Top Document: comp.graphics.rendering.raytracing FAQ (part 2/2) Previous Document: 5 - Further Information and Resources Next Document: 7 - Roll the Credits See reader questions & answers on this topic! - Help others by sharing your knowledge Now that you've been blasted with lists of FTP sites, utilitites, software, books, etc., etc., the only questions you could possibly have left to ask are those that...erm...aren't about FTP sites, utilities, software or books, I suppose. So this section attempts to answer all the other questions that don't fit in above. ------------------------------ Subject 6.1 - "Can I post binaries/images to this group?" In a word, NO. The group is part of the comp.graphics hierarchy which should be, and is, strictly non-binary. The reason for this is that uuencoded binaries tend to be very large. By restricting binary postings to the comp.binaries and alt.binaries hierachies, those sites who do not want to carry large volume groups can easily ignore anything under these two streams. Remember that most sites pay to transfer and store news and if they find that comp.graphics.rendering.raytracing is getting too expensive, they can just stop carrying it. That is their right and priviledge. Also remember that many individuals download this group via modems and pay for every byte. They tend to get a bit annoyed when they have to fork out lots of money to download stuff they might not even want. But what if you're really desperate to share with us your latest ray tracing you've done depicting a mutant star camel exploding in a super nova while naked dancers melt into a checkered floor? (The checkered floor always turns up sooner or later). Great! I'm sure we'd love to see it, you should post it to news:alt.binaries.comp-graphics or news:alt.binaries.pictures.misc. If you're posting it (obviously not to c.g.r.r), you should remember to uuencode it and split it into small (less than 64k) parts. Make sure to use an informative title like: RAY TRACING: MUTANT.GIF: mutant star camel scene, part 1 of 6 and include a text posting (part 0 of n) that describes the picture, states what format it's in (.gif, .jpg, etc.), what size it is, how many colours, and anything else you want to mention. The more you put, the better. You can then post to news:comp.graphics.rendering.raytracing, along with a few lines saying "I've just posted this image to alt.binaries.pictures.misc". By the way, ray tracing pictures generally get a good response over in a.b.p.m and you'll often see request for them in news:alt.binaries.pictures.d (discussion group). The other alternative is to upload the picture or utility to an ftp site and use comp.graphics.rendering.raytracing to announce it in the same way. ------------------------------ Subject 6.2 - "Where can I find model data for..." The former Avalon site has been closed down, and the Avalon model site has been moved to Viewpoint, a commercial model vendor, as of 07/95. It is the promise of Viewpoint that the Avalon data remain freely available to all. Avalon is now located at: ftp://avalon.viewpoint.com/avalon/ or http://www.viewpoint.com/avalon.html or ftp://ftp.povray.org/pub/mirrors/avalon/ is a mirror. Avalon is probably the best site you'll find for free 3D model data. However, the home page at Viewpoint also has pointers to their free and commercial models if you can't find what you need at Avalon. Another commercial model vendor on the net is MeshMart at: http://cedar.cic.net/~rtilmann/mm/ (See also 2 - FTP Sites, Web Sites, Mailing Lists) ------------------------------ Subject 6.3 - "How can I view these pictures?" If you're using Unix, you can use XV which is available as a source distribution from many sites, or ImageMagick, again available on many sites. It should be noted that XV v3.00, which is installed at some sites, does not display TGA files, although XV v3.10 and ImageMagick do. If XV and/or ImageMagick do not support a particular image format you have, it probably doesn't actually exist :-). However, if you need to handle large numbers of images in batch form, or if you don't have an X windows display and you want to manipulate images (but not necessarily view them), chances are that the netpbm package is what you need. Netpbm is a command line utility, and can converting images from practically any format to any other, but it does not display the images themselves. If you're on a PC and using DOS, you'll probably want to get one of the myriad of image display programs, such as QPV or PICLAB to do the displaying. For MS-Windows users, lview seems to be a popular display/editing program, and for OS/2 there is PMJpeg. There are kegs-o-megs of PC image viewers at most ftp sites, so take your time and find one you like that has the features you need. These packages are available in countless locations on the Internet (see 4 - Utilities and Other Software). ------------------------------ Subject 6.4 - "What's the difference between rendering and ray tracing?" Ray tracing *is* rendering. Rendering is the term which refers to the act of "painting" a digital image from some stored data. There are many different methods of rendering, such as ray tracing, radiosity, z-buffer, painter's algorithm, etc. Each method has its own merits, usually a trade-off between speed and quality or capabilities. ------------------------------ Subject 6.5 - "This picture doesn't trace." I know it might sound a bit obvious, but have you read the error message and tried to understand it? Did you look in the manual? Still nothing? I know I sound cynical, but it's not uncommon for people to have something go wrong and then post straight to the 'net without even *trying* to figure out what went wrong. A little patience and thought will solve the problem a lot quicker. Here's some common problems: * POV-Ray versions A lot of people get fooled when trying to trace old POV-Ray code with a new version. Use the -MV1.0 option or use #version in the code to get the parser to treat it as old code. You may find that you have to change any references to "shapes.inc" to "shapes.old". The POV-Ray docs can help you out here. What do you mean "I have't read the docs"? Go read them. * Include files Have you checked that you've #included any include files that your scene requires? Include files tend to define colours, textures or objects that your scene may use. Make sure you've told the ray tracer where to look for include files. For example, POV-Ray uses the -L option to specify the directory where include files are, eg. -L/home/adilger/povray/include The POV-Ray docs can help you out here. What do you mean "I haven't read the docs"? Go read them. ------------------------------ Subject 6.6 - "I traced my picture, but I can't see anything." If the picture is totally dark, there are a few things you can check: * Have you added any light sources? * Are the light sources blocked by anything? (This is a favourite of Andy's - he puts in a large sphere for the sky and then adds or moves lights *outside* the sky sphere. Where did the lights go?) * Where are you looking? Is your camera inside an object (oops)? * Have you applied textures to your objects. If you haven't, you might find that your ray tracer defaults your object to be black. Have you actually put anything into the picture? This isn't as silly as it sounds. If you #declare on object (POV-Ray, again) like this: #declare my_object= union { sphere { <0, 0, 0> 1 } cylinder { <-2, 0, 0> <2, 0, 0> 0.5 } } Then you have just told the ray tracer that when you refer to "my_object", you actually mean a union of a sphere and a cylinder as shown. To use the object, you must explicitly put it in: object { my_object } ------------------------------ Subject 6.7 - "I traced my picture, but the output is garbage." Did you specify the correct output file format? Most ray tracers have several options for output file formats. If you haven't explicitly specified the output format, there's a good chance it's not what you want it to be. Also note that using a file name with an extension (like .TGA) does not necessarily mean this is the format of image. This is a common mistake with POV-Ray 2.2 for Unix which uses an obscure output format by default. Similarly, if you don't compile in the URT support for Rayshade, you will get MTV format output files. What is MTV you ask? It's one of the very first freeware ray tracers, written by Mark Terrence VandeWettering, now with Pixar. Some image display programs use the file extension to determine the file contents, so if you call the file output.tga, and it's actually a PNG image, your display program may complain that the TGA file is corrupted. This is especially a problem with TGA files, since they do not start with a "magic number", and this makes file identification difficult. ------------------------------ Subject 6.8 - "What does this mean..." Some ray tracing and related terms you might come across: * CSG (Constructive Solid Geometry) - A term describing ways in which you can build up complex shapes from simple primitives like cubes, speres, and cylinders. By combining the primitives in different ways, namely adding them together (union), taking one away from the other (difference) or getting the part where they intersect (intersection) you can make small building blocks, which can in turn be used to make more complex CSG objects. * Height Field - A height field can be thought of as a 3 dimensional bar graph. It is a grid of data where the value at any point corresponds to the "altitude" of that point. Height fields are typically stored as grayscale images with the lighter areas being higher, and the darker areas lower. Heightfields are usually used to create natural looking terrain, such as mountains, hills, and craters, but they can be used anywhere that you need to extrude a shape (eg a prism, text, or an embossed pattern). You can get software that will convert actual altitude data into a heightfield image (DEM2POV), software that will create realistic heightfields mathematically (HF-Lab, Terrain Maker, Vista Pro, Fractint), or software to create raised patterns (Level Connector). * Radiosity - Most ray tracers use an empirical lighting model - that is the parameters specified for lights and objects do not really correspond to physical properties, but are selected to make things look good. Radiosity calculates the reflections and lighting between all objects in the scene, and gives a more realistic rendering of the scene. This method is very good at representing the diffuse lighting in a scene, while ray tracing is better at handling the reflection. In some renderers, both techniques are used to give spectacular results. Needless to say, radiosity is even more computationally complex than ray tracing. ------------------------------ Subject 6.9 - "Rotating/scaling this object doesn't work properly." With most ray tracers, rotating on object in a given direction rotates it around the axis *not* around its own centre. If your object is centred on the X axis and you rotate it in the X direction, it will spin. However, if it is some distance from the axis and you rotate it, it will "orbit" the X axis, tracing a circle with a radius equal to the distance of the object from the axis. Confused? Think of the Earth spinning on it's axis. It doesn't go anywhere because it is centred on its axis (ignoring rotation around the Sun). The moon, however is some distance from the Earth's axis and as it rotates around that axis, it travels through space, orbiting the Earth. To work out which way something will move, you need to know if your ray tracer uses a left or a right handed co-ordinate system. POV-Ray, for example, uses a left handed system. To work out which way an object will turn, point your thumb in the positive direction of the axis you're rotating in and the way you fingers curl indicate the direction of positive rotation. The hand you use to do this depends on your ray tracer; left-handed, use left hand, right handed, use right hand. The same thing goes for scaling. If your object is already some distance away from the origin, that distance will also get scaled. For example, if you have a sphere 2 units away from the origin, with a radius of 1 and you scale it by 2, the radius will now be 2 *and* the distance from the origin will be 4. ------------------------------ Subject 6.10 - "Why is the Z axis is pointing the wrong way?" A common complaint in c.g.r.r is why POV (or other computer graphic program) has the Z axis pointing in the "wrong" direction. What's wrong with the people who make this software? Didn't they take elementary geometry? The truth is, what is the right co-ordinate system in computer graphics, depends on where you started out. Engineering and mathematics people use a right-handed co-ordinate system. The X and Y axes form a horizontal plane, with X increasing to the right and Y increasing "upwards". When we have a Z axis, it is usually considered the "height" or "altitude" axis, and it would be coming out of the page of a 2D graph. The origins of computer graphics was in 2D, shown on a monitor, with the same X and Y axes (X positive to the right and the Y positive upwards). When 3D was added in, the Z axis was used as the "depth" into the monitor, since one was only interested in items "in front" of the user, and not those behind where they couldn't be seen. Since it was easiest to only store positive numbers for the Z value, the Z axis is positive away from the viewer. This is a left-handed co-ordinate system. Because of the way the graphics appear on the monitor, it is often easiest to consider that Y is the vertical axis, since it is consistent for both 2D and 3D graphics. As for which one is better - you decide. However, don't complain about software which uses the one that you don't like, since you can always go ahead and write your own software... ------------------------------ Subject 6.11 - "Which 3D accelerator card will speed up raytracing best?" The answer to this question is generally "None". Commercial 3D cards accelerate the transformation of 3D polygons, shading, z-buffering, rasterizing, and related functions. These are all related to scan-line rendering, but are not really as useful for ray tracing. It's not because 3D cards are new, and it's not because people who write ray tracers don't know about these cards, but because these cards are simply not useful for speeding up ray tracing. ------------------------------ Subject 6.12 - "Who is..." This section looks at some of the ray tracing artists and people who are particularly well known for their work, be it images or software. The list is in strict alphabetical order as I don't fancy the task of trying be subjective about who's pictures are better than who's. A VERY IMPORTANT POINT: A lot of these people have to pay for their Email and 'net access. DO NOT send them large images or other posts without checking with them first. Certain members of the POV team have recently had some pretty hideous costs (like $30 for 1 mail item) because of this. (Was that OK, Dan?) * Truman Brown Truman Brown <71477.221@compuserve.com> is particularly well known for his "woild" series of images. He is a self-confessed "Obsessed Programmer / Trace-aholic" and has written a range of very useful utilities, including Connect The Dots Smoother (CTDS), Circle Master (CM) and its companion, HYPE. He has an understanding wife but his kids wish he didn't hog the PC so much. His utilities are available from most FTP sites and you can check out some of his images at: ftp://ftp.povray.org/pub/povray/Hall-Of-Fame/ http://www.povray.org/hof/ * Dan Farmer One of the original POV-Ray development team, Dan Farmer has created a large portion of the POV-Ray demo scenes, as well as other amazing images including the stunning "frosty.gif". Dan explains how he did it: "The image was done in POV-Ray. It's really quite simple. The face is a freely available dataset produced by Mira Imaging... I'm sure it exists on the net somewhere. The fractal shape is done with Fractint, using the 16 bit continuous potential features. It's an inverted Mandelbrot set. The silver texture is Silver1 in textures.inc. The sky is the usual bozo, but it's mapped onto a plane, not a sphere. Floor is an imagemapped plane. That's all there is to it!" Frosty's at ftp://ftp.povray.org/pub/povray/Hall-Of-Fame/frosty.gif The Mira dataset ftp://ftp.povray.org/pub/povray/scenes/ Unfortunately, Dan rarely releases his source code any more due to certain unscrupulous sorts using his images for commercial purposes without payment or even permission. Luckily, he has made the scene file for this image available on the POV-Ray CD-ROM which is also available online (see 1 - Ray Tracing Software). Dan has taken a leave of absence from the POV Team because he wants to spend more time with his real life than answering questions. He asks that people not contact him with questions about POV-Ray. * Eric Haines Eric A. Haines <erich@eye.com> has probably done as much as anyone to make ray tracing as understandable and accessible as it currently is. His many, many hours compiling the Ray Tracing News helped lots of people understand and develop ray tracing software, as well as serve as a forum for discussion between those interested in the art. (See 5 - Further Information and Resources). * Mike Miller If you ever need inspiration to see what can be done using POV-Ray, a piece of graph paper and a pencil, then look at some of Mike Miller's <70353.100@compuserve.com> images. His pictures never fail to impress and he has undoubtedly produced some of the best pictures ever created with POV-Ray. Mike created many of the demo scenes that come with POV-Ray and he is responsible for the excellent textures in "stones.inc". The cover story of the January 1994 IEEE Computer Graphics and Applications is entitled "Mike Miller's Many Hats" and looks at his work and includes many of his pictures. You can find his images and scene files on many sites. A good one to start with is ftp://ftp.povray.org/pub/povray/Hall-Of-Fame/ or ftp://ftp.povray.org/pub/povray/images/. Particular ones to look out for are benz9.jpg (model of a 1928 Mercedes Benz), camera.jpg, bug1.gif, etc., etc., the list goes on. * Ken Musgrave Ken Musgrave <musgrave@siggraph.org> was called "the first true fractal-based artist" by Benoit Mandelbrot, the father of fractals. His work shows the artistic side of what can be done with mathematics and inspiration. Many have seen his image "Blessed State" inside the cover of "Computer Graphics, Principles and Practice" by Foley & van Dam, the authoratative computer graphics book. He has an excellent exhibit of his works available on the WWW at: http://www.wizardnet.com/musgrave/ Ken is currently applying his skills to creating an entire world model with algorithmic principles. This project is named Slartibartfast, after the designer of worlds in the "Hitchiker's Guide to the Galaxy" series. User Contributions:Top Document: comp.graphics.rendering.raytracing FAQ (part 2/2) Previous Document: 5 - Further Information and Resources Next Document: 7 - Roll the Credits Part1 - Part2 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: mk@cyrus.ruhr.de
Last Update March 27 2014 @ 02:11 PM
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