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TACHYMETRY

TACHYMETRY. LESSON 6 Stadia Field Practice & Accuracy of stadia observation. Stadia Field Practice. Stadia tachymetry is mainly used in surveying details in selected areas .

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TACHYMETRY

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  1. TACHYMETRY LESSON 6 Stadia Field Practice & Accuracy of stadia observation

  2. Stadia Field Practice • Stadia tachymetry is mainly used in surveying details in selected areas. • Adequate horizontal and vertical control, supplied by traversing and leveling is required to orientate the survey and to provide station levels. It is best suited to open ground where few hard levels are required.

  3. Stadia field work Figure below shows an area which needs topographic survey. There are some object illustrated in that figure, such as station (A), building(B), road(C), fence(D)and drainage(E). 2 3 1 4

  4. Accuracy of stadia observation Accuracy of distance measurement: Using an ordinary levelling staff with 10 mm divisions practical accuracies approximate to the following: Accuracy of height measurement : Provided that the staff is held vertically with reasonable care and angles of sighting are less than 10˚, then heights should be accurate to within 0.01 per cent of the sighting distance. 1 2

  5. Accuracy of tachymetry work Errors in horizontal distances • Errors in • elevations 1 2

  6. Errors in horizontal distances • The error of careless staff holding can be resolved by using staff bubbles when implementing field observation. • Error in reading the stadia intercept, which is immediately multiplied by 100(K1), thereby making it significant. This source of error will increase with the length of sight. The obvious solution is to limit the length of sight to ensure a good resolution of the graduations. • Error in the determination of the instrument constants K1 and K2, resulting in an error in distance directly proportional to the error in the constant K1 and directly as the error in K2. • Effect of differential refraction on the stadia intercepts. This is minimized by keeping the lower reading 1 to 1.5m above the ground. • Random error in the measurement of the vertical angle. This has a negligible effect on the staff intercept and consequently on the horizontal distance.

  7. The main sources of error in elevation are errors in vertical angles and additional errors rising from errors in the computed distance. Errors in elevations

  8. Thank You !

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