Land based surveys-slideshare

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Land based surveys-slideshare

  1. 1. Data capture on the ground:fundamentals of land surveying Traditional survey techniques Electronic and satellite based techniques
  2. 2. Traditional Plane Surveying• The measurement, recording and calculation of the horizontal location of details of the land, and the preparation of maps from those records.
  3. 3. The basic parts of a plane survey DetailStation point Control line Control framework Detail line
  4. 4. Basic definitions• Detail; the actual geographical entities of interest• Control framework; carefully measured network of points and lines which tie together detail measurements• Control lines; carefully measured straight lines making up a control framework• Station points; points on a control framework locating the ends of control lines.• Go from the whole to the part: control to detail
  5. 5. The whole: control frameworksChain survey:control frameworkbuilt of trianglesTraverse survey:control frameworkof lines and anglesbetween the lines
  6. 6. The part: detail measurements Station point Control lineStation point Detail line: tie line Detail line:offset line part of a triangle at right angles to control line
  7. 7. Drawing up the surveyFirst draw the control line-then draw the detail lines-then join the dots
  8. 8. Height surveying equipment
  9. 9. Spirit levelling: measuring relative heights directly. Automatic level on tripod Horizontal line of sight
  10. 10. Spirit levelling: measuring relative heights directly. 4m levelling staff4m3.1 Automatic level on tripod 0m Horizontal line of sight
  11. 11. Spirit levelling: measuring relative heights directly.3.1 2.9 Automatic level on tripod 0m Horizontal line of sight
  12. 12. Spirit levelling: measuring relative heights directly.4m3.1 2.9 3.0 Automatic level on tripod 0m Horizontal line of sight
  13. 13. Spirit levelling: measuring relative heights directly.4m3.1 2.9 3.0 2.1 1.6 0.5 Automatic level on tripod 0m Horizontal line of sight The difference between any two readings is the relative difference in height between those two points
  14. 14. Relative heights and reduced levels• The relative height between Cirencester and Birdlip is surveyed at 98.7m Birdlip 98.7m Cirencester
  15. 15. Relative heights and reduced levels• The relative height between Cirencester and Birdlip is surveyed at 98.7m• The height of Cirencester above Mean sea level is known to be 127.3 m, its “reduced level above datum” Birdlip 98.7m Cirencester 127.3m Mean sea level=0.0m (The datum level)
  16. 16. Relative heights and reduced levels• The relative height between Cirencester and Birdlip is surveyed at 98.7m• The height of Cirencester above Mean sea level is known to be 127.3 m, its “reduced level above datum” Birdlip 98.7m Cirencester 127.3m 226.0m Mean sea level=0.0m (The datum level) • The reduced level of Birdlip is Cirencester’s reduced level plus the relative height between the two towns 127.3 + 98.7= 226.0m
  17. 17. Converting relative measurements to reduced levelsAdd or subtract sequential relative heights from previous reduced level 4m 3.1 2.9 3.0 2.1 1.6 0.5 102.6m 101.5m 101.0m 100.2m 100.1m Height above datum of 100 m AMSL 0m 100m one point is needed (Above Mean Sea Level OS datum (msl)
  18. 18. Ordnance survey datum level and bench marksOS public bench mark OS fundamental bench mark Levelled height survey Newlyn: OS tidal station = OD Cirencester 127.3m AOD
  19. 19. Measuring large changes in height in small steps• Big changes in height measured by adding/subtracting lots of small changes• Two bits of equipment used – The “level” on a tripod – The survey staff Birdlip staff level ? aCirencester
  20. 20. Measuring large changes in height in small steps• Big changes in height measured by adding/subtracting lots of small changes• Two bits of equipment used – The “level” on a tripod – The survey staff Birdlip staff level ? b aCirencester
  21. 21. Measuring large changes in height in small steps• Big changes in height measured by adding/subtracting lots of small changes• Two bits of equipment used – The “level” on a tripod – The survey staff Birdlip staff level ? b aCirencester
  22. 22. Measuring large changes in height in small steps• Big changes in height measured by adding/subtracting lots of small changes• Two bits of equipment used – The “level” on a tripod – The survey staff Birdlip staff level ? b aCirencester
  23. 23. Measuring large changes in height in small steps• Big changes in height measured by adding/subtracting lots of small changes• Two bits of equipment used – The “level” on a tripod – The survey staff Birdlip staff e d level c ? b aCirencester
  24. 24. Measuring large changes in height in small steps• Big changes in height measured by adding/subtracting lots of small changes• Two bits of equipment used – The “level” on a tripod – The survey staff Birdlip staff e d level c ? b aCirencester ?=a+b+c+d-e
  25. 25. Measuring large changes in height in small steps• Big changes in height measured by adding/subtracting lots of small changes• Two bits of equipment used – The “level” on a tripod – The survey staff Birdlip staff e d level c ? b aCirencester “change points” ?=a+b+c+d-e
  26. 26. Accuracy of this simple technique• Great Trigonometrical Survey of India, 1802 – 1832• Height accuracy at Nepalese, compared to starting point in Madras, was 6”Maps © Royal Geographical Society
  27. 27. Trigonometrical leveling: relative heights calculated targetTheodolite (measureshorizontal andvertical angles) L h o d h=Lsin o Knowing L is the tricky part. This is now measured electronically
  28. 28. Electro-optical distance measurement (EDM) IR pulse returns to unit. Distance is calculated from the time difference between transmission and reception of IR pulse EDM unit Right angledEDM unit sends a reflector (cornerfocussed pulse of Infra- cube)sends IRred (IR) radiation beam directly back to EDM unit
  29. 29. EDM used to monitor Mount St Helens • EDM stations are permanently established • At regular intervals measurements are taken between these stations • Changes in measurements show change to the shape of the volcano
  30. 30. Electronic Field Equipment• Electro-optical distance measuring (edm) device• Electronic theodolite that measures angles automatically• Both are now usually combined into a single unit known as a total station or to give it its technical name electro-optical tacheometer
  31. 31. Total station equipment
  32. 32. Trigonometrical surveying with EDM based “Total station” reflector Total station: measures L by EDM and o electronically L h o d h=Lsin oKnowing L is now easy. Total stationautomatically calculates h and d d=Lcos o
  33. 33. Laser surveying• Light• Amplified• Stimulated• Emission of• Radiation• LASER beams are coherent and do not disburse, so can travel enormous distances and still remain visible Light Laser
  34. 34. Laser distance measurement• LIDAR: LIght Detecting And Ranging• Visual equivalent of RADAR• LASER based EDM where distance from LASER unit to point at which it strikes and object is measured and recorded
  35. 35. LASER scanning• LIDAR based LASER Scanner scans a series of laser pulses over the surface of distant object.• By measuring the distance of each point scanned and the angle to the scanning beam, the location of the scanned point can be calculated and displayed in 3-D, creating a “point cloud” image of the object
  36. 36. LASER scanning output

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