Lecture 2- Dec204survkliuc

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Lecture 2 - DEC 204 ( Surveying)

Basic Elements in Surveying :

Measurement : (Basic Components)

Distance Measurement

Bearing/Angle Measurement

Height Measurement

Basic Controls in Surveying

Horizontal Control

Vertical ControlScales and Product of Field Measurement: (Survey Data)

Scales

Plan/PlottingCharts

Maps

Document

Co-ordinates(Plane, Geodetic)Contoursetc

Errors in Surveying

Various types of errors (Systematic, Random, Gross)Error factor

Basic Measurement Components in Surveying

In Surveying we are basically involved in the measurement of Distances,

Angles/Bearings, and Heights. These three components are the basic data

obtained through surveying. From these three measurements, coordinates of

points (x, y, z) may be derived. Other products obtained through surveying mayalso be derived from these three basic components.

Distances

In much of the survey operation, distance is the basic measurement and distances

referred to is usually the horizontal distances. Measuring accurate distances in the

past was difficult compared to measuring angles. When accurate distancemeasurements became possible through advancement in technology, traverse

control were widely accepted, especially when triangulation was difficult.

Distances are needed for various purposes:

i) Base for the determination of Scale in Triangulation

ii) Additional requirement for angle measurements in triangulation

Surveying DEC 204June 2011/Lect 2

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iii) Trilateration

iv) Distances in traverses

v) Demarcation of details/features using distances and bearingsvi) Chainage measurements

Angles/Bearings

Angles or Bearing is another basic component measured in surveying. Angles are

obtained by comparing two directions ( AB and AD) or two bearings, while

bearing is the direction of a line with respect to a north line AN (see diagram) N

B Bearing of AB = 20Bearing of AD = 80

20 Angle BAD (

) = 60

= 60 D AN is the direction of True North

A

80

The bearing above refers to one type of north , the True North . There arehowever various types of Northing namely:

True North The line of true north is also referred to as a meridian (line passing

through the geographical North and South pole) . This north isactually the geographical north and determined accurately by

astronomical means

Magnetic North This is a line coincident to the line formed by a freelysuspended magnetic needle. A magnetic needle will always point

North-South. ThePrismatic Compass is a typical example of an

instrument giving reading referred to the magnetic north. Thedifferences between line of true north and line of magnetic north

differs and referred to as magnetic declination which changes from

year to year and point to point. A line of same magnetic

declination is called isogonic lineGrid North - This north direction refers to theNational Mapping Grid. A grid

is a system of squares whose sides may be of any convenient size

chosen to map an area, place or country.

Arbitrary North This is a line conveniently chosen to start a survey, usually in

the engineering survey work. Any convenient line may be chosento represent north even though it is not a line of magnetic or true

north


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Azimuth - Itis usually referred to in Cadastral Surveying and is exchangeable

to true bearing. The azimuth of a line is the angle the line makes

with reference to the meridian or the direction of the True North.

From the understanding above ,bearings may be classified into :

True Bearing or Azimuth(wrt True North) , Magnetic Bearing(wrt Magnetic

North) , Grid Bearing(wrt Grid North) and Arbitrary Bearing(wrt Arbitrary

North)

Bearings may be further grouped into :

Whole Circle Bearing ( 0 to 360 ) and Quadrant Bearing (eg N 45 E , S 30W)

0 N

270 90 W E

180 S Whole Circle Bearing Quadrant Bearing

Heights

Height is another main element measured in surveying. If distances and bearingsare components giving planimetric (x,y) information, heights provide z

information. Height values are referred to the Mean Sea Level (MSL) which is theDatum for height measurement. At the Datum point height has value 0.000meter. Heights that refers to the MSL as the datum is called Orthometric height.

This is the height normally used in spirit levelling. It is mainly used in

Engineering Surveys for example in the design and construction of roads andhighways, railway tracks, canals, waterways, drainage, reservoirs etc There is

another kind of height not normally heard. This kind of height is not referred to

the mean sea level. Instead it is referred to the Geopotential surface which isrelated to the pull of gravity. This kind of height is calledDynamic height.

Types of Height

As mentioned before heights are categorised into two types namely:

i) Orthometric Heightii) Dynamic Height


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Orthometric Heights are heights normally determined using spirit levelling. Their

values are in meters or feet above the MSL or the datum and marked on Bench

Marks.Dynamic Heights are not given in meters or feet because they are not referred to

the sea level. This type of heights is in geopotential numbers and are related to the

gravitational force. Dynamic heights are measured using instruments that canmeasure gravitational pull of the earth such as a Gravimeter. Sea surface is

actually a surface having the same potential numbers or same gravitational pull.

Another surface may have a different potential number and therefore the dynamicheight is different. Using a certain formula orthometric heights can be

transformed to dynamic heights and vice versa.

Basic Control in Surveying

Control Framework

Control framework is a basis requirement in survey work. If the survey is for planimetricdetails (x,y) a control framework to map planimetric details is used. Likewise if the

survey is to obtain height details (z) a control framework to map height details must beused The framework for planimetry cannot be used to collect height details and vice

versa.

Planimetric Control

Framework control for planimetry includes - Triangulation, Trilateration, Traversing,

Astronomy etc while framework control for heights includes Levelling, GlobalPositioning System (GPS) etc.

1) Triangulation

Triangulation is a form of survey whereby field observations are done to

determine the exact direction and length of one side of a triangle and angles of

each triangle. By so doing the length and direction of every side of the trianglecould be determined. By extending the framework of triangles, coverage of a big

area (even the whole country) could be obtained through network of triangles.

Field procedures therefore is the measurement of accurate angles of every triangle2) Trilateration

In Trilateration the basic figure is also a triangle. The technique in trilateration is

to measure all the sides of the triangles and to measure only one of the angles in

the triangle. If a network of triangles are extended throughout the country as donein triangulation and the sides of the triangles now measured, the whole area or

country could be controlled using Trilateration. This method was not that much

used because angle measurement as in triangulation proved easier and instrumentsneeded not that elaborate.


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3) Traverse

Until the advent of Electronic Distance Measurement (EDM) trilateration as well

as traverse did not prove that popular because distance measurement was timeconsuming and to obtain sufficient accuracy was difficult. Traversing technique

over long distances also could not maintain high accuracy. As a result

triangulation control for large areas in the past remain the general practice.

4) Combination

In recent years distance measurement using EDM became more useful and

convenient because of its high precision and accuracy. As a result combined

network of triangulation, trilateration, and also traverse was possible and capable

of obtaining higher accuracy. As long as the survey is properly observed andadjusted, combined network can result in the most accurate form of horizontal

control.

5) Astronomical Observations

The position of any point on the earth surface can be determined by astronomicalobservations . It can produce results of the highest order. Typical data obtained

from such observations are latitude, longitude, azimuth of lines, time which are

of concern to surveyors. Astronomical observations makes use of the celestial

objects namely the stars and the sun and because these objects are positionedpermanently in the sky with their coordinates known, the position of objects on

the earth can be referred to them For areas not yet ventured by mankind,

astronomical observations to obtain intitial coordinates of points are neededbefore any system of control such as triangulation or trilateration can be done.

Practical astronomy is thus a valuable tool to surveyors

6) Levelling

The previous method of control mentioned above is the horizontal control. They

are used to capture planimetric data (x,y) such as roads, rivers, building structures.To map height features (z) such as height of terrain or object a network of vertical

controls are needed. Levelling network is a form of control for height features.

As practiced in horizontal control where triangulation are categorised into first,

second, and third order control, levelling network are also broken down intovarious order of control. The first order control is initially established using

instruments of high accuracy (eg precise levelling instruments). From this a

second order network of control is build and thereafter the third order network.Subsequently contours can be drawn to depict the terrain of the area so that the

information obtained could be used to plan construction of highways and roads

for example.


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7) Global Positoning System (GPS)

In the past, control network determination has to be separated into horizontal and

vertical. It was convenient then because each instrument were designed for oneparticular purpose. A theodolite for example is designed to be used for horizotal

control determination and not for heights. Likewise a levelling instrument is so

designed to be used for vertical control. GPS however is capable of giving bothhorizontal as well as the vertical information to the highest accuracy. GPS

instruments can thus provide the x, y and z co-ordinates of individual points and a

network of horizontal and vertical control instantaneously could be establishedthroughout the country .

Product of Field Surveys /Presentation of Field Measurement

Scales

Ground features whether natural or artificial cannot be brought to drawing

without putting it to scale. For this reason scaling has to be doneScales can be represented by various ways :

a) Numerical Scale - for example a Map Scale of 1/ 100 ora Map Scale of 1 : 100

means 1mm on drawing/map equals 100 mm on ground

b) Line Scale -0 1Km 2 Km 3 Km

A line scale is a graphical representation and can be represented in a very

simple form. This type of scale is most commonly found on maps

From the measurements made in the field, various products could be produced

either in the graphical or digital form:

- Plan or Plotting at a desired scale ( Engineering, Cadastral, Topographical)

- Manuscript and finally Maps on a certain projection

- Documents (eg Field Book, Plotting)- Hydrographic Charts (Bathymetry )

- Height information such as Contours

- Provison of control points in monitoring Engineering Project- Calculation of Areas and Volumes (Earthworks etc)

- Co-ordinates (X , Y , Z) (Plane Co-ordinates,Scale,and Geodetic Co-ords)

- Digital Terrain Models (DTM)

Plan or Plotting

Many survey work end up as a plan or plotting at a certain scale, usually large

scale especially in Engineering Surveying, Topographical Surveying andCadastral Surveying.

In Cadastral Surveying the final product is a plotting called Certified Plan (CP)

(Plan Akui/PA). Various scales are adopted ie 1 : 2 000 , 1 : 5 000 , 1 : 7 500 or1: 10 000 for country lot


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For urban areas/city areas scales are usually at 1 : 200 , 1 : 500 , 1 : 2000, 1: 5000

In Engineering and Topographical Surveying the scales adopted may follow that

of the cadastral surveying but includes in it details of heights usually in the formof contours and spot heights

ChartsCharts are plotting of Hydrographic Survey. The main concern in charts is to

provide information about the safe movements of water vessel around ports and

harbors. Where area of concern is far from ports, small and medium scales areused (1:25 000 and smaller). When it concerns areas within harbors and ports

large scales of 1: 7500 are used. In Malaysia the Royal Malaysian Navy is the

authority on hydrographic surveys and navigation charts are their concern.

Therefore where plans, plotting and maps concerns measurements made on land,charts are referred to surveys made with regards to water feature such as surveys

made for ports and harbors, shorelines, water depth etc.

MapsMaps are ploting of large areas such as the whole country. The activity of

mapping is usually handled by Government Agencies. In Malaysia Jabatan Ukurdan Pemetaan Negara (JUPEM) or the Department of Survey and Mapping is the

authority on the matter of surveying and mapping. Maps of Peninsular Malaysia

are drawn on a projection called Rectified Skew Orthomorphic (RSO) while in

cadastral surveying, data are produced with reference to the Cassini-Soldner projection . Field data in order to be used at the national level for mapping

therefore need to be transformed. Conversion from RSO to Cassini-Soldner and

vice versa is available.Topographic maps are produced by JUPEM using a numbering system. The

region of Malaysia is given an alphabet L which also includes China, Japan,

and the south east asian countries. Thailand and Malaysia being small is furthergiven a numeric 0 . Besides the alphabet and numeric to denote where

Malaysia is, the scale of map is futher given an identity (5 for small scale and 9

for large scale ie in the range of 1 : 15000 1 : 5000.

Map of Series L 707 means Area code L L

Scale of map 7 L7

Number (for small country/area) 0 L70

Series of numbers for specific area 7 L707

Documents

The survey work carried out in the field has to recorded either on paper or using

some form of electronic recording. In the past and even to-day field books areused. Survey measurements have to transferred to the field book with care .

Sketches must be legible and clear. Whatever cancellation must also be made in a

proper manner. The field book especially in cadastral survey is a document and

can be used for legal proceedings of disputes.


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Survey plans is also another form of legal document because both the field book

and the plans especially in cadastral survey has to be checked, signed by the

surveyor concerned and the whole work approved correct by JUPEM

Co-ordinates

Co-ordinates are derived from measurements carried out in the field. Of concernhere is the plane co-ordinates. They are usually derived from both the planimetric

survey to obtain x and y coordinates such as in traversing and the height surveys

using leveling techniques to obtain z coordinates. Co-ordinates have to beadjusted before they can be of use.

Contours

Information about terrain is best represented by contours. Each contour line depict

a particular height above MSL . Contour intervals are designed to give an idea

about the nature of terrain. A close interval may be needed for undulating and

irregular terrain while a sparce interval is sufficient for flat terrain.

Errors in Surveying

All survey work contains error no matter how meticulous we plan or execute the survey.

We are not perfect and errors are inevitable. Nevertheless we cannot tolerate errors andeffort must be done to reduce errors.

Errors can generally be categorised into three groups :

1) Systematic Error

This type of error exist in all survey work and arise from some physical

phenomenon which can be mathematically modelled. They are cumulative

in nature which means they are either +ve or ve. For example if ameasuring tape is 0.1 mm shorter than the standard tape all measurements

made using this tape will always be more by 0.1 mm . At the end of the

day measurements becomes more than what it should be and should be

subtracted by 0.1mm for every tape length measured.

2) Random Error

This type of error is difficult to rationalise. It cannot be mathematically modelled.It is also not cumulative and have a tendency to compensate one another

and as such difficult to eliminate. The magnitude of error may be small

though, but it is present even in cases where extreme care is exercised. Toreduce such errors observations are repeated and those not within

expectation are eliminated. Theoretically random errors are the left-over

after gross and systematic errors are eliminated.3) Gross Errors/Mistakes


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This type of error originate from negligence during observations and

booking which may occur due to inexperience and careless act of the

observer or because of tiredness or fatigue. Mistakes are the most seriousof all the errors and cannot be adjusted or corrected. To avoid such

mistakes a system of check must be devised during field observation,

booking, and plotting.

Error Factor

Besides knowing the types of errors present in survey field operation we also have toappreciate the nature of errors in surveying. Several factors contribute towards the build-

up of errors. They play an influential role and affect quality of the observations and hence

the magnitude of errors made. Among the main factors are:

1. Instrument Factor

This is the main factor. Familiarising with the instruments is very important as

technology changes rapidly. Instruments also have some form of life because ofwear and tear. Their accuracy and calibration may change. If they are physically

graduated for example in levelling staff and measuring tape it may fade over yearsof usage. Electronic-based instrument can be unstable at times. Sophisticated

technology needs new input and refinements may simplify procedures. New

findings may therefore override previous procedures. Materials also advanced

through current research findings. Calibration and checks from time to time has tobe done. Instruments may also be manufactured with some form of defects even

with great care during manufacture. This is a common phenomenon in mass

production.

2. Environmental Factor

From day to day and time to time, changes happen to the environment. Hourly

changes may happen to the suns ray, wind and atmosphere. Observations in the

morning may not be affected by shimmering and refraction compared to noon orlate afternoon observation. Changes of wind, temperature and rain cannot be

easily predicted. All these may change the standards which the equipment were

calibrated.

3. Observers Factor

Surveying as of now is very human-dependent. Instrument operators have to beproperly trained. Skilled labor is important. Poor attitude and discipline of these

individuals cannot be tolerated. But strange thing can happen. Wrong reading and

careless booking is still common. Superior technology may fail if observers areindiscipline, inexperienced and procedures not adhered to.


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Lecture 2- Dec204survkliuc

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Transcript of Lecture 2- Dec204survkliuc