Lesson 2. Classification
and basic principles – Linear Measurement
Surveying
The practice of measuring angles and
distances on the ground so that they can be accurately plotted on a map
distances on the ground so that they can be accurately plotted on a map
GENERAL PRINCIPLE OF SURVEYING
The general principles of surveying are:
1. To work from the whole to the part, and
2. To locate a new station by at least two
measurements (linear or angular) from fixed reference points.
measurements (linear or angular) from fixed reference points.
According to the first principle, the
whole area is first enclosed by main stations (i.e. controlling stations) and
main survey lines (i.e. controlling lines). The area is then divided into a
number of parts by forming well conditioned triangles. A nearly equilateral
triangle is considered to be the best well-conditioned triangle. The main
survey lines are measured very accurately with a standard chain. Then the sides
of the triangles are measured. The purpose of this process of working is to
prevent accumulation of error. During this procedure, if there is any error in
the measurement of any side of a triangle, then it will not affect the whole
work. The error can always be detected and eliminated.
whole area is first enclosed by main stations (i.e. controlling stations) and
main survey lines (i.e. controlling lines). The area is then divided into a
number of parts by forming well conditioned triangles. A nearly equilateral
triangle is considered to be the best well-conditioned triangle. The main
survey lines are measured very accurately with a standard chain. Then the sides
of the triangles are measured. The purpose of this process of working is to
prevent accumulation of error. During this procedure, if there is any error in
the measurement of any side of a triangle, then it will not affect the whole
work. The error can always be detected and eliminated.
·
But,
if the reverse process (i.e. from the part to the whole) is followed, then the
minor errors in measurement will be magnified in the process of expansion and
stage will come when these errors will become absolutely uncontrollable.
But,
if the reverse process (i.e. from the part to the whole) is followed, then the
minor errors in measurement will be magnified in the process of expansion and
stage will come when these errors will become absolutely uncontrollable.
According to the second principle, the new
stations should always be fixed by at least two measurements (linear or
angular) from fixed reference points. Linear measurements refer to horizontal
distances measured by chain or tape. Angular measurements refer to the magnetic
bearing or horizontal angle taken by a prismatic compass or theodolite.
stations should always be fixed by at least two measurements (linear or
angular) from fixed reference points. Linear measurements refer to horizontal
distances measured by chain or tape. Angular measurements refer to the magnetic
bearing or horizontal angle taken by a prismatic compass or theodolite.
·
In
chain surveying, the positions of main stations and directions of main survey
lines and check lines.
In
chain surveying, the positions of main stations and directions of main survey
lines and check lines.
CLASSIFICATION OF SURVEYING
Generally, surveying is divided into two
major categories: plane and geodetic surveying.
major categories: plane and geodetic surveying.
PLANE SURVEYING is a process of surveying
in which the portion of the earth being surveyed is considered a plane. The
term is used to designate survey work in which the distances or areas involved
are small enough that the curvature of the earth can be disregarded without
significant error. In general, the term of limited extent. For small areas,
precise results may be obtained with plane surveying methods, but the accuracy
and precision of such results will decrease as the area surveyed increases in
size. To make computations in plane surveying, you will use formulas of plane
trigonometry, algebra, and analytical geometry.
in which the portion of the earth being surveyed is considered a plane. The
term is used to designate survey work in which the distances or areas involved
are small enough that the curvature of the earth can be disregarded without
significant error. In general, the term of limited extent. For small areas,
precise results may be obtained with plane surveying methods, but the accuracy
and precision of such results will decrease as the area surveyed increases in
size. To make computations in plane surveying, you will use formulas of plane
trigonometry, algebra, and analytical geometry.
A great number of surveys are of the plane
surveying type. Surveys for the location and construction of highways and
roads, canals, landing fields, and railroads are classified under
surveying type. Surveys for the location and construction of highways and
roads, canals, landing fields, and railroads are classified under
plane surveying. When it is realized that
an arc of 10 mi is only 0.04 greater that its subtended chord; that a plane
surface tangent to the spherical arc has departed only about 8 in. at 1 mi from
the point of tangency; and that the sum of the angles of a spherical triangle
is only 1 sec greater than the sum of the angles of a plane triangle for a
triangle having an area of approximately 75 sq mi on the earth’s surface, it is
just reasonable that the errors caused by the earth’s curvature be considered
only in precise surveys of large areas.
an arc of 10 mi is only 0.04 greater that its subtended chord; that a plane
surface tangent to the spherical arc has departed only about 8 in. at 1 mi from
the point of tangency; and that the sum of the angles of a spherical triangle
is only 1 sec greater than the sum of the angles of a plane triangle for a
triangle having an area of approximately 75 sq mi on the earth’s surface, it is
just reasonable that the errors caused by the earth’s curvature be considered
only in precise surveys of large areas.
In this training manual, we will discuss
primarily the methods used in plane surveying rather than those used in
geodetic surveying.
primarily the methods used in plane surveying rather than those used in
geodetic surveying.
GEODETIC SURVEYING is a process of
surveying in which the shape and size of the earth are considered. This type of
survey is suited for large areas and long lines and is used to find the precise
location of basic points needed for establishing control for other surveys. In
geodetic surveys, the stations are normally long distances apart, and more
precise instruments and surveying methods are required for this type of
surveying than for plane surveying. The shape of the earth is thought of as a
spheroid , although in a technical sense, it is not really a spheroid. In 1924,
the convention of the International Geodetic and Geophysical Union adopted
41,852,960 ft as the diameter of the earth at the equator and 41,711,940 ft as
the diameter at its polar axis. The equatorial diameter was computed on the
assumption that the flattening of the earth caused by gravitational at traction
is exactly 1/297. Therefore, distances measured on or near the surface of the
earth are not along straight lines or planes, but on a curved surface. Hence,
in the computation of distances in geodetic surveys, allowances are made for
the earth’s minor and major diameters from which a spheroid of reference is
developed. The position of each geodetic station is related to this spheroid.
The positions are expressed as latitudes (angles north or south of the Equator)
and longitudes (angles east or west of a prime meridian) or as northings and
castings on a rectangular grid.
surveying in which the shape and size of the earth are considered. This type of
survey is suited for large areas and long lines and is used to find the precise
location of basic points needed for establishing control for other surveys. In
geodetic surveys, the stations are normally long distances apart, and more
precise instruments and surveying methods are required for this type of
surveying than for plane surveying. The shape of the earth is thought of as a
spheroid , although in a technical sense, it is not really a spheroid. In 1924,
the convention of the International Geodetic and Geophysical Union adopted
41,852,960 ft as the diameter of the earth at the equator and 41,711,940 ft as
the diameter at its polar axis. The equatorial diameter was computed on the
assumption that the flattening of the earth caused by gravitational at traction
is exactly 1/297. Therefore, distances measured on or near the surface of the
earth are not along straight lines or planes, but on a curved surface. Hence,
in the computation of distances in geodetic surveys, allowances are made for
the earth’s minor and major diameters from which a spheroid of reference is
developed. The position of each geodetic station is related to this spheroid.
The positions are expressed as latitudes (angles north or south of the Equator)
and longitudes (angles east or west of a prime meridian) or as northings and
castings on a rectangular grid.
Classifications of Surveying
Based on the purpose (for which surveying
is being conducted), Surveying has been classified into:
is being conducted), Surveying has been classified into:
• Control surveying :
To establish horizontal and vertical
positions of control points.
positions of control points.
• Land
surveying :
surveying :
To determine the boundaries and areas of
parcels of land, also known as property survey, boundary survey or cadastral
survey.
parcels of land, also known as property survey, boundary survey or cadastral
survey.
• Topographic
survey :
survey :
To prepare a plan/ map of a region which
includes natural as well as and man-made features including elevation.
includes natural as well as and man-made features including elevation.
• Engineering
survey :
survey :
To collect requisite data for planning,
design and execution of engineering projects. Three broad steps are
design and execution of engineering projects. Three broad steps are
1) Reconnaissance survey :
To explore site conditions and
availability of infrastructures.
availability of infrastructures.
2) Preliminary survey :
To collect adequate data to prepare
plan/map of area to be used for planning and design.
plan/map of area to be used for planning and design.
3) Location survey :
To set out work on the ground for actual
construction/execution of the project.
construction/execution of the project.
•Route survey :
To plan, design, and laying out of route
such as highways, railways, canals,pipelines, and other linear projects.
such as highways, railways, canals,pipelines, and other linear projects.
Construction surveys :
Surveys which are required for
establishment of points, lines,grades, and for staking out engineering works
(after the plans have been prepared and the structural design has been done).
establishment of points, lines,grades, and for staking out engineering works
(after the plans have been prepared and the structural design has been done).
•Astronomic surveys :
To determine the latitude, longitude (of
the observation station) and azimuth (of a line through observation station)
from astronomical observation.
the observation station) and azimuth (of a line through observation station)
from astronomical observation.
•Mine surveys :
To carry out surveying specific for
opencast and underground mining purposes
opencast and underground mining purposes
SPECIAL SURVEYS
As mentioned earlier in this chapter,
SPECIAL SURVEYS are conducted for a specific purpose and with a special type of
surveying equipment and methods. A brief discussion of some of the special
surveys familiar to you follows.
SPECIAL SURVEYS are conducted for a specific purpose and with a special type of
surveying equipment and methods. A brief discussion of some of the special
surveys familiar to you follows.
LAND SURVEYS (sometimes called cadastral
or property surveys) are conducted to
or property surveys) are conducted to
establish the exact location, boundaries,
or subdivision of a tract of land in any specified area.
or subdivision of a tract of land in any specified area.
This type of survey requires professional
registration in all states. Presently, land surveys generally consist of the
following chores:
registration in all states. Presently, land surveys generally consist of the
following chores:
1. Establishing markers or monuments to
define and thereby preserve the boundaries of land belonging to a private concern,
a corporation, or the government.
define and thereby preserve the boundaries of land belonging to a private concern,
a corporation, or the government.
2. Relocating markers or monuments legally
established by original surveys. This requires examining previous survey
records and retracing what was done. When some markers or monuments are
missing, they are re-established following recognized procedures, using
whatever information is available.
established by original surveys. This requires examining previous survey
records and retracing what was done. When some markers or monuments are
missing, they are re-established following recognized procedures, using
whatever information is available.
3. Rerunning old land survey lines to
determine their lengths and directions. As a result of the high cost of land,
old lines are re-measured to get more precise measurements.
determine their lengths and directions. As a result of the high cost of land,
old lines are re-measured to get more precise measurements.
4. Subdividing landed estates into parcels
of predetermined sizes and shapes.
of predetermined sizes and shapes.
5. Calculating areas, distances, and
directions and preparing the land map to portray the survey data so that it can
be used as a permanent record.
directions and preparing the land map to portray the survey data so that it can
be used as a permanent record.
6. Writing a technical description for
deeds.
deeds.
CONTROL SURVEYS provide “basic
control” or horizontal and vertical positions of points to which
supplementary surveys are adjusted. These types of surveys (sometimes termed
and traverse stations and the elevations of bench marks. These control points
are further used as References for hydrographic surveys of the coastal waters;
for topographic control; and for the control of many state, city, and private
surveys.
control” or horizontal and vertical positions of points to which
supplementary surveys are adjusted. These types of surveys (sometimes termed
and traverse stations and the elevations of bench marks. These control points
are further used as References for hydrographic surveys of the coastal waters;
for topographic control; and for the control of many state, city, and private
surveys.
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