Unit 5. Levelling

Unit 4: Plane table surveying Topics covered Definition, Terms associated with levelling Spirit levelling Instruments for spirit levelling Simple numerical examples 18/01/2019 Unit 4: Plane table surveying

Unit 4: Plane table surveying 5.1 Definition Levelling 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 18/01/2019 Unit 4: Plane table surveying

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 18/01/2019 Unit 4: Plane table surveying

Unit 4: Plane table surveying Levelling Methods of levelling Barometric levelling Trigonometric levelling ( Indirect levelling) Spirit levelling Instruments used A level A levelling staff 18/01/2019 Unit 4: Plane table surveying

Unit 4: Plane table surveying Levelling Level The purpose of level is to provide horizontal line of sight It consists of 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 18/01/2019 Unit 4: Plane table surveying

Some Terminology S1 BS RL A RL B RL C A B C Level staff on A Back Sight (BS) reading is first reading

S2 Level staff on B FS RL A RL B A B C RL C Level staff on A Back Sight (BS) reading is first reading Fore Sight (FS) reading is last reading Move instrument to new position

BS Move instrument to new position RL A RL B RL C A B C S3 (CP) CP Level staff stays on B The instrument has changed its position about point B Point B is known as a Change Point 2nd instrument position starts with BS to B

S4 S3 BS RL A RL B RL C A B C FS FS to C and finishes with

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

Thank you for your attention! Any questions? Querries? 18/01/2019 Unit 4: Plane table surveying