Linear Measurement/Surveying In these lectures we will cover: The role of linear measurement Equipment Procedures and rules Errors Application of linear measurement / surveying
Introduction Distance is one of the most basic engineering measurement. Early measurement were made in terms of dimension of the body E.g. Foot, cubits, Pacing and Fathom
Introduction Being able to take accurate measurements and record data are important science skills. Students also need to know how to use math formulas to convert different units of measurement. Geomatics provides real-world applications of a variety of math and science skills
Basic surveying measurement 5 basic quantities: Slope distance AB, along with Vertical angle B’AB (or zenith angle A’AB),
B A’
Horizontal distance AB’ = AB cos(BAB’)
B’
Vertical distance B’B
Horizontal angle B’AC’ also needed to orient C relative to AB’ on the plot
C
A
c’
What is linear measurement? Simple the measurement of distance:
50.5 metres
27.9 metres
New building siteHow big is it?
Errors in Measurement Surveying measurement science: All measurements contain errors Identify sources of errors Devise method of dealing with them
Types of errors Blunders Mistakes and gross errors
Systematic errors Repeated size and sign Affect accuracy
These errors types apply to any measurement technique used in surveying
Random errors Small and usually undetectable (noise) Affect precision
Method of distance measurement
Distance Measurement
Direct (length measurement) e.g Measuring tape
Indirect (distance measurement)
Geometrical (optical) e.g tacheometry
Electronic (Wave Physics) e.g EDM, GPS
Tape measurements For measuring lengths: Measuring tape Direct linear measurements Cheap & robust For small details
Distance measuring equipment and typical accuracies Pacing (1:100) Optical range finder (1:300) Trundle wheel (1:500) Stadia tacheometry (1:1,000) Taping or chaining (1:10,000) Electronic distance measurements (EDM) (1:50,000)
Electronic Distance Measurement (EDM)
Sources of error in EDM Personal Careless centering of instrument and or reflector Faulty temperature and measurements
Instrumental Instrument not calibrated Electrical center Prism constant
Natural Varying ‘atmospheric” condition Turbulence in air
Slope correction
∆H θ Horizontal distance = h To calculate horizontal distance:
h = s cos θ or h = (s2 – ∆H2)1/2
More advanced instrument Total station Theodolite, EDM, data processor & display unit combined into one. Provides instant data conversion into threedimensional coordinates & interface with computers.
Total station and prism
Ensure that the prism is properly sighted & being held steady
GPS – measuring distances using satellites Use signal from GPS satellites to determine positions (x,y,z coordinates). Operated by the US Department of Defense. Need to use special receivers in order to receive the signals. Provides an efficient way of collecting data
Methods and uses Method
Uses
Pacing
Reconnaissance and rough planning
Stadia
Mapping, rough surveys, checking more precise work
EDM
Geodetic survey and all types of survey (e.g land survey and precise construction work)
GPS
Position determination locating control points, all types of survey including construction
Application of distance measurement Dimensions of building features Block dimensions Location and size of site features Setting out for construction Clearances
An example of data from distances measurement Road width Site boundary clearances Building setbacks Block/building dimensions Underground services
Importance of accurate measurement
Surveying measurement is related to the work of civil engineers and architects, since an accurate survey is the first step in land development and construction projects.
Negotiating obstructions Weather Buildings Lake Tree mine
Plotting the survey (AutoCAD)
Drawing unit
Menu – Format – Units Length type : select the Decimal Precision : select 0.000 (three decimel.) Angle type : select Deg/Min/Sec Precision : select 0d00’00” Click on box : Clock Wise Drawing units for DesignCentre Blocks When inserting blocks into this drawing,scale them into : select Millimeters. The next step, click on Direction box and you can see the display Direction Control box. Base Angle : select North. Click : OK (direction control box) Click : OK (Drawing units box)
Plotting the survey (AutoCAD) Draw the line, angle, distance Command : _line From point: Command : Line [enter] From point : 0,0 [enter] (absolute coordinate) To point : @420<0d [enter] (relative coordinate) To point : 594,420 [enter] To point : @420<180d [enter] To point : C [enter] ( close )
Plotting the survey (AutoCAD) Another command Command : Cut Clip Command : Zoom Command : Move Command : mirror Command : erase Command : Trim Etc…
Length type : select the Decimal. â. Precision : select 0.000 (three decimel.) â. Angle type : select Deg/Min/Sec. â. Precision : select 0d00'00â. â. Click on box : Clock Wise. â. Drawing units for DesignCentre Blocks When inserting blocks into this drawing,scale them into : select Millimeters. â. The next step, click on ...
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