Definition of Chain Surveying :—
A Chain survey, in which only linear measurements . generally, it is suitable for all kinds of small size, and very straight ,extent as well for the area which is fairly flat. This chain survey used for triangle types.
Definition of compass Surveying :—
The use of this type of surveying where the area to be measured large, as well as the time in which they were rolling . this is based review of the method is that of a series of lines that are connected to each other.
Different between chain & compass survey : —
chain survey : —
i) Chain surveying is recommended when a small area is to be surveyed and well conditioned triangles is easy.
ii) The principle of chain surveying is triangulation
iii) No angular measurement is involved
iv) The running of check liens is necessary.
v) It is simple kind of surveying.
Instruments used in Chain Surveying :—
(i) Metric chain (20m or 30 m) (ii) Arrows (10 nos)
(iii) Metallic tape (15 m)
(iv) Ranging Rods (3.nos)
(v) Clinometers (1 no)
(vi) Offset rod (1 no)
(vii) Optical square or cross shaft (1 no)
(viii) Prismatic compass with stand (1 no)
(ix) Plum bob (1 no) i bibi
(x) Mallet (1 no) an isostomo
(xi) Field book.(1 no)
Sources of Errors in Chain Surveying : —
(i) Incorrect holding of the chain.
(ii) Errors in measurement of right angles with chain.
(iii) The length of chain being shorter than the standard length.
(iv) Sag in the chain
(v.) Elongation of the links due to heavy pull
(vi). The temperature during measurement being much higher than the standard
temperature.
(vii) Variable tension in the chain
(viii) Chain getting out of line due to wrong ranging.
(ix) While making entries in- the field book, figure may be interchanged due to carelessness.
compass survey : —
i) Compass surveying is recommended when a large area is to be surveyed and triangulation is not possible.
ii) The principle of compass surveying is traversing
iii) The direction of survey liens are fixed by angular measurements.
iv) The running of check lines is not necessary.
v) Angular measurement is involved, so it is not as simple as chain surveying.
Instruments for Measurements of Distance :—
Engineers, Gunter's & metric chain Ranging Types: —
What is the Ranging :—
All the process of the formation of an intermediate point on a straight line between the two end points, it is well-known as a social institution. There are two ways to do this, ranging from the.
(i) Direct Ranging .
(ii) indirect Ranging.
(i) What is Direct Ranging : –
i) When intermediate ranging rod are fixed on a straight line by direct observation.
ii) Direct ranging is possible when the end stations are inter-visible.
iii) No correction is needed in measuring the length.
(ii)What is indirect Ranging —
i) Intermediate ranging rod are fixed on the on line in any indirect way.
ii). Indirect ranging is adopted when the end stations are not intervisible.
iii) Slope correction is necessary to measure the correct length.
Define base line, check line, tie line, offset.
Base line: —
Base line is defined as a line on which the framework of the survey is built. Generally, the longest of the main survey line is taken as base line.
Check line: —
The line joining the apex point of a triangle to some fixed point on its base is known as check line. It is taken to check the accuracy of the triangle and sometimes helps to locate interior details.
Tie line: —
Line joining the lie stations are known as lie lines. Tie lines are mainly taken to fix the direction of adjacent sides of the chain survey map and sometimes helps to locate interior details.
Offset: —
The lateral measurement taken from an object to the chain line is known as offset. Offset are taken to locate object with reference to the chain line.
Types: — offset are two types.
perpendicular offset.
When the lateral measurement are taken perpendicular to the chain line, they are known as perpendicular offset.
Oblique offset:
Any off set not perpendicular to the chain line is known as oblique offset. Oblique offsets are taken when the objects are at a long distance from
chain line or when it is not possible to set up a right angle due to some difficulties.
What do you understand by field book. —:
a) The notebook in which field measurements are noted is known as the field book. The size of the field book is 20cm x 20cm and it is opens lengthwise.
Type :—
i) Single line
ii) Double line
Process of data entered into the field book.
b) Ranging and chaining is started from the base line, which should be measured carefully. The magnetic bearings of the base line are measured by prismatic compass. These measurements are noted in the field book showing the offsets to the left or right according to their position. Then the other survey lines are ranged and chained maintaining the sequence of the traverse.
The offsets check lines, tie lines and other field records are noted simultaneously.
Procedure of field wIDK in chain surveying
Procedure of field work in chain surveying: —
The field measurements, sketches ad relevant notes are recording for future reference in a note book is known as field book. The field book use in a note book is about 20X12 cm and open length wise. There are two kinds of field book: –
i) Single line field Book
ii) Double line field book.
i) Booking is commenced at the bottom of the page and worked upwards and carried continuously through the successive pages so that while writing, the centre line of book and the chain on the ground correspond with the surveyor's own direction.
ii) The number or name of the station from where the line starts are written at the commencement of each line.
iii) Alldistances along the chain line are entered in the central column.
iv) The objects offsetted are sketched with conventional signs towards right or left of the chain line on the ground.
v) Offset measurements are written close to the points offsetted and exactly opposite to and in line with the chainages from which they are taken.
vi) Sufficient space is allowed between rows of booking along or across the page to avoid conjestion.
vii) When any features such as road, fence, hedge or a wall etc crosses the chain line , chainage of the point of intersection in the central column and direction of the feature sketched.
viii) A symbol A is used to denote a main station in the field book. The zero chainage at the commencement and closing chainage at the end of a line are written inside the symbol. The name of the station is written close to the symbol.
ix) At the commencementof the tie or check line in the field book, the position of the tie station is described tie station. Similar it is described at the finish of the line.
Correction of tape chain surveying formula :—
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