pgmcrater man page on CentOS

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Pgmcrater User Manual(0)			      Pgmcrater User Manual(0)

NAME
       pgmcrater - create cratered terrain by fractal forgery

SYNOPSIS
       pgmcrater

       [-number n]

       [-height|-ysize s]

       [-width|-xsize s]

       [-gamma g]

DESCRIPTION
       This program is part of Netpbm(1).

       pgmcrater  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 for‐
       mula used to obtain crater radii governed by this law from a  uniformly
       distributed pseudorandom sequence was developed by Rudy Rucker.

       High resolution images with large numbers of craters often benefit from
       being piped through pnmsmooth.  The averaging performed by this process
       eliminates  some	 of  the jagged pixels and lends a mellow ``telescopic
       image'' feel to the overall picture.

       pgmcrater 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 Coperni‐
       cus  and Tycho on the Moon, have a ``walled plain'' shape with a cross-
       section more like:

		       /			    /	       _____/  ____________/____________/  _____

       Larger craters should really use this profile,  including  the  central
       peak, and totally obliterate the pre-existing terrain.

       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.

OPTIONS
       All options can be abbreviated to their shortest unique prefix.

       -number n
	      Causes  n	 craters to be generated.  If no -number 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.

       -height height
	      Sets  the	 height	 of the generated image to height pixels.  The
	      default height is 256 pixels.

       -width width
	      Sets the width of the generated  image  to  width	 pixels.   The
	      default width is 256 pixels.

       -xsize width
	      Sets  the	 width	of  the	 generated image to width pixels.  The
	      default width is 256 pixels.

       -ysize height
	      Sets the height of the generated image to	 height	 pixels.   The
	      default height is 256 pixels.

       -gamma factor
	      The  specified  factor  is used to gamma adjust the image in the
	      same manner as performed by pnmgamma.  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.

	      Note  that  this	is  separate from the gamma correction that is
	      part of the definition of the PGM format.	  The  image  pnmgamma
	      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.

DESIGN NOTES
       The-gamma  option isn't really necessary since you can achieve the same
       effect by piping the output from pgmcrater through pnmgamma.   However,
       pgmcrater  performs an internal gamma map anyway in the process of ren‐
       dering the elevation array into the PGM format,	so  there's  no	 addi‐
       tional overhead in allowing an additional gamma adjustment.

       Real craters have two distinct morphologies.

SEE ALSO
       pnmgamma(1), pnmsmooth(1) pgm(1),

       [1]    Peitgen,	H.-O.,	and  Saupe,  D.	 eds.,	The Science Of Fractal
	      Images, New York: Springer Verlag, 1988.

AUTHOR
       John Walker
       Autodesk SA
       Avenue des Champs-Montants 14b
       CH-2074 MARIN
       Suisse/Schweiz/Svizzera/Svizra/Switzerland
	   Usenet:kelvin@Autodesk.com
	   Fax:038/33 88 15
	   Voice:038/33 76 33

       Permission to use, copy, modify, and distribute this software  and  its
       documentation  for any purpose and without fee is hereby granted, with‐
       out any conditions or restrictions.  This software is provided 'as  is'
       without express or implied warranty.

HISTORY
       The original 1991 version of this manual contains the following:

   PLUGWARE!
       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.

netpbm documentation	       20 November 2008	      Pgmcrater User Manual(0)
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