The document discusses control surveying methods for establishing horizontal and vertical control networks. It describes primary and secondary horizontal control points used in triangulation networks and benchmarks used for vertical control. Triangulation involves measuring base lines and angles to interconnected triangles that cover large areas. Different orders of triangulation provide varying levels of accuracy depending on factors like maximum triangle closure. The document outlines equipment, procedures and considerations for establishing horizontal and vertical control networks.

1. UNIT I
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2. CONTROL SURVEYING
Fixing the point with respect to horizontal
and vertical control.
Using surveying instruments.
Methods
Horizontal control
Vertical control
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3. CONTROL SURVEYING
Horizontal control
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4. CONTROL SURVEYING
Vertical control
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5. CONTROL SURVEYING
Horizontal control and its methods employed:
 Reference mark on known plan position
 Large structure primary and secondary control points are
used
 Primary control points are used in triangulation
 Secondary control points are reference to primary control
stations.
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6. CONTROL SURVEYING
Reference grid:
 Used for accurate setting out of works of large magnitude
Types:
 Survey grid
 Site grid
 Structural grid
 Secondary grid
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7. CONTROL SURVEYING
Survey grid:
 Drawn on survey plan from the original traverse
 Original traverse from the control points on the grid
Site grid:
 Used by the designer
 Design points are related to site grid
 Site grid should be actually the survey grid
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8. CONTROL SURVEYING
Structural grid:
 Used at when the structural components are large
numbers.
 Used for accuracy
 It is set out from the site grid points
Secondary grid:
 Used for internal details of the building
 Other grids are not shown
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9. CONTROL SURVEYING
Vertical control and methods:
 Determine elevation with respect to sea level
 Used to BM for other survey and high accuracy
 Also used for boundary survey, route survey, construction
and topographic surveys
 Need at lest two BM and more may be required at
depending upon the needs and complexity of the project
 Also used for construction of water, sewer system,
highways, bridges, drains and other infrastructures
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10. CONTROL SURVEYING
cont.....
 Can be done in alone but after often done in conjunction
with a horizontal control survey
 Its used in NOAA ( national oceanic and atmospheric
administration)
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11. CONTROL SURVEYING
Equipments:
 Boning rods and travellers (T shape)
 Sight rails (drilling to ground)
 Slope rails or batter boards (slope area)
 Profile boards (board cuts at edges)
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12. CONTROL SURVEYING
Triangulation:
 The system consists of inter connected triangles in which
the length of one line called base line
 Angle of the triangles are measured very precisely
 Knowing the length of one side and three angles
 The length of other two sides are computed
Disadvantages:
 Accumulate errors and azimuth
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13. CONTROL SURVEYING
Classification of Triangulation system:
 First order or primary triangulation (total whole country)
 Second order or secondary triangulation (in between frame
work)
 Third order or tertiary triangulation (within frame work)
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14. CONTROL SURVEYING
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S.
N
PARAMETERS 1st ORDER 2nd ORDER 3rd ORDER
1 Average triangle closure Less than 1 second 3 sec 6 sec
2 Maximum triangle closure Not more than 3
seconds
8 sec 12 sec
3 Length of base line 5 to 15 kilometers 1.5 to 5 km 0.5 to 3 km
4 Length of the sides of triangles 30 to 150
kilometers
8 to 65 km 1.5 to 10 km
5 Actual error of base 1 in 300,000 1 in 150,000 1 in 75,0000
6 Probable error of base 1 in 1,000,000 1 in 500,000 1 in 250,000
7 Discrepancy between two
measures of a section
10 mm kilometers 20 mm kilometers 25 mm kilometers
8 Probable error or computed
distance
1 in 60,000 to 1 in
250,000
1 in 20,000 to 1 in
50,000
1 in 5,000 to 1 in
20,000
9 Probable error in astronomic
azimuth
0.5 seconds - 5 sec.
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15. CONTROL SURVEYING
Common figure of system:
 Single chain triangulations – not accurate
 Double chain triangulation – used to cover grater area
 Central point figures – flat countries ( pentagon and
hexagon)
 Quadrilateral – hilly countries (four side)
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16. CONTROL SURVEYING
Routine of triangulation survey:
 Reconnaissance survey
 Measurement of base line
 Measurement of horizontal angle
 Erection of signals and towers
 computing
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17. CONTROL SURVEYING
1.Reconnaissance survey:
Detailed survey
 Location of the site
 Characteristics of the contours
 Selection of triangulation system
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18. CONTROL SURVEYING
Factors governing the selection of triangulation station:
 Easily accessible
 No obstacles
 Material available at nearer area
 Transportation facility
Important factors:
 Determination of distance b/n 2 points or stations
 Determination of elevation
 Profile of the intervening (obstacle) ground
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19. WHAT IS THIS ?
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20. CONTROL SURVEYING
Signals and Towers:
Towers:
 A tower is a structure erected over a station for the support
of the instrument and observing party and is provided when
the station or the signal or both are to be elevated.
 Inner tower - support the instrument only
 Outer tower- support the observer and signal
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21. CONTROL SURVEYING
Towers:
 Independent to each other-masonry , timber and steel
 For small height masonry suitable otherwise uneconomical
 Timber are commonly used-50m height
 Steel towers are easily erected and dismantled also light
weight (BILBY tower 30 to 40m ht-3hours-5men-3tonnes)
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22. CONTROL SURVEYING
Signals :
 A signal is a devices erected to define the exact position of
an observed station.
Classification :
 Day light or non luminous (opaque) signal
 Sun or luminous signal
 Night signal
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23. CONTROL SURVEYING
Requirements of Signals :
 It should be conspicuous- clear visible against any
background
 Accurate cantered over the station mark
 It should be suitable for accurate bisection
 It should be free from phase or exhibit little phase
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24. CONTROL SURVEYING
Day light or non luminous (opaque) signal:
 Consist of various type-Direct sight less then 30km
 Pole signals used for 6km
 Signal should be dark colour for visibility against the sky and should
painted white.
 Flag at top the signal
 Diameter of the signal pole in cm = 1.3D to 1.9D (D in km)
 Height of signal pole in cm = 13.3D (D in km)
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25. CONTROL SURVEYING
Sun or luminous signal:
 Sun signals are those in which the sun’s rays are reflected to the
observing theodolite, either directly as from a beacon or
indirectly from a signal target.
 Used to when the length of sight exceed 30km
Instruments used:
 Heliotrope – consist of plane mirror- Direct reflected rays
 Heliograph – cantered over the station mark.
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26. CONTROL SURVEYING
Night signal:
 Used in triangulation system at night time.
 Various forms of oil lamps with reflector or optical
collimators for line of sight less than 80km
 Acetylence lamp designed by captain G.T.Mccaw line of
sight up to 80km
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27. CONTROL SURVEYING
Phase of signals:
 Phase signal is the error of bisection which arises from the fact
that under lateral illumination the signal is partly in light and
partly in shade.
 Observer sees only the illumination portion and bisects.
Two conditions
1. When the observation is made on the bright portion – ref fig A
2. When the observation is made on the bright line – ref fig B
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28. CONTROL SURVEYING
Base line measurement:
 It is most important part of triangulation operations and
need to great accuracy
Selection of site for base line
 Fairly level, slope should be uniform and gentle
 Free from obstruction
 Base should be inter visible at ground level
 Firm and smooth, water gaps should be few
 The site should be extension to primary triangulation
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29. CONTROL SURVEYING
Standard of lengths:
 Marked on meters by metals but small changes in
accuracy
a) Great britian – yard of bronze
b) The united states – meter to feet
c) India – old 10 feet bar A = 9.9999566 British feet
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30. CONTROL SURVEYING
Base measuring apparatus:
 Rigid bars (before tape)
a) Contact apparatus (continue end)
b) Optical apparatus (microscope)
c) Compensating base bar (maintain length by 2
metals)
d) Bimetallic non-compensating base bars (using
thermometer)
e) Monometallic base bar ( using ice)
 Flexible apparatus
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31. CONTROL SURVEYING
The Colby apparatus:
 Designed by Maj-Gen
 Eliminate the effect of change of temperature
 Linear expansion 3:5 ratio
 Steel and brass metals are using
 Brass is coated with a special preparation for steel
 Compound bar and sprite level are fixed at middle
 Consist of micro wires (cross wires)
 5 frame works (10 ft x 5 + 6 in x 5) = 52ft 6in
 This work is continued till the end of the base is
reached.
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32. CONTROL SURVEYING
Flexible apparatus:
 Long length, time saving, no losses, accuracy, using
rough ground also, water gap areas, less expansive,
speed of measurements and more check bases.
1. Steel and inverted tape
2. Steel and brass wires
Steel tape
 Thermal expansion nearly 0.00000645/ºF
 Not accurate at day time, accurate at cloudy and night
time
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33. CONTROL SURVEYING
Inver tape and wires:
 Steel alloy containing about 36% nickel
 The co-efficient of thermal expansion is 0.0000005/ºF
 Length is changed slowly so never used standard
Equipment for base line measurement:
 Three standardised tapes
 Straining device, marking tripod or sticks
 Six thermometers
 Accurate spring balance
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34. CONTROL SURVEYING
The field work:
 The setting out party
Two surveyors and a number of parties
 The measuring party
Two observers, recorder, leveller and staff man
(accurate at 0.5 to 1km)
Methods:
1.Wheeler’s method by wheeler’s base line apparatus
2.Jaderin’s method
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35. CONTROL SURVEYING
Tape corrections:
 Correction for absolute length
 Correction for temperature
 Correction for pull or tension
 Correction for sag
 Correction for slope
 Correction for alignment
 Reduction to sea level
 Correction to measurement in vertical plane
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36. CONTROL SURVEYING
Correction for absolute length (Ca):
Ca = L.c/l
 Ca- correction for absolute length
 L-measure length of the line
 C-correction per tape length
 L-designed length of the tape
Correction for temperature (Ct):
Ct = α (Tm-To)L
 α- co efficient of thermal expansion
 Tm-mean temperature in the field during measurements
 To- mean temperature during standardisation of the tape
 L- measured length
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37. CONTROL SURVEYING
Correction for temperature (Ct):
Jaderin’s method:
Ct (brass) = αb (Ls-Lb)/αb - αs
Ct (steel) = αs (Ls-Lb)/αb – αs
Correction for pull or tension (Cp or Ct):
Cp = (P-Po)L/AE
 P- pull applied during measurements (N)
 Po- standard pull (N)
 L-measurement length (m)
 A-cross section area of the tape (cm2)
 E-young’s modulus of elasticity (N/cm2)
 The pull applied in the field should be less than 20 times
the weight of the tape.
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38. CONTROL SURVEYING
Correction for Sag (Cs):
Cs = NCs + sag correction for any
fractional tape length
 N-number of whole length tape
 Cs – tape correction per tape length
Cs = nlw2/24p2
l -total length of the tape
W-total weight of the tape
n = number of equal span
P = pull applied
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39. CONTROL SURVEYING
Normal tension(Pn):
Pn = 0.204w1 √AE/√ (Pn - Po )
The value of Pn is to be determined by trial and
error method.
Correction for slope or vertical alignment:
AB = L = inclined length measured
AB1 = horizontal length
h = difference in elevation between the ends.
Cv = slope correction or correction due to vertical
alignment
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40. CONTROL SURVEYING
Cv = AB- AB1 = L-√L2-h2
If the grades are uniform length L, we get total slope
correction = sum of h2 /2L
If the angle (θ) of slope is measured insted of h, the correction
is given by
Cv = L-Lcosθ = l(1-cosθ)
Cv =2Lsin2θ/2
Correction for horizontal alignment
(a) Bad ranging = Ch = d2/2L
(b) Deformation of the tape in horizontal plane = Ch =
(d2/2L1)+(d2/2L1)
(c) Broken base = Ch = (acβ2 /(a+c)) x 4.2308x10-8
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41. CONTROL SURVEYING
Reduction to mean sea level:
Correction (Cmsl) = L-D = Lh/R
Correction to measurement in vertical plane:
Sx = gx/AE ((M+0.5m(2l-x)-po/g))
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42. CONTROL SURVEYING
Measurement of horizontal angle:
 Two types of instruments are used in triangulation of
high precision
1. Repeating theodolite (Double vertical axis, using 2
or more verniers)
2. Direction theodolite (1 vertical axis and accuracy)
(a) Wild T-3 precision theodolite
(b) Wild T-4 universal theodolite
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43. CONTROL SURVEYING
Methods of horizontal angle:
 Method of repetition
 Reiteration or direct or method of series
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44. CONTROL SURVEYING
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45. CONTROL SURVEYING
Methods of horizontal angle:
 Method of repetition
 Reiteration or direct or method of series
Satellite station : Reduction to centre:
 In order to secure well conditioned triangle or better
visibility objects such as church spires, steel post,
flag poles, towers etc..
 Sometimes selected as triangulation station, when the
observations are to taken from such a station, it is
impossible to set up an instrument over it.
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46. CONTROL SURVEYING
 In such cases a subsidiary station known as satellite
station or eccentric station or false station is
selected as near to the main station.
 Observations are taken from same precision as would
have been used in the measurement of angle at the
true stations.
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47. CONTROL SURVEYING
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 Gale’s Table
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