PROCEDURE OF FIELD
WORK
WORK
Field work of chain
survey should be carried out according to the following steps:
survey should be carried out according to the following steps:
1.Reconnaissance
Before starting survey
work, the surveyor should walk over the whole area to be surveyed in order to
examine the ground and determine the possible arrangement of framework of
survey. During this investigation, he should examine the intervisibility of the
main survey stations. He should ensure that the whole area is enclosed by main
survey lines, and also that it is possible to form well-conditioned triangles.
He should observe various objects and boundary lines carefully and select the
survey lines in such a manner that the objects can be located by short offsets.
The base line should preferably be taken through the centre of the area and on
fairly level ground.
work, the surveyor should walk over the whole area to be surveyed in order to
examine the ground and determine the possible arrangement of framework of
survey. During this investigation, he should examine the intervisibility of the
main survey stations. He should ensure that the whole area is enclosed by main
survey lines, and also that it is possible to form well-conditioned triangles.
He should observe various objects and boundary lines carefully and select the
survey lines in such a manner that the objects can be located by short offsets.
The base line should preferably be taken through the centre of the area and on
fairly level ground.
2.Index sketch
After preliminary
inspection of the area, the surveyor should prepare a neat hand sketch showing
the arrangement of the framework and approximate position of the objects. He
should note the names of the stations on the sketch maintaining some
order (clockwise or anticlockwise). The field work should be executed according
to this index sketch. The names and sequence of chain lines should be followed
as directed in the index sketch. The ‘base line’ should be clearly indicated in
the index sketch.
inspection of the area, the surveyor should prepare a neat hand sketch showing
the arrangement of the framework and approximate position of the objects. He
should note the names of the stations on the sketch maintaining some
order (clockwise or anticlockwise). The field work should be executed according
to this index sketch. The names and sequence of chain lines should be followed
as directed in the index sketch. The ‘base line’ should be clearly indicated in
the index sketch.
3. Marking the stations
on the ground
on the ground
After reconnaissance,
the stations are marked on the ground by wooden pegs. These pegs are generally
2.5 cm square and 15 cm long, and have pointed ends. They are driven into the
ground firmly, and there should be a height of 2.5 cm above the ground. The
station point is marked with a cross so that it can be traced if the wooden peg
is removed by somebody
the stations are marked on the ground by wooden pegs. These pegs are generally
2.5 cm square and 15 cm long, and have pointed ends. They are driven into the
ground firmly, and there should be a height of 2.5 cm above the ground. The
station point is marked with a cross so that it can be traced if the wooden peg
is removed by somebody
4. Reference sketches
To take precautions
against station pegs being removed or missed, a reference sketch should be made
for all main stations. It is nothing but a hand sketch of the station showing
at least two measurements from some permanent objects. A third measurement may
also be taken
against station pegs being removed or missed, a reference sketch should be made
for all main stations. It is nothing but a hand sketch of the station showing
at least two measurements from some permanent objects. A third measurement may
also be taken
5.Taking measurements of
survey lines and noting them in the field book
survey lines and noting them in the field book
Ranging and chaining is
started from the base line, which should be measured carefully. The magnetic
bearings of the base line are measured by prismatic compass. These measurements
are noted in the field book showing the offsets to the left or right according
to their position. Then the other survey lines are ranged and chained
maintaining the sequence of the traverse. The offsets and other field records
are noted simultaneously. The check lines and tie lines are also measured and
noted at the proper place. The station marks are preserved carefully until
field work is completed.
started from the base line, which should be measured carefully. The magnetic
bearings of the base line are measured by prismatic compass. These measurements
are noted in the field book showing the offsets to the left or right according
to their position. Then the other survey lines are ranged and chained
maintaining the sequence of the traverse. The offsets and other field records
are noted simultaneously. The check lines and tie lines are also measured and
noted at the proper place. The station marks are preserved carefully until
field work is completed.
3.9 CONVENTIONAL SYMBOLS
In a map the objects are
shown by symbols and not by names. So the surveyor should know the following
standard conventional symbols for some common objects.
shown by symbols and not by names. So the surveyor should know the following
standard conventional symbols for some common objects.
EQUIPMENTS FOR PLOTTING
1. Drawing board (normal
size – 1000 mm x 700 mm)
size – 1000 mm x 700 mm)
2. Tee-square
3. Set-square (450 and
600)
600)
4. Protractor
5. Cardboard scale – set
of eight
of eight
6. Instrument box
7. French curve
8. Offset scale
9. Drawing paper of good
quality (normal size – 880 mm x 625 mm)
quality (normal size – 880 mm x 625 mm)
10. Pencils of good
quality – 2 H, 3 H or 4 H
quality – 2 H, 3 H or 4 H
11. Eraser (rubber) of
good quality
good quality
12. Board clips or pins
13. Ink (Chinese ink or
Indian ink) of required shade
Indian ink) of required shade
14. Colour of required
shade
shade
15. Inking pen (or
Hi-tech pen) and brushes
Hi-tech pen) and brushes
16. Handkerchief, knife
, paperweight, etc.
, paperweight, etc.
17. Mini drafter
3.10 PROCEDURE OF
PLOTTING
PLOTTING
1. A suitable scale is
chosen so that the area can be accommodated in the space available on the map.
chosen so that the area can be accommodated in the space available on the map.
2. A margin of about 2
cm from the edge of the sheet is drawn around the sheet.
cm from the edge of the sheet is drawn around the sheet.
3. The title block is
prepared on the right hand bottom corner.
prepared on the right hand bottom corner.
4. The north line is
marked on the right-hand top corner, and should preferably be vertical. When it
is not convenient to have a vertical north line, it may be inclined to
accommodate the whole area within the map.
5. A suitable position
for the base line is selected on the sheet so that the whole area along with
all the objects it contains can be drawn within the space available in the map.
marked on the right-hand top corner, and should preferably be vertical. When it
is not convenient to have a vertical north line, it may be inclined to
accommodate the whole area within the map.
5. A suitable position
for the base line is selected on the sheet so that the whole area along with
all the objects it contains can be drawn within the space available in the map.
6. The framework is
completed with all survey lines, check lines and tie lines. If there is some
plotting error which exceeds the permissible limit, the incorrect lines should
be resurveyed.
completed with all survey lines, check lines and tie lines. If there is some
plotting error which exceeds the permissible limit, the incorrect lines should
be resurveyed.
7. Until the framework
is completed in proper form, the offsets should not be plotted.
is completed in proper form, the offsets should not be plotted.
8. The plotting of
offsets should be continued according to the sequence maintained in the field
book.
offsets should be continued according to the sequence maintained in the field
book.
9. The main stations,
substations, chain line, objects, etc. should be shown as per standard symbols
substations, chain line, objects, etc. should be shown as per standard symbols
10. The conventional
symbols used in the map should be shown on the right-hand side.
symbols used in the map should be shown on the right-hand side.
11. The scale of the map
is drawn below the heading or in some suitable space. The heading should be
written on the top of the map.
is drawn below the heading or in some suitable space. The heading should be
written on the top of the map.
12. Unnecessary lines,
objects etc. should be erased.
objects etc. should be erased.
13. The map should not
contain any dimensions.
contain any dimensions.
Inking of the map
The inking should be
begun from the left-hand-side towards the right-hand-side, and from the top
towards the bottom.
begun from the left-hand-side towards the right-hand-side, and from the top
towards the bottom.
Colouring of the map
In general, colour washing
of engineering survey maps is not recommended. However, if it is necessary, the
colour shades should be very light, and according to the colour conventions.
The colouring should also be started from the left-hand-side towards the right
and from the top towards the bottom.
of engineering survey maps is not recommended. However, if it is necessary, the
colour shades should be very light, and according to the colour conventions.
The colouring should also be started from the left-hand-side towards the right
and from the top towards the bottom.
3.11 CROSS-STAFF AND
OPTICAL SQUARE
OPTICAL SQUARE
A. Cross-staff
The cross-staff is a
simple instrument for setting out right angles. There are three types of
cross-staves.
simple instrument for setting out right angles. There are three types of
cross-staves.
- Open
- French
- Adjustable
The open cross-staff is
commonly used.
commonly used.
Open cross-staff
The open cross-staff
consists of four metal arms with vertical slits. The two pairs of arms (AB and
BC) are at right angles to each other. The vertical slits are meant for
sighting the object and the ranging rods. The crossstaff is mounted on a wooden
pole of length 1.5m and diameter 2.5 cm. The pole is fitted with an iron shoe.
consists of four metal arms with vertical slits. The two pairs of arms (AB and
BC) are at right angles to each other. The vertical slits are meant for
sighting the object and the ranging rods. The crossstaff is mounted on a wooden
pole of length 1.5m and diameter 2.5 cm. The pole is fitted with an iron shoe.
For setting out a
perpendicular on a chain line, the cross-staff is held vertically at the
approximate position. Suppose slits A and B are directed to the ranging rods
(R, R1) fixed at the end stations. Slits C and D are directed to the
object (O). Looking through slits A and B, the ranging rods are bisected. At
the same time, looking through slits C and D, the object O is also bisected. To
bisect the object and the ranging rods simultaneously, the cross staff may be
moved forward or backward along the chain line
perpendicular on a chain line, the cross-staff is held vertically at the
approximate position. Suppose slits A and B are directed to the ranging rods
(R, R1) fixed at the end stations. Slits C and D are directed to the
object (O). Looking through slits A and B, the ranging rods are bisected. At
the same time, looking through slits C and D, the object O is also bisected. To
bisect the object and the ranging rods simultaneously, the cross staff may be
moved forward or backward along the chain line
B. Optical Square
An optical square is
also used for setting out right angles. It consist of a small circular metal
box of diameter 5 cm and depth 1.25 cm. It has a metal cover which slides round
the box to cover the slits. The following are the internal arrangements of the
optical square.
also used for setting out right angles. It consist of a small circular metal
box of diameter 5 cm and depth 1.25 cm. It has a metal cover which slides round
the box to cover the slits. The following are the internal arrangements of the
optical square.
1. A horizon glass H is
fixed at the bottom of the metal box. The lower half of the glass is unsilvered
and the upper half is silvered.
fixed at the bottom of the metal box. The lower half of the glass is unsilvered
and the upper half is silvered.
2. A index glass I is
also fixed at the bottom of the box which is completely silvered.
also fixed at the bottom of the box which is completely silvered.
3. The angle between the
index glass and horizon glass is maintained at 450.
index glass and horizon glass is maintained at 450.
4. The opening ‘e’ is a
pinhole for eye E, ‘b’ is a small rectangular hole for ranging rod B, ‘P’ is a
large rectangular hole for object P.
pinhole for eye E, ‘b’ is a small rectangular hole for ranging rod B, ‘P’ is a
large rectangular hole for object P.
5. The line EB is known
as horizon sight and IP as index sight.
as horizon sight and IP as index sight.
6. The horizon glass is
placed at an angle of 1200 with the horizon sight. The index
glass is placed at an angle of 1050 with the index sight.
placed at an angle of 1200 with the horizon sight. The index
glass is placed at an angle of 1050 with the index sight.
7. The ray of
light from P is first reflected from I, then it is further reflected from
H, after which it ultimately reaches the eye E
light from P is first reflected from I, then it is further reflected from
H, after which it ultimately reaches the eye E
Principle
According to the
principle of reflecting surfaces, the angle between the first incident ray and
the last reflected ray is twice the angle between the mirrors. In this case,
the angle between the mirrors is fixed at 450. So, the angle between
the horizon sight and index sight will be 900.
principle of reflecting surfaces, the angle between the first incident ray and
the last reflected ray is twice the angle between the mirrors. In this case,
the angle between the mirrors is fixed at 450. So, the angle between
the horizon sight and index sight will be 900.
Setting up the
perpendicular by optical square
perpendicular by optical square
1.
The observer should
stand on the chain line and approximately at the position where the
perpendicular is to be set up.
The observer should
stand on the chain line and approximately at the position where the
perpendicular is to be set up.
2.
The optical square is
held by the arm at the eye level. The ranging rod at the forward station B is
observed through the unsilvered portion on the lower part of the horizon glass.
The optical square is
held by the arm at the eye level. The ranging rod at the forward station B is
observed through the unsilvered portion on the lower part of the horizon glass.
3.
Then the observer looks
through the upper silvered portion of the horizon glass to see the image of the
object P.
Then the observer looks
through the upper silvered portion of the horizon glass to see the image of the
object P.
4.
Suppose the observer
finds that the ranging rod B and the image of object P do not coincide. The he
should move forward or backward along the chain line until the ranging rod B
and the image of P exactly coincide
Suppose the observer
finds that the ranging rod B and the image of object P do not coincide. The he
should move forward or backward along the chain line until the ranging rod B
and the image of P exactly coincide
5.
At this position the
observer marks a point on the ground to locate the foot of the perpendicular.
At this position the
observer marks a point on the ground to locate the foot of the perpendicular.
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