This document discusses station marks and signals used in triangulation surveys. It describes: 1. Station marks are permanent marks buried below the surface to mark survey points. They are usually made of bronze or copper embedded in concrete or rock. 2. Signals are devices erected directly above station marks to define survey points. They can be opaque (pole, target, brush) or luminous (sun, night lamps) depending on lighting conditions. 3. Various types of opaque signals are described including pole signals, target signals, brush signals, stone cairns, and towers. Luminous signals include heliotropes and night lamps using oil or acetylene. Signals must be visible, centered over

1. Prepared by
Mrs. Sapana Amol Chougule
Assistant Professor,
Civil Engineering Department,
ATS’s SBGI Miraj
Signals in
Triangulation

2. Station marks
1. Object of station marks is to provide a
surface mark with a permanent mark buried
below the surface on which a target or
instruments is to centered over it
2.Should be bronze or copper marks
cemented into rock or concrete surface
3.Normally station marks are buried below the
ground surface to protect from the
disturbances

3. • Control points canbe constructed in
concrete with center mark in bronze
or copper and buried at the required
place
• Fewdead measurements are taken
using permanent features around
the stationand keep asa diagram
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4. Station Marks
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5. Signals
• Theyare the deviceserected to definethe exact
position of astation
• Asignalis placed at eachstation sothat the line of
sights are established between triangulation
stations
• Signalsmaybe opaque (3-4 leggedtype) or
luminous

6. Requirements of Signal
1. It should clearly visible, kept
at least 75 cm above the
station mark.
2. Capable of being accurately
centered over the station
mark.
3. It should be suitable for
accurate bisection from other
stations.

7. Classification of signals
1.Non-luminous, opaque or
daylight signals
2.Luminous signals-
a. Sun signals
b. Night Signals
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8. Non-luminous, opaque or
daylight signals
1. Pole Signal
2. Target Signal
3. Pole and Brush Signals
4. Stone Cairn
5. Beacon
6. Elevated Tower

9. Pole Signal
• It consistsof around pole
paintedblack and white
in alternate
• It is supported vertically
over the station mark on
a tripod.
• Polesignalsare suitable up
to adistance of 6km.
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10. • It consistsof apole carrying two
square or rectangular targets
placed at rightanglesto each
other
• Thetargets are
generally madeof cloth
stretched on wooden
frames
• Targetsignalsare suitable up to
adistanceof 6km
Target Signal
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11. Pole and Brush Signals
• It consists of a straight pole about
2·5 meter long with a bunch of
long grass tied symmetrically round
the top making across
• The signal is erected vertically
over the station mark by
heaping a pile of stones up to 1·7
meters
round the pole
• A rough coat of white wash is
applied to make it more
conspicuous to be seen against a
blackback ground
Signals in Triangulation 11

12. • It consistsof stones
built up to aheight
of 3 meters in a
conicalshape.
• Thiswhite
washed opaque
signal isvery
useful if the
back-ground is
dark.
Stone Cairn
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13. • It consists of red and white
cloth tied round the three
straightpoles.
• This canbe easily centered
over the station marks
• Beaconsare useful when
simultaneous observations
are made at both the
stations.
Beacon
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14. • If the country is quite
plane, elevated
towers are erected
over the station
mark.
• These signals are
used up to a distance
of 30 to 40 km
Elevated Tower
Signals in Triangulation 14

15. • Those signals which reflect the rays of the sun
towards the station of observation, are known
asheliotropes.
• Suchsignalscanonly be usedin clear weather.
• Heliotropes do not give better resultsas
compared to the opaquesignals.
Sun signals
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16. Heliotrope
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17. Signals in Triangulation 17

18. Night Signals
• While making observations at night,
night signalsare used.
• Various types of night signalsare:
– Various forms of oil lamps with a reflector.
These are usedfor sights lessthan 80km.
– Acetylene lamps designed by captain G.T
.
McCaw. These are used for sights more than 80
km.
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19. Signals in Triangulation 19