GROUP MEMBERS

UMER FAROOQ 26/FET/BSCE/F-14

MUHAMMAD MOHSIN 27/FET/BSCE/F-14 ASAD ULLAH KHAN 29/FET/BSCE/F-14

IMTIAZ ASHRAF 30/FET/BSCE/F-14

•Methods Of Contouring:

CONTOURING

Direct Method: In-Direct Method:

Direct Method:In the direct method, the contour to be plotted is actually traced on the ground. Points which happen to fall on a desired contour are only surveyed, plotted and finally joined to obtain the particular contour. This method is slow and tedious and thus used for large scale maps, small contour interval and at high degree of precision.

Random Method:

Radial Method:

Direct method of contouring is employed using Level, Tripod Stand, Staff Rod, Plane Table, Plaster of Paris and Measuring tape.

There are two types of Direct Method, as follow;

Random Method: In this method, a benchmark is required in the project area. The level and Plane Table is set up on any commanding position and back sight is taken on the bench mark.

Let the back sight(BS) reading on the bench mark be 5 feet. If the reduced level of the bench mark(BM) is 100 feet, the height of instrument(HI) would be 100 + 5 = 105 feet.

Formula → HI = BM + BS

The horizontal distance between any two consecutive contours is known as the Horizontal Equivalent.

For a given contour interval, the horizontal equivalent depends upon the steepness of the ground.

HORIZONTAL EQUIVALENT IS SMALLER

Because ofSTEEP SLOPE

HORIZONTAL EQUIVALENT IS GREATER

Because ofGRADUAL SLOPE

Horizontal equivalent

Horizontal equivalent

STEEP SLOPE GRADUAL SLOPE

The vertical distance between contour lines is called the contour intervalDepending on the accuracy required, they may be plotted at 0.1-m to 0.5-m intervals in flat terrain and 1-m to 10-m intervals in undulating terrain. The interval chosen depends on:(1) The type of project involved; for instance, contouring an airstrip requires an extremely small contour interval.(2) The type of terrain, flat or undulating(3) The cost, for the smaller the interval the greater the amount of field data required, resulting in greater expense.

Contour

Interval

From the known elevations of the contours and the HI, the required staff readings to fix positions on the various contours lines(contour points) are obtained by subtracting the elevation of each of the contours from the HI.

New Elevation = H.I – Staff Reading(F.S)Suppose the . To locate the points on the 104’, 103’, and 102’ contours, the staff readings will be respectively as contour interval is taken 1’.

B.M=100’, B.S=5’, and H.I = 105’1’, 2’ and 3’

104’

104’

104’

103’

103’

103’

102’

102’

• The staff is held on an estimated position of a point.• It is then moved up or down the slope until the desired reading is obtained.• The point so determined is marked by means of a white and their position is determined by measuring the distance from plane table using MEASURING TAPE.

15m

30m

45m

104’

103’102’

104’103’

1’ 2’ 3’

102’

Can we draw a contour of 106’ , if H.I=105’ ?QUESTION

ANSWER:If H.I=105’ it means that 105 is the maximum reading we can take according to this H.I.To measure 105’ elevation point according to H.I=105’ the staff reading (F.S) will be ZERO.

B.S=5’ H.I=105’

R.L=105’F.S = 0’

H.I=105’

R.L=106’

So we can't measure 106’ elevation point according to H.I=105’.

To draw a contour of 106’ we must have to change the H.I upto106’ or more than 106’.

B.S=6’ H.I=106’

From this height of instrument we can draw a contour of 106’

Several points are thus determined and marked on each contour.

Then the points having same elevation are joined by contour line.

Contour LineOr

Contour

Points having same elevation

Radial Method:In this method the contours to be plotted are actually located on the ground with a level by marking various points on the RAIDIAL LINES ( radiating from one common point, their positions are relative with each other by measuring ANGLES between them ). In this method, first of all radial lines are drawn (by theodolite or compass radiating and their positions are fixed up by horizontal angles and bearings) from one common point at an angle (Ѳ) in the project area.

RAIDIAL LINE

Angle between two RAIDIAL LINES

In this method a Temporary bench mark is first established in the projected area.The level and Plane Table is set up on any commanding position and back sight is taken on the bench mark.Let the back sight(BS) reading on the bench mark be 5 feet. If the reduced level of the bench mark(BM) is 100 feet, the height of instrument(HI) would be 100 + 5 = 105 feet.

Formula → HI = BM + BS

From the known elevations of the contours and the HI, the required staff readings to fix positions on the Radial Lines are obtained by subtracting the elevation of each of the contours from the HI.

New Elevation = H.I – Staff Reading(F.S)Suppose the . To locate the points on the 104’, 103’, and 102’ contours, the staff readings will be respectively as contour interval is taken 1’.

B.M=100’, B.S=5’, and H.I = 105’1’, 2’ and 3’

104’103’102’

• The staff is held on an estimated position of a point.• It is then moved up or down the slope (along the RADIAL LINE) until the desired reading is obtained.• The point so determined is marked by means of a white and their position is determined by measuring the distance from plane table using MEASURING TAPE.

104’

103’

102’

104’ 103’ 102’

Plane table Auto Level

10m

20m30m

F.S=1’ F.S=2’ F.S=3’

104’103’102’

Several points are thus determined and marked on each contour.Then the points having same elevation are joined by contour line.

104’ 103’ 102’104’103’102’

104’

103’102’