1. Electronic Distance Measurement (EDM)
CE Dr.Mohammad Al-Sugayer
Electronic Distance Measurement (EDM)
Ms Siti Kamariah Md Sa’at
PPK Bioprocess
Universiti Malaysia Perlis

2. ERT 247-GEOMATICS ENGINEERING
Principle of operation:
Velocity = distance / time
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3. History Theodolite & Tape Stadia EDM & Theodolite
CE Dr.Mohammad Al-Sugayer
History
Theodolite & Tape
Stadia
EDM & Theodolite
EDM, Theodolite & Data Collector
Prior to the total station, Theodolite with EDMs and data collectors were used to record large numbers of points, and for measuring long distances.
The systems were heavy, prone to failure, and many times the parts incompatible.
Prior to these systems, optical (stadia) and manual (tape) systems were used to measure distances.
The first two will be covered later in the course
The Alidade is useful for rough direct work as it makes the map in the field.
Self-reducing /Tacheometer – a modified Transit that uses direct reading
stadia, not much used now that the EDMs are in use.
The last two are the main development of the Total Station.
ERT 247-GEOMATICS ENGINEERING

4. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
History
First introduced in the late 1950’s
At first they were complicated, large, heavy, and suited primarily for long distances
Current EDM’s use either infrared (light waves) or microwaves (radio waves)
Microwaves require transmitters/receivers at both ends
Infrared use a transmitter at one end and a reflecting prism at the other and are generally used more frequently.
ERT 247-GEOMATICS ENGINEERING

5. ERT 247-GEOMATICS ENGINEERING
EDM Properties
They come in long (10-20 km), medium (3-10 km), and short range (.5-3 km). Range limits up to 50 km
They are typically mounted on top of a theodolite, but can be mounted directly to a tribrach.
Total station =
Theodolite with built in EDM +
Microprocessor
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6. ERT 247-GEOMATICS ENGINEERING
EDM Classifications
Described by form of electromagnetic energy.
First instruments were primarily microwave (1947)
Present instruments are some form of light, i.e. laser or near-infrared lights.
Described by range of operation.
Generally microwave are km range. (med)
Developed in the early 70’s, and were used for control surveys.
Light EDM’s generally km range. (short)
Used in engineering and construction
ERT 247-GEOMATICS ENGINEERING

7. ERT 247-GEOMATICS ENGINEERING
EDM is very useful in measuring distances that are difficult to access or long distances.
It measures the time required for a wave to sent to a target and reflect back.
ERT 247-GEOMATICS ENGINEERING

8. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Principles of EDM
Operation:
A wave is transmitted and the returning wave is measured to find the distance traveled.
ERT 247-GEOMATICS ENGINEERING

9. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Principles of EDM
Transmitted Energy
Returned Energy
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10. General Principle of EDM
CE Dr.Mohammad Al-Sugayer
General Principle of EDM
Electromagnetic energy
Travels based on following relation:
Intensity modulate EM energy to specific frequency
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11. Velocity of light can be affected by:
Principles of EDM
Distances determined by calculating the number of wavelengths traveled.
Errors are generally small and insignificant for short distances.
For longer distances they can be more important.
Errors can be accounted for manually, or by the EDM if it has the capability.
Velocity of light can be affected by:
Temperature
Atmospheric pressure
Water vapor content
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12. The Total Station Measures and Records: Horizontal Angles
CE Dr.Mohammad Al-Sugayer
The Total Station
Measures and Records:
Horizontal Angles
Vertical Angles
and
Slope Distances
Calculates:
Horizontal Distance
Vertical Distance
Azimuths of Lines
X,Y,Z Coordinates
Layout
Etc.

13. ERT 247-GEOMATICS ENGINEERING
EDM Characteristics
meters range
Accurate to ±5mm + 5 ppm
Operating temperature between -20 to +50 degrees centigrade
1.5 seconds typical for computing a distanc, 1 second when tracking.
Slope reduction either manual or automatic.
Some average repeated measurements.
Signal attenuation.
battery operated and can perform between 350 and 1400 measurements.
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14. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Prisms
Made from cube corners
Have the property of reflecting rays back precisely in the same direction.
They can be tribrach-mounted and centered with an optical plummet, or they can be attached
to a range pole and held vertical on a point with the aid of a bulls-eye level.
ERT 247-GEOMATICS ENGINEERING

15. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Prisms
Prisms are used with electro-optical EDM instruments to reflect the transmitted signal
A single reflector is a cube corner prism that has the characteristic to reflecting light rays precisely back to the emitting EDM instrument
The quality of the prism is determined by the flatness of the surface and the perpendicularity of the 90˚ surface
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16. ERT 247-GEOMATICS ENGINEERING
Accuracy
Distance is computed by (no. of wavelengths generated + partial wavelength)/2.
Standard or Random errors are described in the form of +(Constant + parts per million).
Constant is the accuracy of converting partial wavelength to a distance.
ppm is a function of the accuracy of the length of each wavelength, and the number of wavelengths.
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17. ERT 247-GEOMATICS ENGINEERING
EDM Accuracy
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18. Error & Accuracy o-------------------------------o-------------o
Blunders:
Incorrect ‘met’ settings
Incorrect scale settings
Prism constants ignored
Incorrect recording settings
(e.g. horizontal vs. slope)
Error & Accuracy
Typical accuracy ± 5 mm + 5 ppm
Both the prism and EDM should be corrected for off-center characteristics.
The prism/instrument constant (about 30 to 40 mm) can be measured by measure AC, AB, and
BC and then constant = AC-AB-BC
o o o
A B C
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19. ERT 247-GEOMATICS ENGINEERING
Sources of Error in EDM:
Personal:
Careless centering of instrument and/or reflector
Faulty temperature and pressure measurements
Incorrect input of T and p
Instrumental
Instrument not calibrated
Electrical center
Prism Constant (see next
slide)
Natural
Varying ‘met’ along line
Turbulence in air
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20. ERT 247-GEOMATICS ENGINEERING
Determination of System Measuring Constant A B C
Measure AB, BC and AC
AC + K = (AB + K) + (BC + K)
K = AC- (AB + BC)
If electrical center is calibrated, K rep-
resents the prism constant.
Good Practice:
Never mix prism types and brands on same project!!!
Calibrate regularly !!!
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21. Systematic Errors/Instrumentation Error
Microwave
Atmospheric conditions
Temperature
Pressure
Humidity - must have wet bulb and dry bulb temperature.
Multi-path
Reflected signals can give longer distances
Light
Prism offset
Point of measurement is generally behind the plumb line.
Today usually standardized as 30mm.
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22. EDM instrument operation
1.Set up
EDM instruments are inserted in to the tribrach
Set over the point by means of the optical plummet
Prisms are set over the remote station point
The EDM turned on
The height of the prism and the EDM should me measured
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23. EDM instrument operation
2.Aim
The EDM is aimed at the prism by using either the built-in sighting devices on the EDM
Telescope (yoke-mount EDMs) will have the optical line of sight a bit lower than the electronic signal
When the cross hair is sight on target the electronic signal will be maximized at the center of the prism
Set the electronic signal precisely on the prism center
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24. EDM instrument operation
3. Measure
The slope measurement is accomplished by simply pressing the measure button
The displays are either liquid crystal (LCD) or light emitting diode (LED)
The measurements is shown in two decimals of a foot or three decimals of a meter
EDM with built in calculators can now be used to compute horizontal and vertical distances, coordinate, atmosphiric,curveture and prism constant corrections
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25. EDM instrument operation
4. Record
The measured data can be recorded in the field note format
Can be entered manually into electronic data collector
The distance data must be accompanied by all relevant atmospheric and instrumental correction factors
ERT 247-GEOMATICS ENGINEERING

26. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Uses
Topo / Pickup – pre-design work
As built – post design
Construction Layout
Monitoring – note the fixed post.
Control – the establishment of a net work from which to base future surveys.
Topographic
&
As Builts
Monitoring
&
Control
Construction Layout
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27. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Uses
Total stations are ideal for collecting large numbers of points.
They are commonly used for all aspects of modern surveying. Only when harsh conditions, exist or distances are short will a transit and tape be used.
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28. ERT 247-GEOMATICS ENGINEERING
Problems
Total stations are dependant on batteries and electronics. The LCD screen does not work well when it is cold .
Battery life is also short, batteries and electronics both do not work well when wet.
Total stations are typically heavier that a transit and tape
Loss of data is an important consideration
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29. “The Flat Earth Society” Plane geometry vs. Spherical geometry
CE Dr.Mohammad Al-Sugayer
Plane Geometry
“The Flat Earth Society”
Plane geometry vs. Spherical geometry
Angles
error ≈ 1” within 200 km2 area
Distances
Error ≈ mm per km
Similar triangles
Basic trig functions
Basic laws – Sin & Cos
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30. ERT 247-GEOMATICS ENGINEERING
Plane Geometry
CE Dr.Mohammad Al-Sugayer A O H β A C B γ α β
Similar triangles
Basic trig functions
Basic laws – Sin & Cos
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31. Geometry of EDM Measurement
Relatively simple if hi = HR
More complicated when the EDM is on top of the theodolite and the prism is higher than the target
(delta HR not equal to delta hi).
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32. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Plane Coordinates R
Pt. A BS α
Pt. 1 R
Pt. A BS α
Pt. 1 N Y X
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33. Horizontal Coordinates
CE Dr.Mohammad Al-Sugayer
Horizontal Coordinates BS
Pt. A β
α+β ΔY HD N α ΔX
Pt. 1
β = BS Bearing
α = HA
α+β = Bearing of 1toA
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34. ERT 247-GEOMATICS ENGINEERING
CE Dr.Mohammad Al-Sugayer
Vertical Coordinates HD VD SD
Pt. A
Zenith
Pt. 1 VA
Zenith = Up
Nadir = Down
Horizon = 90°
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35. Trigonometry Levelling
CE Dr.Mohammad Al-Sugayer
Trigonometry Levelling
Zenith HT SD
Pt. A VD VA ΔZ HI HI HD
Pt. 1
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