Advantages of Electronic Distance Measurment in Surveying

Advantages of Electronic Distance
Measurement in Surveying
Types of EDM instrument
Microwave
Make use of microwaves.
Such instruments were invented as early as
1950 in South Africa by Dr. T.L Wadley and
named theam as Tellurometers.
The instruments need only 12 to 24 V batteries.
They are light and highly portable.
Tellurometers can be used in day as well as in
night.
The range of these instruments is up to 100km.
It consists of two identical units. One unit is
used as master unit and the other as remote
unit.
Infrared wave
In these instrument amplitude modulated
infrared waves are used.
Prism reflectors are used at the end of line to be
measured.
With these instruments accuracy achieved is +/
10mm.
800m1km (singe prism)
The range of these instrument is up to 3km.
Light wave
These type of instrument was first developed in
Sweeden and was named as Geodimeter
During night its range is up to 2.5 km while in
day its range is up to 3 km.
Accuracy of these instrument varies from 0.5
mm to 5mm / km distance.
These instruments are also very useful for civil
engineering projects.
Disadvantage of EDM
the instrument is complicated to use
accuracy affected by atmospheric conditions
can be expensive
Advantage of EDM
line of sight instrument
capable of measuring long distance
reflectorless are single per on operation
the speed and accuracy in measurement
several obstacle to chaining are automatically
overcome when these instrument are used
Uses of EDM
measuring distnace
operate instrument to measure the distance
an EDM is set over one point and a prism over
the other
setting up distance between equipment
at a trial distance, measure a slope
distance.(convey this information to chainman
by hand signal or radio)
then move the prism to a new trial position.
(when the prism is within 23m of its requiredd
position, compute a horizontal distance)
measure the difference between trial and
required position with a tape and move the
prism to the new position
the distance can be checked and the ground
markd as required.
measuring difference in height
proceed to measure the slope distance
with basic EDM the difference in height is
calculated from (slope distance x sine of vertical
angle)
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