Measuring vertical distances (leveling)
You want to know levels (altitudes) along the roads depicted on the picture. The purpose might be to prepare a project for laying down pipes for sewer or controlling the level of road surface during construction. The survey is closed in order to have a check against errors.
The result will be
- a plan with altitudes, locations of stations/rod shots and
- a vertical profile.
From the plan should be also clear
- path and location, where rod shots were taken,
- locations of the stations.
Equipment and procedure
We work with
- level instrument and with
- a rod equipped by a numbered scale.
By means of level instrument and rods, we are able to find out
- relative vertical distances from comparing foresight (FS) vs backsight (BS),
- approximate distance between instrument setup and the rod (useful later to distribute error as a correction),
- approximate angle between rods (not much useful).
- Relative vertical distances are evaluated from comparing the reading of backsight BS (known altitude) against foresight FS (unknown altitude to be determined by the measurement).
- Once measurement of both BS and FS is completed (and altitude of FS is determined) the instrument is moved over turning point (that means over the FS) to a new position to establish new setup.
- FS remains at the same position and becomes BS of known altitude needed for the next step.
- New FS of unknown altitude is established at desired point and measured against BS then.
For each reading, all 3 wires from crosshair are recorded. The purpose is A. better precision, B. protection against errors/blunders, C. distances can be evaluated as well.
When using level instrument, approximate distance between the instrument and the rod is evaluated from reading upper against lower wire of crosshair. The difference is multiplied by 100 (the magnifier of our instrument) to get distance in metres.
- Mark the starting point (station, position of the rod) by scratch, sprayer, because it will be finally also your closing point.
- Evaluate the average of upper and lower wire and compare it to the middle wire during recording. Thus you can detect a blunder/error in the field.
- Useful data and comfortable reading is achieved when rods are in rough distance of around 50 m from telescope.
- Move the level instrument only when both BS and FS were read already.
- Move yourselves and the instrument on pavement but take the altitudes of the road (close to the pavement).
- Keep the original field books. Attach them to the protocol.
- Follow rules of maintaining the field book.
Since we have no benchmark points, you are free to fix altitude of the starting point according to your judgement.