Slide 1

Measuring Wheels

Tape and Chain

Electronic Distance Measurement (EDM) SystemsEDMs are very useful in measuring distances that are difficult to access or long distancesChain SurveyingChain surveying the simplest method of surveying in which only linear measurements are made and no angular measurements are taken.

The area to be surveyed is divided into a number of triangles and the sides of the triangles are directly measured in the field.

Since the triangle is a simple plane geometrical figure, it can be plotted from the measured length of its sides alone.

In chain surveying, a NETWORK of TRIANGLES is preferred.Preferably all the sides of a triangle should be nearly equal having each angle nearly 60o to ensure minimum distortion due to errors in measurement of sides and plotting.Generally such an ideal condition is not practical always.Usually attempt should be made to have WELL CONDITIONED TRIANGLES in which no angle is smaller than 30 o and no angle is greater than 120o.

Chain SurveyingThe arrangement of triangles to be adopted in the field depends on the shape, topography and the natural or artificial OBSTACLES met with.Chain surveying is suitable for the following cases:Ground fairly level and open with simple detailsLarge scale plans (1 cm = 10 m)Extent of the area comparatively small

Chain surveying is unsuitable for the following cases:Area crowded with many detailsWooded countriesUndulating areasExtent of large areaDefinitions:Main survey stationsIs a point where TWO SIDES OF A TRIANGLE MEET. THESE ARE THE POINTS AT THE BEGINNING AND AT THE END OF THE CHAIN LINE.Tie stations (or) subsidiary stations:These are the points selected on the main survey lines for running auxiliary lines.Main survey lines: These are chain lines joining the main survey stationsTie or subsidiary linesThe chain lines joining the tie stations or subsidiary stations are called as tie or subsidiary lines.These lines help in locating the interior details which are far away from the main survey lines.Chain SurveyingDefinitions:Base Line the longest of the main survey line various survey stations are plotted w.r.t. this line. Check Lines:Those lines which are run to check the accuracy of the field work are called as check lines or proof lines.The length of the check line in the plan must agree with its measured length in the field. each triangle must be provided with a check line.Offsets: Offsets are lateral distances measured from survey linesOffsets are taken from survey lines to determine the locations of details.Perpendicular offsets are called as simply OFFSETSOblique offsets are called as oblique offsets.Chain Surveying

Tape and ChainChain SurveyingChain SurveyingMetric surveying chains:Length of chain: 20 m or 30 mNumber of links per meter length : 5Length of each link : 20 cmTallies are provided at every 5 mSmall brass rings are provided at every meter except where tallies are provided.Metallic tape:Length of tape: 20 m or 30 mThe linen tape is reinforced with fine brass or copper wires to prevent stretching or twisting of fibres and is then called as a metallic tape.Chain SurveyingArrows:These are also called as marking or chaining pins10 arrows are provided along with each chain.Used to mark end of the chain during the process of chaining.

Cross Staff: - used to make perpendicular linesBasic TrignometryabcABCA2 + B2 = C2a+ b+ c = 180o