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
28 image) of cratered terrain. The terrain is as if a given number of
29 impacts into a surface create craters with random position and size.
30 The size distribution of the craters is based on a power law which
32 results 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
34 described on pages 31 and 32 of Peitgen and Saupe[1]; cratered bodies
35 in the Solar System are observed to obey this relationship. The for‐
36 mula used to obtain crater radii governed by this law from a uniformly
37 distributed 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
62 peak, and totally obliterate the pre-existing terrain.
63 The maxval of the PAM image is always 65535.
65 The randomness in the image is limited before Netpbm 10.37 (December
67 2006) -- if you run the program twice in the same second, you may get
68 identical output.
69
73 In addition to the options common to all programs based on libnetpbm
74 (most notably -quiet, see
75 Common Options ⟨index.html#commonoptions⟩ ), pamcrater recognizes the
76 following command line options:
77 All options can be abbreviated to their shortest unique prefix.
79 -number n
83 This causes pamcrater to generate n craters. If you do not
84 specify -number, it generates 50000 craters. Don't expect to
85 see them all! For every large crater there are many, many more
86 tiny ones which tend simply to erode the landscape. In general,
87 the more craters you specify, the more realistic the result;
88 ideally you want the entire terrain to have been extensively
89 turned over again and again by cratering. High resolution
90 images containing five to ten million craters are stunning but
91 take longer to create.
92 -height height
95 This sets the height of the generated image to height pixels.
96 The default height is 256 pixels.
97 -width width
100 This sets the width of the generated image to width pixels. The
101 default width is 256 pixels.
102 -randomseed=integer
105 This is the seed for the random number generator that generates
106 the pixels.
107 Use this to ensure you get the same image on separate invoca‐
109 tions.
110 By default, pamcrater uses a seed derived from the time of day
112 and process ID, which gives you fairly uncorrelated results in
113 multiple invocations.
114 This option was new in Netpbm 10.61 (December 2012).
116 -verbose
119 This causes pamcrater to issue additional messages about what it
120 is doing.
121 This option was new in Neptbm 10.69 (December 2014).
123
128 $ pamcrater | pamshadedrelief | pamx
129 $ pamcrater -number=500000 -height=1000 -width=1000 >craters.pam
131
135 Real craters have two distinct morphologies.
136
140 pamshadedrelief(1), ppmrelief(1), pnmsmooth(1) pam(1),
141 [1] Peitgen, H.-O., and Saupe, D. eds., The Science Of Fractal
145 Images, New York: Springer Verlag, 1988.
146
151 pgmcrater, from which this is derived, was written by John Walker:
152 John Walker
154 Autodesk SA
155 Avenue des Champs-Montants 14b
156 CH-2074 MARIN
157 Suisse/Schweiz/Svizzera/Svizra/Switzerland
158 Usenet:kelvin@Autodesk.com
159 Fax:038/33 88 15
160 Voice:038/33 76 33
161 Permission to use, copy, modify, and distribute this software and its
163 documentation for any purpose and without fee is hereby granted, with‐
164 out any conditions or restrictions. This software is provided "as is"
165 without express or implied warranty.
166
170 John Walker wrote pgmcrater in 1991 and it was included in Pbmplus.
171 pgmcrater did the equivalent of pamcrater | pamshadedrelief. In Netpbm
172 10.68 (September 2014), Bryan Henderson split the functions of pgm‐
173 crater into two programs, one (pamcrater) to compute elevations, and
174 the other (pamshadedrelief) to generate a shaded relief visual image
175 showing those elevations. Bryan did this because it is more in keeping
176 with Netpbm's modular architecture, and because the pamshadedrelief
177 might be useful with other inputs.
178 (Like all Netpbm programs, pgmcrater was not static between the two
180 events described above; minor changes, including replacement of most of
181 the code, happened in between).
182 The original 1991 pgmcrater manual contains the following:
184 PLUGWARE!
187 If you like this kind of stuff, you may also enjoy "James Gleick's
188 Chaos--The Software" for MS-DOS, available for $59.95 from your local
189 software store or directly from Autodesk, Inc., Attn: Science Series,
190 2320 Marinship Way, Sausalito, CA 94965, USA. Telephone: (800)
191 688-2344 toll-free or, outside the U.S. (415) 332-2344 Ext 4886. Fax:
192 (415) 289-4718. "Chaos--The Software" includes a more comprehensive
193 fractal forgery generator which creates three-dimensional landscapes as
194 well as clouds and planets, plus five more modules which explore other
195 aspects of Chaos. The user guide of more than 200 pages includes an
196 introduction by James Gleick and detailed explanations by Rudy Rucker
197 of the mathematics and algorithms used by each program.
198
200 This manual page was generated by the Netpbm tool 'makeman' from HTML
201 source. The master documentation is at
202 http://netpbm.sourceforge.net/doc/pamcrater.html
204netpbm documentation 03 November 2014 Pamcrater User Manual(0)