Skip to content

12 - Introduction

12 - Introduction

Pages 127-129 of Surveying and Mapping

The Global Positioning System (GPS), also known as the NAVigation Satellite Time And Ranging (NAVSTAR) system had its first satellite launched back in February 1978. GPS is a one-­way radio ranging system which provides real­time knowledge of one’s Position and Velocity, and a very accurate Time reference as well (all together referred to as PVT).

GPS: system architecture

The GPS system consists of three segments:

  1. The space segment, consisting of 24 or more satellites, with accurate atomic clocks on board, continuously transmitting ranging signals to Earth.
  2. The control segment, consisting of a number of ground stations, which monitors the satellites, computes their orbits and clock offsets, and uploads this information to the satellites, which in turn encode this information on the ranging signal (the so-­called navigation data).
  3. The user segment, simply consisting of many GPS receivers, which each track four or more GPS satellites, and compute their own position.

Market developments

Nothing interesting.

Delft perspective on GPS

In 1993, Delft University of Technology professor Peter Teu­nissen invented the Least-­squares AMBiguity Decorrelation Adjustment method (LAMBDA method), by means of which instantaneous carrier phase cycle integer ambiguity resolution became possible. The ambiguity is the unknown integer number of wavelengths that fit into the satellite-­receiver distance. The LAMBDA method enabled instantaneous high­-precision GPS positioning.

Overview of this part

Chapter 13 presents the basic concepts of the measurement of travel­time of a radio signal from a GPS satellite to a receiver. With these measurements of range as input, Chapter 14 describes the default mode of GPS positioning, referred to as stand­alone or single­point positioning. The next chapter introduces the concept of relative positioning, by means of which high­accuracy, centimeter­level positioning is made possible. Chapter 16 presents, after a brief overview of the four major Global Navigation Satellite Systems (GNSS), an overview of the wide range of applications of GPS/GNSS in today’s society.