L10Sep30

L10Sep30 - Distance Measurement Types of distance...

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CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 1 Chapter 3 Distance Measurement CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 2 Distance Measurement Types of distance measurement •T a p i n g • Electromagnetic Distance Measurement (EDM) CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 3 Distance Measurement Horizontal distance Vertical distance Slope distance CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 4 Chains and tapes are used in the measurement of linear distance • Offset tape is used for short distance measurement (2 – 5 metres) • Stylon tapes for medium measurement range (30 – 50 metres) • Chains may be used for longer measurement range (50 – 100 metres) • Stylon tape is made of plastic-coated steel, giving both stability and durability • Chain is made of steel, which has good stability and less bulk than a stylon reel, but is more prone to damage and wear Measurement by tape
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CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 5 Plumb Bob and Spring Balance • A Plumb Bob is used to align a tape or chain along a particular line of sight, and for marking the end of a tape or chain when measuring distances on sloping ground or across obstacles. • Spring Balance is used to apply tension to a tape or chain during distance measurement. Measurement by tape CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 6 Precision • Pacing accuracy ~ 1 / 100 • Tacheometry (stadia) accuracy ~ 1 / 100 • Taping accuracy ~ 1 / 5,000 • Electronic Distance Measurement (EDM) accuracy ~ 1 / 1,000,000 Methods of Horizontal Distance Measurements Tacheometry CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 7 Definition • Appling a known length of tape to a line Standard lengths • Surveyor’s and Engineering’s steel tapes: 30, 60, 100 and 150 m Taping procedures • Head (Forward) Tapeperson • Leads with zero end of tape, heading directly toward desired point • Sets chaining pins or keel marks when at end of tape or when “breaking tape” • Reads graduations on tape • Applies correct tension as suggested by tape manufacturer ¾ Flat: 10 pounds ¾ Suspended: 20 pounds (a suspended tape needs higher tension due to sag by the effect of gravity) • Records distances in survey fieldbook Taping CIVL1009 Survey (2010-2011 Semester 1) Chapter 3 Distance Measurement 8 Taping procedures (cont’d) • Rear Tapeperson • Follows with “100 ft” end of tape, notifying first person when end is being reached • Maintains alignment by guiding forward tapeperson towards desired point • Maintains level by eyeballing or by using hand level or other instrument • Picks up chaining pins and notes total full tape length measured • Lining in • Mark the line at both ends and at intermediate points as necessary • Applying tension • The rear tapeperson calls “Tape” when reaching end of tape • The forward tapeperson is lined in holding the zero end of the tape • Tape should be straight and held at the same elevation • A specified tension is applied to the tape Taping
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This note was uploaded on 12/01/2010 for the course CIVL 1009 taught by Professor Proftam during the Spring '10 term at HKU.

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L10Sep30 - Distance Measurement Types of distance...

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