Background
Theodolite
Is a surveying instrument used for angular
measurement
Angular measurements refers to,
Horizontal angle
Vertical angle
Background contn…
Type of Theodolites
The optical mechanical type
The electronic digital type,
Optical mechanical
Theodolite
Electonic Theodolite (Total
station)
Background Contn….
Distances were measured by
tape/EDM/Tacheometry
Levelling were/still done by levels, e.g. spirit
levelling etc.
Computations were done/is done manually
Total station have replaced these instrument and
their computations
Ground taping
Tape is laid on the ground
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obstruction t an
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measured distance required
distance
7
Level and Levelling
Staff
Scientific Calculator
Parts of Total station
Parts of total station
1) Telescope
Reticles with cross-hair etched on grass and
Equipped with rifle sight or collimator
Telescope has two focusing control
Objective lens: to focus on object being viewed
Eyepiece lens: focus on reticles
If there is no coincident on focusing of the lenses,
Parallax will exits
Parts of total station
2) The angle measurement system
For horizontal and vertical circle reading
3) Communication port
Enable external data collector to be connected to the
instrument. E.g data logger
Some instrument has internal data collector
4) Micro-processor
Provide several significant functions
Parts of total station
5) Key board and Display
Provide means of communicating with the micro-processor
Most of total station has keyboard and display on both sides
6) Optical plummet
Permit accurate centring over a point
In newer instruments, laser plummet have replaced the optical
plummet
7) Tribrach
consists of 3 screws, clamping device and thread to
attach it to the head of tripod
Parts of total station
8) Bases of total station
Designed to permit interchange of the instrument with
sighting targets and prism in tribrach without disturbing
the previously established centring over a surveyed
point
9) Rotation of the telescope about vertical axis
controlled by Lock and tangent screws
Handling and Setting Up a
Total Station Instrument
Careful lifted from its carrying case
Securely fixed to the tripod by means of the tribrach
prior observations, careful setup over a specific point
The set up process of the instrument, follows the same
procedure as in optical theodolite, e.g. levelling
Handling and Setting Up a
Total Station Instrument
When moving between setups in the field, proper care
should be taken
Before is removed from the tripod, the foot screws should be
returned to the mid points of the posts
The instrument should NEVER be transported on the tripod,
since this causes stress to tripod head, tribrach and instrument
base.
If the instrument is wet, it should be wiped down and left
in open case until it is dry
Field to Finish Operation
Total Station
Is an integrated Theodolite/EDM combinations
It accomplish not only all angle measurements but
also accurate and quick distance measurements.
They can make computations with angle and
distance measurements, hence capacity to give out
coordinates
Display the results in real time/Display .
Distance measurement
Total
station
19
Total station can be used for
Topographic surveys
Hydrographic surveys
Cadastral surveys
Construction surveys
Characteristics of Total
Station Instruments
They combine three basic components :
An electronic distance measuring (EDM)
An electronic angle measuring component
A computer or micro-processor
Other Components
Data Collector (built in or separate unit)
Data Storage (internal or memory card)
Measurement performed by
Total Station
The devices can automatically measure
Horizontal and vertical angles
Slope distance
Capabilities after measurements
Manipulation
Computation performed
Horizontal distance component
Vertical distance component
Elevations
Coordinates
AND
Display the results on a Liquid Crystal Display (LCD)
Functions Performed by
Total Station Instruments
With their micro-processors, can perform a
variety of functions and computations
depending on how they are programmed, i.e.
basic survey operations e.g. topographic
survey. etc
Functions Performed by
Total Station Instruments
1) Averaging of multiple angle and distance measurements
2) Correcting electronically measured distances for:
o Prism constants,
o Atmospheric pressure
o Temperature
3) Correction of Earth curvature and refraction to elevations
determined by trigonometric leveling.
Curvature of the Earth
Due to the curvature of the Earth, the line of sight at
the instrument will deviate from a horizontal line as
one moves away from the level
Curvature of the Earth and
Refraction
Curvature of the Earth”
Line of sight is not a level line but a horizontal
line tangential to a level line
When sights are long, the deviation of tangent
from a circle becomes appreciable
Hence, correction must be applied when sights
are long
Functions Performed by
Total Station Instruments
4) Reducing slope distances to their horizontal and vertical
components.
5) Calculating point elevations
6) Computing coordinates of surveyed points
Servo-Driven and Remotely
operated Total Station
“Robotic” total station instrument
Servo driven mechanism enable the
telescope to aim automatically at a point
to be set
Equipped with servo drive mechanism,
consists of;
• Automatic search function
• Aim function
• Communication function
Remote Positioning Unit
(RPU)
The total station can be controlled from
a distance
It has a built-in telemetry link for
communication with the total station
RPU is attached to the prism pole
RPU also operate as a data collector
Operating the System
The robotic instrument first be set up
and oriented
How?
Entering the coordinates of the point where
the total station is located
Taking a backsight along a line of known
azimuth
Operator carries the RPU to any
convenient location and site to the
instrument
Operating the System
(contn...)
The vertical angle of sight is
telemetered to the robotic instrument
Servo motor then activates and swing
around until it finds the prism and lock
on RPU
The computer retrieves the directions
to the points stored/compute and
activates the servomotor to turn the
telescope to that direction
Operating the System
(contn...)follow its further
Automatically
movements.
If lock is lost, the search routine is
repeated
Instrument is completely controlled
through the keyboard of the remote
unit
Advantages
Enable one person to conduct a
complete survey
Speeds the work
Eliminates mistakes in identifying
points
uses
Construction survey, e.g. Setting out
Topographic surveys
Sources of errors in total
station work
1) Instrumental errors
Plate bubble out of adjustment
Eccentricity of centres
Circle graduation error
2) Natural errors
a. Wind
cause vibration of tripod and
instrument, causing the bubble goes off
Remedy : shieliding the instrument
Natural errors (contn...)
b. Temperature
cause unequal expansion of various
parts of total station, cause the bubble
goes off
Remedy :
shading by umbrella from source of
extreme heat
Natural errors (contn...)
c) Refraction
bends the line of sight and cause an
apparent shimmering of the observed
object
Remedy:
o Keep line of sight above the ground
o Avoid sights close to the building
Natural errors (contn...)
d. Tripod settlement
the weight of instrument may cause the
tripod to settle. E.g. Soft ground
Remedy:
o ?
Source of errors contn
3) Personal error
a) Instrument not set up exactly over a point
The amount of error depends on the position
of the instrument in relation to point
b) Bubble not centred perfectly
c) Improper use of clamps and foot screws
d) Poor focusing
e) Careless plumbing and placement of rod
f) Leaning on the tripod, or placing hard on the
instrument when pointing or taking readings
Relationships of angle
and distances
Determination of the relative position
of a points is obtained by
measurement of both angles and
distances
The best-quality surveys result when
there is a compatibility between the
accuracies of these two different
kind of measurements
Relationships of angle
and distances
Formula for relating distances to angles is given by the
geometric relationship below
S=R.Ө
WHERE,
S = is the arc length subtended at a distance R by an arc
Ө in radian
Angle and distance
relationship
S=R.Ө
1’ of arc = 3 cm. at
100 m.
1” of arc = 0.5 m. at
100 km.
Relationships of angle
and distances
The relationship is helpful for:
1)Selecting instruments and survey
procedure necessary for achieving
consistency
2)Evaluate the effect of the error due
to various sources
Measuring horizontal
angles
Horizontal angles are measured in
horizontal plane
After set up and levelling the
instrument, its horizontal circle is in
a horizontal plane
Measuring horizontal
angles
To eliminate instrumental errors and
increase precision, angle
measurements should be repeated
an equal number of times in each of
the direct and reversed modes, and
the average taken.
Methods of horizontal
angle measurements
Three methods exists
1)Repetition method
2)Direction method
3)Closing the horizon method
1) Repetition method
Repetition method
Instrument set up and centred over a
station I and levelled
Back sight taken at station J
Put initial value entered in a display
Turn the telescope clockwise towards
a point K to make a foresight
Repetition method
Take face left and face right at
different rounds, and get the mean.
Built in computer will automatically
perform the averaging and display
the final result
The procedure described for
observing is Repetition method
Repetition method
2) Direction method
Direction method
Consists of measuring directions to
successful stations sighted around the
horizon
Then by taking the difference in
directions between any two stations, the
angle between them is determined
The procedure is efficiency when
multiple angles are been measured at a
station e.g. triangulation
Direction method
3) Closing the horizon
Closing the horizon
Consists in using the direction method
but including all angles around a point
Angle Z is also measured thereby
providing for additional check
A final foresight pointing is made on
the initial back sight station and this
provides a check because it should
give the initial back sight reading
Closing the horizon
