Case Studies: Concepts in Distance Measurement

Case Study 1: Choosing a Measurement Method

Example

A surveyor needs to determine the distance between two points under three different scenarios:
  1. A rough estimate for a preliminary route survey through a densely wooded area.
  2. A precise measurement across a busy 100-meter wide highway where traffic cannot be stopped.
  3. A highly accurate baseline measurement for a geodetic control network over flat terrain.
Recommend the most appropriate method for horizontal distance measurement for each scenario.

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Case Study 2: Understanding Tape Corrections

Example

During a taping operation, a surveyor uses a 50 m50 \text{ m} steel tape that was standardized at 20C20^\circ \text{C} with a pull of 50 N50 \text{ N} fully supported.
Explain whether the measured distance recorded in the field book will be too long or too short compared to the true distance under the following conditions:
  1. The field temperature is 35C35^\circ \text{C}.
  2. The tape is supported only at the ends (0m and 50m marks).

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Solved Problems: Taping and Optical Computations

Problem 1: Pacing Calculations (Basic)

Example

A surveyor walked a 50 m50 \text{ m} course 5 times with the following number of paces: 62, 63, 61, 64, and 62. They then walked an unknown distance ABAB with the following paces: 145, 148, 146, and 147.
Determine the surveyor's pace factor and the approximate distance of line ABAB.

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Problem 2: Temperature Correction (Intermediate)

Example

A 100 m100 \text{ m} steel tape is standardized at 20C20^\circ \text{C}. A line is measured with this tape and found to be 850.25 m850.25 \text{ m} at an average field temperature of 32C32^\circ \text{C}. The coefficient of linear expansion for steel is α=0.0000116/C\alpha = 0.0000116 / ^\circ \text{C}.
Calculate the total temperature correction and the corrected length of the line.

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Problem 3: Sag and Pull Corrections (Advanced)

Example

A 50 m50 \text{ m} tape weighing 0.03 kg/m0.03 \text{ kg/m} (total mass 1.5 kg1.5 \text{ kg}) is standardized under a pull of 5 kg5 \text{ kg}. The cross-sectional area is 0.04 cm20.04 \text{ cm}^2 and E=2.1×106 kg/cm2E = 2.1 \times 10^6 \text{ kg/cm}^2. During measurement, the tape is supported only at its ends (0 m0 \text{ m} and 50 m50 \text{ m}) and a pull of 8 kg8 \text{ kg} is applied.
Calculate the pull correction (CpC_p) and the sag correction (CsC_s) for one tape length. Determine the effective length of the tape under these conditions.

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Problem 4: Normal Tension (Advanced)

Example

Using the data from Problem 3 (L=50mL=50\text{m}, W=1.5kgW=1.5\text{kg}, Ps=5kgP_s=5\text{kg}, A=0.04cm2A=0.04\text{cm}^2, E=2.1×106 kg/cm2E=2.1\times 10^6\text{ kg/cm}^2), determine the Normal Tension (PnP_n) required to make the elongation from pull exactly counteract the shortening from sag.

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Problem 5: Stadia Measurement (Intermediate)

Example

A transit is set up over point A. A stadia rod is held vertically at point B. The transit has a stadia interval factor (KK) of 100 and a stadia constant (CC) of 0.30 m. The upper stadia hair reading is 2.450 m and the lower stadia hair reading is 1.150 m. The line of sight is horizontal.
Determine the horizontal distance from the transit to the rod.

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