ALAT SIPAT DATAR

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The Kinds of LEVELLING The Kinds of LEVELLING Instrument Instrument Classifications Levelling Instrument : a. Based Degree of Precision : 1. Precisions Level → 0,2 – 0,5 mm 2. Universal Level →1 – 2 mm 3. General Purpose Level →3 – 5 mm 4. Builder Level → 6 – 10 mm b. Broadly speaking levels can be divided in to 3 main groups : 1. Dumpy Level 2. Tilting Level 3. Automatic Level

Transcript of ALAT SIPAT DATAR

The Kinds of LEVELLINGThe Kinds of LEVELLING Instrument Instrument

Classifications Levelling Instrument :a. Based Degree of Precision :

1. Precisions Level → 0,2 – 0,5 mm 2. Universal Level →1 – 2 mm3. General Purpose Level →3 – 5 mm4. Builder Level → 6 – 10 mm

b. Broadly speaking levels can be divided in to 3 main groups :1. Dumpy Level2. Tilting Level

3. Automatic Level

Dumpy LevelDumpy Level

Tilting LevelTilting Level

Automatic LevelAutomatic Level

Name of Parts Levelling InstrumentName of Parts Levelling Instrument

PARTS OF LENS AUTOMATIC LEVEL

The Essentials of Levelling Instrument :The Essentials of Levelling Instrument :

1. The Vertical axis must be trully vertical when the bubble of the spirit level is central.

2. The Line of Sight must be parallel to the newly adjusted spirit level, in other words, the line of sight must be horizontal.

3. The Cross-Hairs Diaphragm must be horizontal

Setting Up the Levelling Setting Up the Levelling InstrumentInstrument : :

1. Setting the Tripode2. Mounting the Instrument3. Levelling the Instrument4. Parallax elimination

PARTS OF LENS AUTOMATIC LEVEL

READING THE READING THE CIRCLESCIRCLES

A. Methods the reading System Horizontal Circle:1. Sentisimal system ==> Grade, Centi-

grade, Centicenti-grade2. Seksadesimal System ==> Degree, Minute,

Second.

B. Methods Reading Scale Horizontal Angle :1. Cara Vernier 2. Cara Optis

• Reading Horizontal Circle

• Horizontal Circle Reading

1. CIRCULAR LEVEL ( PERPENDICULAR ALIGNMENT WITH THE VERTIKAL AXIS)

Checking :

Adjust the levelling screws to centre the bubble in the circular level (A), and turn the instrument 1800 ( or 200 gr)

The bubble does shift (B), compensate for one-half of the shift by adjusting the levelling screws ( C ), and eliminate the remaining half with the circular level adjusting screws (D). Repeat the above check and adjustment untill no bubble shift occurs in any telescope direction.

CHECKING AND ADJUSMENTCHECKING AND ADJUSMENT

Figure Adjustment Circular Figure Adjustment Circular LevelLevel

LINE OF SIGHT or LINE OF COLLIMATIONLINE OF SIGHT or LINE OF COLLIMATION( Test Two Peg )( Test Two Peg )

• Check by “ levelling from the middle “ :• Set up instrument in G1

• The distance Sr = Sv ( Back sight distance = Foresight distance )• Take staff reading R1 and V1

• Error-free height difference results from Δ h1 = R1 - V1

• Set up instrument in G2 shortest distance to the foresight staff • Take staff reading V2 and R 2 calculate the height difference Δh2= R2 -

V2

• If the height difference value indicates a difference, the horizontal cross line must be adjusted.( Δ h1 ≠ Δh2).

Figure “ Test two Peg “Figure “ Test two Peg “

Reading the staffReading the staff

Reading the staffReading the staff

LevellingLevelling• Principles and Definitions

1. Definition of Leveling : Leveling is the process of measuring the difference in height between points on the surface of the earth.2. A level surface or level line: This is a surface or line, all points of which are normal or at right-angles to the pull of gravity as shown by plumb-line.3. A horizontal surface or a horizontal line : This is a plane, flat surface or straight line which passes through a point at right-angles to the pull of gravity at the point.4. A datum surface : This is any level surface to which the elevations of points may be referred. The surface most commonly adopted as a datum is the mean level of the sea. As the mean or average level of the sea varies at different places because of the effect of winds, currents and tides, the mean level at one place is adopted as a datum surface and is called the mean sea level ( M S L )5. A reduced level : The reduced level of a point is its height or elevation above the surface adopted as a datum.6.Bench Mark : Bench Marks are stable reference points, the reduced levels of which are accurately determined by spirit leveling.7.Diffrerence of level between two points. In order to find this it is necessary to establish a level surface above or below the two points and to measure the vertical distance from it to the points.8.Stations In Levelling, a station is that point where the level rod is held and not where level is set up9.Backsight. Back sight is the sight taken on a rod held at a point of known elevation.10.Fore sight is taken on a rod held point of unknownelevation.11.Station : In levelling a station is that point where the rod is helh and not level is set up.12 Intermediate Station : Is a point intermediate between two turning points on which only one sight is taken to determine the elevation of the station.

METHODS OF LEVELLINGMETHODS OF LEVELLING• BAROMETRIC LEVELLING : Makes use of the phenomenon that

difference in elevation between two points is proportional to the difference in atmospheric pressures at these points. A barometer, therefore may be used and the readings observed at different points would yield a measure of the relative elevations of those points. At given point, the atmospheric pressure does not remain constant in the course of the day, even in the course of an hour. The method is therefore, relatively inaccurate and is little used in surveying work except on reconnaissance or exploratory.

• TRIGONOMETRIC LEVELLING ( INDIRECT LEVELLING ) : Trigonometric or indirect Leveling is process of leveling in which the elevations of points are computed from the vertical angles and horizontal distances measured in the field, just as the length of any side in any triangle can be computed from proper trigonometric relations. In a modified form called stadia levelling, commonly used in mapping, both the difference in elevation and the horizontal difference in elevation and the the horizontal distance between the points are directly computed from the measured vertical angle and staff readings.

Spirit Levelling ( Direct Levelling )Spirit Levelling ( Direct Levelling )• It is that branch of levelling in which the vertical

distances with respect to a horizontal (line perpendicular to the directions of gravity ) may be used to determine the relative diffrerencein elevations between two adjacent points. A horizontal plane of sight tangent to level surface at any point is readily established by means of spirit level. In spirit levelling a spirit level and a sighting device ( telescope ) are combined and vertical distance are measured by observing on graduated rods placed on the points.

TYPES OF SPIRIT LEVELLING or TYPES OF SPIRIT LEVELLING or Classification of LevellingClassification of Levelling

• DIFFERENTIAL LEVELLING : It is method of direct levelling the object of which is solely to determine the difference in elevation of two points regardless of the horizontal positions of the points with respect of each other. When the points are apart, it may be necessary to set up the instrument several times. This type of levelling is also known as fly levelling.

• PROFILE LEVELLING : It is the method of direct-levelling the object of which is to determine the elevations of points at measured intervals along a given line in order to obtain a profile of the surface along that line.

TYPES OF SPIRIT LEVELLING orTYPES OF SPIRIT LEVELLING orClassification of levellingClassification of levelling

• CROSS SECTIONING : Cross Sectioning or cross-levelling is process of taking levels on each side of a main line at right angles to that line in order to determine a vertical cross section of the surface of the ground, or of underlying strata, or of both.

• RECIPROCAL LEVELLING : It is the method of levelling in which the difference in elevation between two points is accurately determined by two sets of reciprocal observations when it is not possible to set up the level between the two points.

• PRECISE LEVELLING : It is the levelling in which the degree of precision required is to great too be attained by ordinary methods, and which, therefore, special precautions or both are necessary to eliminate, as far as possible all sources of error.

ERRORS IN LEVELLINGERRORS IN LEVELLING

• INSTRUMENTAL :– Error due to imperfect adjustment– Error due to sluggish bubble– Error due to movement of objective slide– Rod not of standard length– Error due to defective joint

ERRORS IN LEVELLINGERRORS IN LEVELLING• NATURAL

– Earth’s curvature– Atmospheric refraction– Variations in temperature– Settlement of tripode or turning points– Wind vibrations

ERRORS IN LEVELLINGERRORS IN LEVELLING

• PERSONAL– Mistakes in manipulation– Rod handling– Mistake in reading the rod– Errors in sighting– Mistake in recording

Curvature and RefractionCurvature and Refraction• To Calculate the effect of curvature and

Refraction

R = mean radius of the earth ( 6370 km)By Pythagoras’s Theorem :( CD + R )2 = ( K 2 + R 2 ) CD 2 + 2 CD.R + R 2 = K 2 + R 2

CD 2 + 2 CD.R = K 2 ---- CD ( CD+2R)=K 2

CD so small compared with R that fore can be ignored < R

Curvature and RefractionCurvature and Refraction• CD= K2/ 2R ---- CD = K2/ 12740 km

• Correction for curvature= 0.0785 K2 m

• The effect of Refraction -- The Value is not constant so correction taken as 1/7

curvature.Combined Correction = 0.0785 L2 - 1/7( 0.0785 K2

= 6/7 ( 0.0785 K2)

= 0.0673 K2 ..m ( Where K in km )

Reciprocal LevellingReciprocal Levelling• Difference Level between A and B is

obtained by the procedure :– The Level set up at X, 5m from A, anh

both staffs are observed - Giving diff. level

– The level is next set up at Y, 5m from B, again both staffs are observed Giving second diff. level.

Reciprocal LevellingReciprocal Levelling– The errors of observation from each set-up are

approximately the same.– The True diff.level : (as example)

• Observations from Station X :• On staff held at A = 1.470• On staff held at B = 3.562• Diff. level = 2.092• Observations from Station Y :• On staff held at A = 0.516• On staff held at B = 2.620• Diff.level = 2.104

Reciprocal LevellingReciprocal Levelling

• The True Difference in level =

2.092 + 2.104-------------------- = 2.098 m

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