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Laser Scanning for Cave Surveying

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  • 1. Laser Scanning for Cave Surveying and Visualisation Kevin Dixon CPC Geospatial 3D
  • 2. Overview
    • Why ?
    • Technology
    • Issues
    • Hardware
    • Software
    • Cave Surveying
    • Summary
  • 3. Why Laser Scan ?
    • Expensive £15k-90k
    • Big, heavy (>10kgs) sensitive equipment
    • Lots of batteries required
    • Time consuming 1-4hr per detailed scan
    • So why do it ?
    • 3D realisation
    • Record the geological structure
    • Visualise black holes
    • Virtual cave exploration for non-cavers
  • 4. Laser Principles
    • L ight A mplification by S timulated E mission of R adiation
    • Gain medium is energy pumped to excite electrons to emit light which is amplified in optical cavity to produce a coherent light beam often at specific frequency
    • Most common uses
      • DVD/CD Players and Burners, Fibre-optic Communication
      • Bar-code Readers, Laser Printers, Laser Pointers, Mouse
    • Other uses
      • Medical, dentistry, lightshow
      • industrial cutting and marking
      • Military target painting, ranging
      • Directed energy weapon
  • 5. Semiconductor Lasers 375 to 1800nm
    • Most common wavelengths for ranging:
      • 532nm visible green, can measure through water
      • 650/690nm visible red
      • 785/870/905nm near infra-red
      • 1064nm near infra-red, typically used for airborne LIDAR
      • 1535nm inherently eye-safe, not absorbed by water
  • 6. Laser Safety
    • Class I/1 is safe
    • Class II/2 is safe during normal use < 1mW
    • Class IIIa/3R pose small risk of eye damage < 5mW
    • Class IIIb/3B severe eye damage < 500mW
    • Class IV/4 can burn skin > 500mW
    • Protection
      • Wavelength specific glasses
      • Security Key Control
      • Labels
  • 7. Range Performance Range requires some laser energy to be reflected back to the laser detector Reflectivity is a function of: Surface Shape Incidence Angle Colour Target Size Texture Atmosphere Prism Flat Convex
  • 8. 3D Lasers
    • Laser plus
      • Angle Encoders
      • Motors
    • Optional
      • Viewfinder
      • Camera
      • Accelerometers
      • Gyro
      • Compass
    • Polar Coordinate System (Range, HA, VA)
      • Add Station Coordinates
      • Add Reference Azimuth
    • Get Cartesian Coords (Easting, Northing, Height)
    Vertical Angle Horizontal Angle Station Coordinates Range Reference Azimuth
  • 9. Different Scanner Hardware $ $$ $$$ $$$$$$
  • 10. Scanner Gear for Caves Mini 3kg or Normal 6kg Tripod Normal Transit Case Scanner 10kg, Case 4kg Lightweight Case 2kg (Floats) Plastic Bags for Protection Large Tackle Bag plus Internal Protection 2kg Big Battery 5kg / 8hrs Small Battery 3kg / 3hrs
  • 11. Laser Scan Integration
    • Two Options
    • Coordinates
      • Traverse
      • Series of control points
      • Requires more time
      • Best for complex spaces
    • Overlap
      • Adjacent scans have sufficient common data
      • Software registration
      • Quick
      • Suitable for simple spaces
  • 12. Shadow
    • Line of Sight System
    • Creates ‘Shadow’
  • 13. Shadow
    • Line of Sight System
    • Scan From Another Direction
    • Reduces Shadow
  • 14. Shadow
    • Line of Sight System
    • Scan From Other Direction
    • Fills Shadow
    • Shadow Under Scanner ?
  • 15. Scanning Issues
    • High humidity limits range
    • Water buildup on scanner lenses
    • Reflectivity ≡ Range
      • Best: white flat perpendicular limestone
      • Poor: Wet, Muddy, Mossy, Dark
    • Short ranges <0.5m can be difficult
    • Difficult Setups for Vertical Shafts
    • Curious cavers and tourists
      • ‘ Tripod kick’ and ‘Laser Block’
    • Equipment Weight
    • Very Little Data from Narrow Rifts and Flat-out Passage
    Waterfall ‘ Cloud’
  • 16. Stay Out of the Scan !
  • 17. Software
    • QuarrymanPro Scanner logs data on internal CF card
    • VoidScanner requires ruggedised laptop
    • MDL Model Software Creates Cartesian Space
    • MDL VoidWorks - Dedicated for Underground Mining
      • Data Edit and Registration
      • Void Modelling And Volumetrics
    • Data colour coded by area, height or reflectivity
    • Output options OBJ, DXF, CSV, VRML, Vulcan (Mine data format)
  • 18. Cave Survey Grades
    • 1 Low accuracy sketch with no measurements made
    • 2 Intermediate survey between Grades 1 & 3
    • 3 Magnetic survey. Angles ± 2.5º; distances ± 50cm; station position error < 50cm.
    • 4 Intermediate survey between Grades 3 & 5
    • 5 Magnetic survey. Angles ± 1º; distances ± 1cm; station position < 10cm.
    • 6 Magnetic survey that is more accurate than grade 5 .
    • X Survey based on theodolite or total station.
  • 19. Cave Survey Detail Grades
    • A All passage details based on memory.
    • B Passage details estimated and recorded in the cave.
    • C Measurements of detail made at survey stations only.
    • D As per C and at significant changes in passage
    • Is another classification required ??
    • E Measurements of detail made for majority of passage
    • XE Laser Scan Survey ????
  • 20. Yordas Cave, Yorkshire
    • First trial laser scan for caves
    • QuarrymanPro Laser Scanner used on Tripod
    • 3 Setups, 5 hours scanning
  • 21. Reads Cavern, Mendips
    • Cave Electronics and Radio Group 19-20 April 2008
    • Demonstration of QuarrymanPro Laser Scanner
    • 2 Setups, 2 hours scanning
  • 22. OFD2, Wales
    • Main Chamber and Top Entrance Series
    • QuarrymanPro Laser Scanner on Tripod
    • 11 Setups, 8 hours scanning
  • 23. OFD2 TBCNTE
  • 24. St Michaels Cave, Gibraltar
    • QuarrymanPro Laser Scanner
    • 45 stations
    • 5 days scanning
    • Determine cave volume for study
    • Laser scans identify geological features running through rift
  • 25. Gaping Gill, Yorkshire
    • QuarrymanPro and VoidScanner
    • Main Chamber, Entrance Shaft, Shakehole and River Bed
    • Also Mud Hall
    • 20 setups including half way down winch
    • 4 weekends scanning
  • 26. GG Mud Hall
  • 27. GG From West to East
  • 28. GG Revolution
  • 29. GG Heights for 2008
  • 30. GG Jumbo x 2
  • 31. Cave Scanning in the News Yorkshire Post 27 Aug 2008 Yorkshire Dalesman Oct 2008
  • 32. In-Work
    • Titan, Derbyshire
      • 8 scans in 1 weekend so far
      • Humidity Issues Below Event Horizon
      • Yorks v. Derbys (GG v Titan)
    • York Minster
      • Is GG as big as Minster ?
    • UK Big Cave/Pothole List
      • Dimensions, Volume
      • GG, GB, Titan, Time Machine, Smoo, Mud Hall...............
    • Big Chambers Worldwide
    Scanning at Titan Breakthrough Pitch Head Picture Rob Eavis
  • 33. Titan Side Elevation Scans so far
  • 34. Titan Revolution
  • 35. Summary
    • Current Laser Scanners for Cave Surveying are
      • Expensive, Hard Work
      • Not Suitable for Very Small Passages
      • Need to be Controlled by Traverse and/or Scan Overlap
    • 3D Realisations
      • Aid Cave Studies
      • Add Detail to Cave Mapping - Class XE Cave Survey ??
      • Provide a new means of Promoting Caves to non-Cavers
    • A smaller, low power, faster scanner with photogrammetry and ‘dead-reckoning’ would be useful
      • Unlikely to be within typical Caver budget !!
  • 36. Thank You
    • Yordas Cave - Roo Walters
    • Reads Cavern - BCRA CREG
    • OFD2 - Allan Richardson, SWCC, Meg Stark
    • St Michaels Cave - Dave Mattey, Gibraltar Caving Group
    • Gaping Gill - Meg Stark, Bradford PC, Craven PC
    • Titan - Dave Nixon, Rob Eavis, Katie Dent, Meg Stark
  • 37. Future
    • Set up new Company Geospatial 3D
    • Riegl Laser Scanner
      • 6mm Accuracy
      • Camera Photo Overlay
      • 100m Range
    • 3D Laser Scanning
      • Heritage
      • Underground
      • Quarries and Mines
    • OFD2 Columns ??
  • 38. Laser Range Techniques
    • Pulse (Time of Flight)
    • High Measurement Rate
    • Long Range
    • Better for Passive Targets
    • Good Outdoor
    • Phase (Carrier Wave)
    • High Accuracy
    • Lower Cost
    • Can be Visible
    • Low Power
  • 39. Phase (Carrier Wave) Turn on the Laser Beam and modulate the intensity Monitor the reflected signal Compare the two signals Phase Angle Phase Angle 2 x π x Modulation Speed Time Delay x Speed of Light 2 Speed of Light 2 x Modulation Speed LASER LASER Time Delay = Range = Range =
  • 40. Pulse (Time of Flight) Send a short pulse of light out from the laser LASER Monitor the reflected signal Compare the two signals Time Delay Time Delay x Speed of Light 2 LASER REFLECTOR REFLECTOR Range =
  • 41. Handheld Lasers
    • None Are Waterproof
    • Only 2 have Tilt and Compass