Post on 10-Apr-2018
Yabancı Dil III (GEO/YDL285)
Distance measurements
Yrd. Doç. Dr. Saygın ABDİKAN
2017-2018 Öğretim Yılı Güz Dönemi
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Distance measurements
Why do we need?
In science, measurement is the process of
estimating or determining the magnitude of a
quantity, such as length or mass, relative to a
unit of measurement, such as a meter or a
kilogram.
The term measurement can also be used to
refer to a specific result obtained from the
measurement process
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The word geometry is derived from the Greek
meaning geo- "earth", -metron "measurement“
Types of surveys:
Land surveys
Topographic surveys - location of objects and
measuring the relief, roughness, or three–
dimensional variations
Route surveys - location of natural and artificial
objects along a proposed route for a highway,
railroad, canal, pipeline, power line, or other
utility 3
City or municipal surveys - use to lay out streets, plan sewer
(kanalizasyon) systems, and prepare maps
Construction (yapi) surveys - locating structures (bina/yapi) and
providing required elevation points during their construction
Hydrographic surveys - pertain to lakes, streams (akarsu), and other
bodies of water
Marine surveys - related to hydrographic surveys, but they are
thought to cover a broader area
Mine surveys - relative positions and elevations of underground
shafts, geological formations, etc.
Forestry and geological surveys
Photogrammetric surveys - photographs (generally aerial) are used
in conjunction with limited ground surveys
Control surveys - provides vertical and horizontal reference points
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TYPES OF MEASUREMENT
• Horizontal distances
• Vertical distances
• Slope distances
• Horizontal angles
• Vertical angles
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UNITS OF MEASUREMENT
Length: Feet, Meters, Chains
Angles: Degrees Minutess Seconds (DMS), Grads (400gr = 360°)
Radians (2 PI = 360°)
Area: Ft2, acres, square meters, hectares, square kms
(1 ha = 2.471 acres) acres-dönüm
(1 ha = 10,000 m2)
Measurement techniques
Distance is one of the most basic engineering measurements
Early measurements were made in terms of the dimensions of the
body
Cubits: the distance between the tip of your middle finger to the
elbow (~0.46m) (arşın)
Fathom: distance between the tips of your middle finger when
your arms are outstretched (~1.83m) (kulaç)
Foot/Feet: distance from the tip of a man’s big toe to the heel
(1 feet ~30.48cm)
A pace is defined as one step and a stride is two steps
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http://surveying.structural-analyser.com/chapter04/
Chaining (Gunter’s chain/ Gunter’s measurement)
A Gunter’s chain (named after its inventor Edmund
Gunter 1581-1626) is 66 feet long and is divided into 100
links, each 7.92 inches long. (1 inch=0,08333 feet)
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Taping/chaining
clear line
lay out tape on ground making sure there are no kinks
(bükülme/kırılma)
apply tension (~5 kg) (gerilim)
use plumb-bob on uneven ground (düzensiz)
plumb-bob or a plummet is a weight, usually with a pointed tip on the
bottom, that is suspended from a string and used as a vertical
reference line, or plumb-line.
read the tape
(steel tape measure- çelik şerit metre) 8
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Taping on steep slope
The term breaking tape is used to describe the procedure for
measuring directly horizontal distance on sloping ground
Breaking tape (basamaklı ölçüm) – range pole (jalon)
The sum of horizontal lengths (L1 & L2 & L3) equals the horizontal
distance of the slope from A to D.
The horizontal distance is always shorter than the measurement
on the slope.
To reduce the sag break tape measurement
into shorter lengths.
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L1
L2
L3
A
B
C
D
Slope
angle
COMMON TAPING
ERRORS
1. Incorrect length of tape
2. Temperature variation
3. Non-standard tension
4. Sag (catenary) (sarkma)
5. Poor alignment (kötü
doğrultma)
6. Slope
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TAPE STANDARDIZATION
- Done by comparison with standard
tape or known baseline.
- Standardization usually defined in
terms of:
- tension (e.g. ~5 kg)
- temperature (e.g. 20°C)
Short measurements may minimize sag effect
EDM (electronic distance measurement)
Electronic distance measurement (EDM) instruments
determine lengths using phase changes that occur as
electromagnetic energy of known wavelength travels
from one end of a line to the other end and returns.
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Gediometer (geodetic
distance meter) – which
is developed in 1948
based on a modulated
light beam (ışık
demeti/hüzmesi)
(measuring the distance
between two points by
means of a laser)
Tellurometer employs
modulated microwaves
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EDMs are now being incorporated with
theodolites having automatic angle readout
capabilities, so called total stations
(electronic tacheometers).
They can simultaneously and automatically
measure both distances and angles.
There are two kinds of EDM
Electro-optical System
Microwave instruments
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Electro-optical System
An EDM uses electromagnetic (EM) energy to determine the
length of a line. The energy originates at an instrument at one
end of a line and is transmitted to a "reflector" at the other
end from where it is returned to the originating instrument.
The nature of the "reflector" is dependent on the type of EM.
They transmit light having wavelengths in the range of 0.7 to 1.2
micrometers within or slightly beyond the visible region of the
spectrum.
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Microwave instruments
They transmit microwaves with frequencies in the
range of 3 to 35 GHz corresponding to wavelengths of
about 1.0 to 8.6 millimeters.
In either case the measurement is the total distance
from the instrument to the reflector and back to the
instrument.
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Comparing the two EM types:
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EM Type Advantages Disadvantages
Electro-optical Less susceptible to atmospheric
conditions.
Less expensive: only a single
transmitter needed.
Shorter range.
Microwave Can penetrate fog and rain.
Longer range.
Transmitter at both ends allows
voice communication.
Atmospheric affects are
greater.
Susceptible (duyarlı) to
ground reflected signals.
More expensive: requires
two transmitters.
An EDM does not determine distance by measuring the travel
time of the EM signal. Instead, an EDM uses the signal structure
and determines the phase shift. The EM signal has
a sinusoidal wave form. This wave form repeats every 360°.
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Different wavelengths are generated at different
modulation frequencies, f. Wavelength,
frequency, and the speed of light are related by:
An EDM measures the line of sight distance between
the instrument and reflector. This is a slope
distance and not horizontal unless the EDM and
reflector are at the same elevation.
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In order to determine a horizontal or vertical distance
additional information is needed. Combining an EDM with
a digital theodolite results in a Total Station
Instrument (TSI). When distance measurement is made,
the TSI measures the slope distance and a zenith angle.
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Total station
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Single reflector Multiple reflector
FACTS ABOUT MEASUREMENTS
• No measurement is exact
• Every measurement contains error
• The true value of a measurement is never known
• Exact error in measurement is always unknown
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SOURCES OF ERROR
1. NATURAL ERRORS:
Errors caused by natural phenomena, such as wind, temperature,
humidity, multiple refraction of the signal, etc
2. INSTRUMENT ERRORS:
Errors resulting from imperfections in measuring instruments,
such as graduations (derece işareti) on theodolite circle or tape
3. PERSONAL ERRORS:
Errors caused by human limitations of the observer, such as
vertical crosshair not aligned perfectly on target
Inaccuracy in initial setups of EDMs and the reflectors over the
preferred stations
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TYPES OF ERRORS
1. SYSTEMATIC ERRORS
These errors conform (uymak) to mathematical and physical laws
(e.g. temperature) and can generally be computed and correction
applied
2. RANDOM ERRORS
Errors that obey (tabi olmak) the laws of probability (beyond
control of observer) - no absolute method to compute and
eliminate these errors, but they can be estimated using statistical
methods
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Kaynaklar
Yrd.Doç.Dr. Himmet Karaman, Lecture notes on Geodesy, GPS
and GIS
Prof.Dr. Uğur Şanlı, Lecture notes on Vocational English
http://jerrymahun.com/library/Distance/a.htm
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