Question

Two main reference surfaces to approximate the shape of Earth are:

• A. Geoid, Ellipse
• B. Grid, Ellipse
• C. Geoid, Ellipsoid
• D. Reference plane, Datum

Hint:

Earth reference surfaces: \[ \boxed{ \begin{aligned} \text{Geoid} &\rightarrow \text{Physical Earth (Mean Sea Level)} \text{Ellipsoid} &\rightarrow \text{Mathematical approximation} \end{aligned} } \]

Answer 1

The Correct Option is C

Concept: The Earth's shape is represented using two principal reference surfaces.

Step 1: Understand the two reference surfaces.
• Geoid: Represents the mean sea level and the Earth's true gravitational surface.
• Ellipsoid: A mathematically defined smooth surface used for calculations and mapping.

Step 2: Identify the correct pair. Therefore, \[ \boxed{\text{Geoid and Ellipsoid}} \] are the two principal reference surfaces used in geodesy. Hence, the correct option is \[ \boxed{(C)\;\text{Geoid, Ellipsoid}.} \]