What does epoch mean in GPS?

Epoch, in astronomy, refers to some astronomical variables, such as celestial coordinates or the number of elliptical orbits of celestial bodies, because these will change with time due to zd motion. These astronomical variables that will change with time may include the angle of meridian or perihelion, the intersection of orbit with reference to datum, the direction of perihelion and apohelion or orbital arch, and the size of semi-major axis of orbit.

Ephemeris is a set of data describing the orbit of a satellite. GPS positioning is to determine the position and speed by using the satellite orbit information described by the satellite orbit calendar and the user observation data. Accurate description of ephemeris is the basis of accurate positioning.

Extended data:

Global Positioning System (GPS) is developed on the basis of meridian satellite navigation system, which absorbs the successful experience of meridian system. Like meridian system, GPS consists of three parts: space part, ground monitoring part and user receiver. According to the current scheme, the space part of GPS uses 24 satellites with a height of about 20,200 kilometers to form a satellite constellation.

2 1+3 satellites all have nearly circular orbits, with an operating period of about 1 1 hour 58 minutes, distributed on six orbital planes (four satellites in each orbital plane), and the orbital inclination angle is 55 degrees. The distribution of satellites makes it possible to observe more than four satellites anywhere in the world at any time, and maintain the geometric figure (DOP) with good positioning accuracy. This provides a global navigation capability that is continuous in time.