xearth(1)xearth(1)NAMExearth - displays a shaded image of the Earth in an X window
SYNOPSISxearth [-proj proj_type ] [-pos pos_spec ] [-rot angle ] [-sunpos
sun_pos_spec ] [-mag factor ] [-size size_spec ] [-shift shift_spec ]
[-shade|-noshade] [-label|-nolabel] [-labelpos geom ] [-mark‐
ers|-nomarkers] [-markerfile file ] [-showmarkers] [-stars|-nostars]
[-starfreq frequency ] [-bigstars percent ] [-grid|-nogrid] [-grid1
grid1 ] [-grid2 grid2 ] [-day pct ] [-night pct ] [-term pct ] [-gamma
gamma_value ] [-wait secs ] [-timewarp timewarp_factor ] [-time
fixed_time ] [-onepix|-twopix] [-mono|-nomono] [-ncolors num_colors ]
[-font font_name ] [-root|-noroot] [-geometry geom ] [-title title ]
[-iconname iconname ] [-name name ] [-fork|-nofork] [-once|-noonce]
[-nice priority ] [-gif] [-ppm] [-display dpyname ] [-version]
DESCRIPTION
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 with the
-wait option (see below); updates can be disabled completely by using
the -once option (see below).
If desired, Xearth can be configured to create and render into its own
top-level X window instead of the root window; see the -root, -noroot,
and -geometry options (below). Finally, xearth can also render directly
into PPM and GIF files instead of drawing into an X window; see the
-ppm and -gif options (below).
This man page documents version 1.1 of xearth.
OPTIONS
Xearth understands the following command line options (corresponding X
resources can be found in the following section):
-proj proj_type
Specify the projection type xearth should use. Supported projec‐
tion types are mercator, orthographic, and cylindrical; these
can either be spelled out in full or abbreviated to merc, orth,
or cyl, respectively. Xearth uses an orthographic projection by
default.
-pos pos_spec
Specify the position from which the Earth should be viewed. The
pos_spec (position specifier) consists of a keyword, possibly
followed by additional arguments. Valid keywords are: fixed,
sunrel, orbit, moon, and random. (If you're having problems get‐
ting xearth to accept a position specifier as a command line
argument, make sure and read the comments about position speci‐
fier delimiters and using explicit quoting in the sixth para‐
graph following this one.)
The position specifier keyword fixed should be followed by two
arguments, interpreted as numerical values indicating the lati‐
tude and longitude (expressed in decimal degrees) of a viewing
position that is fixed with respect to the Earth's surface. Pos‐
itive and negative values of latitude correspond to positions
north and south of the equator, respectively. Positive and nega‐
tive values of longitude correspond to positions east and west
of Greenwich, respectively.
The position specifier keyword sunrel should be followed by two
arguments, interpreted as numerical values indicating the off‐
sets in latitude and longitude (expressed in decimal degrees) of
a viewing position that is fixed with respect to the position of
the Sun. Positive and negative values of latitude and longitude
are interpreted as for the fixed keyword.
The position specifier keyword orbit should be followed by two
arguments, interpreted as numerical values indicating the period
(in hours) and orbital inclination (in decimal degrees) of a
simple circular orbit; the viewing position follows this orbit.
Astute readers will surely note that these parameters are not
sufficient to uniquely specify a single circular orbit. This
problem is solved by limiting the space of possible orbits to
those positioned over 0 degrees latitude, 0 degrees longitude at
time zero (the Un*x epoch, see time(3)).
The position specifier keyword moon should not be followed by
any arguments. When this keyword is used, the viewing position
is the current position of the moon, recalculated at each
update.
The position specifier keyword random should not be followed by
any arguments. When this keyword is used, the viewing position
is selected at random each time an update occurs.
Components of a position specifier are delimited by either
whitespace, forward slashes (/), or commas. Note that using
whitespace to separate position specifier components when invok‐
ing xearth from a shell may require explicit quoting to ensure
the entire position specifier is passed as a single argument.
For example, if you want to use spaces to delimit components and
are using a "typical" shell, you'd need to use something like:
-pos "fixed 42.33 -71.08"
or
-pos 'fixed 42.33 -71.08'
to make things work. If you'd rather not have to explicitly
quote things, you can use forward slashes or commas instead of
spaces to separate components, as shown below.
-pos fixed,42.33,-71.08
-pos fixed/42.33/-71.08
If a position specifier is not provided, xearth uses a default
position specifier of "sunrel 0 0" (such that the entire day
side of the Earth is always visible).
-rot angle
Specify a rotated viewing position such that the north is not
"straight up" in the center of the rendered image. The angle can
be specified either as a numeric value or the keyword galactic.
When angle is a numeric, it represents the number of degrees by
which the image is to be rotated. Positive values of angle
rotate the rendered image counterclockwise; negative values
rotate the rendered image clockwise. The keyword galactic ori‐
ents the image so that the galactic north is straight up: the
sun is positioned somewhere on the plane passing through the
horizontal center of the screen. The default value of angle is
0.
-sunpos sun_pos_spec
Specify a fixed point on the Earth's surface where the Sun is
always directly overhead. The sun_pos_spec (Sun position speci‐
fier) consists of two components, both numerical values; these
components are interpreted as the latitude and longitude (in
decimal degrees) of the point where the Sun is directly over‐
head.
The details provided for position specifiers (see above) about
the interpretation of positive and negative latitude and longi‐
tude values and the characters used to delimit specifier compo‐
nents apply to Sun position specifiers as well.
By default, xearth calculates the actual position of the Sun and
updates this position with the progression of time.
-mag factor
Specify the magnification of the displayed image. When the
orthographic projection is in use, the diameter of the rendered
Earth image is factor times the shorter of the width and height
of the image (see the -size option, below). For the mercator and
cylindrical projections, the width of the rendered image is fac‐
tor times the width of the image (see the -size option, below).
The default magnification factor is 1.
-size size_spec
Specify the size of the image to be rendered. The size_spec
(size specifier) consists of two components, both positive inte‐
gers; these components are interpreted as the width and height
(in pixels) of the image.
The details provided for position specifiers (see above) about
the characters used to delimit specifier components apply to
size specifiers as well.
When rendering into the X root window, these values default to
the dimensions of the root window. When producing a PPM or GIF
file instead of drawing in the X root window (see the -ppm and
-gif options, below), both values default to 512.
When rendering into its own top-level X window, any values spec‐
ified using this option are ignored; dimensions for the top-
level window can be specified using the -geometry option.
-shift shift_spec
Specify that the center of the rendered Earth image should be
shifted by some amount from the center of the image. The
shift_spec (shift specifier) consists of two components, both
integers; these components are interpreted as the offsets (in
pixels) in the X and Y directions.
The details provided for position specifiers (see above) about
the characters used to delimit specifier components apply to
shift specifiers as well.
By default, the center of the rendered Earth image is aligned
with the center of the image.
-shade | -noshade
Enable/disable shading. When shading is enabled, the surface of
the Earth is shaded according to the current position of the Sun
(and the values provided for the -day, -night, and -term
options, below). When shading is disabled, use flat colors
(green and blue) to render land and water. Shading is enabled by
default.
-label | -nolabel
Enable/disable labeling. If labeling is enabled and xearth is
rendering into an X window, provide a label that indicates the
current date and time and current viewing and sun positions. The
position of the label can be controlled using the -labelpos
option (see below). Labeling is disabled by default.
-labelpos geom
Specify where the label should be drawn. If labeling is enabled
and xearth is rendering into an X window, geom is interpreted as
the "position" part an X-style geometry specification (e.g.,
{+-}<xoffset>{+-}<yoffset>; positive and negative values of
xoffset denote offsets from the left and right edges of the dis‐
play, respectively; positive and negative values of yoffset
denote offsets from the top and bottom edges of the display,
respectively) indicating how the label should be positioned.
The label position defaults to "-5-5" (i.e., five pixels inside
the lower right-hand corner of the display).
-markers | -nomarkers
Enable/disable markers. If markers are enabled and xearth is
rendering into an X window, display small red circles and text
labels indicating the location of interesting places on the
Earth's surface. Markers are enabled by default.
-markerfile file
Specify a file from which user-defined marker data (locations
and names) should be read. Each line in the marker data file
consists of three required components: the latitude and longi‐
tude (expressed in decimal degrees) followed by the text of the
label that should be used. Individual components are delimited
by either whitespace, forward slashes (/), or commas. Components
that need to include delimiter characters (e.g., a multi-word
label) should be enclosed in double quotes. For example, a line
in a typical marker data file might look something like:
42.33 -71.08 "Boston, MA" # USA
Everything between a `#' character and the end of a line, inclu‐
sive, is a considered to be a comment. Blank lines and lines
containing only comments are allowed.
In addition to the three required components, xearth supports
optional following "key=value" components. In this version of
xearth, the only supported "key" is "align", which can be used
to control where marker labels are drawn in relation to the
marker proper. Supported alignment values are "left", "right",
"above", and "below"; the default behavior (if no alignment is
specified) is "align=right".
The marker data file is reread every time xearth redraws an
image into an X window. In this way, the marker positions and
labels can be dynamic (e.g., given appropriate data sources,
markers could be used to encode hurricane positions, where
earthquakes have happened recently, temperatures at fixed loca‐
tions, or other forms of "real-time" data).
Xearth includes a built-in set of marker data for 76 major loca‐
tions around the world. The built-in data can be selected by
specifying "built-in" for the file argument; this is the default
behavior. The built-in set of marker data can be examined either
by using the -showmarkers option (see below) or by reading the
BUILT-IN file included with the xearth source distribution (see
OBTAINING THE XEARTH SOURCE DISTRIBUTION, below).
-showmarkers
This option indicates that xearth should load the marker data
(whether built-in or user-specified), print a copy of it to
standard out in a form suitable for use with the -markers option
(see above), and then exit.
-stars | -nostars
Enable/disable stars. If stars are enabled, the black background
of "space" is filled with a random pattern of "stars" (individ‐
ual white pixels). The fraction of background pixels that are
turned into stars can be controlled with the -starfreq option
(see below). Stars are enabled by default.
-starfreq frequency
Set the density of the random star pattern (see -stars, above);
frequency indicates the fraction of background pixels that
should be turned into "stars". The default value of frequency is
0.002.
-bigstars percent
Set the percentage of double-width stars (see -stars, above); by
default, all stars are a single pixel, but this option can be
used to create some stars that are composed of two horizontal
pixels. This provides a slightly less uniform look to the
"night sky".
-grid | -nogrid
Enable/disable the display of a longitude/latitude grid on the
Earth's surface. The spacing of major grid lines and dots
between major grid lines can be controlled with the -grid1 and
-grid2 options (see below). Grid display is disabled by default.
-grid1 grid1
Specify the spacing of major grid lines if grid display (see
-grid, above) is enabled; major grid lines are drawn with a
90/grid1 degree spacing. The default value for grid1 is 6, cor‐
responding to 15 degrees between major grid lines.
-grid2 grid2
Specify the spacing of dots along major grid lines if grid dis‐
play (see -grid, above) is enabled. Along the equator and lines
of longitude, grid dots are drawn with a 90/(grid1 x grid2)
degree spacing. The spacing of grid dots along parallels (lines
of latitude) other than the equator is adjusted to keep the sur‐
face distance between grid dots approximately constant. The
default value for grid2 is 15; combined with the default grid1
value of 6, this corresponds to placing grid dots on a one
degree spacing.
-day pct
Specify the brightness that should be used to shade the day side
of the Earth when shading is enabled. Pct should be an integer
between 0 and 100, inclusive, where 0 indicates total darkness
and 100 indicates total illumination. This value defaults to
100.
-night pct
Specify the brightness that should be used to shade the night
side of the Earth when shading is enabled. Pct should be an
integer between 0 and 100, inclusive, where 0 indicates total
darkness and 100 indicates total illumination. This value
defaults to 5 (if this seems overly dark, you may want to dou‐
ble-check that appropriate gamma correction is being employed;
see -gamma, below).
-term pct
Specify the shading discontinuity at the terminator (day/night
line). Pct should be an integer between 0 and 100, inclusive. A
value of x indicates that the shading should immediately jump x
percent of the difference between day and night shading values
(see -day and -night, above) when crossing from the night side
to the day side of the terminator. Thus a value of 0 indicates
no discontinuity (the original xearth behavior), and a value of
100 yields a maximal discontinuity (such that the entire day
side of the earth is shaded with the -day shading value). This
value defaults to 1.
-gamma gamma_value
When xearth is rendering into an X window, adjust the colors
xearth uses by a gamma value. Values less than 1.0 yield darker
colors; values greater than 1.0 yield brighter colors. The
default gamma_value is 1.0, appropriate for use on systems with
built-in gamma correction. For systems without built-in gamma
correction, appropriate gamma values are often in the 2.3 to 2.6
range.
See the GAMMA-TEST file included with the xearth source distri‐
bution for information about a simple test that allows you to
directly estimate the gamma of your display system (see OBTAIN‐
ING THE XEARTH SOURCE DISTRIBUTION, below).
-wait secs
When rendering into an X window, wait secs seconds between
updates. This value defaults to 300 seconds (five minutes).
-timewarp timewarp_factor
Scale the apparent rate at which time progresses by time‐
warp_factor. The default value of timewarp_factor is 1.0.
-time fixed_time
Instead of using the current time to determine the "value" of
time-dependent positions (e.g., the position the sun), use a
particular fixed_time (expressed in seconds since the Un*x epoch
(see time(3)).
-onepix | -twopix
Specify whether xearth should use one or two pixmaps when ren‐
dering into an X window. If only one pixmap is used, partial
redraws may be visible at times in the window (when areas of the
window are exposed and redrawn during the time xearth is render‐
ing the next image). If two pixmaps are used, xearth uses them
to double-buffer changes such that partial redraws are (almost?)
never seen. Using only one pixmap has the advantage of using
quite a bit less memory in the X server; this can be important
in environments where server-side memory is a fairly limited
resource. Two pixmaps is the default.
-mono | -nomono
If rendering into an X window, enable/disable monochrome mode.
Monochrome mode is enabled by default on systems with one-bit
framebuffers (see the "depth of root window" information pro‐
vided by xdpyinfo(1)) and disabled by default otherwise.
-ncolors num_colors
If rendering into an X window or a GIF output file, specify the
number of colors that should be used. (If markers are enabled
(see -markers, above), the actual number of colors used may be
one larger than num_colors.) The default value of num_colors is
64.
When rendering into an X window, the maximum allowable value for
num_colors is 1024. In practice, using values of num_colors
larger than twice the number of distinct shades of red, green,
or blue supported by your hardware is likely to provide little
additional benefit, or, in some cases, produce "banding" effects
in the image. Thus, on systems that can support 256 distinct
shades of red, green, or blue (eight bits per component), the
largest practical value of num_colors is around 512. Similarly,
on systems that support only five or six bits per component
(e.g., many systems with 16-bit displays), the largest practical
value of num_colors is probably around 64.
When rendering into a GIF output file, the maximum allowable
value for num_colors is 256.
-font font_name
If rendering into an X window, use font_name for drawing text
labels (see -label and -markers, above). By default, xearth uses
the "variable" font.
-root | -noroot
When rendering into an X window, select whether xearth should
render into the X root window (-root) or create and render into
a top-level X window (-noroot). By default, xearth renders into
the X root window.
-geometry geom
Cause xearth to create and render into a top-level X window with
the specified geometry. When this option is used, the -noroot
option can be elided. Use of the -root overrides the effect of
-geometry. By default (if -noroot is specified by no geometry is
provided), xearth uses a geometry of "512x512".
-title title
When rendering into a top-level X window, this option can be
used to specify the window title string that might be displayed
by a window manager. By default, xearth uses a title of
"xearth".
-iconname iconname
When rendering into a top-level X window, this option can be
used to specify the icon name that might be used by a window
manager for the window. By default, xearth uses an icon name of
"xearth".
-name name
When rendering into an X window, this option can be used to
specify the application name under which X resources are
obtained, rather than the default executable file name. The
specified name should not contain "." or "*" characters.
-fork | -nofork
When rendering into an X window, enable/disable forking. If
forking is enabled, xearth forks a child process to handle all
rendering calculations and screen updates (in essence, automati‐
cally putting itself in the background). Forking is disabled by
default.
-once | -noonce
Disable/enable updates. If updates are enabled and xearth is
rendering into an X window, xearth updates the displayed image
periodically (the time between updates can be controlled via the
-wait option, above). If updates are disabled, xearth only ren‐
ders an image once and then exits. Updates are enabled by
default.
-nice priority
Run the xearth process with priority priority (see nice(1) and
setpriority(2)). By default, xearth runs at the priority of the
process that invoked it, usually 0.
-gif Instead of drawing in an X window, write a GIF file (eight-bit
color) to standard out.
-ppm Instead of drawing in an X window, write a PPM file (24-bit
color) to standard out.
-display dpyname
Attempt to connect to the X display named dpyname.
-version
Print what version of xearth this is.
X RESOURCES
The behavior of xearth can also be controlled using the following X
resources:
proj (projection type)
Specify the projection type xearth should use (see -proj,
above).
pos (position specifier)
Specify the position from which the Earth should be viewed (see
-pos, above).
rot (float)
Specify the viewing rotation (see -rot, above).
sunpos (sun position specifier)
Specify a fixed point on the Earth's surface where the Sun is
always directly overhead (see -sunpos, above).
mag (float)
Specify the magnification of the displayed image (see -mag,
above).
size (size specifier)
Specify the size of the image to be rendered (see -size, above).
shift (shift specifier)
Specify that the center of the rendered Earth image should be
shifted by some amount from the center of the image (see -shift,
above).
shade (boolean)
Enable/disable shading (see -shade, above).
label (boolean)
Enable/disable labeling (see -label, above).
labelpos (geometry)
Specify where the label should be drawn (see -labelpos, above).
markers (boolean)
Enable/disable markers (see -markers, above).
markerfile (file name)
Specify a file from which user-defined marker data (locations
and names) should be read (see -markerfile, above).
stars (boolean)
Enable/disable stars (see -stars, above).
starfreq (float)
Set the density of the random star pattern (see -starfreq,
above).
bigstars (int)
Set the percentage of stars that are double width (see
-bigstars, above).
grid (boolean)
Enable/disable the display of a longitude/latitude grid on the
Earth's surface (see -grid, above).
grid1 (integer)
Specify the spacing of major grid lines if grid display is
enabled (see -grid1, above).
grid2 (integer)
Specify the spacing of dots along major grid lines if grid dis‐
play is enabled (see -grid2, above).
day (integer)
Specify the brightness that should be used to shade the day side
of the Earth when shading is enabled (see -day, above).
night (integer)
Specify the brightness that should be used to shade the night
side of the Earth when shading is enabled (see -night, above).
term (integer)
Specify the shading discontinuity at the terminator (see -term,
above).
gamma (float)
Specify the gamma correction xearth should use when selecting
colors (see -gamma, above).
wait (integer)
Specify the delay between updates when rendering into an X win‐
dow (see -wait, above).
timewarp (float)
Specify the apparent rate at which time progresses (see -time‐
warp, above).
time (integer)
Specify a particular fixed time that should be used to determine
the "value" of time-dependent positions (see -time, above).
twopix (boolean)
Specify whether xearth should use one or two pixmaps when ren‐
dering into an X window (see -onepix and -twopix, above).
mono (boolean)
Specify whether xearth should use monochrome mode when rendering
into an X window (see -mono and -nomono, above).
ncolors (integer)
Specify the number of colors xearth should use (see -ncolors,
above). The ncolors resource is only used when rendering into an
X window -- the number of colors to use when rendering into a
GIF file can only be specified using the -ncolors command line
option.
font (font name)
Use the named font for drawing text labels (see -font, above).
root (boolean)
Specify whether xearth should render into the X root window or a
top-level X window (see -root, -noroot, and -geometry, above).
geometry (geometry)
Specify the geometry of a top-level X window that xearth should
create and render into (see -geometry, above).
title (string)
When rendering into a top-level X window, specify the window
title that xearth should use (see -title, above).
iconname (string)
When rendering into a top-level X window, specify the icon name
that xearth should use (see -iconname, above).
fork (boolean)
When rendering into an X window, enable/disable the automatic
forking of a child process to handle the updates (see -fork,
above).
once (boolean)
When rendering into an X window, disable/enable updates for the
displayed image (see -once, above).
nice (integer)
Specify the priority at which the xearth process should be run
(see -nice, above).
OBTAINING THE XEARTH SOURCE DISTRIBUTION
The latest-and-greatest version of xearth should always be available
via a link from the xearth WWW home page (URL http://www.cs.col‐
orado.edu/~tuna/xearth/index.html), or, for the web-deprived, via
anonymous ftp from cag.lcs.mit.edu in /pub/tuna.
NOTES
Thanks to Frank Solensky for the "-pos moon" and "-rot galactic" stuff.
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 appar‐
ently originally generated by Brian Reid at DEC WRL.
The Graphics Interchange Format(c) is the Copyright property of Com‐
puServe Incorporated. GIF(sm) is a Service Mark property of CompuServe
Incorporated.
Thanks to Robert Berger for allowing me to include his nifty gamma mea‐
surement 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.
COPYRIGHT
Copyright (C) 1989, 1990, 1993-1995, 1999 by Kirk Lauritz Johnson
Portions of the xearth 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, how‐
ever, 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 soft‐
ware 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 CONSE‐
QUENTIAL 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 PER‐
FORMANCE OF THIS SOFTWARE.
AUTHOR
Kirk Johnson <tuna@indra.com>
Patches, bug reports, and suggestions are welcome, but I can't guaran‐
tee that I'll get around to doing anything about them in a timely fash‐
ion.
KLJ November 1999 xearth(1)
