What is indicated by tertiary control in geodetic surveys?

Tertiary control in geodetic surveys primarily refers to the network of control points that are established to support various survey operations, particularly in ensuring that measurements and orientations are accurate throughout the survey process. Specifically, it encompasses the detailing of the instrument orientation along project traverse lines.

This means that during a geodetic survey, the tertiary control points serve as local reference markers that help surveyors to align their instruments correctly, ensuring that all data collected are consistent in terms of direction and position. This aspect of tertiary control is crucial because any misalignment can lead to significant errors in the survey results.

In contrast, the other options do not accurately describe the function of tertiary control in this context. For instance, while elevation accuracy is important, it is more closely associated with other control classifications, such as primary and secondary control. Similarly, establishing starting points pertains more to the initial setup of a survey rather than the continuous referencing needed during instrument operation. Thus, the focus on instrument orientation effectively captures the essence of what tertiary control accomplishes in geodetic surveys.