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Give a brief overview of the structure and contents of Text 9B.
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21. Complete the sentences choosing the best variant according
to Text 9B.
1) A boundary surveyor's job is
a) to mark the corners of the land boundaries desired by a customer.
b) to provide some relevant data.
c) to locate marks on the ground.
2) Pegs are used to
a) verify the boundaries.
b) locate boundaries.
c) make work safe.
3) To establish boundary positions
a) evidence of the existing records is used.
b) the distance between points on a previous survey is
measured.
c) the global positioning system is set up.
4) Checks are made by
a) marking the corners in the field.
b) measuring the distance between pegs.
c) subdividing land.
5) Many properties have problems regarding
a) abutting them.
b) multiple divisions of a land piece.
c) improper calculations.
22. Read Text 9C "Surveying Equipment" and answer the
questions. Discuss your answers with your groupmates.
a) Why is a theodolite regarded as a key surveying instrument?
b) What does a theodolite consist of?
Английский язык для студентов строительных специальностей
UNIT 9. SURVEYING I 209
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c) 
What are both axes of a theodolite equipped with?
d) What is a horizontal axis error?
e) How is the sight axis determined?
f) Why are horizontal axis, collimation, and index errors taken
into account in the choice of the measurement procedure?
g) How is a theodolite adjusted?
h) How is a levelling instrument operated?
i) Why are self-levelling instruments preferred on sites?
j) What is a digital electronic level?
• TEXT 9C
Surveying Equipment
As late as the 1990s the basic tools used in planar surveying were a tape measure, a theodolite and a level.
A theodolite is an instrument for measuring both horizontal and vertical angles. It is a key tool in surveying and engineering work, particularly on inaccessible ground, but theodolites have been щ adapted for other specialized purposes in fields like meteorology and rocket launch technology. A modern theodolite consists of a movable telescope mounted within two perpendicular axes — the horizontal or trunnion, and the vertical axis. When the telescope is pointed at a desired object, the angle of each of these axes can be measured with great precision, typically on the scale of arcseconds.
| An optical theodolite, manufactured in the Soviet Union in 1958 and used for topographic surveying. |
Both axes of a theodolite are equipped with graduated circles that can be read out through magnifying lenses. The vertical circle should read 90° when the sight axis is horizontal, or 270° when the instrument is in its second
position, that is, turned over or plunged. Half of the difference between the two positions is called the index error.
The horizontal and vertical axes of a theodolite must be perpendicular. The condition where they deviate from perpendicularity and the amount by which they do is referred to as a horizontal axis error. The optical axis of the telescope, called the sight axis and defined by the optical center of the objective and the center of the crosshairs in its focal plane, must similarly be perpendicular to the horizontal axis. Any deviation from perpendicularity is the collimation error.
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A horizontal axis error, a collimation error, and an index error are regularly determined by calibration and are removed by mechanical adjustment at the factory in case they grow large. Their existence is taken into account in the choice of the measurement procedure in order to eliminate their effect on the measurement results.
A theodolite is mounted on its tripod head by means of a forced centering plate containing four thumbscrews, or in some modern theodolites, three, for rapid levelling. Before its use, a theodolite must be placed precisely and vertically over the point to be measured — centering — and its vertical axis aligned with local gravity — levelling.
The level instrument is an optical instrument used in surveying and building to transfer, measure, or set horizontal levels. It is set up on a tripod and, depending on the type, either roughly or accurately set to a levelled condition using levelling screws. The operator looks through the eyepiece of the telescope while an assistant holds a tape measure or graduated staff vertical at the point under measurement.
The instrument and staff are used to gather and/or transfer elevations (levels) during site surveys or building construction. Measurement generally starts from a benchmark with known height determined by a previous survey, or an arbitrary point with an assumed height.
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