TITLE: Mir Is Crashing
NAME: Franck Angella & Arnaud Vallat
COUNTRY: France
EMAIL: angella@tsi.u-bordeaux.fr
WEBPAGE: http://www.tsi.u-bordeaux.fr/angella/raytracing.html
TOPIC: UNBELIEVABLE
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
JPGFILE: favparis.jpg
ZIPFILE: favparis.zip
RENDERER USED: 
    Povray.3.02.watcom.win32, Povray.3.1e for Linux, Microsoft Visual
C++ 5.0

TOOLS USED: 
    2 brains, 4 hands

RENDER TIME: 
    82 hours

HARDWARE USED: 
    2 PII350 (64M & 128M)


IMAGE DESCRIPTION: 

 -- Place de l'Etoile, Paris, on Wed, 11 August 1999.
 As predicted by a famous haute couture designer and by the 16th century
 French seer Nostradamus before him, the burning Mir space station crashes down
 in the center of the city, directly in the 'Arc de Triomphe'. This exactly
 happens during the total solar eclipse occuring in France.

 Note: Scientists proved that the Mir station won't crash down in Paris.
       So, please, do not cancel your holidays :)



DESCRIPTION OF HOW THIS IMAGE WAS CREATED: 

 Here is a brief description of our common work, followed by our two different
contributions
 descriptions.

 COMMON PARTS
 * The whole scene was rendered using a focal blur, in order to highlight the
most important
 part of it. There is a second reason for using the camera focal blur feature:
the scene
 uses a lot of little particles around the Mir station, which used to disappear
when using
 the antialiasing mode (except of course if we have had more time to run more
accurate
 antialiased renderings). The final result with a focal blur let these particles
visible;
 ok, we admit that there is a part of black magic in it, but we are working on
understanding
 why it works !

 * There are two ground fogs and an isotropic scattering atmosphere, mainly used
so that
 the beams of streetlights can be visible.

 * The scene uses a main area light source with atmosphere off. Another area
light source is
 placed  under the big halo so that the scene looks orange around the Mir
station. All the other
 light sources use atmospheric interactions. There are 4 of them around the "Arc
de Triomphe"
 and one for each streetlight.

 * In addition, radiosity was used for the final rendering, in order to
intensify the lighting
 effects.

 * The scene uses a lot of objects (about 280,000). It is memory-greedy (365M is
the peak
 memory used...). We choosed to skip the light buffer precalculations (-UL
switch), thinking
 that our computers were dying during the parsing stage... The zip file
downloadable on the
 IRTC website was limited to the first row of buildings. The background
buildings were greatly
 simplified to reduce the size of the zip file. We can provide the whole script
if you want it.

 * We wanted to add some logos on this picture so that it would look like a TV
snapshot. For
 those who read (and maybe write in) the IRTC discussion mailing list, thank you
for your
 advices. Unfortunately, we hadn't time to re-render the final picture. The
major issue to
 solve was to add a logo (with a transparent plane in front of the camera for
example) while
 using a focal blur camera (of course with the logo not being in the focal
plane). And we found
 a way to do it ! An easy solution is to use a transparent and totally
reflecting plane in front
 of the camera, but rotated from 45 degrees. Then, place the logo or any object
you want to appear
 in front of the camera above the plane. The distance must be chosen so that the
optical paths
 from the camera to the focal point and from the camera to the logo are the
same. Even with a
 focal blur, the logo looks sharp.

 THE CITY (Franck)
 * All the buildings were created using CSG. The scripts (18M !) were generated
using different
 C programs. Here is a short description of how it was done:

   1. A first program was written in order to get the corners of each building
using the mouse.
   The buildings that you can see on the picture are located at the REAL places.
This was done
   using an aerial photo of the "Place de l'Etoile" in Paris and clicking the
buildings' corners.


   2. The second program is used to link all the corners (vertices).

   3. We then have groups of buildings (neighboring buildings). The third
program determines
   whether a building side is a fa_ade or not. It then generates the whole
script. There are
   a lot of parameters such as the number of floors, the angle of the roof or
the size of a
   window. Most of those parameters are slightly modified using random
variations for each
   fa_ade. The scripts contains the position of random chimneys and antennas
too. In addition,
   some windows are lighted and some other are not (in fact there are no lights,
but different
   textures only). To conclude this part, let's say that the buildings are at
the right places,
   but of course they do not look like the real ones. The C program generates
complete buildings
   given their corners only, so the global view makes it look like Paris
Haussman's buildings.

   4. Three other programs were created to manually place sidewalks,
streetlights and trees.
   We would like to thank Paul T. Dawson for his ptd_tree include file, which
was used in this
   scene for the trees.

 * The "Arc de Triomphe" only uses CSG too. The sculptures are basic height
fields using
 pictures of the real monument. Four spots light up the construction.

 MIR STATION & PAVING STONES (Arnaud)
 * In order to destroy the Mir station, we first had to build it ! This was done
using CSG and
 a lot of patience. The measurement of the station were taken in a scientific
journal. Even if
 only a small 'complete' part of the station can be seen on this picture, the
whole thing was
 modelled. Each part of the station is a distinct object, so that it was easy to
destroy it,
 by moving and rotating each part (solar panels, satellite dishes, etc.) from
its initial
 position.

 * The flame was done using an emitting halo. The container is a scaled sphere.
In fact there
 are six halos. One of them is the flame, the other is a red light source with
the looks like
 keyword (the looks like object is a dust halo). With such a light source, all
the parts of
 the Mir station cast shadows on the ground and on the buildings. The other
halos use conic
 or cylindrical containers to produce the steam ribbons. These halos used to
work well without
 the use of atmosphere. With the atmosphere, white halos saturate the picture
(white spots).
 That is the reason why the main halo (the orange one) container was removed
(using the CSG
 difference) from the white halos.

 * The particle/scrap is a collection of randomly rotated and translated
objects. Those objects
 are little pyramids (mesh objects) which reflects lights.

 * The paving stones are a collection of superellipsoids. The script was
generated with a C
 program. This program calculates the position of each object, so that there is
no gap between
 them (surface cobbling). In addition, each object is randomly rotated in order
to have a
 'chaotic' surface.

