451102 Introduction to Surveying LINEAR MEASUREMENT

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451-102Introduction to SurveyingLINEAR
MEASUREMENT

• Dr Philip Collier
• Department of Geomatics
• The University of Melbourne
• p.collier_at_unimelb.edu.au
• Room 316

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Linear Measurement

• In these lectures we will cover
• The role of linear measurement
• Equipment
• Procedures and rules
• Errors
• Applications of linear measurement

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What is linear measurement?

• Simply the measurement of distance

New building site - how big is it?
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Distance measuring equipment and typical
accuracies

• Pacing (1100)
• Optical range finder (1300)
• Trundle wheel (1500)
• Stadia tacheometry (11000)
• Taping or chaining (110,000)
• Electronic distance measurement (150,000)
• More details on plane surveying web site

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Some things to note

• Equipment is fairly cheap (except EDM)
• Equipment is easy to maintain and adjust (?)
• Distances are easy to measure
• Very accurate results can be achieved
• Measurement line needs to be unobstructed
• Errors occur and need to be managed or minimised

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Taping procedures

• Tape must always be straight
• Tape must not be twisted
• Use chaining arrows for intermediate points
• Tape horizontally if possible
• Tape on the ground if possible
• Slope taping needs to be reduced
• Catenary taping requires correction
• Step taping suits some applications

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Tape must be straight
obstruction
measured distance ? required distance
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Use chaining arrows
measured distance ? required distance
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Slope correction
For example s 30.589 m q 2.5o DH 1.334
m then h 30.589 cos(2.5) h 30.560 m
Or. s 30.589 m DH 1.334 m then h
(30.5892 - 1.3342)1/2 h 30.560 m
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Step taping
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Catenary taping
measured distance ? required distance
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Types of errors
These error types apply to any measurement
technique used in surveying

• Blunders
• mistakes and gross errors
• Systematic errors
• repeated size and sign
• affect accuracy
• Random errors
• small and usually undetectable (noise)
• affect precision

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Accuracy and precision
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Sources of error in taping

• Temperature correction
• L? L L.c.?T
• where
• L? is the corrected distance
• L is the measured distance
• c 1.15 x 10-5 m/oC (for a steel band)
• ?T Tactual - Tstandard

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Sources of error in taping

• Standardisation
• The tape is not of true length

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Sources of error in taping

• Catenary (sag)
• A suspended tape will measure too long
• where
• M is the mass per unit length (0.011 kg/metre)
• g is gravity (9.8 metre/sec2)
• T is the tension (50 Newton)
• ? is the slope angle

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Sources of error in taping

• Tension
• Tape length will depend on applied tension
• Slope
• Distances must always be reduced to horizontal

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Applications

• Dimensions of building features
• Block dimensions
• Location and size of site features
• Setting out for construction
• Clearances and tolerances

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An example
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451-102Introduction to SurveyingLINEAR
MEASUREMENT

• Dr Philip Collier
• Department of Geomatics
• The University of Melbourne
• p.collier_at_unimelb.edu.au
• Room D316