1Pamcrater User Manual(0)                              Pamcrater User Manual(0)
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NAME

6       pamcrater - create cratered terrain by fractal forgery
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SYNOPSIS

11       pamcrater
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13       [-number n]
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15       [-height pixels]
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17       [-width pixels]
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19       [-randomseed=integer]
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21       [-verbose]
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DESCRIPTION

25       This program is part of Netpbm(1).
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27       pamcrater  creates a PAM image which is a terrain map (not a visual im‐
28       age) of cratered terrain.  The terrain is as if a given number  of  im‐
29       pacts into a surface create craters with random position and size.
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31       The  size distribution of the craters is based on a power law which re‐
32       sults in many more small  craters  than  large  ones.   The  number  of
33       craters  of  a  given  size varies as the reciprocal of the area as de‐
34       scribed on pages 31 and 32 of Peitgen and Saupe[1]; cratered bodies  in
35       the  Solar  System are observed to obey this relationship.  The formula
36       used to obtain crater radii governed by this law from a uniformly  dis‐
37       tributed pseudorandom sequence was developed by Rudy Rucker.
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39       A  terrain map is a two dimensional map of terrain elevations.  the PAM
40       image that pamcrater produces is therefore not a  visual  image  but  a
41       depth-one  image of tuple type "elevation", with the sample value being
42       proportional to an elevation.
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44       You can visualize the terrain map by generating a shaded  relief  image
45       of it with pamshadedrelief.
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47       High resolution images with large numbers of craters often benefit from
48       being piped through pnmsmooth.  The averaging performed by this process
49       eliminates  some  of  the jagged pixels and lends a mellow ``telescopic
50       image'' feel to the overall picture.
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52       pamcrater generates only small  craters,  which  are  hemispherical  in
53       shape (regardless of the incidence angle of the impacting body, as long
54       as the velocity is sufficiently high).  Large craters, such as Coperni‐
55       cus  and Tycho on the Moon, have a ``walled plain'' shape with a cross-
56       section more like:
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58                       /\                            /\
59                 _____/  \____________/\____________/  \_____
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62       Larger craters should really use this profile,  including  the  central
63       peak, and totally obliterate the pre-existing terrain.
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65       The maxval of the PAM image is always 65535.
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67       The  randomness  in  the image is limited before Netpbm 10.37 (December
68       2006) -- if you run the program twice in the same second, you  may  get
69       identical output.
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OPTIONS

74       In  addition  to  the options common to all programs based on libnetpbm
75       (most notably -quiet, see
76        Common Options ⟨index.html#commonoptions⟩ ), pamcrater recognizes  the
77       following command line options:
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79       All options can be abbreviated to their shortest unique prefix.
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83       -number n
84              This  causes  pamcrater  to  generate  n craters.  If you do not
85              specify -number, it generates 50000 craters.   Don't  expect  to
86              see  them all!  For every large crater there are many, many more
87              tiny ones which tend simply to erode the landscape.  In general,
88              the  more  craters  you  specify, the more realistic the result;
89              ideally you want the entire terrain  to  have  been  extensively
90              turned  over  again and again by cratering.  High resolution im‐
91              ages containing five to ten million  craters  are  stunning  but
92              take longer to create.
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95       -height height
96              This  sets  the  height of the generated image to height pixels.
97              The default height is 256 pixels.
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100       -width width
101              This sets the width of the generated image to width pixels.  The
102              default width is 256 pixels.
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105       -randomseed=integer
106              This  is the seed for the random number generator that generates
107              the pixels.
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109              Use this to ensure you get the same image  on  separate  invoca‐
110              tions.
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112              By  default,  pamcrater uses a seed derived from the time of day
113              and process ID, which gives you fairly uncorrelated  results  in
114              multiple invocations.
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116              This option was new in Netpbm 10.61 (December 2012).
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119       -verbose
120              This causes pamcrater to issue additional messages about what it
121              is doing.
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123              This option was new in Neptbm 10.69 (December 2014).
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EXAMPLES

129           $ pamcrater | pamshadedrelief | pamx
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131           $ pamcrater -number=500000 -height=1000 -width=1000 >craters.pam
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DESIGN NOTES

137       Real craters have two distinct morphologies.
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SEE ALSO

142       pamshadedrelief(1), ppmrelief(1), pnmsmooth(1) pam(1),
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146       [1]    Peitgen, H.-O., and Saupe, D. eds., The Science Of  Fractal  Im‐
147              ages, New York: Springer Verlag, 1988.
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AUTHOR

153       pgmcrater, from which this is derived, was written by John Walker:
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155       John Walker
156       Autodesk SA
157       Avenue des Champs-Montants 14b
158       CH-2074 MARIN
159       Suisse/Schweiz/Svizzera/Svizra/Switzerland
160           Usenet:kelvin@Autodesk.com
161           Fax:038/33 88 15
162           Voice:038/33 76 33
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165       Permission  to  use, copy, modify, and distribute this software and its
166       documentation for any purpose and without fee is hereby granted,  with‐
167       out  any conditions or restrictions.  This software is provided "as is"
168       without express or implied warranty.
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HISTORY

173       John Walker wrote pgmcrater in 1991 and it  was  included  in  Pbmplus.
174       pgmcrater did the equivalent of pamcrater | pamshadedrelief.  In Netpbm
175       10.68 (September 2014), Bryan Henderson split  the  functions  of  pgm‐
176       crater  into  two  programs, one (pamcrater) to compute elevations, and
177       the other (pamshadedrelief) to generate a shaded  relief  visual  image
178       showing those elevations.  Bryan did this because it is more in keeping
179       with Netpbm's modular architecture,  and  because  the  pamshadedrelief
180       might be useful with other inputs.
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182       (Like  all  Netpbm  programs,  pgmcrater was not static between the two
183       events described above; minor changes, including replacement of most of
184       the code, happened in between).
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186       The original 1991 pgmcrater manual contains the following:
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189   PLUGWARE!
190       If  you  like  this  kind  of stuff, you may also enjoy "James Gleick's
191       Chaos--The Software" for MS-DOS, available for $59.95 from  your  local
192       software  store  or directly from Autodesk, Inc., Attn: Science Series,
193       2320  Marinship  Way,  Sausalito,  CA  94965,  USA.   Telephone:  (800)
194       688-2344  toll-free or, outside the U.S. (415) 332-2344 Ext 4886.  Fax:
195       (415) 289-4718.  "Chaos--The Software" includes  a  more  comprehensive
196       fractal forgery generator which creates three-dimensional landscapes as
197       well as clouds and planets, plus five more modules which explore  other
198       aspects  of  Chaos.   The user guide of more than 200 pages includes an
199       introduction by James Gleick and detailed explanations by  Rudy  Rucker
200       of the mathematics and algorithms used by each program.
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DOCUMENT SOURCE

203       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
204       source.  The master documentation is at
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206              http://netpbm.sourceforge.net/doc/pamcrater.html
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208netpbm documentation           03 November 2014       Pamcrater User Manual(0)
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