Trigonometric levelling | surveying #civilengineering

This video serves as a comprehensive educational lecture on Trigonometric Levelling, a method used to determine the difference in elevation between two stations by measuring vertical angles and horizontal distances. Key Concepts Covered: • Fundamentals of Trigonometric Levelling: The process involves calculating the elevation difference using observed vertical angles and known distances, often employing a theodolite (0:00 - 1:39). • Two Main Heads of Study: 1. Observations for Height and Distance: Based on plane surveying principles where distance is assumed to be small, allowing curvature and refraction effects to be neglected or applied linearly (2:16 - 3:30). 2. Geodetic Observations: Applied to large distances where ordinary plane surveying principles are insufficient, requiring direct application of curvature and refraction corrections to angular measurements (3:33 - 4:17). • Procedural Cases: The video details specific scenarios for calculating elevations: • Base of the object is accessible: Where the horizontal distance is measured accurately (6:42 - 11:07). • Base of the object is inaccessible: Discussed in contexts where the instrument stations are either in the same vertical plane or different planes relative to the object (29:10 - 56:50, 56:50 - 1:08:27). • Corrections for Curvature and Refraction: • Explains that as the distance increases, the effects of Earth's curvature and atmospheric refraction become significant (11:38 - 12:08). • Detailed analysis on how these corrections impact the observed angles (e.g., subtracting for angles of elevation and adding for angles of depression) (13:30 - 14:15, 1:32:30-1:41:20). • Coefficient of Refraction: Discusses the ratio between the angle of refraction and the angle subtended at the center of the earth (1:41:18 - 1:44:05)