Chain Surveying: Principles and Operations
•
Chain surveying can be used when the area to
be surveyed is comparatively small and is
fairly flat. but when the area is large
undulated and crowded with many details
triangulation is not possible. In such area
method of traversing is adopted.
Chain surveying
Principles of Chain
Surveying
•
The
principle
of chain surveying
is
to
divide the
area
into
a
number of triangles
.
•
As a
triangle
is
the only simple plane geometrical
figure
which can be plotted from the length of the
three
sides even if
the angles are not known. A
network of
triangles
is
preferred
to
chain
surveying.
•
Triangulation is
the principle of chain surveying.
If
the area
to
be
surveyed
is
triangle
in
shape
and
if
the lengths and sequence of
its
three
sides
are
recorded, the plan of the area can be
easily
drawn.
Principles of Chain
Surveying
Principles of Chain
Surveying
Well
conditioned triangle, ill
conditioned triangle and
ideal
triangle.
•
A triangle is
said
to
be well conditioned
triangle when
no
angle in it is
neither
less
than 30
nor
greater
than
120.
•
If in a triangle an angle is less than 30 or
greater
than 120 is
called
ill
conditioned
triangle.
•
An
equilateral
triangle
having
each angle of 60
is an ideal
triangle.
Operation in Chain
Surveying
•
The following operations are involved in
chain
surveying.
•
Chaining
•
Ranging
•
Offsetting
•
These three operations are done
simultaneously during chain
Surveying.
Offsets
•
Lateral measurements
to
chain
lines for
locating
ground
features are known as
offsets.
For this
purpose
perpendicular or
oblique
offsets
may be
taken
. If
the object to
be
located
(say road) is
curved more number of
offsets
should be taken.
For
measuring
offsets
tapes
are commonly
used.
•
Offset
which
can be
judged
by
naked
eye
or
offset
less
than 15m
is called short
offset
and
offset
greater than
15m
is
called long
offset.
•
Most commonly short
offsets
are
perferred.
Offsets
•
Offset
may also be
classified as
Perpendicular
Offsets
and
oblique
offset.
Perpendicular
Offsets
•
The
offsets
which are taken perpendicular
to
the
chain
line
are termed
as
perpendicular
offsets.
These
offsets
are
taken
Perpendicular
Offsets
Offsets
Oblique
Offset
•
O
b
l
i
que
distance
i
s
alw
a
ys
greater
p
e
rpend
i
c
u
lar
dis
t
a
n
ce.
All
the
o
f
fsets
t
han
whi
c
h
are not taken at
the right
angle
to
chain line
are
known
as oblique
offsets.
Oblique
Offset
Offsets
DEFINITIONS
A Survey
Stations
•
Survey stations
are
the points at
the
beginning
and the end
of
a
chain line. They
may
also occur at
any
convenient points
on
the
chain line.
Such
stations
may
be:
1.
Main
stations
2.
Subsidiary stations
and
3.
Tie
stations
1. Main stations
Stations
taken along
the boundary
of
an
area
as
controlling
points
are
known
as
‘main
survey lines’.
The main
survey lines should
cover
the
whole
area
to
be
surveyed.
The
main
stations are
denoted
by
‘ ’
with
letters
A,
B, C, D,
etc.
The chain lines
are
denoted
by “__
…
__
...
__...__...__...__”.
2.
Subsidiary
stations
Stations
which
are
on the
main
survey lines
or
any
other
survey
lines
are
known
as
“Subsidiary
stations”.
These
stations
are
taken
to
run
subsidiary
lines
for
dividing
the
area
into triangles,
for
checking
the
accuracy of
triangles
and
for
locating interior
details.
These
stations
are
denoted
by
‘’
with letters S
1
,S
2
,S
3
,
etc.
3. Tie stations
These
are
also
subsidiary
stations
taken
on
the
main
survey
lines.
Lines
joining
the
tie
stations
are
known
as
tie
lines.
Tie
lines
are
mainly
taken
to
fix
the
directions
of
adjacent sides
of
the
chain
survey map.
These
are also
taken
to
form ‘chain
angles’
in
chain
traversing, when triangulation
is
not
possible.
Sometimes
tie
lines
are
taken
to
locate interior
details.
Tie
stations
are
denoted
by
‘’ with
letters T
1
,
T
2
, T
3
.
Etc.
Procedure
of field
work
•
Reconnaissance
•
Index
sketch
•
Marking the
stations
on
ground
•
Reference
sketches
•
Taking
measurement of
survey
lines
and
noting
them.
1.
Reconnaissance
survey
•
The preliminary inspection
of
the area
to
be
surveyed
is
called reconnaissance. The
surveyor
inspects the
area
to
be
surveyed,
survey
or
prepares index
sketch
or
key
plan.
Walk
the
whole
area
and
thoroughly
examine
the
ground, note
the
position of boundaries,
road,
and
river etc.,
various
difficulties
to
chain
lines, select
stations,
and
prepare neat
sketches
called
index
sketches
or
key
plan
2. Index
sketch
•
After
preliminary inspection
of
the
area,
the
surveyor should prepare a neat hand sketch
showing the
arrangement of
the
framework
and
approximate
position
of
the
objects.
He
should
note
the
names of
the
stations
on
the
sketch
maintaining
some order (clockwise
or
anticlockwise).
The
field
work
should
be
executed according
to
this
index
sketch.
The
names
and
sequence of chain
lines
should
be
followed
as
directed
in
the
index
sketch.
The
‘base
line’
should
be
clearly
indicated
in
the
index
sketch.
3
. Marking
stations
•
Stations
are marked
with
ranging
rod,
or
wooden
peg,
driving
a
nail or
spikes
if
hard
surface,
or
embedding
stone
with a
cross
mark.
4
.
Reference
sketches
•
After
marking the
station
should be
referenced
i.e.
located
by measurement
called ties
taken
from
3
permanent points
which
are
easily
identified
such
as
corner
of
building
And in
the
final
required
measurements
are
taken
and
located
on field
book.
•
EQUIPMENTS FOR CHAIN
SURVEY
•
The
following
equipment's
are
required
for
conducting
chain
survey:
1.
Metric
chain
(20
m)
2.
Arrows
3.
Metallic tape
(15
m)
4.
Ranging
rods
5.
Offset
rod
6.
Clinometer
7.
Plumb bob
with
thread
8.
Cross
staff
or
optical
square
9.Prismatic
compass
with
stand
10. Wooden
pegs
11.Field
book
12.
pencil
13. Eraser
(rubber)
•
Chain
surveying
is recommended
when:
1.
The ground
surface
is
more
or less
level
2.
A
small
area
is
to
be
surveyed
3.
A
small-scale map
is to be
prepared
and
4.
The formation of
well-conditioned
triangles
is
easy
Chain
surveying
is
unsuitable
when:
1.
The area
is
crowded
with
many
details
2.
The area
consists
of
too
many
undulations
3.
The area
is
very
large
and
4.
The formation of
well-conditioned
triangles becomes
difficult
due
to
obstacles
Chain surveying is a method used for small, flat areas while traversing is preferred for larger, undulated terrains. Principles involve dividing areas into triangles for accurate plotting, with well-conditioned triangles being ideal. Operations such as chaining, ranging, and offsetting are essential in chain surveying to ensure precise measurements of ground features.
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Presentation Transcript
Chain surveying Chain surveying can be used when the area to be surveyed is comparatively small and is fairly flat. but when the area is large undulated and crowded with many details triangulation is not possible. In such area method of traversing is adopted.
Principles of Chain Surveying The principle of chain surveying is to divide the area into a number of triangles . As a triangle is the only simple plane geometrical figure which can be plotted from the length of the three sides even if the angles are not known. A network of triangles surveying. Triangulation is the principle of chain surveying. If the area to be surveyed is triangle in shape and if the lengths and sequence of its three sides are recorded, the plan of the area can be easily drawn. is preferred to chain
Well conditioned triangle, ill conditioned triangle and ideal triangle. A triangle is said to be well conditioned triangle when no angle in it is neither less than 30 nor greater than 120. If in a triangle an angle is less than 30 or greater than 120 is called ill conditioned triangle. An equilateral triangle having each angle of 60 is an ideal triangle.
Operation in Chain Surveying The following operations are involved in chain surveying. Chaining Ranging Offsetting These three operations are done simultaneously during chain Surveying.
Offsets Lateral measurements to chain lines for locating ground features are known as offsets. For this purpose perpendicular or oblique offsets may be taken. If the object to be located (say road) is curved more number of offsets should be taken. For measuring offsets tapes are commonly used. Offset which can be judged by naked eye or offset less than 15m is called short offset and offset greater than 15m is called long offset. Most commonly short offsets are perferred.
Offsets Offset may also be classified as Perpendicular Offsets and oblique offset. Perpendicular Offsets The offsets which are taken perpendicular to the chain line are termed as perpendicular offsets. These offsets are taken
Offsets Oblique Offset Oblique distance is always greater perpendicular distance. All the offsets are not taken at the right angle to chain line are known as oblique offsets. than which
A Survey Stations Survey stations are the points at the beginning and the end of a chain line. They may also occur at any convenient points on the chain line. Such stations may be: 1.Main stations 2.Subsidiary stations and 3.Tie stations
1. Main stations Stations taken along the boundary of an area as controlling points are known as main survey lines . The main survey lines should cover the whole area to be surveyed. The main stations are denoted by with letters A, B, C, D, etc. The chain lines are denoted by __ __ ... __...__...__...__ . 2. Subsidiary stations Stations which are on the main survey lines or any other survey lines are known as Subsidiary stations . These stations are taken to run subsidiary lines for dividing the area into triangles, for checking the accuracy of triangles and for locating interior details. These stations are denoted by with letters S1,S2,S3, etc. 3. Tie stations These are also subsidiary stations taken on the main survey lines. Lines joining the tie stations are known as tie lines. Tie lines are mainly taken to fix the directions of adjacent sides of the chain survey map. These are also taken to form chainangles in chain traversing, when triangulation is not possible. Sometimes tie lines are taken to locate interior details. Tie stations are denoted by with letters T1, T2, T3. Etc.
Procedure of field work Reconnaissance Index sketch Marking the stations on ground Referencesketches Taking measurement of survey lines and noting them.
1. Reconnaissance survey The preliminary inspection of the area to be surveyed is called surveyor inspects the area to be surveyed, survey or prepares index sketch or key plan. Walk the whole area and thoroughly examine the ground, note the position of boundaries, road, and river etc., various difficulties to chain lines, select stations, and prepare neat sketches called index sketches or key plan reconnaissance. The
2. Index sketch After preliminary inspection of the area, the surveyor should prepare a neat hand sketch showing the arrangement of the framework and approximate position of the objects. He should note the names of the stations on the sketch maintaining some order (clockwise or anticlockwise). The field work should be executed according to this index sketch. The names and sequence of chain lines should be followed as directed in the index sketch. The baseline should be clearly indicated in the index sketch.
3. Marking stations Stations are marked with ranging rod, or wooden peg, driving a nail or spikes if hard surface, or embedding stone with a cross mark. 4. Reference sketches After marking the station should be referenced i.e. located by measurement called ties taken from 3 permanent points which are easily identified such as corner of building And in the final required measurements are taken and located on field book.
EQUIPMENTS FOR CHAIN SURVEY The following equipment's are required for conducting chain survey: 1.Metric chain (20 m) 2.Arrows 3.Metallic tape (15 m) 4.Ranging rods 5.Offset rod 6.Clinometer 7.Plumb bob with thread 8.Cross staff or optical square
9.Prismatic compass with stand 10. Wooden pegs 11.Field book 12. pencil 13. Eraser (rubber)
Chain surveying is recommended when: 1.The ground surface is more or less level 2.A small area is to be surveyed 3.A small-scale map is to be prepared and 4.The formation of well-conditioned triangles is easy
Chain surveying is unsuitable when: 1.The area is crowded with many details 2.The area consists of too many undulations 3.The area is very large and 4.The formation of well-conditioned triangles becomes difficult due to obstacles
