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| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2014-07-26 21:25:32 +0000 |
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| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2014-07-26 21:25:32 +0000 |
| commit | db5bf0f8bb59b9f7e05fce40afc03e6f071138de (patch) | |
| tree | 8697007439e3b0fd434ed3119e4509679725b4a2 /pgmcrater.html | |
| parent | 6c4af97b085e04914d39e928768b59d331f404f2 (diff) | |
| download | netpbm-mirror-db5bf0f8bb59b9f7e05fce40afc03e6f071138de.tar.gz netpbm-mirror-db5bf0f8bb59b9f7e05fce40afc03e6f071138de.tar.xz netpbm-mirror-db5bf0f8bb59b9f7e05fce40afc03e6f071138de.zip | |
miscellaneous update
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@2228 9d0c8265-081b-0410-96cb-a4ca84ce46f8
Diffstat (limited to 'pgmcrater.html')
| -rw-r--r-- | pgmcrater.html | 196 |
1 files changed, 29 insertions, 167 deletions
diff --git a/pgmcrater.html b/pgmcrater.html index df57dfe1..eb0ae703 100644 --- a/pgmcrater.html +++ b/pgmcrater.html @@ -2,12 +2,11 @@ <HTML><HEAD><TITLE>Pgmcrater User Manual</TITLE></HEAD> <BODY> <H1>pgmcrater</H1> -Updated: 20 November 2008 +Updated: 26 July 2014 <BR> <A HREF="#index">Table Of Contents</A> -<H2>NAME</H2> - +<H2 id="name">NAME</H2> pgmcrater - create cratered terrain by fractal forgery <H2 id="synopsis">SYNOPSIS</H2> @@ -24,189 +23,52 @@ pgmcrater - create cratered terrain by fractal forgery [<b>-randomseed=</b><i>integer</i>] +<P> +All options can be abbreviated to their shortest unique prefix. You +may use two hyphens instead of one to designate an option. You may +use either white space or equals signs between an option name and its +value. + <H2 id="description">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. - -<p>The randomness in the image is limited before Netpbm 10.37 (December -2006) -- if you run the program twice in the same second, you may get -identical output. - -<H2 id="options">OPTIONS</H2> - -<P>All options can be abbreviated to their shortest unique prefix. - -<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> +<p><b>pgmcrater</b> is obsolete. All it does now is invoke +<b>pamcrater</b>, <b>pamshadedrelief</b>, and <b>pamtopnm</b>. You should use +those programs in any new application, or if you are modifying an old program +or process that does not have to work with a version of Netpbm before 10.68 +(September 2014). <b>pgmcrater</b> exists only for backward compatibility. -<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>The combination of the three programs mentioned above performs the same +function as traditional <b>pgmcrater</b>. -<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. +<p><b>pgmcrater</b>'s <b>-number</b>, <b>-height</b>, <b>-width</b>, +and <b>-randomseed</b> options are equivalent to the options of the same name +on <b>pamcrater</b>. -<dt><b>-randomseed=</b><i>integer</i> +<P><b>pgmcrater</b>'s <b>-gamma</b> option is equivalent to +the option of the same name on <b>pamshadedrelief</b>. -<dd>This is the seed for the random number generator that generates the -pixels. +<P><B>pgmcrater</B>'s <b>-ysize</b> option is identical to <b>-height</b>; +<b>-xsize</b> is identical to <b>-width</b>. -<p>Use this to ensure you get the same image on separate invocations. +<p>Note: The former <b>pgmcrater</b> code was split into <b>pamcrater</b> +and <b>pamshadedrelief</b>. The reason for the split is that having separate +programs is more consistent with Netpbm's building block philosophy. It is +possible the separate components can be used in other applications. -<p>By default, <b>pgmnoise</b> uses a seed derived from the time of day -and process ID, which gives you fairly uncorrelated results in multiple -invocations. - -<p>This option was new in Netpbm 10.61 (December 2012). - -</DL> - -<H2 id="designnotes">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. <H2 id="seealso">SEE ALSO</H2> +<B><A HREF="pamcrater.html">pamcrater</A></B>, +<B><A HREF="pamshadedrelief.html">pamshadedrelief</A></B>, +<B><A HREF="pamtopnm.html">pamtopnm</A></B>, -<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. - -<H2 id="history">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> <H2 id="index">Table Of Contents</H2> <UL> <LI><A HREF="#synopsis">SYNOPSIS</A> <LI><A HREF="#description">DESCRIPTION</A> -<LI><A HREF="#options">OPTIONS</A> -<LI><A HREF="#designnotes">DESIGN NOTES</A> <LI><A HREF="#seealso">SEE ALSO</A> -<LI><A HREF="#author">AUTHOR</A> -<LI><A HREF="#history">HISTORY</A> </UL> </BODY> </HTML> |