Surveying
OBJECTIVE: Study of various instruments used in chain surveying and their uses
INSTRUMENTS:
1) Chain or tape
2) Arrows
3) Ranging rods
4) Cross staff
5) Offset rods
6) Pegs
7) Plumb bob
DESCRIPTION OF INSTRUMENTS:
1 a) Chain:
The chain is composed of 100 or 150 pieces of galvanized mild steel wire, 4mm in diameter called links .The ends of each link are bent into a loop and connected together by means of three oval rings. The ends of the chain are provided with handles for dragging the chain on the ground, each wire with a swivel joint so that the chain can be turned without twisting. The length of the chain is measured from the outside of one handle to the outside of another handle.
The chain is composed of 100 or 150 pieces of galvanized mild steel wire, 4mm in diameter called links .The ends of each link are bent into a loop and connected together by means of three oval rings. The ends of the chain are provided with handles for dragging the chain on the ground, each wire with a swivel joint so that the chain can be turned without twisting. The length of the chain is measured from the outside of one handle to the outside of another handle.
Following are the various types of chain in common use:
1) Metric chains
2) Gunter` s chain or surveyors chain
3) Engineers chain
4) Revenue chain
5) Steel band or Band chain
Metric chain:
Metric chains are made in lengths 20m and 30m. Tallies are fixed at every five-meter length and brass rings are provided at every meter length except where tallies are attached
Metric Chain
b) Tapes:
The following are the various types of tapes
The following are the various types of tapes
i) Cloth tape
ii) Metallic tape
iii) Steel tape
iv) Invar tape
Among the above, metallic tapes are widely used in surveying. A metallic tape is made of varnished strip of waterproof line interwoven with small brass, copper or bronze wires. These are light in weight and flexible and are made 2m, 5m 10m, 20m, 30m, and 50m.
2. Arrows:
Arrows are made of good quality hardened steel wire of 4 mm diameter.
The arrows are made 400 mm in length, are pointed at one and the other end is bent into a loop or circle
2. Arrows:
Arrows are made of good quality hardened steel wire of 4 mm diameter.
The arrows are made 400 mm in length, are pointed at one and the other end is bent into a loop or circle
Arrows3. Ranging rods:
Ranging rods are used to range some intermediate points in the survey line The length of the ranging rod is either 2m or 3m. They are shod at bottom with a heavy iron point. Ranging rods are divided into equal parts 0.2m long and they are painted alternately black and white or red and white or red, white and black. When they are at considerable distance, red and white or white and yellow
flags about 25 cm square should be fastened at the top.
Ranging rods are used to range some intermediate points in the survey line The length of the ranging rod is either 2m or 3m. They are shod at bottom with a heavy iron point. Ranging rods are divided into equal parts 0.2m long and they are painted alternately black and white or red and white or red, white and black. When they are at considerable distance, red and white or white and yellow
flags about 25 cm square should be fastened at the top.
4. Cross staff: The simplest instrument used for setting out a right angle. The common forms of cross staff are:
Cross Staffs
5) OFFSET ROD:
The offset rod is used for measuring the off set of short lengths. It is similar to a ranging rod and is usually of 3m lengths.
The offset rod is used for measuring the off set of short lengths. It is similar to a ranging rod and is usually of 3m lengths.
6) PEGS:
These are rods made from hard timber and tapered at one end, generally 25mm or 30mm square and 150mm long wooden pegs are used to mark the position of the station on.
7) PLUMB BOB:
While chaining along sloping ground, a plumb bob is required to transfer the points to the ground.
Plumb Bob
PRACTICING UNFOLDING AND FOLDING OF A CHAIN
OBJECTIVE: To learnt the technique of unfolding and folding of a metric chain.
INSTRUMENTS: Metric chain
PROCEDURE:
UNFOLDING:
» Remove the strap of the folded chain and take both the handles in the left hand and hold the remaining portion of the chain in the right hand.
» Holding both the handles in the left hand, throw the remaining portion o f the chain in the forward direction on the ground.
» Now the follower stands at the starting station by holding one handle and directs the
leader to move forward by holding the other handle until the chain is fully stretched.
FOLDING:
» Bring the two handles together on the ground by pulling the chain at the center.
» Commencing from the center two pairs of links are taken at a time with the right hand and placed alternatively in both directions in the left hand.
» When the chain is completely folded the two brass handles will appear at the top.
» Now tie the chain with leather strap.
CHAINING A LINE BY DIRECT RANGING
OBJECTIVE: To measure the distance between two points on a level ground by ranging.
INSTRUMENTS:
| Chain 20m / 30m | 1 No | .Arrows | 10 Nos. |
| Ranging rods | 04 Nos. | Pegs | 2 Nos. |
Ranging Rod Method
PROCEDURE:
» Fix the ranging rods at the two given stations, where pegs are already driven on the ground.
» The follower stand behind station A and directs the leader, with ranging rod to come in line with AB by signals of ranging
» When the ranging rod comes in the line of AB the follower directs the leader to fix the ranging rod in position.
» Let the intermediate point be C which should be less than 20m / 30 m .
» Now the leader taken another ranging rod and stands between A and B about 2/3 distance from A
» The follower directs the leader to come in line of AB by using signals of ranging.
» As and when the point is located in the line of AB the follower instructs to fix the ranging rod in position.
» Let the other intermediate position be D which is less than 20 m / 30 m from B
» Now A, B, C and D are in one line.
» Fix the ranging rods at the two given stations, where pegs are already driven on the ground.
» The follower stand behind station A and directs the leader, with ranging rod to come in line with AB by signals of ranging
» When the ranging rod comes in the line of AB the follower directs the leader to fix the ranging rod in position.
» Let the intermediate point be C which should be less than 20m / 30 m .
» Now the leader taken another ranging rod and stands between A and B about 2/3 distance from A
» The follower directs the leader to come in line of AB by using signals of ranging.
» As and when the point is located in the line of AB the follower instructs to fix the ranging rod in position.
» Let the other intermediate position be D which is less than 20 m / 30 m from B
» Now A, B, C and D are in one line.
Now the leader and follower measure the distance by measuring along A, C, D, B.
RESULT: The distance between AB = __________ meter.
FIELD APPLICATION:
» It can be extended to measure the lengths of more than two chain lengths.
» By measuring the boundaries of given traverse the areas can be calculated.
» The features can be located either by measuring oblique or perpendicular offset from the chain line.
CHAINING A LINE BY INDIRECT RANGING
OBJECTIVE: Chaining a line when a hill or high ground intervenes preventing Intervisibility of ends of line.
| Chain 20m / 30m | 1 No | .Arrows | 10 Nos. |
| Ranging rods | 04 Nos. | ||
Indirect Ranging Rod Method
PROCEDURE:
» Fix the two ranging rods at the given stations A and B which are not intervisible due to raising ground.
» Select two intermediate points M1 and N1 such that from each point both A and B are visible.
» The person at M1 directs the person at N1 to move to a new position N2 in line with M1B.
» The person at N2 then directs the person at M1 to move to a new position M2 in line with N2A.
» The person at M2 directs the person at N2 to a new position N3 in line with M2B.
» The person at N3 directs the person at M2 to a new position M3 in line with N3A.
» The process is repeated till the points M and N are located in such a way that M finds the person at N in line with AB and the person at N finds the person at M in line with AB.
» After fixing the points M and N, other points are also fixed by direct ranging and the length of the line is measured.
» Fix the two ranging rods at the given stations A and B which are not intervisible due to raising ground.
» Select two intermediate points M1 and N1 such that from each point both A and B are visible.
» The person at M1 directs the person at N1 to move to a new position N2 in line with M1B.
» The person at N2 then directs the person at M1 to move to a new position M2 in line with N2A.
» The person at M2 directs the person at N2 to a new position N3 in line with M2B.
» The person at N3 directs the person at M2 to a new position M3 in line with N3A.
» The process is repeated till the points M and N are located in such a way that M finds the person at N in line with AB and the person at N finds the person at M in line with AB.
» After fixing the points M and N, other points are also fixed by direct ranging and the length of the line is measured.
Result:
Length of AM = ____ meter.
Length of MN = ____ meter.
Length of NB = ____ meter.
Therefore distance of AB = distance AM + distance MN + distance NB
MEASUREMENT OF AREA BY CHAIN TRIANGULATION
OBJECTIVE: To measure the area of the given field by chain triangulation..
| Chain 20m / 30m | 1 No | .Arrows | 10 Nos. |
| Ranging rods | 06 Nos. | Pegs | 5 Nos. |
Chain Triangulation Method
PROCEDURE:
» Let ABCDE be the given field whose area is to be measured, fix the pegs at A, B, C, D & E.
» Divide area into three triangles ADE, ABD and BCD by joining AD and BD.
» Measure the lengths AB, BC , CD, DE, EA, AD and BD.
» Calculate the area of the triangles.
» The sum of the areas of the three triangles is the area of the given field.
» Let ABCDE be the given field whose area is to be measured, fix the pegs at A, B, C, D & E.
» Divide area into three triangles ADE, ABD and BCD by joining AD and BD.
» Measure the lengths AB, BC , CD, DE, EA, AD and BD.
» Calculate the area of the triangles.
» The sum of the areas of the three triangles is the area of the given field.
RESULT:
The area of the given field = _______ Square meter.
The area of the given field = _______ Square meter.
CHAIN TRIANGULATION AROUND A BUILDING
OBJECTIVE: To chain around the building to cover small area by chain triangulation
INSTRUMENTS:
| Chain 20m / 30m | 1 No | .Arrows | 10 Nos. |
| Ranging rods | 4 Nos. | Pegs | 4Nos. |
| Tape 20m / 30m | 1 No | Cross staff | 1No |
Chain Triangulation Around a Building
PROCEDURE:
» Select three survey stations A, B and C such that from each survey station the other two stations are visible..
» Fix the ranging rods at A, B and C
» Fix the intermediate stations along the chain line AB, BC and CA by ranging.
» Measure the offsets of the corners of the building either perpendicular or oblique.
» Each point requires two measurements from two definite reference points on the same line or from two adjacent chain lines.
» Measure the points which are very far away from the main chain lines from tie line i.e , the corners points of building R and S. Measure the check line CD.
» Select three survey stations A, B and C such that from each survey station the other two stations are visible..
» Fix the ranging rods at A, B and C
» Fix the intermediate stations along the chain line AB, BC and CA by ranging.
» Measure the offsets of the corners of the building either perpendicular or oblique.
» Each point requires two measurements from two definite reference points on the same line or from two adjacent chain lines.
» Measure the points which are very far away from the main chain lines from tie line i.e , the corners points of building R and S. Measure the check line CD.
RESULT: From the recorded measurements of the building area is plotted.
NOTE: The student should prepare a layout of the given area covering building roads etc.
COMPASS SURVEYING
- Familiarity with instruments used in compass surveying – prismatic compass.
- Setting up the compass – observation of bearings.
- Traversing with prismatic compass and chain calculation of included angles and check.
- Traversing with prismatic compass and chain closed traverse covering the given area
recording. - Traversing with prismatic compass and chain open traverse and recording.
FAMILIARITY WITH INSTRUMENTS USED IN COMPASS SURVEYING PRISMATIC COMPASS
OBJECTIVE: To identify different parts of prismatic compass and to know their functionsSKETCH:
Prismatic Compass
Parts List
| 1. Compass Box | 2. Magnetic Needle | 3. Graduated Ring |
| 4. Pivot | 5. Objective Vane | 6. Eye Vane |
| 7. Adjustable Mirror | 8. Spring Brake | 9. Brake Pin |
| 10. Lifting Lever | 11. Lifting Pin | 12. Prism |
| 13. Focusing Stud | 14. Glass Cover | 15. Prism Dust Cap |
| 16. Sun Glasses |
COMPASS BOX: It is a circular box of diameter 85 to 110 mm having pivot at the center and covered with plain glass at top.
MAGNETIC NEEDLE: It facilitates in taking the bearings of survey lines with reference to the magnetic north.
GRADUATED RING: The bearings are marked inverted on the graduated rings from 0° to 360° in a clockwise starting 0° from south.
PIVOT: Magnet is freely held with this.
OBJECT VANE: It consists of prism with a sighting slit at the top. The prism magnifies and erects the inverted graduations.
BRAKE PIN: It is pressed to stop the oscillations of the graduated ring.
LIFTING PIN: On pressing it brings the lifting lever into action.
COLOUR GLASSES: Red and blue glasses are provided with the prism to sight luminous objects.
SETTING UP THE COMPASS – OBSERVATION OF BEARINGS
OBJECTIVE : To perform station adjustments and to observe magnetic bearings using a prismatic compass.INSTRUMENTS: Prismatic compass, tripod and ranging rods.
SKETCH:
Tripod and Ranging Rod Method
The following station adjustments are to be done at each station where the compass is set up.
1. CENTERING:
a. Centering is the process of keeping the prismatic compass over the station point.
b. By moving the legs of the tripod suitably, centering will be done.
c. Centering is checked by dropping a stone so that it falls on the top of the peg.
2. LEVELLING:
a. Leveling is the process of making the compass exactly horizontal.
b. Level the compass by means of ball and socket arrangements.
c. When the compass is leveled, the aluminum ring swings freely.
3. FOCUSSING:
To adjust the height of the prism so that the observations can be read clearly.
4. OBSERVING BEARINGS:
a. Set up the prismatic compass over station ‘O’ and perform station adjustments.
b. Rotate the compass till the line of sight bisects the object at ‘A’.
c. Read the graduated ring through prism. The reading directly gives the magnetic bearing of ‘OA’ in whole circle bearing system.
d. Follow the same procedure to observe the magnetic bearings ‘OB’ ‘OC’ also.
TRAVERSING WITH PRISMATIC COMPASS AND CHAIN – CALCULATION OF INCLUDED ANGLES
OBJECTIVE: To find the bearings of various station points and to calculate the included angles.
INSTRUMENTS: Prismatic compass, Tripod, Ranging rods, etc.
SKETCH:
» Let ‘O’ be the instrument station selected from which all other points are visible.
» Complete all station adjustments like setting, centering and leveling accurately.
» Sight the object ‘A’ looking through the prism vane, while the object vane is directed towards the object.
» Observe the bearing by looking through the prism. Enter the readings in the tabular form.
» Repeat the process at all objects stations B,C,D etc and enter the readings.
FORMULA:
Included angle: bearing of 2nd line bearing of first line. (If the value is more than 180º than subtract the value from 360º ).
TABULAR FORM
Sl.No. | Station | Sighted to | W.C.B |
TRAVERSING WITH PRISMATIC COMPASS AND CHAIN – CLOSED
TRAVERSE COVERING THE AREA (Given) RECORDING
OBJECTIVE : To conduct compass survey along the closed traverse.TRAVERSE COVERING THE AREA (Given) RECORDING
INSTRUMENTS: Prismatic compass, chain, ranging rods.
SKETCH:
Closed Traverse Method
PROCEDURE:» Fix the closed traverse A B C D E .
» Set up the compass at the station ‘A’.
» Perform the temporary adjustments.
» Sight the object at ‘B’ and note down the FB of line AB and measure the distance.
» Sight the object at E and note down the BB of EA.
» Sight the instrument to station ‘B’ performs all the temporary adjustments.
» Sight the object at ‘A’ and take the ‘BB’ of ‘AB’.
» Take ‘FB’ of ‘BC’ and measure the length of ‘BC’.
» Check whether the difference of ‘FB’ and ‘BB’ is 180º or not, at all stations.
» Continue the same process all at other stations.
FORMULA: Included angle = B.B of previous line – F.B of next line.
CHECK: The sum of the included angles should be equals to (2n-4) x 90º
Where ‘n’ is number of sides of the traverse.
TRAVERSING WITH PRISMATIC COMPASS
AND CHAIN – OPEN TRANRSE AND RECORDING
AND CHAIN – OPEN TRANRSE AND RECORDING
OBJECTIVE: To perform the compass survey in open traverse formed by series of connected straight lines.
INSTRUMENTS: Prismatic compass, tripod, tape, chain, arrows and ranging rods.
SKETCH:
PROCUDURE:
» Set the instrument at the starting station ‘A’ and perform all the necessary adjustments.
» Sight the next station ‘B’, take fore bearing of ‘AB’ and measure the distance ‘AB’.
» Take F.B of ‘AE which provides check; similarly bearing of any line AC, CE, … etc. also provides the check.
» Shift the instrument to subsequent station ‘B’. After fixing the instrument sight the previous station ‘A’ and observe the reading, which gives the B.B. of AB.
» Sight next station ‘C’ observe F.B of BC and measure the distance BC.
» Locate the details surrounding the traverse station if necessary, by taking bearings or lengths or both from chains line.
» Repeat the process at every station.
» Set the instrument at the starting station ‘A’ and perform all the necessary adjustments.
» Sight the next station ‘B’, take fore bearing of ‘AB’ and measure the distance ‘AB’.
» Take F.B of ‘AE which provides check; similarly bearing of any line AC, CE, … etc. also provides the check.
» Shift the instrument to subsequent station ‘B’. After fixing the instrument sight the previous station ‘A’ and observe the reading, which gives the B.B. of AB.
» Sight next station ‘C’ observe F.B of BC and measure the distance BC.
» Locate the details surrounding the traverse station if necessary, by taking bearings or lengths or both from chains line.
» Repeat the process at every station.
» It is to be noted that first and last stations have only fore bearing and back bearings respectively.
» Take Back bearings of the first point from the last point.
» Take Back bearings of the first point from the last point.
CHECK: The difference between Fore bearing and back bearing of each line should be 180º, if no local attraction exists at either station.
SIR GEORGE EVEREST AND SURVEY OF INDIA
The highest mountain in the world is named for a surveyor, Colonel Sir George Everest. It is a fitting tribute to the man who, for more than twenty-five years and despite numerous hardships, prevailed in surveying the longest are-of-the-meridian ever accomplished at the time. The Great Trigonometrical Survey India, begun at Cape Comorin in 1806 by William Lambton, would then run almost 2,400 kilometers north to the Himalayas, extending over 20 along the meridian. During this tremendous undertaking, Everest was relentless in his pursuit of accuracy. To that end, he made countless adaptations to the surveying equipment, methods, and mathematics in order to minimize problems specific to the Great Survey: immense size and scope, the terrain, weather conditions, and the desired accuracy.When Everest "inherited" the position in 1823, the equipment originally employed by Lambton consisted of one 36" theodolite manufactured by London instrument maker Cary, a zenith sector by Jesse Ramsden, a Ramsden 100 foot steel chain, and a chronometer. The Cary theodolite, weighing over one thousand pounds, had been damaged in two separate mishaps, and was badly in need of repair. The micrometer screw on the zenith sector was worn out, and the steel chain had not been calibrated in twenty-five years. To further complicate matters, Everest became so dangerously ill that he could not carry on with the Survey, and work was suspended.
England was the solution to these problems. In November of 1825, Everest returned to England, bringing with him the mathematical observations and calculations for the Great Arc thus far. For the next five years he worked on improvements for the survey and compiled an account of the work achieved between the parallels of 18 degrees 03' and 24 degrees 07'. Everest spent a great deal of time in the workshop of instrument-makers Troughton and Simms, where an additional 36" theodolite, a new zenith sector, and six small theodolites were under construction. Of the last, Everest wrote: "I have devoted some consideration to the improvement of the common theodolite which is both cumbersome and more expensive than need be and after frequent examination of all the best devices I could meet with in the shape of the various makers in London, Mr. Simms has at my suggestion designed an instrument which contains all the useful parts of the old construction, is quite free from superfluous apparatus and is cheaper by one-fourth...The model has only a 5 inch diameter but the principle is so perfectly applicable to all instruments for secondary triangles that I should respectfully recommend the propriety of adopting this as the Honorable East India Company's form for all small theodolites not exceeding 12 inches diameter and preserving on all future occasions the strictest uniformity."
The next issue Everest addressed was the measuring of distances. He learned of Col. Colby's work with compensating bars on the Irish Survey, and visited him there in 1829. Being very much impressed with Colby's system, he acquired a double set of six bars for the Great Trigonometrical Survey, and practiced with them at Greenwich.
At the same time, Everest produced a clever document which summarized the repair and replacement needs of the Survey, showing that the most cost-effective solution was to have an instrument maker placed in India. His request was granted, and Henry Barrow was appointed to the job. Later, in India, it was Barrow who laboriously repaired the damaged Cary theodolite, earning his praise from Everest: "I must do that artist (Barrow) the justice to say that for excellence of workmanship, accuracy of division, steadiness, regularity, and glibness of motion, and the general neatness, elegance and nice fitting of all its parts, not only were my expectations exceeded but I really think it is as a whole as unrivalled in the world as it is unique."
In June of 1830, George Everest returned to India, this time as Surveyor General, in addition to his post as superintendent of the Great Trigonometrical Survey. During the first year he spent little time on field work, as he organized general mapping surveys. Everest's first work on the Arc was to create a baseline near Dehra Dun using the Colby compensating bars. The 39,183.783 foot baseline was meticulously surveyed, using every precaution to safeguard its accuracy. He then connected the Dehra Dun baseline to the Sironj baseline, a distance of over 400 miles, using a triangulation gridiron. This was across a vast plain, which necessitated the construction of masonry towers, designed by Everest, most of them 50 feet high. The great theodolite was then hoisted to the top, and Everest performed and recorded the observations. By day, heliotropes were placed on distant points, reflecting bright flashes of sunlight towards the survey towers. On days when refraction became a problem, observations were taken at night, using an Indian version of the reverberatory lamp which could be seen for thirty miles, and sometimes by using cylindrical blue lights whose visible range could exceed fifty miles. Transportation was interesting; a typical foray included 4 elephants for the tiger-wary principals, 30 horses for the military officers, and 42 camels for supplies and equipment. The 700 or so laborers traveled on foot. Progress was steady; by May of 1836 half of the gap between Sironj and Dehra Dun had been completed, and the rest was completed the following season.
Everest next turned his attention to astronomical observations throughout the arc of meridian, especially at Kalianpur (24 degrees 07'). Unfortunately, ill health prevented him from completing this task, so it was Andrew Waugh who stepped in to finish the job, including re-measuring the Bidar baseline with the Colby compensating bars. The subsequent error of closure between the observed and computed length of the Bidar base, after 425 miles and 85 triangles from Sironj, was 0.36 feet in a line length of 41,578 feet.
By 1841, twenty-three years had passed from the time Everest had first begun work on the Great Arc. It would take him two more years to complete the computations, and compile the results before he retired and returned to England.
In 1848, he was awarded high honors by the Royal Astronomical Society. In making the presentation, Sir John Herschel said: 'The Great Meridianal Arc of India is a trophy of which any nation, or any government of the world would have reason to be proud, and will be one of the most enduring monuments of their power and enlightened regard for the progress of human knowledge."
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