wearth() wearth() NAME wearth - displays a shaded image of the Earth in the root window SYNOPSIS wearth [-proj proj_type ] [-pos pos_spec ] [-rot angle ] [-sunpos sun_pos_spec ] [-mag factor ] [-size size_spec ] [-shift shift_spec ] [-shade|-noshade] [-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 ] [-once|-noonce] [-nice priority ] [-gif] [-ppm] [-version] DESCRIPTION Wearth sets the Windows Desktop wallpaper 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, wearth 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). Wearth can also render directly into PPM and GIF files instead of drawing in the root window; see the -ppm and -gif options (below). This man page documents version 1.0 of wearth. OPTIONS Wearth understands the following command line options -proj proj_type Specify the projection type wearth should use. Supported projection types are mercator and orthographic; these can either be spelled out in full or abbreviated to merc or orth, respectively. Wearth 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, and random. (If you're having problems getting wearth to accept a position specifier as a command line argument, make sure and read the comments about position specifier delimiters and using explicit quoting in the fifth paragraph following this one.) The position specifier keyword fixed should be followed by two arguments, interpreted as numerical values indicating the - 1 - Formatted: July 4, 1996 wearth() wearth() latitude and longitude (expressed in decimal degrees) of a viewing position that is fixed with respect to the Earth's surface. Positive and negative values of latitude correspond to positions north and south of the equator, respectively. Positive and negative 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 offsets 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 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 invoking wearth 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, wearth uses a default - 2 - Formatted: July 4, 1996 wearth() wearth() 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. Positive values of angle rotate the rendered image counterclockwise; negative values rotate the rendered image clockwise. 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 specifier) 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 overhead. The details provided for position specifiers (see above) about the interpretation of positive and negative latitude and longitude values and the characters used to delimit specifier components apply to Sun position specifiers as well. By default, wearth 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 projection, the width of the rendered image is factor 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 integers; 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 wallpaper, these values default to the dimensions of the root window. When producing a PPM or GIF file - 3 - Formatted: July 4, 1996 wearth() wearth() instead of drawing in the window (see the -ppm and -gif options, below), both values default to 512. -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. -stars | -nostars Enable/disable stars. If stars are enabled, the black background of "space" is filled with a random pattern of "stars" (individual 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 - 4 - Formatted: July 4, 1996 wearth() wearth() 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, corresponding to 15 degrees between major grid lines. -grid2 grid2 Specify the spacing of dots along major grid lines if grid display (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 surface 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 double-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 wearth 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 - 5 - Formatted: July 4, 1996 wearth() wearth() defaults to 1. -gamma gamma_value When wearth is rendering into the wallpaper, adjust the colors wearth 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 wearth source distribution for information about a simple test that allows you to directly estimate the gamma of your display system (see OBTAINING THE WEARTH SOURCE DISTRIBUTION, below). -wait secs When rendering into the wallpaper, 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 timewarp_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 wearth should use one or two pixmaps when rendering into the wallpaper. If only one pixmap is used, partial redraws may be visible at times in the root window (when areas of the root window are exposed and redrawn during the time wearth is rendering the next image). If two pixmaps are used, wearth uses them to double-buffer changes such that partial redraws are (almost?) never seen. -mono | -nomono If rendering into the wallpaper enable/disable monochrome mode. Monochrome mode is enabled by default on systems with one-bit framebuffers (see the "depth of root window" information provided by xdpyinfo(1)) and disabled by default otherwise. - 6 - Formatted: July 4, 1996 wearth() wearth() -ncolors num_colors If rendering into the wallpaper 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 the wallpaper, 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. -once | -noonce Disable/enable updates. If updates are enabled and wearth is rendering into the wallpaper, wearth updates the displayed image periodically (the time between updates can be controlled via the -wait option, above). If updates are disabled, wearth only renders an image once and then exits. Updates are enabled by default. -nice priority Run the wearth process with priority priority (see nice(1) and setpriority(2)). By default, wearth runs at the priority of the process that invoked it, usually 0. -gif Instead of drawing in the wallpaper, write a GIF file (eight-bit color) to standard out. -ppm Instead of drawing in the wallpaper, write a PPM file (24-bit color) to standard out. -version Print what version of wearth this is. - 7 - Formatted: July 4, 1996 wearth() wearth() COPYRIGHT Copyright (C) 1995, 1996 by Erwin Yu Copyright (C) 1989, 1990, 1993, 1994, 1995 by Kirk Lauritz Johnson Portions of the wearth source code, as marked, are: Copyright (C) 1989, 1990, 1991 by Jim Frost Copyright (C) 1992 by Jamie Zawinski Permission to use, copy, modify and freely distribute wearth 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 wearth) 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. AUTHOR Kirk Johnson MIT Laboratory for Computer Science Patches, bug reports, and suggestions are welcome, but I can't guarantee that I'll get around to doing anything about them in a timely fashion. - 8 - Formatted: July 4, 1996