Introduction
Topcon HiPer Lite and HiPer Lite+ Operator’s Manual
1-4
Calculating Positions
Once the receiver locks on to a satellite, it starts recording
measurements and receiving the various digital information
(ephemeris, almanac, and so on) the satellites broadcast. To
calculate a position, receivers use the following formula:
Velocity x Time = Distance
Where Velocity is the speed at which radio waves travel
(i.e., the speed of light) and Time is the difference between
the signal transmission time and signal reception time.
To calculate absolute 3-D positions—latitude, longitude,
altitude—the receiver must lock on to four satellites. In a
mixed, GPS and GLONASS scenario, receiver’s must lock
onto at least five satellites to obtain an absolute position.
To provide fault tolerance using only GPS or only
GLONASS, the receiver must lock onto a fifth satellite. Six
satellites will provide fault tolerance in mixed scenarios.
Usually, the number of GPS and GLONASS satellites in
view does not exceed twenty (20).
Once locked on to a satellite, the receiver collects
ephemerides and almanacs, saving this information to its
NVRAM (Non-Volatile RAM).
• GPS and GLONASS satellites broadcast ephemeris
data cyclically, with a period of 30 seconds.
• GPS satellites broadcast almanac data cyclically with a
period of 12.5 minutes; GLONASS satellites broadcast
almanac data cyclically with a period of 2.5 minutes.
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