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| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2006-12-25 03:06:05 +0000 |
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| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2006-12-25 03:06:05 +0000 |
| commit | 1017cbebe5d5edd859e0fddad0a8600f509f4821 (patch) | |
| tree | 78bdf336648566f7a7d55f42837357dea3dd674c /pgmcrater.html | |
| parent | 16f2ac126651015a376eba864a3a35f738b0b25a (diff) | |
| download | netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.tar.gz netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.tar.xz netpbm-mirror-1017cbebe5d5edd859e0fddad0a8600f509f4821.zip | |
Place user guide into Subversion repository
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@181 9d0c8265-081b-0410-96cb-a4ca84ce46f8
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diff --git a/pgmcrater.html b/pgmcrater.html new file mode 100644 index 00000000..7aa1fc43 --- /dev/null +++ b/pgmcrater.html @@ -0,0 +1,203 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<HTML><HEAD><TITLE>Pgmcrater User Manual</TITLE></HEAD> +<BODY> +<H1>pgmcrater</H1> +Updated: 15 October 1991 +<BR> +<A HREF="#index">Table Of Contents</A> + +<A NAME="lbAB"> </A> +<H2>NAME</H2> + +pgmcrater - create cratered terrain by fractal forgery + +<A NAME="lbAC"> </A> +<H2>SYNOPSIS</H2> + + +<B>pgmcrater</B> + +[<B>-number</B> <I>n</I>] + +[<B>-height</B>|<B>-ysize</B> <I>s</I>] + +[<B>-width</B>|<B>-xsize</B> <I>s</I>] + +[<B>-gamma</B> <I>g</I>] + + +<P>All options can be abbreviated to their shortest unique prefix. + +<A NAME="lbAD"> </A> +<H2>DESCRIPTION</H2> + +<p>This program is part of <a href="index.html">Netpbm</a>. + +<P><B>pgmcrater</B> creates a PGM image which mimics cratered terrain. +The PGM image is created by simulating the impact of a given number of +craters with random position and size, then rendering the resulting +terrain elevations based on a light source shining from one side of +the screen. The size distribution of the craters is based on a power +law which results in many more small craters than large ones. The +number of craters of a given size varies as the reciprocal of the area +as described on pages 31 and 32 of Peitgen and Saupe[1]; cratered +bodies in the Solar System are observed to obey this relationship. +The formula used to obtain crater radii governed by this law from a +uniformly distributed pseudorandom sequence was developed by Rudy +Rucker. + +<P>High resolution images with large numbers of craters often benefit +from being piped through <B>pnmsmooth</B>. The averaging performed by +this process eliminates some of the jagged pixels and lends a mellow +``telescopic image'' feel to the overall picture. + +<P><B>pgmcrater</B> simulates only small craters, which are +hemispherical in shape (regardless of the incidence angle of the +impacting body, as long as the velocity is sufficiently high). Large +craters, such as Copernicus and Tycho on the Moon, have a ``walled +plain'' shape with a cross-section more like: + +<PRE> + /\ /\ +<BR> + _____/ \____________/\____________/ \_____ +</PRE> + + +Larger craters should really use this profile, including the central +peak, and totally obliterate the pre-existing terrain. + +<A NAME="lbAE"> </A> +<H2>OPTIONS</H2> + +<DL COMPACT> +<DT><B>-number</B> <I>n</I> + +<DD>Causes <I>n</I> craters to be generated. If no <B>-number</B> +specification is given, 50000 craters will be generated. Don't expect +to see them all! For every large crater there are many, many more +tiny ones which tend simply to erode the landscape. In general, the +more craters you specify the more realistic the result; ideally you +want the entire terrain to have been extensively turned over again and +again by cratering. High resolution images containing five to ten +million craters are stunning but take quite a while to create. + +<DT><B>-height</B> <I>height</I> + +<DD>Sets the height of the generated image to <I>height</I> pixels. +The default height is 256 pixels. + +<DT><B>-width</B> <I>width</I> + +<DD>Sets the width of the generated image to <I>width</I> pixels. The +default width is 256 pixels. + +<DT><B>-xsize</B> <I>width</I> + +<DD>Sets the width of the generated image to <I>width</I> pixels. The +default width is 256 pixels. + +<DT><B>-ysize</B> <I>height</I> + +<DD>Sets the height of the generated image to <I>height</I> pixels. +The default height is 256 pixels. + +<DT><B>-gamma</B> <I>factor</I> + +<DD>The specified <I>factor</I> is used to gamma adjust the image in +the same manner as performed by <B>pnmgamma</B>. The default value is +1.0, which results in a medium contrast image. Values larger than 1 +lighten the image and reduce contrast, while values less than 1 darken +the image, increasing contrast. + +<P>Note that this is separate from the gamma correction that is part +of the definition of the PGM format. The image <B>pnmgamma</B> +generates is a genuine, gamma-corrected PGM image in any case. This +option simply changes the contrast and may compensate for a display +device that does not correctly render PGM images. + +</DL> + +<A NAME="lbAF"> </A> +<H2>DESIGN NOTES</H2> + +The<B>-gamma</B> option isn't really necessary since you can achieve +the same effect by piping the output from <B>pgmcrater</B> through +<B>pnmgamma</B>. However, <B>pgmcrater</B> performs an internal gamma +map anyway in the process of rendering the elevation array into the +PGM format, so there's no additional overhead in allowing an +additional gamma adjustment. + +<P>Real craters have two distinct morphologies. + +<A NAME="lbAG"> </A> +<H2>SEE ALSO</H2> + +<B><A HREF="pnmgamma.html">pnmgamma</A></B>, + +<B><A HREF="pnmsmooth.html">pnmsmooth</A></B> + +<B><A HREF="pgm.html">pgm</A></B>, + +<DL COMPACT> +<DT>[1] +<DD>Peitgen, H.-O., and Saupe, D. eds., The Science Of Fractal Images, +New York: Springer Verlag, 1988. + +</DL> + +<A NAME="lbAH"> </A> +<H2>AUTHOR</H2> + +<PRE> +John Walker +Autodesk SA +Avenue des Champs-Montants 14b +CH-2074 MARIN +Suisse/Schweiz/Svizzera/Svizra/Switzerland + <B>Usenet:</B><A HREF="mailto:kelvin@Autodesk.com">kelvin@Autodesk.com</A> + <B>Fax:</B>038/33 88 15 + <B>Voice:</B>038/33 76 33 +</PRE> + +<P>Permission to use, copy, modify, and distribute this software and +its documentation for any purpose and without fee is hereby granted, +without any conditions or restrictions. This software is provided +"as is" without express or implied warranty. + +<a name="history"></a> +<H2>HISTORY</H2> + + +<P>The original 1991 version of this manual contains the following: + +<h3>PLUGWARE!</h3> + +<p>If you like this kind of stuff, you may also enjoy "James Gleick's +Chaos--The Software" for MS-DOS, available for $59.95 from your +local software store or directly from Autodesk, Inc., Attn: Science +Series, 2320 Marinship Way, Sausalito, CA 94965, USA. Telephone: +(800) 688-2344 toll-free or, outside the U.S. (415) 332-2344 Ext +4886. Fax: (415) 289-4718. "Chaos--The Software" includes a more +comprehensive fractal forgery generator which creates +three-dimensional landscapes as well as clouds and planets, plus five +more modules which explore other aspects of Chaos. The user guide of +more than 200 pages includes an introduction by James Gleick and +detailed explanations by Rudy Rucker of the mathematics and algorithms +used by each program. + +<HR> +<A NAME="index"> </A> +<H2>Table Of Contents</H2> +<UL> +<LI><A HREF="#lbAB">NAME</A> +<LI><A HREF="#lbAC">SYNOPSIS</A> +<LI><A HREF="#lbAD">DESCRIPTION</A> +<LI><A HREF="#lbAE">OPTIONS</A> +<LI><A HREF="#lbAF">DESIGN NOTES</A> +<LI><A HREF="#lbAG">SEE ALSO</A> +<LI><A HREF="#lbAH">AUTHOR</A> +<LI><A HREF="#history">HISTORY</A> +</UL> +</BODY> +</HTML> |