From: David Caballero GNOMO Subject: TECH: Virtual Forests rendering Date: Wed, 20 Jan 1993 19:48:39 CST 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.