1.1 linear measurement original: chaining & ranging
TRANSCRIPT
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BY: Rakesh Kumar Verma A s s i s t a n t P r o f e s s o r , ( P . I . E . T )
P a r u l U n i v e r s i t y , V a d o d a r a
SURVEYING: Linear
Measurements
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LINEAR MEASUREMENTS
measurement of distances between points on the surface of the earth
In Horizontal (Assumed) plane
p2 p1
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Methods of
LINEAR SURVEYING
Direct measurement Distances are actually measured on the surface of the earth using Chain or Tape measurements 0r Ranging
Indirect Measurements
Measurement by optical means Observations are taken through a telescope and distances are determined by calculation as in tachometer or triangulation
Electronic methods Distances are measured with instruments that rely on propagation, reflection and subsequent reception of either radio or light waves
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Direct
Measurements
Directly Measure Distance on Ground
Using:
1. Chain or
2. Tape
3. Arrow
4. Ranging Rod
5. Cross Staff
CHAIN
ARROW
TAPE
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Length:10cm to 60cm Sides:15mm to 25mm
In general use L=15cm or 20cm
20mm
50mm Dia. 4mm Dia.
400mm±5mm
1m to 3m
Red Band
White Band
@20cm
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Types of Chain
Metric chains 20m and 30m Tallies @every five-meter length brass rings @ every meter length
Gunter's chain or surveyors chain Length = 66 ft (22 yards), No of links = 100, Each link = .66’ Used for measuring distances in miles or furlongs (220 yards), acres (Area).
Engineers chain Length = 100 ft , No of links = 100, Each link = 1’ Used in all Engineering Surveys.
Revenue chain Length = 33ft, No of links = 16 Commonly used for measuring fields in cadastral Survey
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5m
15m 1o m
20cm
20cm
1st Link
2nd Link
Tallies
13cm 13cm
D-13cm D-13cm
Brass Handle
Ring
Ring
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Measuring Tapes
1. Cloth or linen tape Used for subsidiary measurements Very light, easy to handle May effect by moisture 2. Metric steel tape Made of steel Outer end is provided with a ring for holding 3. Invar tape Used for high precision work Made of alloy steel 4. Synthetic tape Made of glass fiber with PVC coating These are used for short measurements
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Chain Survey
Simplest method of surveying.
In chain survey only measurements are taken in the field, and the rest work, such as plotting calculation etc. are done in the office.
Only linear measurements
No angular measurements
Most suitable adapted to small plane areas with very few details.
If carefully done, it gives quite accurate results.
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When we can use Chain?? What are Survey Station??
For comparatively small Areas
Fairly level Ground
For open areas and
For simple detailing and less information.
Main Stations
Subsidiary or tie
Chain Surveying
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Main Stations Subsidiary or tie stations
Main stations are the end of the lines, which command the boundaries of the survey, and the lines joining the main stations re called the main survey line or the chain lines.
Subsidiary or the tie stations are the point selected on the main survey lines, where it is necessary to locate the interior detail such as fences, hedges, building etc.
Stations
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Lines
Base Lines It is main and longest line, which passes approximately
through the center of the field. Detailing work carryout with respect of this line.
Check Line Or Proof line is a line joining the apex of a triangle to
some fixed points on any two sides of a triangle. To check the accuracy of the framework.
The length of a check line, as measured on the ground should agree with its length on the plan.
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A B
C
D
E
F
G
H
Tie Point
Check Line
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Offsets
Lateral measurements from the base line
To fix the positions of the different objects
May be taken by using a tape.
Types of offsets:
Perpendicular offsets
Oblique offsets.
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Perpendicular Offset
The measurements are taken at right angle to the survey line called perpendicular or right angled offsets. For setting perpendicular offsets any one of the following methods are used:
Swinging
Using cross staffs
Using optical or prism square
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Oblique Offset
Offset at some angle
Well conditioned triangle must be maintained
A B
φ≠90ᵒ Φ=90ᵒ
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FIELD BOOK
For record all observations and measurements size 200 mm × 120 mm (Size of Pocket) There are two forms of the book (i) single line and (ii) double line Single book :red line along in middle of width represent main survey line. Space on either side of the line :used for sketching the object and for noting offset distances. Double line book: two blue lines with a space of 15 to 20 mm is the middle of each book. Space between the two lines: used for noting the chain-ages.
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Procedure in chain survey
Reconnaissance: preliminary inspection Marking Station: fixes up the required no stations at places
with maximum visibility Methods used for marking are: 1. Fixing ranging poles 2. Driving pegs 3. Marking a cross if ground is hard 4. Digging and fixing a stone. Selects main survey line Fix ranging roads on the stations Start chaining and Make ranging if required Field book Entry
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A
B
Oblique Offset
Perpendicular Offset
D1
D2
Field Work
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Earth
Water Tank
Home B1
B 3
A B 1
2
3 5
6 8
9
10 11
12 13
4 7
d2 d4 d7 h8 h10
d12 d13
d1 d6 d11
d9 d5 d3
wt1
wt2
B 2
B21
B11
B12 T
B31
Here; 1,2,3,………….,12,13 are the chain-edge( Where offset meets perpendicular to chain) d1,d2,d3,……….,d12,d13 are the offset distances wt1, wt2, B11, B12, B31 and B21 are the references/ oblique offset from permanent structure i.e. Water Tank, Buildings, electric towers T refers to offset taken at tree( shouldn’t consider reference, however it is oblique offset)
B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home
t1
p1
t6
t5
t4 t3 t2
t9 t8 t7
p2
p3 p4
Field Work
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A B
1
2
3 5
6 8
9
10 11
12 13
4 7
d2 d4 d7 h8 h10
d12 d13
d1 d6 d11 d9 d5 d3
wt1
wt2
B21
B11 B12
T
B31
Legends or Coding 1,2,3,………….,12,13 are the chain-edge( Where offset meets perpendicular to chain) d1,d2,d3,……….,d12,d13 are the offset distances wt1, wt2, B11, B12, B31 and B21 are the references/ oblique offset from permanent structure i.e. Water Tank, Buildings, electric towers T refers to offset taken at tree( shouldn’t consider reference, however it is oblique offset)
B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home
Office Work
Legends: Pole Tree Building/Home Water Tank
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A B 1
2
3 5
6 8
9
10 11
12 13
4 7
d2 d4 d7 h8 h10
d12 d13
d1 d6 d11 d9 d5 d3
Area calculation: approximate estimation of surveyed land
B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home
Office Work
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A B
Area calculation: approximate estimation of surveyed land
B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home
Office Work
Calculated Area in meter square
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Ranging in Surveying
To align intermediate points on chain line so that the measurements are along the line
Process of locating intermediate points on survey line is known as ranging
Methods of ranging
1. Direct Ranging
2. Reciprocal Ranging
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Direct Ranging
Used when the stations are intervisible
Done by eye-judgement
Ranging rods are erected vertically beyond each end of survey line
The surveyor stands 2m beyond the ranging rod while the assistant folds the ranging rod vertically in the intermediate stations.
The surveyor directs the assistant to move the rod to the left or right until the three ranging rods appear to be in a straight line.
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Ranging at small Distance & station are visible
Station-A Station-B
Direction of Survey line
Distance to be measured
Ranging Rod-1 Ranging Rod-2
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A
B
C
Ranging at Long Distance & station are visible
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Station-A Station-B
Direction of Survey line
Distance to be measured
Chain Length -1 Chain Length -1 Chain Length -1
Rod-1 Rod-4 Rod-3 Rod-2
All Rods must be in the same line
Ranging at Long Distance & station are visible
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Indirect Ranging/ Reciprocal Ranging
when ends of a line are not inter-visible due hill ground or stations are not clearly inter-visible
needs two assistants one at point M and another at point N, where from those points both station A and station B are visible
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A
B
M1 N1
M3
M2 N2
N3
N4
M4
N M
Reciprocal Ranging: stations are not visible directly
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A B D E F G H C
Reciprocal Ranging: stations are not visible directly
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A
B
Master Reset: Both survey lines readjusted to bring themselves in a straight line
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