pgmcrater - Online in the Cloud

PROGRAM:

NAME

pgmcrater - create cratered terrain by fractal forgery

SYNOPSIS

pgmcrater [-number n] [-height|-ysize s] [-width|-xsize s] [-gamma g]

All options can be abbreviated to their shortest unique prefix.

DESCRIPTION

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 formula
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 Copernicus 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.

OPTIONS

-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 rendering the elevation array into the PGM format, so there's
no additional overhead in allowing an additional gamma adjustment.

Real craters have two distinct morphologies.

Use pgmcrater online using onworks.net services