Question

In general, trilateration is considered to be the principle of GNSS positioning. Which other surveying principle describes GNSS positioning?

• A. Resection
• B. Intersection
• C. Triangulateration
• D. Reduction

Hint:

Think about where the observing instrument physically sits: at the unknown point, or at the known points.

Answer 1

The Correct Option is A

Step 1: Recall the classical geometric principles used to fix an unknown point in surveying.
Intersection determines the position of an unknown point by taking directions or angles from two or more known points, with the instrument set up at the known stations, observing towards the unknown point. Resection determines the position of an unknown point by setting up the instrument or receiver at the unknown point itself and observing directions, angles or distances to two or more known points. Trilateration is the technique of fixing a point using only distance, or range, measurements to known points, and it can be carried out either as an intersection style or a resection style layout.

Step 2: Identify how GNSS positioning actually works.
A GNSS receiver sits at the unknown point, the point whose position is being determined, and measures pseudoranges, distances, to several satellites whose orbital positions are known in advance. The receiver coordinates are then computed by trilateration using those known distances, exactly as stated in the question.

Step 3: Match this observation geometry to the classical principle.
Because the observations, range measurements, are made from the unknown station towards the known stations, the satellites, and not from the known stations towards the unknown point, the geometry of GNSS positioning is that of resection, not intersection. Triangulateration (C) is a hybrid classical network technique combining angle and distance observations across a control network, which is not how a single GNSS fix is obtained. Reduction (D) refers to correcting or adjusting observations, for example reducing slope distances to horizontal, not to a positioning principle.

Step 4: Conclude.
Since the receiver occupies the unknown point and resects its position from known satellite locations using measured ranges, the other surveying principle describing GNSS positioning is Resection.

\[ \boxed{\text{Option (A): Resection}} \]