Archive-name: graphics/faq  This message is automatically posted once a week or so in an effort to cut down on the repetitive junk in comp.graphics.  It was last changed on 26Apr93.  If you have answers to other frequently asked questions that you would like included in this posting, please send me mail.  If you don't want to see this posting every week, please add the subject line to your kill file.  Thank you.  If your copy of the FAQ is more than a couple of weeks old, you may want to seek out the most recent version.  The latest version of this FAQ is always available on the archive site pit-manager.mit.edu (alias rtfm.mit.edu) as pub/usenet/news.answers/graphics/faq.  --- _john  	John Grieggs grieggs@jpl-devvax.jpl.nasa.gov JohnG@portal.com --- Last update: 26Apr93  Sorry I haven't posted this for a couple of weeks, but I was called out of town due to a death in the family.  This is reality, folks.  What's new?  SIGGRAPH Online Bibliography Project (spencer@cgrg.ohio-state.edu).  		grieggs@jpl-devvax.jpl.nasa.gov    Contents:      1) General references for graphics questions.     2) Drawing three-dimensional objects on a two-dimensional screen.     3) Quantizing 24 bit images down to 8 bits.     4) Converting color into grayscale.     5) Quantizing grayscale to black&white.     6) Rotating a raster image by an arbitrary angle.     7) Free image manipulation software.     8) Format documents for TIFF, IFF, BIFF, NFF, OFF, FITS, etc.     9) Converting between vector formats.     10) How to get Pixar films.     11) How do I draw a circle as a Bezier (or B-spline) curve?     12) How to order standards documents.     13) How to FTP by email.     14) How to tell whether a point is within a planar polygon.     15) How to tessellate a sphere.     16) Specific references on ray-tracing and global illumination.     17) SIGGRAPH information online     18) SIGGRAPH Panels Proceedings available     19) Graphics mailing lists     20) Specific references on file formats     21) What about GIF?     22) What is morphing?     23) How to ray-trace height fields     24) How to find the area of a 3D polygon     25) How to join ACM/SIGGRAPH     26) Where can I find MRI and CT scan volume data?     27) Specific references on spatial data structures including quadtrees 	and octrees     28) Where can I get a program to plot XY(Z) data or f(x) data?     29) Specific references on PEX and PHIGS     30) SIGGRAPH Online Bibliography Project   1) General references for graphics questions:      Computer Graphics: Principles and Practice (2nd Ed.), J.D. Foley, 	A. van Dam, S.K. Feiner, J.F. Hughes, Addison-Wesley 1990, ISBN 	0-201-12110-7     Procedural Elements for Computer Graphics, David F. Rogers, McGraw 	Hill 1985, ISBN 0-07-053534-5     Mathematical Elements for Computer Graphics 2nd Ed., David F. Rogers 	and J. Alan Adams, McGraw Hill 1990, ISBN 0-07-053530-2     Three Dimensional Computer Graphics, Alan Watt, Addison-Wesley 1990, ISBN 	0-201-15442-0     An Introduction to Ray Tracing, Andrew Glassner (ed.), Academic Press 	1989, ISBN 0-12-286160-4     Graphics Gems, Andrew Glassner (ed.), Academic Press 1990, ISBN 	0-12-286165-5     Graphics Gems II, James Arvo (ed.), Academic Press 1991, ISBN 	0-12-64480-0     Graphics Gems III, David Kirk (ed.), Academic Press 1992, ISBN 	0-12-409670-0 (with IBM disk) or 0-12-409671-9 (with Mac disk)     Digital Image Warping, George Wolberg, IEEE Computer Society Press 	Monograph 1990, ISBN 0-8186-8944-7     Digital Image Processing (2nd Ed.), Rafael C. Gonzalez, Paul Wintz, 	Addison-Wesley 1987, ISBN 0-201-11026-1     A Programmer's Geometry, Adrian Bowyer, John Woodwark, Butterworths 1983, 	ISBN 0-408-01242-0 Pbk  An automatic mail handler at Brown University allows users of "Computer Graphics: Principles and Practice," by Foley, van Dam, Feiner, and Hughes, to obtain text errata and information on distribution of the software packages described in the book.  Also, users can send the authors feedback, to report text errors and software bugs, make suggestions, and submit exercises.  To receive information describing how you can use the mail handler, simply mail graphtext@cs.brown.edu and put the word "Help" in the Subject line.  Use the Subject line "Software-Distribution" to receive information specifically concerning the software packages SRGP and SPHIGS.  Errata for "An Introduction to Ray Tracing" is available on wuarchive.wustl.edu in graphics/graphics/books/IntroToRT.errata.  Errata for "Digital Image Warping" is in the same directory as "Digital-Image-Warping.errata".  All C code from the "Graphics Gems" series is available via anonymous ftp from princeton.edu.  Look in the directory pub/Graphics/GraphicsGems for the various volumes (Gems, GemsII, GemsIII), and get the README file first.  Errata to _Graphics Gems_ and _Graphics Gems II is available on wuarchive.wustl.edu in graphics/graphics/books.  A list of computer graphics, computational geometry and image processing journals is available from Juhana Kouhia, jk87377@cs.tut.fi.   2) Drawing three-dimensional objects on a two-dimensional screen.  The simple answer is, you divide by the depth.  For a more verbose explanation, see any of the above references, starting with:  The Foley & Van Dam & Feiner & Hughes "Computer Graphics" book is certainly a good start.  Chapter 6 is "Viewing in 3D", then read chapter 15, "Visible-Surface Determination".  For more information go to chapter 16 for shading, chapter 19 for clipping, and branch out from there.   3) Quantizing 24 bit images down to 8 bits.  Find a copy of "Color Image Quantization for Frame Buffer Display" by Paul Heckbert, SIGGRAPH '82 Proceedings, page 297.  There are other algorithms, but this one works well and is fairly simple.  Implementations are included in most raster toolkits (see item 7 below).  A variant method is described in "Graphics Gems", p. 287-293.  Note that the code from the "Graphics Gems" series is all available from an FTP site, as described above.  Check out John Bradley's "Diversity Algorithm", which is incorporated into the xv package and described in the back of the manual.  The ImageMagick package (see section 7 for where it is) contains another quantizing algorithm which is presented as "doing a better job than the other algorithms, but slower".  There's also an implementation of:  Wan, Wong, and Prusinkiewicz, _An Algorithm for Multidimensional Data Clustering_, Transactions on Mathematical Software, Vol. 14 #2 (June, 1988), pp. 153-162.  avialable as princeton.edu:pub/Graphics/colorquant.shar.  This code, in modified form, appears in the Utah Raster Toolkit as well.   4) Converting color into grayscale.  The NTSC formula is:      luminosity = .299 red + .587 green + .114 blue   5) Quantizing grayscale to black&white.  The only reference you need for this stuff is:      Digital Halftoning, Robert Ulichney, MIT Press 1987, ISBN 0-262-21009-6  But before you go off and start coding, check out the image manipulation software mentioned in item 7 below.  All of the packages mentioned can do some form of gray to b&w conversion.   6) Rotating a raster image by an arbitrary angle.  The obvious but wrong method is to loop over the pixels in the source image, transform each coordinate, and copy the pixel to the destination. This is wrong because it leaves holes in the destination.  Instead, loop over the pixels in the destination image, apply the *reverse* transformation to the coordinates, and copy that pixel from the source. This method is quite general, and can be used for any one-to-one 2-D mapping, not just rotation.  You can add anti-aliasing by doing sub-pixel sampling.  However, there is a much faster method, with antialising included, which involves doing three shear operations.  The method was originally created for the IM Raster Toolkit (see below); an implementation is also present in PBMPLUS.  Reference: "A Fast Algorithm for Raster Rotation", by Alan Paeth (awpaeth@watcgl.waterloo.edu) Graphics Interface '86 (Vancouver).  An article on the IM toolkit appears in the same journal.  An updated version of the rotation paper appears in "Graphics Gems" (see section [1]) under the original title.   7) Free image manipulation software.  There are a number of toolkits for converting from one image format to another, doing simple image manipulations such as size scaling, plus the above-mentioned 24 -> 8, color -> gray, gray -> b&w conversions. Here are pointers to some of them:      xv by John Bradley.  X-based image display, manipulation, and format     conversion package.  XV displays many image formats and permits editing     of GIF files, among others. The program was updated 5/92; see the file     contrib/xv-2.21.tar.Z on export.lcs.mit.edu.      PBMPLUS, by Jef Poskanzer.  Comprehensive format conversion and image     manipulation package.  The latest version is always available via     anonymous FTP as ftp.ee.lbl.gov:pbmplus*.tar.Z,     wuarchive.wustl.edu:graphics/graphics/packages/pbmplus/pbmplus*.tar.Z,     and export.lcs.mit.edu:contrib/pbmplus*.tar.Z.      IM Raster Toolkit, by Alan Paeth (awpaeth@watcgl.uwaterloo.ca).     Provides a portable and efficient format and related toolkit.  The     format is versatile in supporting pixels of arbitrary channels,     components, and bit precisions while allowing compression and machine     byte-order independence.  The kit contains more than 50 tools with     extensive support of image manipulation, digital halftoning and format     conversion.  Previously distributed on tape c/o the University of     Waterloo, an FTP version will appear someday.      Utah RLE Toolkit.  Conversion and manipulation package, similar to     PBMPLUS.  Available via FTP as cs.utah.edu:pub/urt-*,     princeton.edu:pub/Graphics/urt-*, and freebie.engin.umich.edu:pub/urt-*.      Fuzzy Pixmap Manipulation, by Michael Mauldin <mlm@nl.cs.cmu.edu>.     Conversion and manipulation package, similar to PBMPLUS.  Version 1.0     available via FTP as nl.cs.cmu.edu:/usr/mlm/ftp/fbm.tar.Z,     ftp.uu.net:pub/fbm.tar.Z, and ucsd.edu:graphics/fbm.tar.Z.      Img Software Set, by Paul Raveling <raveling@venera.isi.edu>.  Reads and     writes its own image format, displays on an X11 screen, and does some     image manipulations.  Version 1.3 is available via FTP as     export.lcs.mit.edu:contrib/img_1.3.tar.Z, and     venera.isi.edu:pub/img_1.3.tar.Z along with a large collection of color     images.      Xim, X Image Manipulator, by Philip R. Thompson.  It does essential     interactive image manipulations and uses x11r4 and the OSF/Motif toolkit     for the interface.  It supports images in 1, 8, 24 and 32 bit formats.     Reads/writes and converts to/from GIF, xwd, xbm, tiff, rle, xim, and     other formats.  Writes level 2 postscript.  Other utilities and image     application library are included.  Not a paint package.  Available via     ftp from gis.mit.edu.      xloadimage, by Jim Frost <madd@std.com>.  Reads in images in various     formats and displays them on an X11 screen.  Available via FTP as     export.lcs.mit.edu:contrib/xloadimage*, and in your nearest comp.sources.x     archive.      xli, by Grame Gill, is an updated xloadimage with numerous improvements     in both speed and in the number of formats supported.  Available in the     same places as xloadimage (contrib tape, comp.sources.x archives).      TIFF Software, by Sam Leffler <sam@okeeffe.berkeley.edu>.  Nice     portable library for reading and writing TIFF files, plus a few tools     for manipulating them and reading other formats.  Available via FTP as     ucbvax.berkeley.edu:pub/tiff/*.tar.Z or ftp.uu.net:graphics/tiff.tar.Z      xtiff, an X11 tool for viewing a TIFF file.  It was written to handle     as many different kinds of TIFF files as possible while remaining     simple, portable and efficient.  xtiff illustrates some common problems     with building pixmaps and using different visual classes.  It is     distributed as part of Sam Leffler's libtiff package and it is also     available on export.lcs.mit.edu, ftp.uu.net and comp.sources.x.     xtiff 2.0 was announced in 4/91; it includes Xlib and Xt versions.      ALV, a Sun-specific image toolkit.  Version 2.0.6 posted to     comp.sources.sun on 11dec89.  Also available via email to     alv-users-request@cs.bris.ac.uk.      popi, an image manipulation language.  Version 2.1 posted to     comp.sources.misc on 12dec89.      ImageMagick, an X11 package for display and interactive manipulation     of images.  Includes tools for image conversion, annotation, compositing,     animation, and creating montages.  ImageMagick can read and write many of     the more popular image formats.  Available via FTP as     export.lcs.mit.edu:contrib/ImageMagick.tar.Z.      Khoros, a huge (~100 meg) graphical development environment based on     X11R4.  Khoros components include a visual programming language, code     generators for extending the visual language and adding new application     packages to the system, an interactive user interface editor, an     interactive image display package, an extensive library of image and     signal processing routines, and 2D/3D plotting packages.  Available via     FTP as pprg.eece.unm.edu:pub/khoros/*.      LaboImage, a SunView-based image processing and analysis package.  It     includes more than 200 image manipulation, processing and measurement     routines, on-line help, plus tools such as an image editor, a color     table editor and several biomedical utilities.  Available via anonymous     FTP as ads.com:pub/VISION-LIST-ARCHIVE/SHAREWARE/LaboImage_3.1.tar.Z      The San Diego Supercomputer Center Image Tools, software tools for     reading, writing, and manipulating raster images.  Binaries for some     machines available via anonymous FTP in sdsc.edu:sdscpub.      The Independent JPEG Group has written a package for reading and     writing JPEG files.  FTP to ftp.uu.net:graphics/jpeg/jpegsrc.v?.tar.Z  Don't forget to set binary mode when you FTP tar files.  For you MILNET folks who still don't have name servers, the IP addresses are:      ads.com			128.229.30.16     cs.utah.edu			128.110.4.21     coral.cs.jcu.edu.au		137.219.17.4     export.lcs.mit.edu		18.24.0.12     freebie.engin.umich.edu	141.212.103.21     ftp.ee.lbl.gov		128.3.112.20     ftp.uu.net			137.39.1.9 or 192.48.96.9     gis.mit.edu			18.80.1.118     gondwana.ecr.mu.oz.au	128.250.70.62     karazm.math.uh.edu		129.7.7.6     marsh.cs.curtin.edu.au	134.7.1.1     nic.funet.fir		128.214.6.100     ftp.ncsa.uiuc.edu		141.142.20.50     nl.cs.cmu.edu		128.2.222.56     pit-manager.mit.edu		18.172.1.27     pprg.eece.unm.edu		129.24.24.10     princeton.edu		128.112.128.1     sdsc.edu			132.249.20.22     ucbvax.berkeley.edu		128.32.133.1     venera.isi.edu		128.9.0.32     weedeater.math.yale.edu	128.36.23.17     wuarchive.wustl.edu		128.252.135.4     zamenhof.cs.rice.edu	128.42.1.75  Please do *not* post or mail messages saying "I can't FTP, could someone mail this to me?"  There are a number of automated mail servers that will send you things like this in response to a message.  See item 13 below for details on some.  Also, the newsgroup alt.graphics.pixutils is specifically for discussion of software like this.  You may find useful information there.   8) Format documents for TIFF, IFF, BIFF, NFF, OFF, FITS, etc.  You almost certainly don't need these.  Read the above item 7 on free image manipulation software.  Get one or more of these packages and look through them.  Chances are excellent that the image converter you were going to write is already there.  But if you still want one of the format documents, many such files are available by anonymous ftp from zamenhof.cs.rice.edu in directory pub/graphics.formats.  These files were collected off the net and are believed to be correct. This archive includes pixel formats, and two- and three-dimensional object formats.  The future of this archive is uncertain at the moment, as Mark Hall <foo@cs.rice.edu> will apparently no longer be maintaining it.  A second graphics file format archive is now being actively maintained by Quincey Koziol (koziol@ncsa.uiuc.edu).  The latest version exists at ftp.ncsa.uiuc.edu in /misc/file.formats/graphics.formats.  Apparently, neither of these is complete, you might want to check both.  FITS stands for Flexible Image Transport System. It's a file format most often used in astronomy.  Despite the name, it can contain not only images but other things as well.  There is a regular monthly FITS basics and information posting on sci.astro.fits - read it if you want to know more.    9) Converting between vector formats.  A lot of people ask about converting from HPGL to PostScript, or MacDraw to CGM, or whatever.  It is important to understand that this is a very different problem from the image format conversions in item 7.  Converting one image format to another is a fairly easy problem, since once you get past all the file header junk, a pixel is a pixel -- the basic objects are the same for all image formats.  This is not so for vector formats. The basic objects -- circles, ellipses, drop-shadowed pattern-filled round-cornered rectangles, etc. -- vary from one format to another. Except in extremely restricted cases, it is simply not possible to do a one-to-one conversion between vector formats.  There is software for converting to and from CGM files on ftp.psc.edu.  The contributor states that it runs on Unix, MS-Windows, and possibly the Mac. A better, more specific blurb would be most welcome.  On the other hand, it is quite possible to do a close approximation, rendering an image from one format using the primitives from another. As far as I know, no one has put together a general toolkit of such converters, but two different HPGL to PostScript converters have been posted to comp.sources.misc.  Check the index on your nearest archive site.  A related frequent question is how to convert from some vector format to a bitmapped image - from PostScript to Sun raster format, or HPGL to X11 bitmap.  For example, some of the commercial PostScript clones for PC's allow you to render to a disk file as well as a printer.  Also, the PostScript interpreters in the NeXT box and in Sun's X11/NeWs can be used to render to a file if you're clever.  But in general, the answer is no.  However, if someone were to put together a vector to vector conversion toolkit, adding a vector to raster converter would be trivial.  GNU ghostscript (from the FSF - current version 2.5.2) includes drivers for both ppm and gif format files, thus it can be used as a PostScript to ppm  or a PostScript to GIF filter.  (It implements essentially all of PostScript level 1 and alot of Display PostScript and level 2).   10) How to get Pixar films.  The various John Lasseter / Pixar computer animated shorts are available on video tape.  You can order them from Direct Cinema Limited:      Film                           Individual Price      Institutional Price     Luxo, Jr.				$14.95			$50.00     Red's Dream				$19.95			$75.00     Tin Toy				$24.95			$75.00     Knickknack				$24.95			$75.00     Luxo, Jr./Red's Dream/Tin Toy	$39.95			$100.00  All tapes are on 1/2" VHS NTSC.  Add $10/tape for PAL format.  Also available:      Tin Toy T-shirt			$15.00     Knickknack 3D T-shirt		$15.00 (includes glasses)  For individual orders, add $5 S&H for the first tape or shirt, $2 for each additional tape or shirt.  For institutional orders, add $5 S&H for the first tape, $3 for each additional tape.  Foreign shipping, add $3/tape or shirt.  Call 800-525-0000 (213-396-4774 international, 213-396-3233 FAX) to charge to your credit card.  Call first to verify prices and availability.  Or, just write to:      Direct Cinema Limited     1749 14th Street     Santa Monica, CA 90404-4342  Allan Braunsdorf has this to say:  At SIGGRAPH they were selling a tape with all four shorts for $25.  That was a sale price.  You can get it for slightly more than that normally.  ($35 maybe.)  I believe it's available from RenderMan Retail (at Pixar's address).      Pixar     1001 West Cutting Blvd.     Richmond, CA. 94804     (510) 236-4000      (510) 236-0388 (FAX)  You can obtain a video directly from Pixar which contains "Luxo, Jr.", "Red's Dream", "Tin Toy" and "Knicknack" for $25.00, plus $2.50 for shipping. They will take your order over the phone or via FAX with a major credit card. I  ordered mine just last week and received it several days later. Don't expect  to be able to rent a copy from your local video store. According to the license agreement printed on the back cover of the case, it cannot be rented.   11) How do I draw a circle as a Bezier (or B-spline) curve?  The short answer is, "You can't."  Unless you use a rational spline you can only approximate a circle.  The approximation may look acceptable, but it is sensitive to scale.  Magnify the scale and the error of approximation magnifies.  Deviations from circularity that were not visible in the small can become glaring in the large.  If you want to do the job right, consult the article:    "A Menagerie of Rational B-Spline Circles"   by Leslie Piegl and Wayne Tiller   in IEEE Computer Graphics and Applications, volume 9, number 9,   September, 1989, pages 48-56.  For rough, non-rational approximations, consult the book:    Computational Geometry for Design and Manufacture   by I. D. Faux and M. J. Pratt,   Ellis Horwood Publishers, Halsted Press, John Wiley 1980.  For the best known non-rational approximations, consult the article:    "Good Approximation of Circles by Curvature-continuous Bezier Curves"   by Tor Dokken, Morten Daehlen, Tom Lyche, and Knut Morken   in Computer Aided Geometric Design, volume 7, numbers 1-4 (combined),   June, 1990, pages 33-41 [Elsevier Science Publishers (North-Holland)]   12) How to order standards documents.  The American National Standards Institute sells ANSI standards, and also ISO (international) standards.  Their sales office is at 1-212-642-4900, mailing address is 1430 Broadway, NY NY 10018.  It helps if you have the complete name and number.  Some useful numbers to know:  CGM (Computer Graphics Metafile) is ISO 8632-4 (1987).  GKS (Graphical Kernel System) is ANSI X3.124-1985.  PHIGS (Programmer's Hierarchical Interactive Graphics System) is ANSI X3.144-1988.  IGES is ASME/ANSI Y14.26M-1987.  Language bindings are often separate but related numbers; for example, the GKS FORTRAN binding is X3.124.1-1985.  Standards-in-progress are made available at key milestones to solicit comments from the graphical public (this includes you!).  ANSI can let you know where to order them; most are available from Global Engineering at 1-800-854-7179.   13) How to FTP by email.  There are a number of sites that archive the Usenet sources newsgroups and make them available via an email query system.  You send a message to an automated server saying something like "send comp.sources.unix/fbm", and a few hours or days later you get the file in the mail.  In addition, there is at least one FTP-by-mail server.  Send mail to ftpmail@decwrl.dec.com saying "help" and it will tell you how to use it.  Note that this service has at times been turned off due to abuse.   14) How to tell whether a point is within a planar polygon.  Consider a ray originating at the point of interest and continuing to infinity.  If it crosses an odd number of polygon edges along the way, the point is within the polygon.  If the ray crosses an even number of edges, the point is either outside the polygon, or within an interior hole formed from intersecting polygon edges.  This idea is known in the trade as the Jordan curve theorem; see Eric Haines' article in Glassner's ray tracing book (above) for more information, including treatment of special cases.  Another method is to sum the absolute angles from the point to all the vertices on the polygon.  If the sum is 2 pi, the point is inside, if the sum is 0 the point is outside.  However, this method is about an order of magnitude slower than the previous method because evaluating the trigonometric functions is usually quite costly.  Code for both methods (plus barycentric triangle testing) can be found in the Ray Tracing News, Vol. 5, No. 3, available from princeton.edu: pub/Graphics/RTNews/RTNv5n3.Z.   15) How to tessellate a sphere.  One simple way is to do recursive subdivision into triangles.  The base of the recursion is an octahedron, and then each level divides each triangle into four smaller ones.  Jon Leech <leech@cs.unc.edu> has posted a nice routine called sphere.c that generates the coordinates. It's available for FTP on ftp.ee.lbl.gov and princeton.edu.  16) Specific references on ray-tracing and global illumination.  Rick Speer maintains a cross-indexed ray-tracing bibliography:  Highlights of this edition-      i) more than 500 citations spanning the period from 1968 through        November '91;     ii) papers from all Siggraph, Graphics Interface, Eurographics, CG         International and Ausgraph proceedings through December, '91;     iii) all citations keyworded for easy lookup;     iv) cross-indices by keyword and author;     v)  glossary of the 119 keywords used.  The bib is in the form of a PostScript file.  The printout is 41 pages long. Below is a list of ftp sites and the dirs that contain the file. It's named "speer.raytrace.bib.ps.Z" and is compressed at most sites-               Site                             Dir 	wuarchive.wustl.edu	graphics/graphics/bib/RT.BIB.Speer/ 	karazm.math.uh.edu	pub/Graphics/ 	gondwana.ecr.mu.oz.au	pub/papers/ 	nic.funet.fi		pub/sci/papers/graphics 	coral.cs.jcu.edu.au     graphics/papers/  Eric Haines (erich@eye.com) maintains ray tracing and radiosity/global illumination bibliographies.  These are in "refer" format, and so can be searched electronically (a simple awk script to search for keywords is included with each).  The bibliographies are available at most of the sites listed above, and the most current versions are maintained at princeton.edu: pub/Graphics/Papers as "RayBib.*" and "RadBib.*".  Tom Wilson (wilson@cs.ucf.edu) has collected over 300 abstracts from ray tracing related research papers and books.  The information is essentially in plaintext, and Latex and troff formatting programs are included.  This collection is available at most of the sites above as "rtabs.*".  17) SIGGRAPH information online  [from Steve Cunningham and Ralph Orlick]  ACM-SIGGRAPH announces its online information site at  siggraph.org (128.248.245.250).  This site now provides SIGGRAPH information via both anonymous ftp and an electronic mail archive server.  The anonymous ftp service is very standard, and the ftp directory includes both conference and publications subdirectories.  To retrieve information by electronic mail, send mail to      archive-server@siggraph.org and in the subject or the body of the message include the message  send followed by the topic and subtopic you wish.  A good place to start is with the command      send index which will give you an up-to-date list of available information.   18) SIGGRAPH Panels Proceedings available  [from Steve Cunningham and Bob Judd]  ACM SIGGRAPH announces the availability of the SIGGRAPH '91 Panels Proceedings at the  siggraph.org  site (128.248.245.250).  The proceedings are available in three formats:      text   (ASCII)      rtf    (rich text format, suitable for many word processors)      word   (MS Word for the Macintosh) They may be retrieved from siggraph.org in two ways:  (1) by anonymous ftp     change to one of the directories        publications/s91/panels_proceedings/[text|rtf|word]     The text and rtf files may be downloaded in ASCII mode, while the word     files are stored in MacBinary format and must be downloaded in binary      mode.      Each directory contains a Table of Contents file (TOC) that describes the     contents of each panel file.  (2) by electronic mail     send mail to        archive-server@siggraph.org     You can retrieve either the  text  or  rtf  files.  We suggest that you     first retrieve the index files by putting one of the messages        send panel91-txt index        send panel91-rtf index     in the subject or body of the message.  You will get the necessary     information to retrieve the actual transcript files.   19) Graphics mailing lists  There are a variety of graphics-related mailing list out there, each covering either a single product or a single topic.  I have been an active participant in one of these for some time now, and find the focus and expertise which can be brought to bear on an isolated topic to be nothing short of amazing.  Please send me the appropriate information if you have any others you would like to see added.  Name:		Imagine mailing list Description:	Discussion forum for users of the Imagine 3D Rendering and 		Animation package by Impulse, Inc. Platforms:	Amiga, IBM Subscription:	imagine-request@email.sp.paramax.com Posting:	imagine@email.sp.paramax.com  Name:		DCTV mailing list Description:	Discussion forum for users of the Digital Creations DCTV 		box, software, and file formats Platforms:	Amiga Subscription:	DCTV-request@nova.cc.purdue.edu Posting:	DCTV@nova.cc.purdue.edu  Name:		Rayshade Users mailing list Description:	Discussion forum for users of the Rayshade raytracer Platforms:	Most UNIX boxes, Amiga, Mac, IBM Subscription:	rayshade-request@cs.princeton.edu Posting:	rayshade-users@cs.princeton.edu  Name:		Lightwave 3D software for Toaster mailing list Description:	Discussion forum for users of Lightwave, the Video 		Toaster modelling and rendering package Platforms:	Amiga Subscription:	lightwave-request@bobsbox.rent.com 		with "subscribe lightwave-l" in your message Posting:	lightwave@bobsbox.rent.com  Name:		POV mailing list Description:	Discussion forum for DKBTrace and POV renderers Platforms:	Unix Subscription:	listserv@trearn.bitnet Posting:	dkb-l@trearn.bitnet  Name:		Mailing List For Massive Parallel Rendering Description:	same? Platforms:	Unix Subscription:	mp-render-request@icase.edu Posting:	mp-render@icase.edu  20) Specific references on file formats      Graphics File Formats, David Kay and John Levine, Windcrest/McGraw-Hill       1992, ISBN 0-8306-3059-7 paper, ISBN 0-8306-3060-0 $36.95 hardcover,       ISBN 0-8306-3059-7 $24.95 paper.  Comments - 26 formats, no software       (this is good, IMHO - I prefer books which are non-platform-dependent).       Questions about this book may be sent to gbook@iecc.cambridge.ma.us.   21) What about GIF?  GIF stands for Graphics Interchange Format.  It is portable and usable upon a wide variety of platforms.  It is quite limited in some ways (yes, the keeper of the FAQ has some opinions after all), and in fact, I don't like it much.  However, it looks to me like the most-Frequently Asked Question which was not previously covered in this list.  The following is a list of newsgroups and the like where one could go to find out about GIF.  Subject: alt.binaries.pictures FAQ - General info Subject: alt.binaries.pictures FAQ - OS specific info Newsgroups: alt.binaries.pictures.d,alt.binaries.pictures.misc, 	alt.binaries.pictures.utilities,alt.binaries.pictures.fractals, 	alt.binaries.pictures.fine-art.d,news.answers  Available in the indicated USENET newsgroup(s), or via anonymous ftp from pit-manager.mit.edu in the files:  /pub/usenet/news.answers/pictures-faq/part1 /pub/usenet/news.answers/pictures-faq/part2  Also available from mail-server@pit-manager.mit.edu by sending a mail message containing any or all of:  send usenet/news.answers/pictures-faq/part1 send usenet/news.answers/pictures-faq/part2  Send a message containing "help" to get general information about the mail server.  Also, you could check out the resources described in sections 7, 8, and 20 above for more information.   22) What is morphing?  Warping is the deformation of an image by mapping each pixel to a new location. Morphing is blending from one image or object to another one. Valerie Hall has written an excellent introduction to warping and morphing. This is available for anonymous ftp from marsh.cs.curtin.edu.au in the directory pub/graphics/bibliography/Morph. There are three files:          morph_intro.ps.Z     (PostScript version, many pictures - 1.5M)         morph_intro.txt.Z    (text version)         m_responses.Z        (Responses to morphing questions)  The files are compressed, so you must use binary transfer and uncompress them afterwards.   23) How to ray-trace height fields  Height fields are a special case in ray-tracing.  They have a number of uses, such as terrain rendering, and some optimization is possible.  Thus, they get their own FAQ section.  Note that further references can no doubt be located via the ray-tracing bibs in section 16 above.  The following paper seems to be the definitive reference:  F. Kenton Musgrave Grid Tracing: Fast Ray Tracing For Height Fields July, 1988 <musg88.ps.Z>  This is available as "Research Report YALEU/DCS/RR-639" from Yale University, it's also in the SIGGRAPH '91 Fractal Modeling in 3D Computer Graphics and Imaging course notes, and (best of all) it's available on the net:      nic.funet.fi		pub/sci/papers/musg88.ps.Z     weedeater.math.yale.edu	pub/Papers/musg88.ms.Z     princeton.edu		pub/Graphics/Papers/musg88.ms.Z     coral.cs.jcu.edu.au		graphics/papers/musg88.ps.Z     gondwana.ecr.mu.OZ.AU	pub/papers/musg88.ms.Z and musg88.ps.Z  An implementation of this paper may be found in Rayshade.  Another paper exists:  %A David W. Paglieroni %A Sidney M. Petersen %T Parametric Height Field Ray Tracing %J Proceedings of Graphics Interface '92 %I Canadian Information Processing Society %C Toronto, Ontario %D May 1992 %P 192-200  And still one more:  Musgrave, Kolb, and Mace "The Synthesis and Rendering of Eroded Fractal Terrains", Computer Graphics Vol 23, No. 3 (SIGGRAPH '89 procedings) p. 41-50    24) How to find the area of a 3D polygon  	The area of a triangle is given by (in C notation),       area = 0.5 * ( ( x[0] * y[1] ) + ( x[1] * y[2] ) + ( x[2] * y[0] ) - 	            ( x[1] * y[0] ) - ( x[2] * y[1] ) - ( x[0] * y[2] ) );  and the area of a planar polygon is given by       area = 0.0;       for ( i = 0; i < n - 1; i++ )          area += ( x[i] * y[i + 1] ) - ( x[i + 1] * y[i] );      area += ( x[n - 1] * y[0] ) - ( x[0] * y[n - 1] );      area /= 2.0;  If the area is a negative number, the polygon or triangle is clockwise, if positive, it is counterclockwise.  >From Ronald Golman's Gem (in Graphics Gems II - see section 1 above), "Area  of Planar Polygons and Volume of Polyhedra:"  The area of a polygon P0, P1, P2, ... Pn, not in the x-y plane, is given by       Area(Polygon) = 1/2 * | N . Sigma { Pk x Pk+1 } |  where N is the unit vector normal to the plane and P is a polygonal vertex.  The . represents the dot product operator and the x represents the cross product operator.  Sigma represents the summation operator.  | | represents the absolute value operator.  Pn+1 is equal to P0.   25) How to join ACM/SIGGRAPH  Probably the easiest way to join ACM/SIGGRAPH is to trot over to your local technical library and find a copy of Communications of the ACM. Somewhere within the first few pages will be an application blank. Fill it out and mail it in.  ACM membership for students costs $23.00, Voting or Associate Membership $77.00 (yearly)  SIGGRAPH student membership costs an additional $16.00, $26.00 for Voting or Associate Members (also yearly).  To get TOG (Transactions on Graphics) it's another $26.00 for students and $31.00 for Voting or Associate Members.  If you just want to join SIGGRAPH without joining ACM, it'll cost you $59.00 (no student discount).  There are surcharges for overseas airmailing of publications.  ACM Member services may be contacted via email at acmhelp@acmvm.bitnet.  Their phone number is (212) 626-0500.  FAX number (212) 944-1318. Snailmail address:                  ACM                 PO Box 12114                 Church Street Station                 New York, New York 10257  SIGGRAPH `93 will be held in Anaheim, California, at the Anaheim Convention Center (just up the street from Disneyland) on August 1-6, 1993.  26) Where can I find MRI and CT scan volume data?  Volume data sets are available from the University of North Carolina at omicron.cs.unc.edu (152.2.128.159) in /pub/softlab/CHVRTD.  (Commerical use is prohibited.)  Head data - A 109-slice MRI data set of a human head.  Knee data - A 127-slice MRI data set of a human knee.  HIPIP data - The result of a quantum mechanical calculation of a SOD data of a one-electron orbital of HIPIP, an iron protein.  SOD data - An electron density map of the active site of SOD (superoxide dismutase).   CT Cadaver Head data - A 113-slice MRI data set of a CT study of a cadaver head.   MR Brain data -  A 109-slice MRI data set of a head with skull partially removed to reveal brain.  RNA data - An electron density map for Staphylococcus Aureus Ribonuclease.   27) Specific references on spatial data structures including quadtrees 	and octrees  H. Samet, The Design and Analysis of Spatial Data Structures, Addison-Wesley, Reading, MA, 1990. ISBN 0-201-50255-0.  H. Samet, Applications of Spatial Data Structures:  Computer Graphics, Image Processing, a nd GIS, Addison-Wesley, Reading, MA, 1990. ISBN 0-201-50300-0.   28) Where can I get a program to plot XY(Z) data or f(x) data?  Gnuplot is a command-driven interactive data/function  plotting program.  It runs on just about any machine, and is very flexible in terms of supported output devices.  The official North American distribution site for the latest version is dartmouth.edu in /pub/gnuplot.  More information is available from the USENET newsgroup comp.graphics.gnuplot and its FAQ, graphics/gnuplot-faq.  ACE/gr (xmgr - Motif/xvgr - XView) is a data/function plotting tool for  workstations or X-terminals using X.  Available from ftp.ccalmr.ogi.edu in /CCALMR/pub/acegr.  robotx (Robot) is a general purpose plotting and data analysis program. Requires XView, X-terminal or workstation.  Available from sunsite.unc.edu in /pub/academic/data_analysis.  Xgraph is a popular two-dimensional plotting program that accepts data in a form similar to the unix program graph and displays line graphs, scatter plots, or bar charts on an X11 display.  Available from ic.berkeley.edu in /pub.  Drawplot is a program for drawing 2D plots on X10/X11 windows, SUNVIEW displays, or HP2648 terminals. Available from xcf.berkeley.edu in /src/local.  29) Specific references on PEX and PHIGS      PEXlib Programming Manual, Tom Gaskins, 1154 pages, O'Reilly & Associates, 	ISBN 1-56592-028-7      PEXlib Reference Manual, edited by Steve Talbott, 577 pages, O'Reilly & 	Associates, ISBN 1-56592-029-5      PHIGS Programming Manual, Tom Gaskins, 908 pages, O'Reilly & Associates, 	ISBN 0-93775-85-4 (softcover), ISBN 0-937175-92-7 (casebound)      PHIGS Reference Manual, edited by Linda Kosko, 1099 pages, O'Reilly & 	Associates, ISBN 0-937175-91-9   30) SIGGRAPH Online Bibliography Project  The ACM SIGGRAPH Online Bibliography Project is a database of over 15,000 unique computer graphics and computational geometry references in BibTeX format, available to the computer graphics community as a research and educational resource.  The database is located at "siggraph.org".  Users may download the BibTeX files via FTP and peruse them offline, or telnet to "siggraph.org" and log in as "biblio" and interactively search the database for entries of interest, by keyword.  Additions/corrections/suggestions may be directed to the admin, "bibadmin@siggraph.org".