[L04]CORRECTIONS IN CHAIN SURVEYING скачать в хорошем качестве

[L04]CORRECTIONS IN CHAIN SURVEYING

This lecture on chain surveying corrections covers several important adjustments made to measurements to ensure accuracy: Correction due to Incorrect Length of Tape or Chain (0:43): This initial correction, briefly recapped from a previous lecture, addresses discrepancies when the actual length of the tape or chain differs from its designated length. The correction is positive if the wrong length (L') is greater than the true length (L), and negative if L' is lesser than L. Slope Correction (2:20): Since chain surveying measures horizontal distances, this correction is applied when measurements are taken on sloping ground. The measured value on a slope will always be greater than the true horizontal distance, making the slope correction always negative (4:42). The video provides both exact (6:18) and approximate (6:50) formulas for calculating this correction, and an alternative formula when the slope angle is known (7:50). Temperature Correction (9:05): This correction accounts for changes in the tape's length due to temperature variations between the time of standardization and the time of measurement. The correction is positive if the measurement temperature (TM) is greater than the standardization temperature (T Not), indicating expansion, and negative if TM is less than T Not, indicating contraction (11:52). Pull Correction (12:58): Similar to temperature, tapes are standardized under a specific tension or "pull." This correction is applied when the pull applied during measurement (PM) differs from the standardization pull (P Not). The correction is positive if PM is greater than P Not (16:33) and negative if PM is less than P Not (17:00). Sag Correction (17:45): This correction addresses the sagging of the tape due to its own weight, especially over longer distances. The measured value in a sagged condition is always greater than the true horizontal distance, making the sag correction always negative (21:26). Normal Tension (22:00): This is a specific value of pull at which the positive pull correction completely neutralizes the negative sag correction, resulting in a net correction of zero. Correction due to Reduction to Mean Sea Level (MSL) (23:54): In geodetic surveying, where the Earth's curvature is considered, measurements taken at higher elevations need to be reduced to their equivalent at mean sea level. This correction is always negative (28:07) because the measured distance on the ground at a higher elevation is greater than its corresponding true length at MSL. Limiting Length of an Offset (29:27): This refers to the maximum permissible length of an offset in chain surveying to ensure that the error on paper, when plotting the measurements, does not exceed 0.025 centimeters (31:16)