Total Station |Components | Functions | Advantages of Total Station Survey
Total Station is an equipment used in surveying, designed for measuring horizontal and vertical
angles, inclusive of measuring sloping distance of object to the instrument. It is a combination
of electronic theodolite and electromagnetic distance measuring (EDM) instrument. It also consists of
a micro-processor with a memory unit which deals with recordings, readings, and the fundamental
calculation of measurements.
Components of a Total Station
TotalStation is a compact instrument which weighs around 50 N to 55 N. It consists of a distance
measuring instrument (EDM), an angle measuring instrument (Theodolite) and a simple
microprocessor. The components used in Total station surveying are as follows:
1. A tripod is used to hold the total station
2. Prism and prism pole which can measure lengths up to 2 km and up to 6-7 km can be
measured with triple prism
3. Battery
4. Currently there are approximately more than 40 different models available. Total-station are
currently the most used instrument in the surveying field. Cheapest instrument is available in
the range of 2000$ to 2500$. Leica is one of the most famous total-station manufacturers.
Basic Steps involved in Totalstation surveying
Step-1: Setting up the of the instrument along with the tripod
Step-2: Levelling of the instrument approximately with the help of “bull’s eye bubble” and then
verifying the levelling electronically
Step-3: Adjustment of reticle focus and image.
Step-4: Recording all the measurements
Step-5: Data Processing
Functions of Total-Station
Angle Measurement:
To measure horizontal and vertical angles, the electronic theodolite of device is used with an
accuracy of 2-6 seconds. For horizontal measurement of angles, any direction can be taken as
reference. In case of vertical measurement of angles, upward direction is taken as reference.
Distance Measurement in TotalStation:
To measure the distance, Electronic Distance Measuring (EDM) instrument of total station is used
with an accuracy of 5-10 mm per km. The range of EDM varies from 2.8-4.2 km.
Data Processing:
Computation of horizontal distances along with X, Y, Z coordinates is done by the instrument
called Microprocessor. Hence, if atmospheric temperature and pressure is applied, the
microprocessor applies suitable correction to the measurements.
Various software are available in the market which can be used to post-process the outputs from the
device. Usually manufacturers provide their software which lets you export the survey results into
other formats. Thus, output can be imported to CAD application or software like MX Roads.
Advantages of Total Station
The first and foremost advantage of using a Totalstation is that it saves time of work on the field. It
understands and supports all the local languages. Setting up of the instrument on the tripod can be
done easily and quickly by laser plummet. The accuracy of measurements is much higher in
comparison to other conventional surveying instruments.
Computerization of old maps can be achieved by Totalstation. The computed data can be saved and
simultaneously transferred to the computer. No writing or recording errors can be detected since
everything is computerized. With the help of data accumulated from Total-station, map making and
contour plotting can also be done. Correction for temperature and pressure can also be made.
Disadvantages
The working conditions of the totalstation should be checked beforehand by the surveyor before using
it. The cost price of the instrument is higher than the other surveying instruments. Checking for errors
or other things during the operation is slightly difficult for the surveyor. Essentially, skilled surveyors
are required to handle it since it is a sophisticated instrument to operate.
Theodolite Traversing
A theodolite is a tool used to accurately measure horizontal and vertical angles. The purpose of
theodolite traversing is to extend survey lines, determine elevation differences, and plan engineering
works needing greater precision, such as ranging highway and railway curves, aligning tunnels, and so
on.
Theodolite traversing refers to the traversing in which the traverse legs are measured by direct
chaining on the ground and the traverse angle at each traverse station is calculated using a theodolite.
A theodolite traverse is used to calculate the relative positions of numerous points on the earth's
surface. It is particularly useful for controlling site surveys in urban areas when triangulation is not
possible. A theodolite, steel tape, two ranging poles, stakes, tacks, plumb bobs, chain pins, tripods etc.
will be needed to complete a theodolite traverse. The traverse can be an open or closed traverse.
The basic principle of theodolite traversing is the same as for any other way of traversing. Firstly,
reconnaissance must begin with a sketch drawing of the terrain utilising the approximate location of
the traverse station, then the vital information must be picked up, and the station's intervisibility must
be checked.
Theodolite traversing necessitates the use of station marking instruments such as pegs, arrows, and so
on, as well as a theodolite with its stand and steel tape.
Types of Traverse
There are two kinds of Traverses. Namely,
1. Open Traverse
2. Closed Traverse
Open Traverse
When a traverse begins at one location and ends at another, it is considered to be an
open traverse, as shown in the picture. Unclosed traverse is another name for the
open traverse. It is appropriate for surveying highways, coastal lines, and so on.
Fig.1: Open Traverse
Closed Traverse
A traverse is considered to be closed when it forms a closed circuit, as seen in the
image. In this scenario, the traverse's starting and ending positions coincide with
each other. It is appropriate for surveying the boundaries of ponds, sports fields,
woodlands, and so on.
Fig.2: Closed Traverse
Methods of Traversing
The traversing is done in four different ways, which are categorised based on the
survey equipment utilised. The procedures are as follows:-
1. Chain Traversing
2. Compass Traversing
3. Theodolite Traversing
4. Plane Table Traversing
Chain Traversing or Surveying
Only linear measurements are taken when we use chain traversing. As a result, a
chain or tape is sufficient for chain traversing. The chain angles concept is used to
calculate the angle between adjacent traverse lines. Chain traversing is used in
places where triangulation is difficult to do, such as ponds.
The concept of chain angles is nothing but determining the angle between two
adjacent sides by forming a third side using tie stations. This angle between the
sides can also be fixed by establishing a known length chord between them.
Compass Surveying
Compass traversing involves taking both linear and angular measurements of
traverse lines with a chain and a compass. Both fore and back bearings are
measured, and any necessary modifications for local attraction are made. If a closing
error is found while plotting a traverse, the Bowditch rule or Transit Rule is used to
adjust the error.
Theodolite Traversing
When theodolite traversing is done, linear measurements are taken using the chain
or stadia method, and angular measurements are taken by theodolite. The magnetic
bearing of the first traverse line is measured using a theodolite, and the magnetic
bearings of the other sides are estimated based on that magnetic bearing. As
compared to other ways, theodolite traversing method is extremely accurate.
Plane Table Surveying
In the case of plane table traversing, the traverse is measured and plotted on paper
at the same time. The plane table equipment is installed one by one at each traverse
station, clockwise or anti-clockwise. On paper, the sides of each traverse station are
drawn to some suitable scale. If there is a closing error, graphical approaches are
employed for its adjustments.
Classification of Theodolites
The theodolites can be classified into two categories:-
1. Transit Theodolite
2. Non-Transit Theodolite
Transit Theodolite
A theodolite is referred to as a transit theodolite if its telescope can be transited, for
example, if it can revolve through a complete revolution about its horizontal axis in a
vertical plane.
Non-Transit Theodolite
The telescope of a non-transit theodolite cannot be transited, that is, it cannot
revolve through a complete revolution about its horizontal axis in a vertical plane.
Measurement with a Theodolite
The method of repetition is used to estimate traverse angles with greater precision
than the least count of the vernier affixed to the theodolite. The upper plate is free to
rotate when swinging from the forwarding station to the rear station. As a result, an
angle reading mechanically adds up to the number of repetitions. The difference
between the first and last readings yields the integrated traverse angle, which is
then divided by the number of repeats to yield the average traverse angle.
Field work during a Theodolite Traversing
The field work during a Theodolite traversing includes:-
o Reconnaissance
o Selection and marking of stations
o Measurement of traverse legs
o Measurement of traverse angles
o Booking of field notes
o Computation.
Reconnaissance
Reconnaissance is the preliminary inspection of the area to be surveyed in order to
gain an understanding of the terrain and the main features of the ground in
theodolite traversing. During reconnaissance, the surveyor extensively studies the
land before deciding on the finest possible arrangement of triangles. During
reconnaissance, the surveyor gathers the necessary information and data on the
shape and size of the area to be surveyed. During reconnaissance, the surveyor
would typically create an index sketch to depict the main characteristics such as
buildings, roads and boundaries. Station and survey line locations are also marked.
Arrowheads indicate the direction of the chain lines.
Selection and Marking of Stations
In Theodolite traversing, every traverse station is chosen so that consecutive
stations are intervisible with little clearance. To reduce systematic error in angular
measurements, the traverse legs are kept as close to the same length as possible.
The closing error in angular measurement is thus divided equally among all traverse
angles assuming equal weights for all angles. Traverse stations should be marked on
important sites as far as possible, such as distance stones, culverts, road crossings,
and so on. A detailed description of each station should be recorded in the field
book, including the exact distance between the markings on easily identifiable
nearby sites. Traverse station descriptions can be found later if they are correctly
written in the field book by the plane tables.
Measurement of Traverse Legs
In theodolite traversing, the distances between traverse stations are measured
directly by chaining, which is more dependable except on rocky terrain. The
following points should be kept in mind when obtaining a distance-
o The measurement should begin and end at the centre of the station markers.
o Vertical arrows should be embedded in the ground properly.
o Chains are always set flat and stretched out to their full length.
o Measurements are taken from the point where the chain pin enters the
grounds.
o Chalk or paint is used to denote the full chain length on rocky terrain or
cemented surfaces.
Measurement of Traverse Angles
In theodolite traversing, the traverse angles can be measured using one of the
following methods:-
o Repetition method
o Reiteration method
o Practical method
Repetition Method
The repetition method is used in theodolite traversing to improve the precision and
accuracy of horizontal angle measurements. The same angle is measured many
times with the survey device rotated to cancel out systematic errors. The arithmetic
mean of these observations yields the correct angle value. The precision of the
measurement can exceed the instrument's least count.
When high accuracy is desired, the repetition method is used. The conventional
method of measuring horizontal angles is employed for rough or approximate survey
work because it is less time intensive.
Reiteration Method
This method is best suited for measuring horizontal angles with a common station.
Many angles are measured sequentially, and a check is made by adding them all up.
The total of all angles at a point is 360 degrees.
Practical Method
This method is used by measuring a group of independent traverse angle data and
then averaging them.
Booking of Field Notes
It should be noted that the greatest care taken in marking field observations will be
useless unless observations are neatly and systematically recorded in field books.
Thus field books must be filled neatly and clearly with the observations that can be
computed to get the desired results.
Computations
The following computations are performed in the following order for the calculation
of independent rectangular coordinates from field data in theodolite traversing:-
o Checking of means of field observations.
o Setting up traverse angles and traverse leg distances.
o Identifying the traverse leg's bearings.
o Running down the bearings.
o Computation of reduced bearings of each traverse leg.
o Calculation of consecutive coordinates.
o Calculation of the closing error.
o Balance for consecutive coordinates.
o Calculation of independent coordinates.
This was all about the Theodolite Traversing. It is an important method of traversing
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Surveying Questions and Answers – EDM –
Total Station
This set of Surveying Multiple Choice Questions & Answers (MCQs) focuses on
“EDM – Total Station”.
1. In total station, data is stored in ___________
a) Pen drive
b) Data card
c) Micro processor
d) External hardware
View Answer
Answer: c
Explanation: Micro processor provided in the instrument helps in saving the
data and helps in transferring it to the system, by which it can be viewed in
different software.
2. Compensator can make complete adjustments in total station.
a) True
b) False
View Answer
Answer: b
Explanation: The use of compensator can be found in case of finding vertical
angles, where the instrument has to be perfectly levelled. But the
compensator isn’t sufficient to provide perfect levelling. Manual operation is
also involved in obtaining perfect level.
3. Vertical angle is measured in the total station as Zenith angle.
a) False
b) True
View Answer
Answer: b
Explanation: The vertical angle is usually measured as a zenith angle which
indicates 0° vertically up, 90° at horizontal, and 180° vertically down. The
zenith angle is generally easier to work.
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4. Which of the following indicates the formula for converting slope distance
to horizontal distance?
a) S = H (sin z)
b) H = S* S (sin z)
c) H*H = S (sin z)
d) H = S (sin z)
View Answer
Answer: d
Explanation: The slope distance obtained can be used for calculating
horizontal distance from the formula, H = S (sin z) where, H= horizontal
distance, S = slope distance.
5. When total station is sighted to the target, which of the operation acts
first?
a) Rotation of optical axis
b) Rotation of vertical axis
c) Rotation of horizontal axis
d) Rotation of line of collimation
View Answer
Answer: a
Explanation: At the time of sighting the instrument towards the target, first
step involves the rotation of the instrument’s optical axis from the instrument
north in horizontal plane.
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6. Which of the following indicates the correct set of the combination of total
station?
a) Theodolite, compass
b) Theodolite, EDM
c) Electronic theodolite, EDM
d) EDM, GPS
View Answer
Answer: c
Explanation: A total station is a combination of an electronic theodolite and
an Electronic Distance Measurement. This combination makes it possible to
determine the coordinates of a reflector by aligning the instruments cross-
hairs on the reflector and simultaneously measuring the vertical, horizontal
angles and slope distances.
7. Which among the following doesn’t indicate the basic calculation of the
total station?
a) Horizontal distance
b) Slope distance
c) Vertical distance
d) Co-ordinate calculations
View Answer
Answer: b
Explanation: The basic calculations of total stations include horizontal
distance, vertical distance, co-ordinate distance in which, slope distance is
used in horizontal distance calculations. It is obtained directly from the total
station equipment.
8. The formula for difference in elevation can be given as__________
a) D = V + (I-R)
b) D = V + (I+R)
c) D = V – (I-R)
d) D = V * (I-R)
View Answer
Answer: a
Explanation: The difference in elevation can be given as D = V + (I-R) where,
V= vertical difference between two points, I =instrument height, R = height
of centre of reflector.
9. In which direction it is best to place the total station for obtaining the best
output?
a) East
b) West
c) South
d) North
View Answer
Answer: d
Explanation: The best procedure while using a Total Station is to set a
convenient “north” and carry this through the survey by using back sight
process when the instrument is moved.
10. The data obtained from total station can be used in which among the
following software directly?
a) Primavera
b) STAAD PRO
c) Autodesk Revit
d) Surfer
View Answer
Answer: d
Explanation: The data obtained from the total station can be indirectly used
in STAAD Pro, Autodesk Revit, Primavera but it can be directly used in
software’s like Arc GIS, Surfer, Auto CAD etc., as they are linked with it.
11. Calculation the elevation difference if the vertical distance is 14.89m,
instrument height is 9.2m, ground is at 2.8m.
a) 21.29 m
b) 12.29 m
c) 21.92 m
d) 41.29 m
View Answer
Answer: a
Explanation: The elevation difference in total station can be calculated as
dz = Vd + (Ih-Rh). On substitution, we get
dz = 14.89 + (9.2-2.8)
dz = 21.29 m.
12. Find the vertical distance if the value of slope distance can be given as
12.98 and the angle is 1˚23ꞌ.
a) 21.97m
b) 12.97m
c) 12.79m
d) 21.79m
View Answer
Answer: b
Explanation: The vertical distance can be calculated by using the formula,
Vd = Sd*cosZa = 12.98*cos (1˚23ꞌ) Vd = 12.97m.
13. Find the elevation of ground beneath the reflector, if the known elevation
of instrument is 12.76m, slope distance = 3.76m, angle is about 3˚43ꞌ,
instrument height = 2.93m, ground is at 0.987 m.
a) 18.54m
b) 81.54m
c) 18.45m
d) 18.97m
View Answer
Answer: c
Explanation: The elevation of ground beneath the reflector can be given as
Rz = Iz + Sd * cosZa + Ih – Rh. On substitution, we get
Rz = 12.76 + (3.76*cos (3˚43ꞌ)) + 2.93 – 0.987
Rz = 18.45 m.
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