1Pamcrater User Manual(0) Pamcrater User Manual(0)
2
6 pamcrater - create cratered terrain by fractal forgery
7
11 pamcrater
12 [-number n]
14 [-height pixels]
16 [-width pixels]
18 [-randomseed=integer]
20 [-verbose]
22
25 This program is part of Netpbm(1).
26 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.
30 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.
38 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.
43 You can visualize the terrain map by generating a shaded relief image
45 of it with pamshadedrelief.
46 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.
51 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:
57 /\ /\
59 _____/ \____________/\____________/ \_____
60 Larger craters should really use this profile, including the central
63 peak, and totally obliterate the pre-existing terrain.
64 The maxval of the PAM image is always 65535.
66 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.
70
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:
78 All options can be abbreviated to their shortest unique prefix.
80 -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.
93 -height height
96 This sets the height of the generated image to height pixels.
97 The default height is 256 pixels.
98 -width width
101 This sets the width of the generated image to width pixels. The
102 default width is 256 pixels.
103 -randomseed=integer
106 This is the seed for the random number generator that generates
107 the pixels.
108 Use this to ensure you get the same image on separate invoca‐
110 tions.
111 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.
115 This option was new in Netpbm 10.61 (December 2012).
117 -verbose
120 This causes pamcrater to issue additional messages about what it
121 is doing.
122 This option was new in Neptbm 10.69 (December 2014).
124
129 $ pamcrater | pamshadedrelief | pamx
130 $ pamcrater -number=500000 -height=1000 -width=1000 >craters.pam
132
137 Real craters have two distinct morphologies.
138
142 pamshadedrelief(1), ppmrelief(1), pnmsmooth(1) pam(1),
143 [1] Peitgen, H.-O., and Saupe, D. eds., The Science Of Fractal Im‐
147 ages, New York: Springer Verlag, 1988.
148
153 pgmcrater, from which this is derived, was written by John Walker:
154 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
163 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.
169
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.
181 (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).
185 The original 1991 pgmcrater manual contains the following:
187 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.
201
203 This manual page was generated by the Netpbm tool 'makeman' from HTML
204 source. The master documentation is at
205 http://netpbm.sourceforge.net/doc/pamcrater.html
207netpbm documentation 03 November 2014 Pamcrater User Manual(0)