major instead of column major.

	There are two types of trees in the background.  I modeled two of the trees using a free bicubic patch editor.  The other trees did not need detail because they are blurred and covered with fog.  So to speed rendering, I drew flat black pictures in Gimp and image mapped them onto large rectangles with transparency.

	The swamp floor is also an isosurface.  A partially transparent box reaches above the isosurface in some places to create pools of dirty water.

	The effort spent on speed optimization paid off.  With a 3x3 area light, antialiasing, radiosity and high quality focal blur, the image took less than 30 minutes to render.