CST GPS & GNSS Surveying Technologies 1 — Questions and Answers
Question 1: What is the minimum number of satellites a GPS receiver must track simultaneously to compute a 3D position fix?
- 2 satellites
- 3 satellites
- 4 satellites (Correct answer)
- 6 satellites
Correct answer: 4 satellites
A minimum of 4 satellites are required: 3 to solve for the three spatial dimensions and a fourth to resolve the receiver clock error, enabling a full 3D position fix.
Question 2: What does the acronym GNSS stand for?
- Global Navigation Satellite System (Correct answer)
- General Navigation Surveying System
- Geodetic Network Satellite Service
- Geographic Navigation Signal Standard
Correct answer: Global Navigation Satellite System
GNSS stands for Global Navigation Satellite System, the umbrella term for all satellite constellations used for navigation, including GPS (USA), GLONASS (Russia), Galileo (Europe), and BeiDou (China).
Question 3: Which reference ellipsoid does the GPS system use as its foundational datum?
- GRS 80
- WGS 84 (Correct answer)
- NAD 83
- Clarke 1866
Correct answer: WGS 84
GPS uses the World Geodetic System 1984 (WGS 84) as its reference ellipsoid, which defines the coordinate system for all GPS-derived positions.
Question 4: Which GPS survey method produces the highest accuracy for establishing control points?
- Real-Time Kinematic (RTK)
- Static differential GPS with post-processing (Correct answer)
- Single-point autonomous positioning
- WAAS-corrected navigation GPS
Correct answer: Static differential GPS with post-processing
Static differential GPS, where two or more receivers simultaneously collect data for extended sessions, achieves sub-centimeter accuracy through rigorous post-processing that eliminates most systematic error sources.
Question 5: What does PDOP measure in GPS surveying?
- Positional Dilution of Precision (Correct answer)
- Primary Data Output Protocol
- Precision Differential Orbital Parameter
- Point Determination of Position
Correct answer: Positional Dilution of Precision
PDOP (Position Dilution of Precision) quantifies the effect of satellite geometry on 3D positional accuracy; values below 4 indicate favorable geometry, while values above 6 significantly degrade accuracy.
Question 6: What is the typical horizontal accuracy achievable by a single-frequency GPS receiver using WAAS correction?
- Sub-millimeter accuracy
- Sub-centimeter accuracy
- 1 to 3 meter accuracy (Correct answer)
- 10 to 20 meter accuracy
Correct answer: 1 to 3 meter accuracy
WAAS-corrected single-frequency GPS receivers typically achieve 1–3 meter accuracy, sufficient for navigation and GIS data collection but not for survey-grade control work.
Question 7: In differential GPS surveying, what is the primary function of the GPS base station?
- To retransmit satellite signals to the rover receiver
- To provide known-position corrections that improve rover accuracy (Correct answer)
- To record atmospheric conditions during the observation period
- To compute and broadcast updated satellite ephemeris data
Correct answer: To provide known-position corrections that improve rover accuracy
The base station, placed at a point of known coordinates, computes the difference between its known and GPS-derived positions and transmits these correction values to the rover to improve its positional accuracy.
CST GPS & GNSS Surveying Technologies 1
What is the minimum number of satellites a GPS receiver must track simultaneously to compute a 3D position fix?