Pamcrater User Manual(1) General Commands Manual Pamcrater User Manual(1)
NAME
pamcrater - create cratered terrain by fractal forgery
SYNOPSIS
pamcrater
[-number n]
[-height pixels]
[-width pixels]
[-randomseed=integer]
[-verbose]
DESCRIPTION
This program is part of Netpbm(1).
pamcrater creates a PAM image which is a terrain map (not a visual im-
age) of cratered terrain. The terrain is as if a given number of im-
pacts into a surface create craters with random position and size.
The size distribution of the craters is based on a power law which re-
sults in many more small craters than large ones. The number of
craters of a given size varies as the reciprocal of the area as de-
scribed 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 dis-
tributed pseudorandom sequence was developed by Rudy Rucker.
A terrain map is a two dimensional map of terrain elevations. the PAM
image that pamcrater produces is therefore not a visual image but a
depth-one image of tuple type "elevation", with the sample value being
proportional to an elevation.
You can visualize the terrain map by generating a shaded relief image
of it with pamshadedrelief.
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.
pamcrater generates 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 maxval of the PAM image is always 65535.
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
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), pamcrater recognizes the
following command line options:
All options can be abbreviated to their shortest unique prefix.
-number n
This causes pamcrater to generate n craters. If you do not
specify -number, it generates 50000 craters. 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 im-
ages containing five to ten million craters are stunning but
take longer to create.
-height height
This sets the height of the generated image to height pixels.
The default height is 256 pixels.
-width width
This sets the width of the generated image to width pixels. The
default width is 256 pixels.
-randomseed=integer
This is the seed for the random number generator that generates
the pixels.
Use this to ensure you get the same image on separate invoca-
tions.
By default, pamcrater uses a seed derived from the time of day
and process ID, which gives you fairly uncorrelated results in
multiple invocations.
This option was new in Netpbm 10.61 (December 2012).
-verbose
This causes pamcrater to issue additional messages about what it
is doing.
This option was new in Neptbm 10.69 (December 2014).
EXAMPLES
$ pamcrater | pamshadedrelief | pamx
$ pamcrater -number=500000 -height=1000 -width=1000 >craters.pam
DESIGN NOTES
Real craters have two distinct morphologies.
SEE ALSO
pamshadedrelief(1), ppmrelief(1), pnmsmooth(1) pam(1),
[1] Peitgen, H.-O., and Saupe, D. eds., The Science Of Fractal Im-
ages, New York: Springer Verlag, 1988.
AUTHOR
pgmcrater, from which this is derived, was written by John Walker:
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
John Walker wrote pgmcrater in 1991 and it was included in Pbmplus.
pgmcrater did the equivalent of pamcrater | pamshadedrelief. In Netpbm
10.68 (September 2014), Bryan Henderson split the functions of pgm-
crater into two programs, one (pamcrater) to compute elevations, and
the other (pamshadedrelief) to generate a shaded relief visual image
showing those elevations. Bryan did this because it is more in keeping
with Netpbm's modular architecture, and because the pamshadedrelief
might be useful with other inputs.
(Like all Netpbm programs, pgmcrater was not static between the two
events described above; minor changes, including replacement of most of
the code, happened in between).
The original 1991 pgmcrater 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.
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML
source. The master documentation is at
http://netpbm.sourceforge.net/doc/pamcrater.html
netpbm documentation 03 November 2014 Pamcrater User Manual(1)
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