Xearth for (Power)Macintosh v0.9 by Johan Lindvall.
A picture generated by xearth
•What does it do?
Xearth for Macintosh is a port of the UNIX program xearth v0.92 by Kirk Johnson (tuna@cag.lcs.mit.edu). The program displays a rendered image of the Earth in a window.
•Using the Program:
There are four menus (Apple, File, Edit and Setup).
The About menu:
The About xearth item displays some information about xearth.
The File menu:
Open opens a window where the Earth will be displayed.
Close closes the window.
Save saves the currently visible Earth picture as a 32-bit colour PICT document.
Quit quits the application.
The Edit menu:
The items in the Edit menu are only used when the setup dialog is active.
The Setup menu:
Setup displays the setup dialog where parameters of the Earth rendering can be changed (see below).
Save setup is not implemented yet.
Load setup is not implemented yet.
•The Setup dialog:
All the information below is available as ballon help in the Setup dialog.
Viewing position:
The position from which the Earth should be viewed can be either fixed, sun relative or an orbital position.
Fixed:
Enter the latitude and longitude 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.
Sun relative:
Enter an offset in longitude and latitude of a viewing position that is fixed with respect to the Sun (see Sun position, below). Positive and negative values of latitude and longitude are interpreted as for the fixed viewing position.
Orbital view:
Enter a period (in seconds) and an orbital inclination (in hours) of a simple circular 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 Unix epoch - 1st January 1970 ).
Sun position:
The Sun position can be either Actual, time-dependent or fixed.
Actual:
The actual position of the Sun is calculated and updated with the progression of time (see Time, below).
Fixed:
Enter the latitude and the longitude of a fixed point on the Earth's surface where the Sun is always directly overhead.
Image size:
The image can be displayed on the full screen or in an ordinary window.
Full screen:
The entire screen is used to display the image of the Earth. If the image is displayed on the entire screen, then click on top of the screen to see the menubar.
Custom:
Enter the desired width and height of the Earth image in the corresponding boxes. The Earth image will be displayed in an ordinary Macintosh window.
Time:
The time used above can be fixed or cointinously updated.
Fixed:
Enter the Year, Month, Day, Hour, Minute and Second of the desired time in the corresponding boxes. If the date in the boxes is illegal, you will be notified when you try to close the dialog.
Now:
The time used in calculating the Sun's position is updated continously, starting from the time when the dialog is closed. Enter the desireed time between window updates in the box after "Update every". The apparent rate of which time progresses can be changed by entering a value in the Timewarp box.
Magnification:
The value in this box controls the magnification of the displayed image. The diameter of the rendered Earth image is (the entered number) times the shorter of the width and height of the image (see Image size, above).
Shift x / Shift y:
The values in the corresponding boxes are interpreted as the amount of offset that the center of the Earth should be shifted from the center of the image.
Shading:
If this option is enabled, the surface of the Earth is shaded according to the current position of the Sun and the values in the Day and Night boxes. The Day and Night values are the brightnesses in percent that should be used to shade the day/night side of the Earth.
Label:
If this option is enabled, a label will be drawn in the lower-right corner of the image that indicates the current date and time and current viewing and sun positions.
Markers:
If markers are enabled, small red circles and text labels indicating the location of interesting places on the Earth's surface will be drawn. These places can be changed by editing the resource 'mrkr' id 0.
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 by entering a value in the corresponding box.
Grid:
If this option is enbaled, a longitude/latitude grid will be drawn on the Earth's surface. The spacing of the major gridlines can be controlled by entering a value in the Grid Lines box. The grid lines are drawn with a 90/(Grid lines) spacing. The dot spacing along major grid lines can be controlled by entering a number in the Dot spacing box. The grid dots are drawn with at 90/(Line spacing x Dot spacing) degree spacing.
•Known bugs and limitations:
The version number is 0.9 because there are some things I want to fix before I release it as 1.0:
The program only runs on a Power Macintosh. It is not yet "ported" to 68k-Macintosh. It will be in a short while.
There are some oddities in the interface/visual bugs that will be fixed in the next release.
The save/load setup will be implemented in the next release.
The error handling will be fixed in the next release. When an error occurs, you will be notified thorugh an Alert saying "Assertion failed...". This should give some more useful information.
I will, however, not modify anything that has do to with the xearth rendering engine.
•Contacting the author:
Send any suggestions/comments/bug reports to me via e-mail. My e-mail address is d2linjo@dtek.chalmers.se
•Copyright & disclaimer:
Copyright (C) 1995 by Johan Lindvall.
Copyright (C) 1989, 1990, 1993, 1994 by Kirk Lauritz Johnson.
Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice(s) appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. 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.
-
Some of this document was copied from the Unix man-page for xearth 0.92.
