Unit 5 Levelling Topics covered Definition Terms associated

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Unit 5. Levelling

Unit 5. Levelling

Topics covered Ø Ø Ø Definition, Terms associated with levelling Spirit levelling Instruments for

Topics covered Ø Ø Ø Definition, Terms associated with levelling Spirit levelling Instruments for spirit levelling Simple numerical examples 11/5/2020 Unit 4: Plane table surveying 2

5. 1 Definition Levelling Ø Ø Ø Branch of surveying that deals about the

5. 1 Definition Levelling Ø Ø Ø Branch of surveying that deals about the measurement in vertical plane Determines the difference in elevation between points on the ground Establishes the points on the given elevation 11/5/2020 Unit 4: Plane table surveying 3

5. 1 Terms associated with levelling Level surface Level line Horizontal plane Horizontal line

5. 1 Terms associated with levelling Level surface Level line Horizontal plane Horizontal line Vertical line Datum Elevation Vertical angle Mean sea level Bench mark 11/5/2020 Unit 4: Plane table surveying 4

Levelling Methods of levelling Ø Barometric levelling Ø Trigonometric levelling ( Indirect levelling) Ø

Levelling Methods of levelling Ø Barometric levelling Ø Trigonometric levelling ( Indirect levelling) Ø Spirit levelling Ø Instruments used v v 11/5/2020 A levelling staff Unit 4: Plane table surveying 5

Levelling Level Ø Ø The purpose of level is to provide horizontal line of

Levelling Level Ø Ø The purpose of level is to provide horizontal line of sight It consists of v v 11/5/2020 A telescope to provide line of sight Level tube to make line of sight horizontal Levelling head to bring the bubble in its centre A tripod to support the instrument Unit 4: Plane table surveying 6

BS Some Terminology S 1 RL A A Level staff on A RL C

BS Some Terminology S 1 RL A A Level staff on A RL C RL B C B Back Sight (BS) reading is first reading 7

FS S 2 RL A A RL C RL B C Level staff on

FS S 2 RL A A RL C RL B C Level staff on A B Back Sight (BS) reading is first reading Level staff on B Fore Sight (FS) reading is last reading Move instrument to new position 8

BS S 3 RL A A RL C RL B CP Move instrument to

BS S 3 RL A A RL C RL B CP Move instrument to new position Level staff stays on B The instrument has changed its position about point B Point B is known as a Change Point (CP) 2 nd instrument position starts with BS to B 9

BS S 3 RL A A FS S 4 RL C RL B C

BS S 3 RL A A FS S 4 RL C RL B C B and finishes with FS to C 10

HI HI BS BS FS FS RL A A RL C RL B C

HI HI BS BS FS FS RL A A RL C RL B C B (CP) RL A is known HPC = RL A + BS RL B = Now the RL B is known So we can repeat the process RL C = HPC - FS HPC = RL B + BS HPC - FS Generally : HI = Known RL + Back Sight Unknown RL = HI - Fore Sight 11

11/5/2020 Unit 4: Plane table surveying 12

11/5/2020 Unit 4: Plane table surveying 12