Which concept realizes a geodetic system through coordinates of defined points that are accessible by direct occupation or observation?

• A. Inertial frame
• B. Geodetic network
• C. Local frame
• D. Reference frame

Answer: (C)

Realizing a geodetic system through coordinates of defined points you can directly occupy or observe describes a local frame. In geodesy, a local frame is anchored to a small set of ground marks whose positions are established in the local coordinate system and can be measured or occupied with surveying instruments. This concrete, field-based realization gives a stable basis for locating features within that area and serves as the reference for nearby measurements.

An inertial frame, by contrast, is a non-accelerating reference frame used in physics and dynamics, not built from ground points you physically occupy. A geodetic network is a broader setup of interconnected points used to determine coordinates, which can realize a system but isn’t inherently defined by the act of directly occupying defined points in the field. A reference frame is a general term for any coordinate system realization, which may be global or local, but the description here specifically points to establishing the system from directly observable ground points—that's the local frame.