From: David Caballero GNOMO <U2014001@VEC.CCUPM.UPM.ES>
Newsgroups: sci.virtual-worlds
Subject: TECH: Virtual Forests rendering
Date: Wed, 20 Jan 1993 19:48:39 CST
Organization: University of Washington
NNTP-Posting-Host: stein.u.washington.edu
Originator: hlab@stein.u.washington.edu


This article is to reply those asking me for a bit more of information about 3D
modelling and rendering of forests, i.e John Curtis, Chris Hand, Diego Montefus
co, Paul Simpson, Thomas Eskridge, Michael Almquist and Thad E Starner:

    I have been involved as analyst and programmer in a research team of Forest
 Fire Simulation from 1989. In such project I developed a first approximation o
f what I thougt a burned forest should seem like. It was entirely programmed on
 a PC with starndard VGA graphics and, may I have to admit it, it was a several
limitation to my espectatives. The first module of the project was then present
ed as a paper in the IXX World IUFRO Congress, at Montreal, Canada, in August o
f 1990. Then I showed it to Peter Kourtz, one of the greats on Forest Fire Rese
arch (he is actually involved in some VR like projects with fire fightning heli
copter simulators and computer programming using voice recognition) at Petawawa
 Forest Institute. He, then, said: "Oh, very nice graphics". Yes, it was, but I
 was seeking a little bit further.

At the end of that very year I went to the II World Congress on Forest Fire Res
earch, an then again, I had the opportunity to show my work to Richard R. Rothe
rmel, Forest Fire Research Leader at Intermountain Research Laboratory (USDA) a
t Montana, and Francis Fujioka, at Riverside (CA, USDA). This last one told me:
"Well, your work sounds interesting but, what do you consider is the next step?
". And the next step, I told him, was the high end graphics and the human inter
facing with computers.

    All this facts lead us to the present. Nowadays I am working with other har
dware and software, but my goals are the same. I intend to a) Represent high en
d computer generated pictures of landscapes to see what can be in the future wi
th such or such activity taking place on natural environments. The area of acti
vities I am refering to is civil engineering and, more close, forest and natura
l environmental engineering. b) To involve VR techniques for the forests and ge
neral natural environmental management, by means of developing new software or
adapting the existing one to VR environments. In this way I am thinking about 3
D GIS whit data input and management via standard VR devices (such as dataglove
s etc.). (I have a lot to speak about this, because I have several ideas that I
 want to be real). c) To develop a VR Operating System for Forest Fire Crew tra
ining. Supose all those guys being involved in hazarous situations when a fire
occurs and are rarely expected. It will take artificial intelligence inputs of
those with experience and, virtually, give the other some hints as the virtual
forest fire simulation take place. d) One of my dreams is to submit a work to I
MAGINA and SIGGRAPH showing how can I represent natural environments, focusing
mostly on tree and forests modelling and rendering. At this point I have got an
 idea called CYBERJACK, a project I want to develop along 1993 year to be prese
nted at 1994. (Is a story about CYBERnetic timberJACKs, really amazing).

    Getting to the point I am nowadays working over a Silicon Graphics IRIS
CRIMSON XS24 (Is hard to find, buy or share such computers in Spain) with TDI s
oftware, i.e. TDI Professional Animator Explore. The package counts with a modu
le of 3D tree modelator, namely TDIAMAP, developed by CIRAD at Montpellier (Fra
nce). As forest engineer I have to say that the species are very realistic ones
but it has a drawback: the huge facets databases it generates. Trying to modela
te a whole forest, with thousand of large, medium and small trees as well as ot
her plant levels such as shrubs and grass, lead us to millions of facets to be
computed for ONE final rendered frame.

    The firsts attempts to render it where unfructuous because only 16 trees co
llapsed the swap disk space. So I decided to render the image in several stages
and then compose all of them with a Z buffering. Because of the type of Z-compo
se involved the same space disk and time rendering, so nothing solved. But, and
 here is the idea, why to Z-compose?.

    So I went to the root of the problem. Why takes so many disk space and time
the rendering of a forest?. Is it because of the complexities of the tree model
 used? The answer was NOT. The rendering routines of TDI Explore analizes each
pixel of the screen tracing a rendering line crossing trough ALL of the facets
that are behind that very pixel. This is the key. To ratify this hyphothesis I
modelled 10 thousand of non-complex objects, i.e. a single hexaedron, and place
d it one in front the other in a single row. Then I placed the virtual camera i
n front of the first one so only one object could be visualized. But there were
10,000 x 2 = 20,000 facets in " front" of each pixel being analized by the rend
er routine. And Tah taaah Y "process stopped due to no more swap space". The sa
me limitation I had with a very complex object.

     The solution then was obvius. I have to render the forest splited in scrip
ts with trees placed roughly in the same plane but with FEW FACETS OVERLAPPING
each other. Then a single compose OVER did the work. I called it Multiple PLane
s Rendering Compose. Some limitations to the method are: 1) The camera is neede
d to move rougly parallel to the normal of the analisys planes. The rendering o
f the quck turns are rather complicated to set. 2) The method implies complex s
cript editing, precise object location and a very carefull order in the final c
omposition. 3) It involves a lot of scripts, one per analisys plane. 3) How to
render the shadow casting over the floor and over the other trees (I think I've
 got the solution projecting the shadow along a vector parallel to the analisys
planes). 4) It is possible to render turns of the camera by succesive composing
 of renders, not by planes, but by concentric cilindric surfaces from the camer
a location.

    At the moment I am programming in C-Shell all the process involved. I will
send you a copy of the code when I finish it.

    Please, send me any comments about this article that, be care of it, is the
 only one being published at the date.

    Thanks all of you sharing knowledges. VR is rougly known here in Spain and
I can't say if there is projects on it. But it is overwhelming how it is being
accepted in the rest of the world. Don't wait for the future, the future is her
e right now.

Cheers.
GNOMO.