SURVEYING
Surveying is a scientific method which determines the three-dimensional
positions and angles of relative points on the surface of the earth. Different
types of surveying methods are used in construction which is described below.
TYPES OF
SURVEYING
Surveying may be divided into two general categories.
1. Geodetic Surveying
and
2. Plane Surveying.
1. GEODETIC SURVEYING:
Geodetic surveying is a particular type of surveying where the curvature
of the earth is taken into account. Since the earth has a spherical shape, the
line connecting any two points on the earth’s surface is curved or is an arc.
Hence it involves spherical trigonometry. In geodetic surveying, large
distances and areas are measured and its degree of accuracy is comparatively
high.
2. PLANE SURVEYING:
Plane surveying is a specific type of surveying
where the surface of the earth is considered as plane and the curvature of the
earth is not taken into account. The line connecting any two points is a
straight line and the angles of polygons are plane angles. This type of
surveying is suitable for small and flat areas, and its degree of accuracy is
comparatively low. In America, the limit for treating a surface as a plane is
about to 250 km2.
Note: The
difference in length between the arc and the subtended chord on the surface of
the earth is only about 0.1 m in 18.2 km, 0.3 m in 54.3 km and 0.5 m in 91 km
respectively.
A. CLASSIFICATION BASED ON THE NATURE OF THE FIELD:
1.
Land Surveying.
2.
Marine Surveying.
3.
Astronomical Surveying.
Land surveying can be sub-divided into following
categories:
§ Topographical Surveys.
§ Cadastral Surveys.
§ City Surveys.
§ Engineering Surveys.
Land surveying mainly deals with the natural and
artificial features of a country such as hills, rivers, buildings, towns,
villages etc.
B. CLASSIFICATION BASED ON THE OBJECT OF THE
SURVEY:
1. Archaeological
survey.
2. Geological Survey.
3. Mine Survey.
4. Military Survey.
C. CLASSIFICATION BASED ON THE INSTRUMENTS
1. CHAIN SURVEYING:
Chain surveying is the simplest method of surveying
in which the linear measurements are directly taken in the field and the
angular measurements are not taken. This type of surveying is used over small
and leveled area.
2. PLANE TABLE SURVEYING:
In plane table surveying the field work and
plotting is done using a graphical method. It is mostly adapted for small and
medium scale mapping where great accuracy is not required.
3. COMPASS SURVEYING:
In this surveying, a compass is used to determine
the direction of survey lines, and the length of survey lines are measured by a
chain or tape.
4. TACHEOMETRIC SURVEYING:
Tacheometric surveying is a method of surveying in
which the horizontal and vertical distances of relative points are determined
without using any sophisticated instruments such as chain , tape etc.
5. THEODOLITE SURVEYING:
In this surveying, a theodolite is used to measure
the horizontal and vertical angles.
6. PHOTOGRAPHIC AND AERIAL SURVEYING:
This types of surveying are done by taking
photographs from elevated ground stations.
D.
CLASSIFICATION BASED ON THE METHODS OF SURVEY:
1.
Triangulation Survey
2.
Traverse Survey.
How TO DO SURVEYING
.
1. CHAIN
SURVEYING:
Chain surveying is the simplest method of surveying
in which the linear measurements are directly taken in the field and the
angular measurements are not taken. This type of surveying is mostly suitable
when,
1.
The area is small.
2.
The ground is fairly level and open.
3.
Plans on a large scale are required.
2. PLANE TABLE
SURVEYING:
In plane table surveying the field work and
plotting is done using a graphical method. It is mostly adapted for small and
medium scale mapping where great accuracy is not required.
3. COMPASS
SURVEYING:
In this surveying, a compass is used to determine
the direction of survey lines, and the length of survey lines are measured by a
chain or tape.
4. THEODOLITE
SURVEYING:
In this surveying, a theodolite (a surveying
instrument) is used to measure the horizontal and vertical angles.
5. LEVELING:
Leveling is a method of surveying which determines
the heights or elevations of relative points on the surface of the earth.
I
would also like to thank Dr. Bharat Lohani ( Department of Civil Engineering, IIT Kanpur) as
his constructive feedback helped me to develop this blog and has also enabled me to overcome the challenges that came during the entire surveying course .