SURVEYING IIPresented by:

ARUN KUMAR K S

Department of civil engineering

THEODALITE SURVEYING

• So far we have been measuring horizontal angles by using a Compass with respect to meridian, which is less accurate and also it is not possible to measure verticalangleswithaCompass. So when the objects are at a considerable distance or situated at a considerable elevation or depression,itbecomesnecessarytomeasurehorizontal and vertical angles more precisely. So these measurements are taken by an instrument known as a theodolite.

THEODOLITE SURVEYING

• The system of surveying in which the angles are measured with the help of a theodolite, is called Theodolitesurveying.

THEODOLITEThe Theodolite is a most accurate surveying instrument mainly used for:

• Measuring horizontal and vertical angles. • Locating points on a line. • Prolonging survey lines.• Finding difference of level. • Setting out grades • Ranging curves • Tacheometric Survey

• CLASSIFICATION OF THEODOLITES Theodolitesmay be classified as

i) Transit Theodolite.

ii) Non Transit Theodolite

DESCRIPTION OF A TRANSIT VERNIER THEODOLITE

• A Transit vernier theodolite essentially consist of the following:

1.LevellingHead2.LowerCircularPlate.3.UpperPlate..4.Telescope. 5.VernierScale.6.T-Frame7.Plumb–bob8.TripodStand

TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE

1.Centering : Centering means setting the theodolite exactly over an instrument- station so that its vertical axis lies immediately above the station- mark. It can be done by means of plumb bob suspended from a small hook attached to the vertical axis of the theodolite.

The centre shifting arrangement if provided with the instrument helps in easy and rapid performance of the centring.

TERMS USED IN MANIPULATING A TRANSIT VERNIER THEODOLITE

2.Transiting : Transiting is also known as plunging or reversing. It is the process of turning the telescope about its horizontal axis through 180 in the vertical plane thus bringing it upside down and making it point , exactly in opposite direction.

3 .Swinging the telescope It means turning the telescope vertical axis in the horizontal plane. A swing is called right or left according as the telescope is rotated clockwise or counter clockwise.

4. FACE LEFT

5. FACE RIGHT

6. CHANGING FACE

7. LINE OF COLLIMATION

8. VERTICAL AXIS

9. HORIZONTAL AXIS

TEMPORARY ADJUSTMENT OF THEODAITE

• CENTERING

• LEVELLING

• FOCUSSING

MEASUREMENT OF HORIZONTAL ANGLES

• ORDINARY METHOD

• REPETATION METHOD

• REITERATION METHOD

MEASUREMENT OF VERTICAL ANGLE

• Vernier angle is the angle which the inclined line of sight to an object makes with the horizontal. It may be an angle of elevation or angle of depression depending upon weather the object is above or below the horizontal plane passing through the trunnion axis of the instrument

TO MEASURE DEFLECTION ANGLE

• A deflection angle is the angle which a survey line makes with the prolongation of the proceeding line.

THEODOLITE TRAVERSING

• Traversing is a type of survey in which a number of connected survey lines form the frame work and the directions and lengths of the survey lines are measured with the help of an angle measuring instrument and a tape or chain respectively.

• When the lines form a circuit which ends at the starting point, it is known as closed traverse.

• If the circuit ends elsewhere, it is said to be an open traverse.

THEODOLITE TRAVERSING

• In this method, the angles between the lines are directly measured by a theodolite. The method is therefore most accurate. The magnetic bearing of any one line can also be measured and the magnetic bearing of other lines can be calculated. The angles measured at different stations may be either:

a) Deflection angles

b) Included angles

Traversing by Deflection angle

• A Deflection angle is the angle which a survey line makes with the prolongation of the preceding line. It is designated as right (R) or left (L) according as it is measured clockwise or anti-clockwise from the prolongation of the previous line. Procedure for measuring a deflection angle is explained

Traversing by included angles

• The direct are the angels measured clockwise from the preceding line to following line. They are also known as angels to the right and May vary from 0⁰ to 360⁰

CHECKS IN CLOSED AND OPEN TRAVERSE

• 1. Traverse by included anglesi. The sum of measured interior angles should be equal to (2N – 4) right

angles. Where N = number of sides of the traverse

ii. If the exterior angles are measured, their sum should be equal to (2N + 4) right angles.

2. Travels by Deflection angles The algebraic sum of the deflection angles should be equal to 360, taking the right- hand deflection angle as positive and left and deflection of angles as negative.

3. Travels by direct observation of bearings : The fore bearing of the last line should be equal to its back bearing ±180 measured at the initial station

TRAVERSE COMPUTATIONS: Consecutive co-ordinates: Latitude and

Departure • The latitude of a survey line may be defined as its

co-ordinate length measured parallel to an assumed meridian direction (i.e. true north or magnetic north or any other reference direction).

• The latitude (L) of the line is positive when measured northward (or upward) and is termed as northing: the latitude is negative when measured southward (or downward) and is termed as southing

L = + l cos Ɵ and D =+ l sin Ɵ

Independent coordinate

CLOSING ERROR

• If a closed traverse is plotted according to the field measurement, the end point of the traverse will not coincide exactly with the starting point, owing to the errors in the field measurements of angles and distances. Such error is known as closing error

•

BALANCING THE TRAVERSE

• The following are common methods of adjusting a traverse:

a. Bowditch‟s method.

b. Transit method

c. Graphical method

d. Axis method

Bowditch‟s method

Transit Method

Following are the bearing of a traverse. Calculate latitude and departure of the lines of the traverse

The co-ordinates of two points C and D are as

follows. Find the length and bearing of C,D.

• The following are the lengths and bearings of the sides of a traverse ABCD the bearings are referred to the magnetic meridian, the value of the declination being 55⁰30' W convert the observed bearing to the true bearings, and find the error of closure.

Adjust the following traverse by Bowditch’s rule

Calculate the error of closure and adjust the following traverse by transit rule

OMITTED MEASUREMENTS

• In order to have a check on field work and in order to balance a traverse, the length and direction of each line is generally measured in the field. There are times, however, when it is not possible to take all measurements due to obstacles or because of some over sight.

The following are the lengths and bearings of the sights of a closed

traverse ABCD.