In GNSS surveying, the essential direct measurement must be with the satellites rather than the stations in the project network; this is described as line of sight to satellites and control.

• A. communications
• B. geometry
• C. signal path
• D. line of sight, control

Answer: (D)

In GNSS surveying, the measurements come from looking directly at satellites through a clear line of sight, since the position calculations rely on precise timing and phase information gathered along that path. At the same time, the network needs a known reference frame, so the observations are tied to a control network that fixes the coordinates and lets the results be consistent across all stations. This combination—a direct line of sight to satellites plus a stable control framework—captures both the measurement path and the reference context needed for accurate positioning. The other terms don’t pair both ideas: communications is about data transfer, geometry is about how points are arranged in space rather than how observations are made or anchored, and signal path focuses on the signal’s route but not the requirement for a fixed, known reference network.