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General Notes Common Mistakes Suggestions for Good Leveling Errors in Differential Leveling

Content. General Notes Common Mistakes Suggestions for Good Leveling Errors in Differential Leveling. General Notes. Accuracy at field work comes first. If only difference between two points is needed, no intermediate sights are required. BS and FS distances shall be equal

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General Notes Common Mistakes Suggestions for Good Leveling Errors in Differential Leveling

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  1. Content • General Notes • Common Mistakes • Suggestions for Good Leveling • Errors in Differential Leveling

  2. General Notes Accuracy at field work comes first. If only difference between two points is needed, no intermediate sights are required. BS and FS distances shall be equal Pay more attention to TP If the point to be measured for elevation is the bottom of a bridge or a ceiling or the top of a barrier such a wall or a column, staff is inverted so that zero is at the point and negative sign is assigned to the measured value.

  3. General Notes

  4. Common Mistakes Misreading the rod - reading 3.54 instead of 4.54 Moving the turning point - use a well– defined TP Field note mistakes - work within your group to check you records Mistakes with extended rod – make sure the leveling rod is fully extended

  5. Common Mistakes Level rod not vertical Settling of leveling rod Leveling rod not fully extended or incorrect length Level instrument not level Instrument out of adjustment Environment - wind and heat

  6. Common Mistakes Level rod not vertical Settling of leveling rod Leveling rod not fully extended or incorrect length Level instrument not level Instrument out of adjustment Environment - wind and heat

  7. Suggestions for Good Leveling Anchor tripod legs firmly Check the bubble level before and after each reading Take as little time as possible between BS and FS Try to keep the distance to the BS and the FS equal Share the rodperson with the level of the rod

  8. Errors in Differential Leveling Systematic Errors Random Errors Blunders

  9. Systematic Errors Due to Earth’s Curvature and Atmospheric Refraction BC = refraction of line of sight from horizontal BD = Error due to earth's curvature CD = Actual net error in the staff reading = BJ - BG Substituting R = 6365 km BD = 0.0786 L2, Where BD is in m L is in km Refraction = BC≈BD/7 =0.0786 L2/7 Actual error in staff reading = CD = BD – BC , CD = 0.0786 L2/7

  10. Therefore, to keep the effect of the earth's curvature and atmospheric • refraction to a minimum, it is advisable that the distance between the level and the staff should not exceed 100 m.

  11. Systematic Errors Maladjustment of the level (collimation error) Correct elevation difference =m-n

  12. Questions?!

  13. Reciprocal leveling

  14. Closure Error Calculated RL for BM2 = Known RL for BM2 Where: n Level setups between two points Δh Elevation difference

  15. Closure Error ε = h' – h Where: h' Calculated Elevation h Known Elevation

  16. Closure Error

  17. Closure Error n1 = 2, Δh1 = 1.74 m n2 = 1, Δh2 = 2.13 m n3 = 2, Δh3 = -3.10 m n4 = 4, Δh4 = -0.45 m BM1 = 761.65 m BM2 = 762.38 m

  18. Closure Error BM2 = 762.38 m (known) Δh1 = 1.74 m Δh2 = 2.13 m Δh3 = -3.10 m Δh4 = -0.45 m ΣΔh = 0.32 m BM2 (Calculated) = BM1 + ΣΔh = 761.65 m + 0.32 m = 761.97 m

  19. Closure Error BM2 = 762.38 m (known) BM2 = 761.97 m (Calculated) Closure Error ε = h' – h = 761.97 – 762.38 = - 0.41 m

  20. Closure Error n1 = 2, Δh1 = 1.74 m n2 = 1, Δh2 = 2.13 m n3 = 2, Δh3 = -3.10 m n4 = 4, Δh4 = -0.45 m ε = - 0.41 m

  21. Group Work Δh2 = -17.212 m n2 = 3 setups Δh3 = -0.525 m n3 = 4 setups Δh1 = 8.107 m n1 = 4 setups Δh6 = 9.206 m n6 = 3 setups Δh4 = -2.387 m n4 = 2 setups Δh5 = 2.790 m n5 = 4 setups

  22. Questions?!

  23. Faculty of Applied Engineering and Urban Planning Surveying Civil Engineering Department 2nd Semester 2008/2009 Countouring

  24. Contouring A contour is an imaginary line connecting points on the ground that have the same elevation.

  25. Contouring • A contour interval the vertical distance or elevation difference between two successive contours • Depends on: • Scale • Purpose • Accuracy, time and cost • The topography • Area covered

  26. Group Work 5 10 15 20

  27. Group Work 20 15 10 5

  28. Group Work 20 15 10 5

  29. Group Work 5 10 15 20

  30. Methods of Contouring Griding 3 1 2 4 5 A B C D

  31. Methods of Contouring 1 cm Griding 12 14 11 x 13 10 12 11

  32. Methods of Contouring L Griding x h2 h1 ho

  33. Methods of Contouring Griding 3 1 2 4 5 A 30 25 20 15 0 B 5 20 10 15 10 C 0 15 5 10 5 D 10 0 0 0 -5

  34. Questions?!

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