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Islamic University of Gaza Civil Engineering Department Surveying II ECIV 2332 By B elal A lmassri

Islamic University of Gaza Civil Engineering Department Surveying II ECIV 2332 By B elal A lmassri. Chapter 6 Electronic Distance Measurement EDM. Introduction. Electro-Optical Instrument. Microwave Instrument. Types of Mounts. Operating Procedure. Trigonometric Levelling.

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Islamic University of Gaza Civil Engineering Department Surveying II ECIV 2332 By B elal A lmassri

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  1. Islamic University of GazaCivil Engineering DepartmentSurveying IIECIV 2332ByBelalAlmassri

  2. Chapter 6 Electronic Distance Measurement EDM Introduction. Electro-Optical Instrument. Microwave Instrument. Types of Mounts. Operating Procedure. Trigonometric Levelling. Corrections and Examples.

  3. Introduction • Definition: A surveying instrument that utilizes an infrared or laser beam to measure the distance from the source point to a defined target point. • Main Types: • Electro-Optical Instruments: Use the light and infrared waves. • Microwave Instruments: Use the radio waves.

  4. Electro-optical Instruments • Use the velocity of light waves to determine the distance between two points. • Those instruments use both the visible lights (wavelength between 0.4-0.7) and the infrared lights (wavelength between 0.7-1.2). • Infrared light much preferable because of the long wavelength. • Source of light: Mercury lambs, Tungsten.

  5. Electro-optical Principle S = Slope Distance. V = Velocity of Light. T = Travel Time.

  6. Microwave Instruments Wave length λ = distance travelled during the period of one cycle. V = Velocity of emission F = Frequency in HZ

  7. Disadvantages of Microwave Type • Two operators are needed to measure a line. • Sometimes there is difficulty to set up two units on both sides. • The accuracy is affected by the atmosphere. • Less accuracy than the electro-optical type.

  8. Types of Mounts In General the EDM can be mounted alone or with another surveying tool, the most popular types as follows: • Separate unit for (20-60 km). • On top of standards of theodolite. • On top of telescope of theodolite. • Integral part of Total Station.

  9. Retro Reflectors • The reflectors used with the electro-optical type are called the retro-reflector using precise prisms which can be single or multiple. • The max distance of measurement of EDM device depends on: The design, The quality and number of prisms, The atmospheric conditions.

  10. Operating Procedure • Set up the instrument over the survey station and record its height HI and set up the reflector on the other side. • Point the instrument toward the reflector using the telescope. • Adjust the pointing of tangents using the screws of the instrument. • Read and record the Temperature, ATM pressure then press the correction button. • Press measure and record the reading.

  11. Corrections for zero centering • The constant error appears in all distances measured by the combination of instrument and reflector. • If AB’ is the measured distance between two points and so AC’, CB’ • The corrected AB = AB’ + c (correction) c = AB’ – AC’ – CB’

  12. Correction for frequency • g = f’ / f f’ : measured frequency. f : theoretical frequency. • AB (corrected) = g. AB’(actual) + c Example 6.1 + 6.2

  13. Trigonometric Levelling – Short Line • Def: It is the process of determining the height difference between two points using the measured distances and vertical angles.

  14. Example 6.6 Δh = hB – hA = s.cosz + i – t Terms: S=Slope Distance, z=Vertical Angle. i=The height of the instrument. t=The height of the sight target.

  15. In case of EDM mounted on top of the standards of the theodolite , the measured slope distance may not coincide with the line of sight in the angular measurement. So the following procedure is followed at that case: • Find the angle difference Δz. Δz = 180(HI-i+t-HT)sinz Π. S • Find the corrected angle Z’=Z+ Δz • Find the height difference ΔH = HB-HA= S.cos Z’ + HI - HT

  16. Example 6.7Example 6.8 • Where HI and HT = Height measurement of the instrument and the reflector of the EDM device.

  17. Extra Practice ! EDM has slope distance AB of 561.276 m. EDM instrument is 1.820 m above station A, and the prism is 1.986 m above station B. The EDM is mounted on a theodolite whose optical center is 1.720 m above the station. The theodolite measured a vertical angle of +6º 21’ 38” to target on prism pole; the target is 1.810 m above station B. Compute both the horizontal distance AB and elevation of station B given an elevation at A of 186.275 m.

  18. Solution !

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