Chain surveying, well condition and ill conditioned triangle, steps in chain surveying,offset , selection of stations, location of offset

1. Chain surveying
M.Z Jamali

2. Chain Surveying
• Chain (Tape) surveying is the simplest form of detail
surveying. In this method the lengths of lines marked on
the field are measured, while the details are measured by
offsets from these line.
• Chain surveying is the type of surveying in which only
linear measurements are taken in the field.
• This type of surveying is done for surveying of small extent
to describe the boundaries of plots of land and to locate the
existing feature on them.
• It is the method of surveying in which the area is divided
into network of triangles and the sides of the various
triangles are measured directly in the field with a chain or a
tape and no angular measurements are taken.

3. Principles of Chain Surveying

4. 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.

5. Principles of Chain Surveying

6. Principles of Chain Surveying

7. Principles of Chain Surveying

8. Principles of Chain Surveying

9. Principles of Chain Surveying

10. • Suitability of chain surveying:
• Chain surveying is recommended when:
Ground surface is more or less level.
Area is small.
Small-scale map is required to prepare.
Formation of well conditioned triangle is easy.
• Chain surveying is not recommended when:
Area is crowded with many details.
Area consists of too many undulations.
Area is very large.
Formation of well conditioned triangle is not
easy.

11. 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.

12. Terms related to Chain
Surveying
Survey Stations
• Survey stations are the points at the beginning
and at the end of a chain line they may also
occur at any convenient position on the chain
line. Such station may be
• Main Stations
• Subsidiary Stations
• Tie Stations

13. Terms related to Chain
Surveying
• Main Station Stations along the boundary of an
area as controlling points are known as ‘Main
Stations’ The lines joining the main station are
called ‘ Main Survey Lines’. The main survey
lines should cover the whole area to be
surveyed. The main stations are denoted by Δ.

14. Terms related to Chain
Surveying
• 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.

15. Terms related to Chain
Surveying
• Tie Stations:
• These stations are also subsidiary stations
taken on the main survey lines. Lines joining
the stations are known as ‘ Tie lines’ Tie lines
are taken to locate interior details.

16. Terms related to Chain
Surveying
Main Survey Lines:
• The line joining the main stations are called
main survey lines or chain lines.

17. Terms related to Chain
Surveying
• Base Line: The line on which the framework of the
survey is built is known as ‘ Base line’. It is the most
important line of the survey. Generally the longest of
the main survey lines is considered as the base line.
This lines should be taken through fairly level ground,
and should be measured very carefully and accurately.

18. Terms related to Chain
Surveying
• Check Line
• The line joining the apex point of a triangle to
some fixed points on its base is known as ‘
Check line’. It is taken to check the accuracy
of the triangle. Sometimes this line helps to
locate interior details.

19. Terms related to Chain
Surveying
• Tie Line
• A line joining tie stations is termed as a tie
line. It is run to take the interior details which
are far away from the main lines and also to
avoids long offsets. It can also serve as check
line.

20. Selection of Survey Station
• The following points should be considered while
selecting survey stations:
• It should be visible from at least two or more
stations.
• As far as possible main lines should run on level
ground.
• All triangles should be well conditioned (No
angle less than 30º).
• Main network should have as few lines as
possible.

21. Selection of Survey Station
• Each main triangle should have at least one
check line.
• Obstacles to ranging and chaining should be
avoided.
• Sides of the larger triangles should pass as
close to boundary lines as possible.
• Base line should be longest survey line.
• Survey line should be taken close to boundary
so that they can be located by short offset.

22. Operation in Chain Surveying
• The following operations are involved in chain
surveying.
• Chaining
• Ranging
• Offsetting
• These three operations are done
simultaneously during chain Surveying.

23. 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.

24. 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
• (a) By holding zero end of the tape at the object
and swinging the tape on the chain line. The
shortest distance measured from object to the
chain line is usually the perpendicular offset.
• (b) By setting right angle in 3:4:5
• (c) By cross-staff or optical square.
• Perpendicular offset usually preferred than
oblique.

25. Perpendicular Offsets

26. Offsets
Oblique Offset
• Oblique distance is always greater than
perpendicular distance. All the offsets which
are not taken at the right angle to chain line are
known as oblique offsets.

27. Oblique Offset

28. Offsets

29. Offsets
• For setting perpendicular offsets any one of the
following methods are used:
• (i) Swinging
• (ii) Using cross staffs
• (iii) Using optical or prism square.

30. Perpendicular Offset by
Swinging
• Chain is stretched along the survey line. An
assistant holds the end of tape on the object.
Surveyor swings the tape on chain line and
selects the point on chain where offset distance
is the least.
• and notes chain reading as well as offset
reading in a field book on a neat sketch of the
object

31. Perpendicular Offset by
Swinging

32. Perpendicular Offset by
Swinging

33. Perpendicular Offset by
Swinging

34. Perpendicular Offset by
Swinging

35. Perpendicular Offsets Using Cross
Staffs
• Three different types of cross staffs used for setting
perpendicular offsets. All cross staffs are having two
perpendicular lines of sights. The cross staffs are
mounted on stand. First line of sight is set along the
chain line and without disturbing setting right angle line
of sight is checked to locate the object.
• With open cross staff (Fig(a)) it is possible to set
perpendicular only, while with French cross staff
• (Fig(b)), even 45º angle can be set. Adjustable cross
staff can be used to set any angle also, since there are
graduations and upper drum can be rotated over lower
drum.

36. Perpendicular Offsets Using Cross
Staffs

37. Perpendicular Offsets Using Cross
Staffs

38. Perpendicular Offsets Using Optical
Square and Prism Square

39. Perpendicular Offsets Using Optical
Square and Prism Square

40. Perpendicular Offsets Using Optical
Square and Prism Square

41. Perpendicular Offsets Using Optical
Square and Prism Square

42. Perpendicular Offsets Using Optical
Square and Prism Square

43. Perpendicular Offsets Using Optical
Square and Prism Square

44. 3-4-5 Method
• AB is the chain line it is required to erect a
perpendicular at C of the chain line. Establish a pt
D at 3 m distance. 5m & 6m marks are brought to
gather to form a loop .The tape is stretched tight
by fastening the end D and C. The point D is
established such that DE = 5 m and CE= 4 m and
CD = 3 m and DE2 = CD2 + DE2
• i.e. 5 2 = 3 2 + 4 2 = 25 thus Angle DCE = 90 0
• i.e. CE is perpendicular to chain line at C

45. 3-4-5 Method

46. 3-4-5 method

47. 3-4-5 method

48. Procedure of field work
• Reconnaissance
• Index sketch
• Marking the stations on ground
• Reference sketches
• Taking measurement of survey lines and
noting them.

49. 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

50. • 2. 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.
• 3. 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.