Part 3/9:
In practical surveying, tools like the theodolite are used to measure angles and elevations with high precision. These instruments operate under the assumption of a curved Earth; for example, when measuring across a lake, surveyors observe that the surface conforms to the Earth's curvature, evidenced by the need to adjust horizontal lines for curvature effects.
Clarifying Horizontal and Level Lines
A key concept in surveying is differentiating between horizontal lines and level lines.
- Horizontal Line: Defined as a line perpendicular to the direction of gravity at a specific point. Because Earth's surface is curved, these lines are only locally tangent and do not necessarily stay parallel over long distances.