2. Chain surveying
This is the process of surveying an area using liner
measurements only.
3. Basic principles of Chain Surveying
Consider three straight boundaries AB, BC and CA. Measure the
distance and plot as follows.
Draw AB to the scale (Base Line)
The length of AC is set to the same scale on a pair of compasses and
arc of the radius AC is drawn.
Similarly an arc of radius BC is drown to intersect the first.
Intersecting point is, Point C
Where an area of ground is bounded by more than three straight
side and if these lengths only measured, an infinite number of
figures can be drawn with this dimensions.
4. There fore lay down a network of triangles in the field
which can be plotted and checked.
First lay down the base line.
Then triangles and other lines.
5. Offsets
As most boundaries are irregular, the method of
surveying their positions is first to lay down a network
of triangles which can be plotted and checked. From
these chain lines off sets are measured, being
perpendicular measurements from chain line to points
of detail.
6. Perpendicularly may be obtained
by
Judging with the eye, the right angle formed between
the two tapes.
By swing the offset tape to obtain the shortest
measurement.
With the optical squire.
7. Chain surveying procedure
Reconnaissance
You should walk all over the site to obtain a picture in
your mind of the whole area while deciding the most
suitable way of carrying out the work economically in
time and energy.
While deciding the best layout, you should prepare a
sketch plan showing the lines chosen to form the frame
work of the survey.
8. During the reconnaissance the following points must
be born in mind as the criteria to provide the best
arrangements of surveying.
Few survey lines
Long base line
Well conditioned triangles
Check lines
Obstacles
Extension lines
9. Station marking
They must be easy and quickly found
Should not be readily disturbed
Should be fairly permanent
As stations are placed they should be witnessed.
This consist of making an outline sketch of the immediate
area around the station, showing existing permanent features,
position of the station and designation.
Measurements are then taken from at least three surrounding
features to the station and record on the sketch.
10. Field Notes
Notes are made in a field book usually with a double
line ruled up the middle of each page. Booking take
place as shown.
22
12
End
Line No. 1 Starts
55
42
35
22
10
To sta. D
12.0
18.5
11. Plotting the survey
Base line :-
The base line is positioned on the drawing sheet in such
a way that the whole area will be contained within the
limits of the paper.
Triangles :-
Plot the triangles. Draw the check lines. Conform to
agree with the field measurement.
12. Offset :-
The distance along the chain lines can be scaled off and light pencil
lines are drawn perpendicular to them, along which the offset
distance are scaled.
Detailed drawing :-
As the offsets are plotted they are joined up to correspond with the
features noted in the field book
Fair Drawing :-
Only the features of the field is traced. Title, Scale, North and other
relevant notes are added
