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 • Taping 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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