GREAT CIRCLE is a program for use by amateur radio operators. Its purpose is to provide antenna direction from one amateur radio station to another. This program calculates, draws and displays a great circle map using the home QTH as the center point. The map will contain the location of both stations, the path, and antenna direction and distances between the two locations This program was compiled using Borland's Turbo C 2.0 for DOS. The program was tested using 8088, 286, 386 and 486 computers. But requires a VGA monitor. Computers with floating point hardware create the map much faster than those requiring software emulation. After the map is created it is saved to a file. Each time the map is displayed, it is loaded from the file into the video memory. Recalculation and recreation of the map are only necessary if the home QTH information is changed A data base containing world wide call areas, latitude, longitude city and country names is included. A simple editor is provided to delete unwanted locations, add new locations and modify or correct existing records in the data base. The data base is loaded into memory when the program is started Using this programming method, the data base must meet a size requirement not to exceed 64K bytes, which is about 700 records. The included data base contains about 550 records of data with room for about 150 additional records the user can enter. Unwanted records can be deleted and replaced with desired location data. This will allow the user to tailor the data base to his particular need A great circle map is drawn using coordinate data created by the Central Intelligence Agency and placed in the public domain by Fred Pospeschil and Antonio Riveria. Each mapping point and segment is read from a file. The distance and direction from the user's home QTH to that point is calculated The result is converted to x, y coordinates and displayed on the monitor as a pixel or line segment. The coasts of continents and islands are drawn, the water areas are color filled and the map is saved to a file for loading upon request When the operator enters a call area or location of a desired station, the data base is searched for a match to the request. If found, the great circle map is loaded and displayed with the path drawn between the two locations The antenna direction, distance and location of each station is also displayed
