🔍 Key Concepts

• GPS trilateration and how distances from satellites define position • Difference between 2D position (latitude/longitude) and 3D position (including altitude) • Role of receiver clock error and how GPS compensates for it

💭 Think About

• Imagine you know your exact distance from one satellite. What does that tell you about where you could be in space? Now add a second, third, and fourth satellite—how does the possible position volume shrink each time? • Think about what extra information is needed to determine not only your position on the Earth’s surface, but also your height and correct for any time error in the GPS receiver. • Ask yourself: how many unknowns are you actually solving for in a full 3D GPS solution, and how many separate equations (satellite measurements) are needed to solve that system?

✅ Before You Answer

• Be clear on the difference between solving for two coordinates (surface position) versus three coordinates (x, y, z). • Remember that GPS also has to solve for receiver clock bias as an additional unknown, not just position coordinates. • Verify how many independent distance measurements you need to solve for all the unknowns in a 3D position fix with an imperfect receiver clock.