Question

For 3D-positioning, Global Navigational Satellite System (GNSS) requires a minimum of __________________ satellites.

• A. 3
• B. 4
• C. 5
• D. 2

Hint:

For 3D GPS positioning, at least four satellites are needed to calculate the position and altitude (height).

Answer 1

The Correct Option is B

The Global Navigation Satellite System (GNSS) is used for positioning, navigation, and timing (PNT) information. GNSS systems such as GPS provide three-dimensional positioning, which requires both horizontal (latitude, longitude) and vertical (altitude) information.
For 2D positioning, which only requires horizontal information (latitude and longitude), a minimum of three satellites are needed. This is because, with three satellites, a GPS receiver can perform trilateration to calculate the position in two dimensions.
However, for 3D positioning, which includes the vertical dimension (altitude), a minimum of four satellites are required. Here's why:
- With three satellites, the GPS receiver can determine the position on a flat plane, but it does not have enough information to calculate the altitude (height above the Earth's surface).
- The fourth satellite is needed to provide the necessary information to calculate the altitude. Additionally, the fourth satellite helps in compensating for timing errors in the receiver's clock.
The reason a fourth satellite is needed is because the GPS receiver’s clock is not perfectly synchronized with the satellite clocks, and the fourth satellite allows the receiver to correct for this time discrepancy.
Thus, to perform 3D positioning, a minimum of four satellites are required. This ensures that the receiver can calculate not only the horizontal position but also the altitude accurately.
Final Answer:
The correct answer is (B) 4 satellites, as they are required for accurate 3D positioning.