The Earth Viewer was first implemented by John Walker in December 1994. Most of the software that generates the various views of the Earth was adapted from Home Planet for Windows. See the details for additional implementation information. It was extended to allow viewing the Moon as well as the Earth in October 1996.
The satellite tracking code is based upon the N3EMO Orbit Simulator:
N3EMO Orbit Simulator routines v3.7 Copyright © 1986,1987,1988,1989,1990 Robert W. Berger N3EMO May be freely distributed, provided this notice remains intact.
The GIF output file generation is based upon the
module of Jef Poskanzer's
pbmplus toolkit, of which many
other components were used in creating the images you see here.
toolkit is a much-extended version of
pbmplus; Earth and Moon Viewer
was developed using only
ppmtogif.c - read a portable pixmap and produce a GIF file Based on GIFENCOD by David Rowley [firstname.lastname@example.org]. Lempel-Ziv compression based on "compress". Modified by Marcel Wijkstra [email@example.com] Copyright © 1989 by Jef Poskanzer. Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. This software is provided "as is" without express or implied warranty. The Graphics Interchange Format© is the Copyright property of CompuServe Incorporated. GIF(sm) is a Service Mark property of CompuServe Incorporated.
JPEG output file generation is based upon the tookit developed by the Independent JPEG Group. Their contribution of industrial-strength JPEG support to the public domain has enabled the development of innumerable software tools, Earth and Moon Viewer among them.
made the task of processing form arguments in the server immeasurably
The Living Earth® image is a composite of Earth satellite imagery developed by The Living Earth, Inc.. This image is © Copyright 1996 The Living Earth, Inc./Earth Imaging, All Rights Reserved and is used here by permission of the publisher. For additional information about this and other images and products, contact The Living Earth via E-mail to firstname.lastname@example.org.
The original images of the Earth by day and night are 8640×4320 24-bit pixels:
more than 110 megabytes each. To permit interactive access in Earth Viewer,
the images were compressed to reduce the number of colours in the day side
image to 1024 and the night side to 64. This reduces the image database
to a large, but manageable, 74.6 megabytes. The ultimate resolution of the
database is about 4.6 kilometres per pixel. The original images and
products based upon them have additional fine detail which had to be
sacrificed to allow quick response to Earth Viewer requests; please
visit The Living Earth for
further details and examples of the full-colour images.
image was assembled from imagery acquired by the
MODIS instrument on the
satellite. Lights on the night side were imaged from
Meteorological Satellite Program
spacecraft. Low resolution image requests use a day/night database
of 8000×4000 pixels, providing resolution of about 5 kilometres
per pixel. When you zoom in for close-up views, Earth and Moon
Viewer automatically switches to a
database with 1 km/pixel
resolution (43200×21600 pixels). There is no night lights database with
comparable resolution, so close-ups of the Earth's night side will
The global topographic map
was developed by the
Marine Geology and Geophysics Division
of the National Geophysical Data Center
operated by the United States Department of Commerce,
National Oceanic and Atmospheric Administration.
The colour resolution in the original image has been reduced to allow rapid
generation of day and night hemispheres. The topographic map is derived from the
ETOPO2 global elevation database, which provides 2 minute of arc (2 nautical mile)
resolution for most of the Earth.
The cloud cover, colour weather, and water vapour density
images are generated on the fly, every three hours, from the
satellite composites made available by
of Wisconsin-Madison Space Science and
I take this image,
then transform it from the Mollweide projection in which it is
published to the Mercator projection expected by Earth Viewer's image
generator (thanks to code from the GCTPc package:
ftp://edcftp.cr.usgs.gov/pub/software/gctpc/) The images are postprocessed for use by Earth and Moon Viewer using tools from the
The images of the Moon are generated based on a 1440×720 lunar relief and albedo databases created by the U.S. Geological Survey Flagstaff Field Center from imagery returned by the BMDO/NASA Clementine lunar orbiter. Albedo (reflectivity) is the intrinsic brightness of the terrain as opposed to its appearance from Earth or space, which depends also upon the angle at which the Sun illuminates the Moon at a given time. Except for high-latitude and polar regions, which are always illuminated obliquely due to the low inclination of the Moon's orbit with respect to the ecliptic, the albedo map represents the appearance of the Moon when the Sun is at the meridian for each longitudinal strip of the image.
Using an albedo map and ignoring the effects of elevation and sun
angle leads to a washed-out appearance near
the terminator (boundary between day and night), especially in the
lunar highlands and most of the far side where there is little
intrinsic albedo difference and most of observed detail results from
terrain features. The relief map shows terrain but neglects albedo;
choose whichever produces the most useful image for your purpose.
The algorithms to calculate the position of the Sun and Moon are given in:
Meeus, Jean. Astronomical Algorithms . Richmond: Willmann-Bell, 1998. ISBN 0-943396-63-8.Return to Earth and Moon Viewer