GEOG 862
GPS and GNSS for Geospatial Professionals

Lesson 3 Overview



The Department of Defense found nearly 120 different types of positioning systems in place in the 1970s. They were all limited in their application and local in their scope. Consolidation was called for. NAVSTAR GPS (NAVigation System with Timing And Ranging, Global Positioning System) was proposed. The new system was built on the strengths and avoided the weaknesses of its forerunners.

In this lesson, we will take a look at the earlier systems and their technological contributions toward the development of GPS. This is not history for its own sake. It is an effort to explain the reasons behind the functioning of the GPS system today, built as it is on lessons learned from experience.


At the successful completion of this lesson, students should be able to:

  • discuss technological forerunners of GPS;
  • recognize terrestrial radio positioning, optical systems, and extraterrestrial radio positioning;
  • explain the role of TRANSIT in GPS development;
  • explain NAVSTAR;
  • describe GPS Segment Organization; and
  • differentiate between the roles of the Space Segment, the Control Segment, and the User Segment.


If you have any questions now or at any point during this week, please feel free to post them to the Lesson 3 Discussion Forum. (To access the forum, return to Canvas and navigate to the Lesson 3 Discussion Forum in the Lesson 3 module.) While you are there, feel free to post your own responses if you, too, are able to help out a classmate.