Leveling :- is the process used to determine a differencein elevation between two points. A Level is an instrument with a telescope that can beleveled with a spirit bubble. The optical line of sightforms a horizontal plane, which is at the same elevationas the telescope crosshair. By reading a graduated rodheld vertically on a point of known elevation (BenchMark) a difference in elevation can be measured and aheight of instrument (H.I.) calculated by adding therod reading to the elevation of the bench mark. Oncethe height of instrument is established, rod readingscan be taken on subsequent points and their elevationscalculated by simply subtracting the readings from theheight of instrument.
Devices are classified leveling in terms of accuracyinto three categories:1 - Precision: the settlement where the bubble is verysensitive as are high magnification power and usesthis type of work and Geodetic Survey businesses thatrequire high precision.2 - Precision medium: It is less accurate than the firstcategory and dominated the use of this type in mostengineering projects.3 - low-precision devices: and make this kind ofhardware specifically for the purposes of settlementapproximate as in building projects Ltd. andsettlement cases within short distance.
Datum line ( M.S.L. ) :- Is the level (line), which areattributed to it points levels on the surface of the Earth.Which is the average sea level.Reduced level ( R.L) :- Is the high point from datum line.Benchmark (B .M ) :- Are fixed points information site andattributed placed in different places until you start racingthem when conducting settlement .Back sight ( B.S.) :- Is the first reading taken after placingthe device in any position so that we see the greatestpossible number of points required to find the elevation .Fore sight (F.S) :- Is the last reading taken before thetransfer device
Intermediate sight ( I.S.) :- Is reading taken between theback sight and fore sight reading .Elevation of line of sight ( H.I) :- Is the imaginary verticallevel determined by the line of sight to the amount ofincrease or decrease for sea level .Tripod :- is a portable three-legged frame, used as a platformfor supporting the weight and maintaining the stability ofsome other object (( plumb bob))
tripodA level is an instrument giving horizontal line ofsight and magnifying the reading at a far awaydistance. It consists of the following parts:(i) A telescope to provide a line of sight(ii) A level tube to make the line of sighthorizontal and(iii) A leveling head to level the instrument
Staff :-Is a wooden or metal ruler one side runway to metersand centimeters. And is a ruler of solid wood 2 , 3 , 4 , 5meters in length and usually 4 meters .
Leveling of the instrument is done to make the verticalaxis of the instrument truly vertical. It is achieved bycarrying out the following steps:Step 1: The level tube is brought parallel to any two of thefoot screws, by rotating the upper part of the instrument.Step 2: The bubble is brought to the centre of the leveltube by rotating both the foot screws either inward oroutward. (The bubble moves in the same direction as theleft thumb.)Step 3: The level tube is then brought over the third footscrew again by rotating the upper part of the instrument.Step 4: The bubble is then again brought to the centre ofthe level tube by rotating the third foot screw eitherinward or outward.
Step 8: By rotating the upper part of the instrumentthrough 180 ° , the level tube is brought parallel to firsttwo foot screws in reverse order. The bubble will remain inthe centre if the instrument is in permanent adjustment.
Method of taking readings on a ruler settlement 1 – direct leveling a back sight is taken on the rod held atthe bench mark ( A ) . H..I = E.L.V of B.M. ( A ) + B.S. Turning the telescope to bring into view the rod held onpoint B afore sight is taken . elev. Point B = H .I – F .S check the work by the following equation :- ∑ B.S. - ∑ F.S. = Last R.L. – First R.L.
Closing the Level LoopA level loop is closed either to another Benchmark orback to the starting Benchmark. To check for errors inthe loop sum the Back sights (BS) and the Foresights(FS). Calculate the difference between the BS and FS(BSFS). Algebraically add this difference to the startingelevation, to yield the closing elevation. This elevationshould be within accepted industry standards tolerancesof the closing Benchmark’s published elevation.
Azimuth:-The azimuth of a line on the ground is its horizontal anglemeasured from the meridian to the line.In plane surveying, azimuths are generally measured from thenorth.Azimuths may have values between 0 and 360 degrees.
Bearings :-The bearing states whether the angle is measured fromthe north or the south and also whether the angle ismeasured toward the east or west. For example, if a linehas a bearing of S 47° E, the bearing angle 47° is measuredfrom the south meridian eastward.