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1458625034-Lecture4TheodoliteSurvey.pdf (Size: 5.13 MB / Downloads: 16)
Introduction
• So far we have been measuring horizontal angles by
using a Compass with respect to meridian, which is less
accurate and also it is not possible to measure vertical
angles with a Compass.
• So when the objects are at a considerable distance or
situated at a considerable elevation or depression ,it
becomes necessary to measure horizontal and vertical
angles more precisely.
• These measurements are taken by an instrument known
as a Theodolite.
The system of surveying in which
the angles are measured with the
help of a theodolite, is called
Theodolite surveying.
• Theodolites are telescopic
instruments used basically for
measuring both vertical and
horizontal angles.
• Theodolites are precision
instruments used extensively in
construction work for measuring
angles in the horizontal and
vertical planes.
• Many different theodolites are
available for measuring angles.
The Theodolite is a most accurate surveying instrument
mainly used for :
• Measuring horizontal and vertical angles.
• Locating points on a line.
• Prolonging survey lines.
• Finding difference of level.
• Setting out grades.
• Ranging curves.
• Tacheometric Survey.
CLASSIFICATION OF THEODOLITES
Theodolites may be classified as ;
A.
i) Transit Theodolite.
ii) Non Transit Theodolite.
B.
i) Vernier Theodolites.
ii) Micrometer Theodolites.
CLASSIFICATION OF THEODOLITES
A.
Transit Theodolite: A theodolite is called a transit theodolite
when its telescope can be transited i.e revolved through a
complete revolution about its horizontal axis in the vertical
plane.
Non-Transit type: The telescope cannot be transited. They are
inferior in utility and have now become obsolete.
SIZE OF THEODOLITE
• A theodolite is designated by diameter of the graduated
circle on the lower plate.
• The common sizes are 8cm to 12 cm while 14 cm to 25 cm
instrument are used for triangulation work.
• Greater accuracy is achieved with larger theodolites as
they have bigger graduated circle with larger divisions
hence used where the survey works require high degree of
accuracy