Hello, I have these 4 satellite informations and need to find a way to calculate the receiver postion. Any ideas? Satellite Name / NORAD Number / Tx Time (GMT) / Latitude / Longitude / Altitude (km) GPS BIIR-3 (PRN 11) / 25933 / 16:02:30.084 / 40.63 / -52.99 / 19808.1 GPS BIIF-2 (PRN 01) / 37753 / 16:02:30.075 / 27.58 / -54.84 / 20072.3 GPS BIIF-5 (PRN 30) / 39533 / 16:02:30.063 / 27.01 / -93.49 / 20153.9 GPS BIIR-5 (PRN 28) / 26407 / 16:02:30.039 / 56.07 / -114.62 / 20715.9 Assumptions: [LIST] [*]All four signals reached your GPS receiver simultaneously [*]The waypoint is at sea level [*]The Earth's atmosphere has no effect on the GPS signal [*]The Earth is a perfect sphere, with a radius of 6370 kilometers [*]The speed of light is 3.00E+08 meters per second [*]GPS receiver has no time differential error [/LIST] thx Ovaron