What does the line of collimation represent in surveying instruments?

The line of collimation represents the imaginary line of sight in a telescope, which is crucial for accurate measurements in surveying. This line is aligned with the optical axis of the telescope and allows surveyors to determine the direction toward which the instrument is aimed. When performing leveling or angular measurements, it is vital that the line of collimation is precisely aligned with the target point to ensure that the readings are accurate. By utilizing the line of collimation, surveyors can obtain correct sights, which are fundamental in establishing points and measuring distances or angles in surveying tasks.

The other options might relate to surveying concepts but do not accurately define the specific function of the line of collimation. The line connecting two survey points describes a physical connection rather than the instrumental aspect. The angle of the objective lens pertains to the specifications of the lens rather than its functional application, while the horizontal axis of a theodolite refers to a structural component rather than a line of sight feature.