README file for xearth, version 1.1
Kirk Lauritz Johnson <tuna@indra.com>
6 November 1999


WHAT IS IT?

    Xearth sets the X root window to an image of the Earth, as seen
    from your favorite vantage point in space, correctly shaded for
    the current position of the Sun. By default, xearth updates the
    displayed image every five minutes; the time between updates can
    be changed using either X resources or a command line
    option. Xearth can also be configured to render into a top-level X
    window or directly into PPM and GIF files; see the man page for
    details.

    See the HISTORY file for a list of changes since earlier versions
    of xearth.


WHERE TO GET IT?

    The latest-and-greatest version of xearth should always be
    available via a link from the xearth WWW home page (URL
    http://www.cs.colorado.edu/~tuna/xearth/index.html), or, for the
    web-deprived, via anonymous ftp from cag.lcs.mit.edu in /pub/tuna.


NOTES

    If you are trying to build xearth under SunOS 4.x using /bin/cc,
    make sure to read the section of the INSTALL file entitled
    "BUILDING UNDER SUNOS 4.x" regarding a compiler bug.

    The map information used in xearth was derived from the "CIA World
    Data Bank II map database," as taken from some "cbd" files that
    were apparently originally generated by Brian Reid at DEC WRL.

    Running in the background on 350 MHz Pentium II, xearth requires
    less than one CPU second each time it redraws an image in the root
    window. With the default time-between-redraws of 300 seconds, I
    simply don't notice the extra CPU load. Your mileage may vary, of
    course, especially on slower machines.

    The Graphics Interchange Format(c) is the Copyright property of
    CompuServe Incorporated. GIF(sm) is a Service Mark property of
    CompuServe Incorporated.

    Thanks to Robert Berger for allowing me to include his nifty Gamma
    Measurement Image and associated text in the xearth source
    distribution.

    Thanks to Jamie Zawinski for suggesting that I look at his
    xscreensaver package for a good example of how to use the resource
    and command line option parts of Xt; his code saved me piles of
    lossage.

    Thanks to Chris Metcalf for the -bigstars stuff, a pile of general
    source code cleaning, and spell checking everything carefully.

    Thanks to Chris Hayward, Chris Metcalf, Sherman Mui, Dan Rich, and
    Leonard Zubkoff for giving the pre-release of version 1.0 a test
    drive.

    Kudos to Jef Poskanzer for his excellent PBMPLUS toolkit.

    Finally, thanks to everybody that sent encouragement, suggestions,
    and patches. Apologies to the many people whose good ideas didn't
    make it into this release.


IDEAS FOR FUTURE WORK

    Better error recovery (better than "assert()", anyway).

    Add options/resources that specify colors other than the default
    green, blue, red, white, and black.

    Code for tracking real-life orbits ("-pos hubble").

    Support for supersampling/antialiasing.


AUTHOR

    Kirk Johnson <tuna@indra.com>

    Patches, bug reports, and suggestions are welcome, although I
    can't guarantee that I'll get around to doing anything about them
    in a timely fashion.


LEGAL STUFF

    Copyright (C) 1989, 1990, 1993-1995, 1999 Kirk Lauritz Johnson

    Parts of the source code (as marked) are:
      Copyright (C) 1989, 1990, 1991 by Jim Frost
      Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>

    Permission to use, copy, modify and freely distribute xearth for
    non-commercial and not-for-profit purposes is hereby granted
    without fee, provided that both the above copyright notice and
    this permission notice appear in all copies and in supporting
    documentation.

    Unisys Corporation holds worldwide patent rights on the Lempel Zev
    Welch (LZW) compression technique employed in the CompuServe GIF
    image file format as well as in other formats. Unisys has made it
    clear, however, that it does not require licensing or fees to be
    paid for freely distributed, non-commercial applications (such as
    xearth) that employ LZW/GIF technology. Those wishing further
    information about licensing the LZW patent should contact Unisys
    directly at (lzw_info@unisys.com) or by writing to

      Unisys Corporation
      Welch Licensing Department
      M/S-C1SW19
      P.O. Box 500
      Blue Bell, PA 19424

    The author makes no representations about the suitability of this
    software for any purpose. It is provided "as is" without express
    or implied warranty.

    THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
    INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
    OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
    LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
    NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
    CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.