1A sample TLE entry for the International Space Station looks like 2this: 3 4ISS (ZARYA) 51 25544U 98067A 01286.44085648 .00059265 00000-0 81723-3 0 5959 62 25544 51.6394 213.7002 0007838 194.2620 314.2054 15.56596996165535 7 8Each line in satfile must begin with a satellite ID number (e.g. 25544 9for the ISS). Each ID must exist in the associated TLE file. 10 11Valid additional keywords are "align", "altcirc", "color", "font", 12"fontsize", "image", "position", "spacing", "thickness", "trail", 13"trail_output", and "transparent". The usage for most of these is 14identical to the usage for arc and marker files. In addition, a 15string to be plotted with the marker may be enclosed in either double 16quotes (""), or braces ({}). If a string is not supplied, the marker 17will take the name of the satellite supplied in the TLE file. 18 19The "altcirc" keyword draws altitude circles on the surface of the 20earth. The format is "altcirc=angle", where a circle is drawn 21bounding the area where the satellite is greater than angle degrees 22above the horizon. For example, altcirc=0 draws a circle bounding the 23region where the satellite is above the horizon, while altcirc=45 24draws a circle bounding the region where the satellite is more than 45 25degrees above the horizon. This may be specified more than once. 26 27The "trail" keyword is used to specify an orbit trail. The format 28must be "trail={ground|orbit,start_time,end_time,interval}", where the 29start and end times and interval are each in minutes. The start and 30end times are relative to the time of the calculation. When using the 31-projection option, trail will always be "ground". 32 33The "trail_output" keyword outputs the satellite's position to a text 34file, using the same time interval specified by "trail". If the 35"trail" option is not also present, "trail_output" has no effect. 36 37A few sample entries are given below: 38 3925544 40This draws a marker with the string "ISS (ZARYA)" for the 41International Space Station. 42 4325544 "The Space Station" 44This draws a marker with the string "The Space Station" for the 45International Space Station. 46 4725544 "" image=iss.png transparent={0,0,0} altcirc=0 48This draws iss.png at the current position of the International Space 49Station. No text string is drawn. A curve containing the area where 50the International Space Station is above the horizon is drawn. 51 5225544 "" image=iss.png transparent={0,0,0} altcirc=0 altcirc=45 trail={orbit,-5,10,2} 53As the previous example, but also draw the orbit trail from five 54minutes before to ten minutes past the current time, calculated every 55two minutes. A second altitude circle bounding the region where the 56International Space Station is more than 45 degrees above the horizon 57is also drawn. 58 59