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Surveying

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					Measurement
   Counting yields exact numbers
   Measuring yields inexact values
       Always some error
       Your job is to minimize it
Errors and Mistakes
   Errors - the difference between true
    and measured values
       Tend to be small
       Can be reduced, but not eliminated
   Mistakes - blunders
       Cannot be compensated or averaged out
       Can be eliminated by careful, consistent
        work
Sources of Errors
   Instrument Errors
   Natural Errors - caused by environment
   Personal Errors - limits of surveyor’s
    abilities
       Recording 3.91 when the true reading was
        3.90 might be a personal error.
       Recording 4.91 when the true reading is
        3.90 is a mistake - redo!
Systematic vs. Random Errors
   Systematic Errors
       Same magnitude and sign each time
       Instrument errors, temperature effects
        are systematic
       Reduce by calculation
   Random Errors
       As likely (+) as (-)
       Usually small
       Reduce by averaging
       Personal errors are typically random.
Estimating Total Error
   Repeated Measurements

      Etotal  E n

   Series of Unrepeated Measurements

      Etotal  E  E  ... E
                1
                 2   2
                     2
                             2
                             n
Measurement
   Surveyors measure:
       Horizontal angles
       Vertical angles
       Horizontal distances
       Vertical distances (elevations)
       Slope distances
Significant Digits
   Carry 1 extra digit in calculations
   Round off final answers
   Surveyors typically measure
       Feet to .01’
       Meters to .01 m = 1 cm
       Angles to limits of instrument: 1’ up to 1”
       Record results that show limits
Accuracy and Precision
   Accuracy - how close your measured
    values come to the actual or true values.
   Precision - how well you can repeat your
    measurements.
   Measurements of 90.03, 90.02, and 90.03
    when the true distance is 100.00
    represents good precision,
    but terrible accuracy.
Field Notes
   Legal Document
       May end up in court
       Sign, date each page
   Represent your work
       Neat, organized layout
       Don’t obliterate mistakes - NO erasures
   Use standard note forms
Field Note Rules
   Names and phone numbers on cover
   Table of Contents
       Number pages together
       Job title, Date, Page number
   Record measurements, not calculations!
   Sketch where helpful
       N arrow
       Reference Points
   Hard (3-H, 4-H) pencil, not pen
   No Erasures
Field Note Pages
Job title

Date

Weather

Crew, ass’ns

Standard form

Signature

				
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posted:3/18/2012
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