Plane and geodetic survey

PLANE & GEODETIC SURVEYING

• Surveying is divided primarily into
Geodetic surveying & Plane
surveying.

• In Geodetic surveying, large areas of
earth’s surface are involved and the
curvature of earth is taken into
account.
• In Plane surveying, relatively small
areas are under consideration, and it is
assumed that the earth’s surface is flat.
• In Plane surveying, measurements
plotted will represent the projection on
the horizontal plane of the actual field
measurements.
For example, AB is plotted as AB’
• A horizontal plane is normal to the
direction of gravity (as defined by a
plumb bob at that point).
• However, such a plane will infact be
tangential to the earth’s surface at
that point.
Thus, if a large area is considered, the
discrepancy will become apparent
between the area of the horizontal
plane and the actual curved area of the
earth’s surface.
• In the above figure if actual area is ABC,
the projected area will become A’B’C’.
Note: That Arc AC will be projected as
Chord A’C’ represented by dotted line. If
Arc AB = 18.5 km then Chord A’B’ will
be 1.52 cm shorter than Arc AB.
• Length AB, BC & CA in Geodetic
surveying are determined using
spherical trigonometry, whereas
lengths A’B’, B’C’ & C’A’ are determined
in plane surveying using plane
trigonometry.
• For Survey up to 195.5 km2 in area, this
discrepancy is not serious and therefore
plane surveying will be adequate.
However precautions are required
when connecting such survey to control
points established and co – ordinate by
geodetic surveys.
• Plane surveys are done for engineering
projects such as factories, bridges,
dams, location & construction of canals,
highways, railways etc.
• Geodetic surveying is done for fixing
widely spaced control point, which
may afterwards be used necessary
control points for fixing minor control
points for plane survey.
• Geodetic survey is carried out by
Department of National Survey of India.
Note: Control points are points of
known co – ordinates. It is used as a
reference for taking other
measurements during surveying.

CLASSIFICATION OF SURVEYING BASED ON PURPOSE 

Based on the purpose the surveys can be
classified as under.

1. Topographical Survey
It is a survey conducted to obtain data
and to make a map indicating
inequalities of land surface by
measuring elevations and locating the
natural and artificial features of the
earth, e.g. rivers, woods, hills, etc. There
scales ranges from 1 : 25000 to 1 :
1000000.
2. Engineering Survey
• These are survey work required before,
during and after any engineering works.
• Before any work is started, large-scale
topographical maps or plans are
required as a basis for design.
• It is especially used for the design and
construction of new routes, e.g. roads
and railways.
• It is also used to calculate the areas and
volumes of land and data for setting out
curves for route alignment.

Typical scales are as follows :
• Building work
• Site plans, Civil engineering works :
• Town surveys, Highway surveys :

3. Cadastral Survey
These are undertaken to produce plans
of property boundaries for legal
purposes. These are also known as
public land survey. Scales are 1 : 1000
to 1 : 5000.
4. Hydrographic Survey
• These surveys are conducted on or near
the water body, such as lakes, rivers,
bays, harbours. Marine surveys are
special type of hydrographic surveys,
covers a broader area near sea for
offshore structures, navigations, tides,
etc.
• The hydrographic survey consists of
locating shore lines, water flow
estimation, and determination of the
shape of area under the water surface,
determination of channel depth,
location of locks, sand bars, buoys, etc.

5. Astronomic Survey
• These surveys are conducted for
determinations of latitudes, azimuths,
local time, etc. at various places on the
earth by observing heavenly bodies (the
sun or stars).
6. Geological Survey
• These surveys are conducted to obtain
information about different strata of the
earth’s surface for the purpose
geological studies. Geological maps are
prepared depicting the details of the
strata.

 CLASSIFICATION OF SURVEY BASED ON INSTRUMENTS USED 

Based on the instruments used, the surveys
can be classified as under :

1. Chain Surveying
It is the simplest type of surveying in
which only linear measurements are
taken either with a chain or a tape.
Note: Angular measurements are not
taken in chain surveying.
2. Compass Surveying
In compass surveying, horizontal angles
are measured with the help of a
magnetic compass, in addition to these
linear measurements taken with chain
or tape.
• Although a magnetic compass is not a
precise angle- measuring instrument,
hence the compass survey is not very
accurate. However, it is more accurate
than a chain survey.
3. Leveling
In this type of survey a leveling
instrument is used for determination of
relative elevations (levels) of various
points in the vertical plane.
4. Plane Table Surveys
In this type of survey, a map (or plan) is
prepared in the field while viewing the
terrain after determining the directions
of various lines and measuring the
linear distances with a chain or a tape.
• The accuracy of the plane table survey
is low. Its main advantage is that
measurements and plotting are done
simultaneously in the field.
5. Theodolite Surveys
• It’s this type of survey horizontal and
vertical angles are measured with the
help of theodolite. A theodolite is a very
precise instrument used for measuring
horizontal and vertical angles.
The theodolite surveys can be
broadly classified into two types:
(i) Traverse survey
(ii) Triangulation survey
• In traverse survey, the various stations
form a polygon. The horizontal angles
are measured with the help of a
theodolite, whereas the linear
measurements are made with a tape.
• In triangulation survey, the lines form a
system of triangles. The base line is
measured accurately and the lengths of
all other lines are computed from the
measured angles.
• Triangulation is used for establishing
control points over extensive areas.
Note: Theodolite surveys are quite
accurate.
6. Tachometric Surveys
• In this type of survey a special type of
theodolite called as Tachometer is used,
which is fitted with a stadia diaphragm
having two horizontal cross hairs in
addition t the central horizontal hair.
• In tachometric surveying, horizontal
angles, horizontal distances and vertical
distances (elevation) are measured
with tachometer.
• Although tachometric surveys are not
very accurate in plane areas, but these
are extremely convenient and gives
better result than the theodolite
surveys in rough terrain.
7. Photogrammetric Surveys
• Photogrammetry is the science of taking
measurements with the help of
photographs.
• Photogrammetry surveys are generally
used for Topographic mapping of large
areas.
• These are extremely useful for
obtaining Topographical details of areas
which are difficult to access.
• Photographs are generally taken from
an aeroplane. However, for certain
areas where suitable sites exist,
photographs can be taken from ground-
based cameras.
8. EDM Surveys
• Trilateration is a type of triangulation in
which all the three sides of each triangle
are measured accurately with the help
EDM instruments.
• Then angles are computed indirectly
form the known sides of the triangles.
• Hence all the sides and angles are
determined.

 PRINCIPLES OF SURVEYING 

There are two basic principles of surveying.
1. Work from whole to part.
2. Locate a point by at least two
measurements.
1. Work from Whole to Part
• The main idea of working from whole to
part is to localize the errors and prevent
their accumulation.
• The survey area is covered with the
simplest possible frame-work of high-
quality measurements. If the rest of the
survey work is carried out within this
area, the possible accumulation of error
can be contained.
• If we work from part to whole, the
errors accumulate and expand to a
greater magnitude in the process of
expansion of survey.

2. Locate a Point by at Least Two
Measurements
• Two control points A & B (any two
important features) are selected in the
area and the distance between them is
measured accurately. Line AB is called
baseline.
• If A and B be the two control points,
whose positions are already known on
the plan, the position of C can be plotted
by any of the following methods.