Understanding GPS
From Pvdwiki
The US GPS system is a collection of satalites placed in a geosyncronous orbit around the earth. By knowing exactly where these satalites are with regard to the earth, comunication with a GPS device can be triangulated to calculate it's postition as well.
The standard for this is constantly in a state of flux, but at this moment, the system is defined by the WGS-84 standard.
