AEG 101 Theory Class 4-29062023-Rangig.pptx

Agriculture Engineering

1. 1 RANGING – DEFINITION OF RANGING, KINDS OF RANGING, RANGING BY LINE RANGER, DEGREE OF ACCURACY IN CHAINING , ERROR IN CHAINING – ERRORS IN LENGTH AND AREA. EXAMPLES ON ERROR IN CHAINING.

2. 2 Ranging Ranging is the process of establishing intermediate point on a straight line between two end points. Ranging must be done before a survey line is chained. It may be necessary to establish a number of intermediate points prior to chaining when chain line is much longer.

3. 25 November 08 Unit 2 :Chain Surveying 2.3 Ranging When the length of survey line is greater than chain or tape length Process of establishing intermediate points Methods Direct Ranging Indirect Ranging A B > one tape length Intermediate points

4. 4 Ranging may be done by direct observation by the naked eye or by line ranger or by Theodolite . Generally, ranging is done by naked eye with the help of three ranging rods. Ranging is of two kinds 1 . Direct Ranging 2. Indirect or reciprocal ranging

5. 5 1. Direct Ranging When intermediate ranging rods are fixed on a straight line, by direct observation from end stations, the process is known as direct ranging. Direct ranging is possible when the end stations are intervisible. Assume that A and B two end stations of chain line, where two ranging rods are already fixed.

6. 25 November 08 Unit 2 :Chain Surveying 2.3 Direct ranging Direct ranging When two end points are intervisible Either by eye or through optical instruments such as Line ranger Theodolite Code of signals used to direct assistant A P B Transverse movement < one tape length

7. 7 Suppose it is required to fix a ranging rod at the intermediate point C on the chain line in such a way that the points A, C &B are in same straight line. The surveyor stands about two meters behind the ranging rod at A by looking towards line AB. The assistant holds ranging rod at C vertically at arms length the rod should be held tightly by the thumb and forefinger.

8. 8 Now the surveyor direct the assistant to move the ranging rod to the left or right until the three ranging rods come exactly the same straight line. The ranging will be perfect, when the three ranging rods coincide and appear as a single rod. When the surveyor is satisfied that the ranging is prefect, he signals the assistant to fix the ranging rod on the ground. By following the same procedure, the other ranging rods may be fixed on the line.

9. 9 2 . Indirect or Reciprocal Ranging Indirect ranging is used when the end stations are not intervisible due to high ground or a hill or if the ends are too long. In such cases, intermediate points can be fixed on the survey line by a process known as reciprocal ranging. Let A & B be the two stations with rising ground or a hill.

10. 10 Let two chainmen with ranging rods take up positions at b and c , such that, chainmen at b can see both rods at c , and B and the chainmen at c , can see the ranging rods at b and A. The chainmen at c directs the chainmen at b t o shift the ranging rod in line with A and then chainman at b directs the chainmen at c to shift the ranging rod in line with B, by successively directing each other to be in line with the end points .

11. 11 Their positions will be changed until finally they are both in line with A & B exactly on line AB. Now the four ranging rods at A b c & B are on same straight line. This method may also be used in ranging a line across a valley or river.

12. 25 November 08 Unit 2 :Chain Surveying 2.3 Indirect ranging Indirect ranging When two end points are not intervisible With the aid of two intermediate points very near to the line A B N M B A M N N 3 N 2 M 2 N 1 M 3 M 1

13. Ranging by line ranger 13 Ranging by Line Ranger is the type of direct ranging  method in which the intermediate points are fixed directly utilizing an instrument known as line ranger. Line Ranger is a light weight instrument consisting of two right-angled isosceles prisms (plane mirrors) placed one above the other and one sight vane such that the surveyor can see the image formed on the prism.

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15. 15 The upper prism is movable and can be adjusted while the lower prism is fixed. Diagonals of the prism are silver coated such that they reflect incident ray. This instrument can be used to locate the intermediate points without going to the other end of the survey line. This method requires only one person to hold the line ranger. 

16. 16 Chaining Measuring distance with chain is called chaining In all chaining operations two men, called chainmen, are required. The chainman at the forward end of the chain is called the leader or head chainman, while the chainman at the rear end the chain is known as the follower or rear chainman.

17. 17 The duties of the leader are ( i ) To drag the chain forward. (ii) To insert arrows at the end of every chain . (iii) To obey instructions of the follower.

18. 18 The duties of the follower are ( i ) To place the leader in line with the ranging rod or pole at the forward station. (ii) To call out instructions to the leader. (iii) Always to carry the rear handle in his hand and not to allow it to drag on the ground. (iv) To pick up the arrows inserted by the leader.

19. 19 The chainman who is more intelligent and experienced be selected as the follower, as upon his care and judgment depends the accuracy of measurements. If the slope of the ground is upto 3°, it is generally taken as level ground.

20. 20 Unfolding the Chain To lay out the chain on the ground, remove the leather strap, take both the handles in the left hand and throw the chain well forward with the right hand. The leader, taking one handle of the chain may then be examined to see if there are any kinks or bent links. This operation is also called unfolding the chain

21. 21 Testing of a chain It is always necessary to check the length of chain before commencing each days work and at frequent intervals, otherwise the measurement will become unreliable. Before testing the chain, the surveyor should see that the links and rings are free from mud that there are no bent links.

22. 22 The chain is tested by comparing it with ( i ) the chain standard (standard chain length) (ii) with the steel tape kept in the surveyors office for this sole purpose. If these are not available, a test gauge may be established by driving two pegs in the required distance apart (20 m or 30m) and inserting nails in their tops to mark exact distance.

23. 23 It is advisable to have a permanent test gauge established in close proximity to the surveyors office. During the first use, the links become bent and consequently the chain is shortened. It is also shortened by mud clogging the links when working over muddy ground. On the other hand, it gets elongated due to wear of many wearing surfaces, stretching of the links and joints, and opening out of the small rings and rough handling in pulling it through hedges and fences.

24. 24 Adjusting the chain If the chain is found to be too long, it may be adjusted by i ) Closing up the joints of the connecting rings (that may be opened out) ii) Hammering back to the shape of the elongated rings iii) Replacing some of the worn out rings with new ones iv) Removing one or more of the small rings

25. 25 If the chain is found to be too short, it may be adjusted by Straightening any bent links Flattening some of the small connecting rings Replacing some of the worn out rings with new ones Replacing a few of the rings by those of the larger size v) Inserting new rings as required

26. 26 Errors in chaining The errors that occur in chaining are classified as i .) compensating and ii) cumulative. These errors may be due to variation in temperature, defects in construction and personal defects in vision

27. 27 Compensating errors These are those which are liable to occur in either direction and hence tend to compensate i.e. they are not likely to make the apparent result too large or too small. Compensating errors are caused due to incorrect holding of the chain, fractional part of the chain may not be correct and during stepping operation, crude method of plumbing is adopted.

28. 28 Cumulative errors These are those which occur in the same direction and tend to add up or accumulate i . e., either to make the apparent measuremental ways too long or too short. ( i ) Positive errors - These errors makes the measured length more than actual length. (ii) Negative errors - making the measured length less than the actual.

29. 29 Errors in measurement due to incorrect length of chain. The length of a chain may be correct at the beginning, but it may change with time as more and more used. Due to continuous use of the chain over rough ground, the oval shaped rings get elongated and thus the length of the chain increases.

30. 30 On the other hand some of the links may get bent As a result the chain length reduces. In a very old chain, some ring or links may be missing. Therefore, before the start of the work the correctness of the chain length should be tested with a steel or invar tape.

31. 31 If the chain is too long, measured distance will be less and if the chain is short, the measured distance will be more than the actual distance. Measurements taken with a chain which is longer or shorter than standard length can be corrected by calculation using the formula.

32. 32 L 1 L+ e Correct distance = --------- X Observed distance = --------- X Observed distance L L Where, e = error L 1 = Incorrect length of chain/tape L = Standard length L+ e = The chain is too long (longer than standard length L) L – e = The chain is too short ( shorter than standard length L)

33. 33 Example 1 The length of a line was found to be 180 m when measured with a 20 m chain. If the chain was 7 cm too long, find the correct length of the line. Answer L= 20 m L 1 = 20 + 0.07 = 20.07 m Correct length of line = (20.07 / 20) x 180 = 180.63 m Computation of area and volume using incorrect chain length True or correct area = L 1 / L ] 2 x measured area True or correct Volume = [L 1 / L ] 3 x measured volume

34. Questions

35. Thank You