Control surveying

control survyeing

1. Control Surveying
Prakash Kumar S

2. Principles and Assumption
Landscape is curved and earth is spherical
Line of sight is not entirely straight because of refraction
Triangles formed during survey is spherical Triangle
Hence curvature correction and refractive correction should be
applied while calculating distance or height
Prakash Kumar S

3. Prakash Kumar S

4. Prakash Kumar S

5. Difference B/w Plane and Geodetic Surveying
Plane Surveying
Land area is considered as Flat
Lines are Straight
Triangles are plane triangles
Instrument used are Chains, Tapes,
Theodolite, Total Station etc.,
Eg: Setting out of Building
Geodetic Surveying
Land area is curved(earth as sphere)
Lines are not straight
Triangles formed are called spherical
triangle
Instrument used are GPS, Signals and
Towers, Total Station etc..,
Eg: Distance between two historical
points
Prakash Kumar S

6. Control Points
Primary Control points are measured with high precision with triangulation than
secondary and tertiary points
Horizontal Control Points –Triangulation, Traversing
Vertical Control Points –Trigonometric levelling
Working from whole to point
Forming Primary Triangle with very high precision then subdivided into secondary
triangle to locate the point to prevent accumulation of error. This is just like a
person’s address.
Prakash Kumar S

7. Triangulation
Prakash Kumar S

8. Triangulation or TrigonometricalSurvey
Find Precise distance between two survey stations A,B (base line)
Find distance b/w AC and BC from the distance AB and the angles formed
Using AC as base line find predict other points and so on.
To avoid Errors several Checking on the base line should be made and all the
angles should be measured.
Prakash Kumar S

9. Prakash Kumar S

10. Geodetic Triangulation
Refer slide 2 for Geodetic Surveying
Just like triangulation Surveying along with azimuth
Azimuth is the angle between Plane meridian and the vertical plane of the station
point
Forms the basic frame work for Cadastral(land registration), Topographical(land
surveying), hydrographical surveying etc.,
Prakash Kumar S

11. Classification of Triangulation system
Primary Triangulation
High precision
Baseline 5 to 15 km
Sides of Triangle 30 to150 km
Secondary Triangulation
Less precision
Baseline 1.5 to 5km
Sides of Triangle 8to 65 km
Tertiary Triangulation
Forms immediate survey reference point for engineering surveys
Accuracy is lower than Secondary Triangulation
Prakash Kumar S

12. Steps in Triangulation
Reconnaissance
Selection of Stations and Base line.
Selection of Triangulation framework
Erection of Signals and Towers
Measurement of Base Line
Horizontal Angles of the Triangles are Measured
Computation of Various Sides of the Triangles
Prakash Kumar S

13. Reconnaissance
Its done to get basic idea of the area, like selection of base line, suitable station
and suitable position etc..,
Instrument used :-Theodalite, barometer, compass, ladders etc..,
Prakash Kumar S

14. Selection of Triangulation Station
Well Condition Triangle
Indivisibility
Accessible
Cover Wide Area
Rigid Station
Line of sight
Economy
Permanent Station
Selected Station should Form Well
Condition Triangle
i.e., interior angles are nearly 60
degree and between 30 and 120
degree
Prakash Kumar S

15. Selection of Triangulation Station
Well Condition Triangle
Indivisibility
Accessible
Cover Wide Area
Rigid Station
Line of sight
Economy
Permanent Station
Stations should be visible to each
other.
Ex: -hilltops, high rise building,
temples and churches
Prakash Kumar S

16. Selection of Triangulation Station
Well Condition Triangle
Indivisibility
Accessible
Cover Wide Area
Rigid Station
Line of sight
Economy
Permanent Station
Station should be Easily accessible to
each other
Transportation, Communication and
carrying of materials
Prakash Kumar S

17. Selection of Triangulation Station
Well Condition Triangle
Indivisibility
Accessible
Cover Wide Area
Rigid Station
Line of sight
Economy
Permanent Station
Covers Wide Area of Triangulation to
limit substation
Prakash Kumar S

18. Selection of Triangulation Station
Well Condition Triangle
Indivisibility
Accessible
Cover Wide Area
Rigid Station
Line of sight
Economy
Permanent Station
Firm Ground for towers and Free
from wind
Prakash Kumar S

19. Selection of Triangulation Station
Well Condition Triangle
Indivisibility
Accessible
Cover Wide Area
Rigid Station
Line of sight
Economy
Permanent Station
Line of Sight Free from Atmospheric
Disturbance
Prakash Kumar S

20. Selection of Triangulation Station
Well Condition Triangle
Indivisibility
Accessible
Cover Wide Area
Rigid Station
Line of sight
Economy
Permanent Station
Cost of Erection of Towers should be
less
Prakash Kumar S
All Station should be marked and shown in Topographical map

21. Selection of Triangulation Station
Magnitude –Well Conditioned Triangle (30-120 degrees)
Triangle Arrangement
Single Chain of Triangle
Double Chain of Triangle
Central point Figure
Quadrilaterals
Prakash Kumar S

22. Signals and Towers
Signals –Erected to mark Station
Daylight or Non-luminous Signals (up to 30km, timber post or mast)
Sunlight or luminous Signals ( Reflecting surface reflects sunlight to theodolite)
Night Signal ( signal during night, oil lamp and acetylene)
Towers
Used to Erect Signal
Supports Signal and Observer seperatly
Masonry towers, Timber tower and steel tower
Prakash Kumar S

23. Prakash Kumar S