In surveying, both the line of sight and the line of collimation are important concepts related to the measurement and alignment of surveying instruments. Here's an explanation of the difference between the two:
Line of Sight: The line of sight refers to the straight line extending from the observer's eye through the surveying instrument, such as a theodolite or a total station, to the target or point being observed. It represents the visual line along which the surveyor aims or looks through the instrument to observe the target. The line of sight is used for aiming the instrument towards a specific point of interest or target.
Line of Collimation: The line of collimation, sometimes referred to as the optical axis, is an imaginary straight line passing through the optical center of the surveying instrument's objective lens or telescope. It is perpendicular to the line of sight and represents the direction of the instrument's principal axis. In simpler terms, it is the line along which the instrument is precisely aligned.
The line of collimation is an essential reference line for surveying measurements. It serves as the basis for taking angular measurements and ensures that the instrument is correctly oriented. By aligning the instrument's line of collimation with a known reference point or benchmark, subsequent observations and measurements can be made relative to that reference.
In practical terms, the line of sight is what the surveyor sees when looking through the instrument, while the line of collimation is the internal reference line within the instrument that aligns the optics and establishes a consistent direction for measurements.
It's important for surveyors to understand and maintain the alignment of the line of collimation, as any errors or misalignments can introduce inaccuracies in the surveying measurements.