pamcrater1

Usage

Overview

This program is part of Netpbm(1) .

pamcrater creates a PAM image which is a terrain map (not a visual image) of cratered terrain. The terrain is as if a given number of impacts into a surface create craters with random position and size.

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.

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 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.

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 images 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 invocations.

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.

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