- Set up the instrument above the specified station and precisely level it with reference to the altitude level.
- Set the vertical circle’s vernier to zero. Then, with the altitude level in the middle of its run, use a measuring tape to precisely measure the instrument’s height (the vertical distance from the top of the peg to the center of the objective).
- Alternatively, the height may be found by keeping the stadia rod first before the telescope and reading through the object-glass.
- Orient the instrument by following the steps listed below:
- The magnetic meridian or the real meridian can be used as the reference meridian.
- When the reference meridian is a magnetic meridian, set one of the verniers to zero and rotate the telescope around the vertical axis, relaxing the bottom clamp until the compass needle points north.
- The correct bearing of a reference point or another station of the traverse with reference to the first station must be known in order to orient the instrument with reference to the real meridian.
- Set up the vernier to read this bearing, and then rotate the telescope about the outer axis until the station or reference object is bisected.
- Take the bearing, the vertical angle, and the top, bottom, and axial hair readings while holding the staff on the benchmark (the line of sight may be horizontal or inclined).
- If there is no local benchmark, fly level from the nearest accessible Bench Mark (B.M.), and a temporary B.M. may be constructed near the region.
- The bearings, vertical angles, and staff readings are used to find all representative locations under the instrument station’s command (to the top, bottom, and the axial hairs). “Side shots” are the phrase for these observations.
- Take a glance at the second station when all the representative spots have been identified from the first station. Record the vertical angle and the staff readings relating to the top, bottom, and axial hairs.
- Change the station of the instrument to the second. As before, set up, center, and level the instrument and measure its height.
- Take a backsight to the first station. Also, pay attention to the bearings, the vertical angle, and the staff reading the top, bottom, and axial hairs.
- Since each station is sighted twice, two values for the station’s distances and altitudes are produced, which must be within the legal limits; otherwise, the operation must be redone.
Procedure for Tacheometric Surveying
