TITLE: Gravity
NAME: Sascha Ledinsky
COUNTRY: Austria
EMAIL: sascha.ledinsky@getronics.com
TOPIC: Force
COPYRIGHT: I SUBMIT TO THE STANDARD RAYTRACING COMPETITION COPYRIGHT.
MPGFILE: gravity.mpg
ZIPFILE: gravity.zip
RENDERER USED: 
    Megapov 0.7

TOOLS USED: 
    Paintshop for work on the image-maps, Animationshop for the title
and credits, TMPGenc for MPEG-encoding

CREATION TIME: 
    Render time approx. 40 hours (P-III 800MHz)

HARDWARE USED: 
    P-III 800 MHz

ANIMATION DESCRIPTION: 

This is my 3rd submission to the IRTC, but my first animation.
This animation tries to visualize how gravity works - As Einstein discovered,
space is curved by masses, and the effects of curved space acting on all well
known objects is known as gravity. In our "real" universe, space is three
dimensional and is curved it into the 4th dimension - but to make the
visualization easier, the universe in this animation is two dimensional and
curved into the 3rd dimension.
At the beginning of the first scene we see our earth, rolling over a floor,
which is possible made of some elastic 

material. After a few seconds, we can see the moon orbiting the earth - by just
following it's gravity-field (or the curved space), much like a ball thrown
into a roullete. Then the camera catches a comet, closes up, moves through it's
tail and watches it, as it is beeging catapulted back into outer space by the
gravity of the sun. The comet's got two tails, one made of gas (white), one of
ions (blue). As the comet's core heats up it "melts" and releases gas, which is
then affected by the pressure of the incoming sunlight and magnetic interaction
with the solar-wind. Thus, the tails always points away from the sun. If you
watch carefully, you can see that if the comet is very close to the sun, the
two tails point in slightly different directions. After the comet's out of
sight, the camera zooms out and we can see the orbits of the nine planets of
our solar system. They all are elliptically, mercury (the innermost planet) and
pluto (the outermost) have the most eccentric orbits.
The second scene shows the birth of a strange object called a black hole. When a
star has "burned up" nearly all its 

hydrogenium it's radiation pressure decreases and it's own gravity causes the
star to collapse. While most stars end up as so called "white dwarfs", some
stars do not: If their mass is large enough, their gravity is that large that
nothing can stop the collapse. They shrink and shrink until gravity on the
surface gets that high, that even light cannot escape anymore - in our model of
"curved space" the black hole has punched a hole into the floor.

VIEWING RECOMMENDATIONS: 

Any mgep-player (e.g. Windows mediaplayer) - Adust brightness/contrast if the
animation looks too dark on your screen

DESCRIPTION OF HOW THIS ANIMATION WAS CREATED: 

The universe (the floor) is an isosurface, the functions used depend on how many
objects are visible (following Newtons law). The grid on the surface adapts to
the viewers distance.
The earth is bulit up by four concentric spheres (water, land, clouds and
atmosphere). The maps for land and clouds have been downloaded from somewhere
on the web, the atmosphere is blue, scattering media.  I've changed the images
and the code, but I left the original text in earth.inc, showing from where you
can download it and who originally created the image-maps . The moon is a
sphere with an image and a bump map, also downloaded from the web, and the
object is motion blurred. The comet consist of approx. 1000 "glows" - the
positions of the glows are calculated by a partice system I wrote. The comet is
moved along an ellipse and moves faster when it's near the sun (according to
Keplers laws). The comet looks cool if the animation runs slower (you can see
the gas move smoothly then) - but in this case due to the fast motion all the
particles would have been "blown away". But you can play around with the
comet.inc file, a short description is at the end...
The sun uses some different emitting medias for the corona. The black hole
finally uses much the same media like the sun-object, it's color goes from red
over green and blue to violet while the surface heats up during the collapse.
The camera location, look_at, viewing angle and the size of the grid (on the
floor) are controlled by splines. To place the spheres on the floor i've used
an iteration method, I was to lazy to solve the equations ;-) The sizes and
distances, as well as the relative masses of all the objects are not realistic,
I've choosen them to look good in the animation.

Everything needed to render the animation is in the zip-file.
If you want to re-render parts of the animation turn off debug and warning
streams (-GW -GD) because my files produce a lot of debugging output. The first
scene (Earth, moon, comet, sun, planet-orbits) is in gravity_final.pov - clock
must run from 0 to 38 -  The second scene is in black_hole2_.pov, clock must
run from 0 to 20. Change the location of the image and bump maps in the
earth.inc and moon.inc file!

About the comet.inc:

The macro comet_position is needed and must return the comet's position at any
given time but can be changed to whatever you want. The macro in my code solves
the Kepler-equation and calculates the true position of the comet.
sun_position is self explaining
The variables with "2" at the end are used for the 2nd tail
new_per_frame:        How many new particles are being created per frame
max_age:        What's the maximum age (in frames) for each particle
step:         Should be set to clock_delta, but can be set to different values
maxv:         The maximum velocity of a particle at creation time
wind:         The speed of the solar wind - different methods are used to
simulate the impact of photons and solar-wind on the two tails
factor:         How the particles are affected by photons and solar wind


