Yabancı Dil III (YDL/GEO285)

Leveling

Yrd. Doç. Dr. Saygın ABDİKAN

2017-2018 Öğretim Yılı Güz Dönemi

1

Cadastral surveying

Cadastral surveying is a

branch of the surveying

profession that is

concerned with land

management, and more

specifically

with issues of land

ownership, measurement

and delineation of property

boundaries.

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Boundary surveying

A survey that establishes or

re-establishes boundaries of

a parcel using a legal

description

It involves the setting or

restoration of monuments

(sınır taşı) or markers at the

corners or along the lines of

the parcel.

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Topography is a combination of methods and

instruments to comprehensively measure and

represent details of the Earth’s surface:

planimetry: to determine the relative positions of the

representation of points on the Earth’s surface with

respect to the same reference surface;

altimetry: to determine the height of the points on the

Earth’s surface with respect to the geoid surface;

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Geoid: is a model of global mean sea

level that is used to measure precise

surface elevations.

The geoid is the shape that the surface

of the oceans would take under the

influence of Earth’s gravity and rotation

alone, in the absence of other influences

such as winds and tides.

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tachymetry: for the planimetric and

altimetric survey of the Earth’s surface

zones;

land surveying: to measure areas,

moving and rectify borders, levelling

zones of the Earth physical surface.

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Topographic Surveys are used to identify

and map;

the contours of the ground and

existing features on the surface of the

earth or slightly above or below the

earth's surface (i.e. trees, buildings,

streets, walkways, manholes, utility

poles, retaining walls, etc.).

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Topographic

maps show

elevation of

landforms above

sea level;

Bathymetric maps

show depths of

landforms below

sea level.

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9

The most common method of representing

the topography of an area is to use contour

lines

A contour line is an imaginary level line

that connects points of equal elevation

http://www.ce.memphis.edu/1101/notes/surveying

yükseklik eğrisi/eşyükseklik eğrisi/münhani

Contours that point up

hill can indicate a

valley or stream

10

http://www.ce.memphis.edu/1101/notes/surveying

Contours show the

steepest part of this

terrain and the

shallowest part of the

topography

Characteristics of Contours

The contour interval should be small enough to give the

desired topographic detail

Usually every fifth contour line is shown in a heavy,

wider line, this is called a index line/principal contour

Closely spaced contours indicate steep slopes

Widely spaced contours indicate moderate slopes

Contours should be labeled to the elevation value

Contour line do not cross

Important points can be further defined by including a

“spot” elevation

Contour lines tend to parallel each other on uniform

slopes 11

INTRODUCTION TO LEVELING

Areas of Application:

• design of highways, railroads, canals, etc.

• Layout construction projects according to specific

design

• calculate earthwork volumes

• investigate drainage characteristics

• map earth’s topography

• monitor earth subsidence

Types of Level

Builder's/Engineer's Level: As implied by

the name, these are used by builders

and engineers.

The accuracy of a single reading will be

about 2-3mm.

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Digital Level: This type of level uses a special

bar-coded staff. The image of the staff passes

through the objective lens and then via a beam

splitter to a photodetector array, where it is

digitized.

The microprocessor compares this image to a

copy of the bar code and calculates the staff

reading, which is displayed and/or stored. The

sensitivity of the device is such that single

reading accuracies of 0.2mm to 0.3mm can be

achieved, and sight lengths can be extended

up to 100m.

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Precise Level: This is a modification of

the conventional level in which a parallel

plate micrometer is placed in front of the

objective lens. This allows the image of

the staff graduation to be moved up or

down by very small measurable

amounts. For sight lengths of under 50m,

single reading accuracies of 0.02mm to

0.03mm can be achieved.

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Dumpy Level

A dumpy level, builder's auto level, leveling

instrument, or automatic level is an optical

instrument used to establish or check points in the

same horizontal plane.

It is used in surveying and building to transfer,

measure, or set horizontal levels.

DEFINITIONS

3. Mean Sea Level (MSL):

Average elevation of the sea surface measured over a period of 19 years

4. Bench Mark (BM):

A permanent reference point with a known elevation (relative to some datum, usually MSL)

5. Leveling:

The process of measuring elevation differences between different points

6. Vertical Control:

A series of points of known elevation established throughout an area

1. Level Surface:

A curved surface that at every point is perpendicular to the direction of gravity (plumbline), e.g.

still lake surface

2. Datum:

A level surface to which elevations are referred (i.e. reference surface such as MSL)

A

B

VERTICAL ANGLE - Angle between line AB and horizontal line

HORIZONTAL LINE - Line perpendicular to the vertical

ELEVATION - Vertical distance (height difference) between datum and point

Levelling

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Differential Leveling (Geometric leveling)

Trigonometric Leveling

Barometric Leveling

Hydrostatic Leveling

GPS Leveling

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LEVELING METHODS

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LEVELING METHODS

1. Differential Leveling (Geometric leveling)

Backsight (BS) FS

8.42

1.20

BM A

(820.00)

TP1

Level set up half way between BM A and TP1 - equal BS and FS

DhAB = BS - FS = 8.42 - 1.20 = 7.22

hB = 820.00 + DhAB

Geri okuma

Bench mark (BM) - relatively permanent point of known elevation

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• Backsight (BS) - a sight taken to the level rod held at a point of

known elevation

• Foresight (FS) - a sight taken on any point to determine its

elevation

• The backsight reading is added to the elevation of the known point

to compute the height of the instrument (HI)

• The level may be moved to a temporary point called a turning point

(TP)

• The elevation of a point is the height of the instrument (HI) minus

the foresight (FS)

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• Leveling rod (surveyor’s rod

- mira) not vertical

• Settling of leveling rod

• Leveling rod not fully

extended or incorrect length

• Level instrument not level

• Instrument out of

adjustment

• Environment - wind and

heat

Common Mistakes

TRIGONOMETRIC LEVELING

Measurement of vertical angle wıth teodolit

B

A

r

z

V

H

S

C

D

hi

a

DZCD = V = S Sin a = S Cos z

= H Cot z

DZAB = hi + V - r OR ZB = ZA + hi + S Sin a - r

= ZA + hi + H Cot z - r

LEVELING METHODS

BAROMETRIC LEVELING

• Barometer measures air pressure which is directly related to elevation

• Changes in pressure due to temperature changes, changes in weather

conditions, etc can be taken into account by leaving one barometer on

a control point (e.g. BM)

• Accuracies of 2-3 ft (0.6 - 1 meter) are possible

LEVELING METHODS

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LEVELING METHODS

Differential Leveling gives ORTHOMETRIC HEIGHTS

(above Mean Sea Level)

GPS gives ELLIPSOIDAL HEIGHTS (above ellipsoid)

GPS Leveling

http://www.esri.com/news/arcuser/0703/geoid1of3.html

Mean Sea Level

For generations, the only way to express topographic or

bathymetric elevation was to relate it to sea level.

Geodesists once believed that the sea was in balance

with the earth’s gravity and formed a perfectly regular

figure.

MSL is usually described as a tidal datum that is the

arithmetic mean of hourly water elevations observed

over a specific 29 year cycle.

MSL is defined as the zero elevation for a local area.

The zero surface referenced by elevation is called a

vertical datum.

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http://www.esri.com/news/arcuser/0703/geoid1of3.html

BASIC PARTS OF A LEVEL

telescope reticle eyepiece

line of sight

level bubble

leveling screws

tripod

objective lens

Gözlem çizgileri

plakası

Oküler

Küresel düzeç

Ayar vidaları

Üç ayak sehpa

Gözlem çizgileri plakası

Older instruments – Dumpy, Wye

Automatic level (compensator)

Laser

Digital

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compensator

Compensating Prism in Automatic Level

Automatic compensator orients line of sight in a horizontal plane

Earth Curvature

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:

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Refraction:

The variable density of the Earth's atmosphere

causes a bending of the ray from the staff to

the level.

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LEVELING FIELD PROCEDURE

Setting up Level:

balance Backsight and Foresight

make sure rod will be visible when instrument leveled

at new position

Rod Person:

hold rod vertical (plumb)

move rod back and forth (minimum reading noted)

select TP’s that are stable

Differential Leveling Procedure:

start with BS on starting BM

take FS and BS on all intermediate points (TP’s)

close with FS on ending BM