Laser Scanning for Cave Surveying and Visualisation Kevin Dixon CPC Geospatial 3D
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Transcript of Laser Scanning for Cave Surveying and Visualisation Kevin Dixon CPC Geospatial 3D
Laser Scanning forCave Surveying
and Visualisation
Kevin DixonCPC
Geospatial 3D
Overview
Why ? Technology Issues Hardware Software Cave Surveying Summary
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
Laser Principles
Light Amplification by Stimulated Emission of Radiation
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
Semiconductor Lasers375 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
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
Range Performance
Range requires some laser energy to be reflected back to the laser detector
Reflectivity is a function of:Surface Shape Incidence
AngleColour
Target Size
Texture
Atmosphere
Prism
Flat
Convex
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
CoordinatesRange
Reference
Azimuth
Different Scanner Hardware
$ $$ $$$ $$$$$$
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
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
Shadow
Line of Sight System Creates ‘Shadow’
Shadow
Line of Sight System
Scan From Another Direction
Reduces Shadow
Shadow
Line of Sight System
Scan From Other Direction
Fills Shadow
Shadow Under Scanner ?
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’
Stay Out of the Scan !
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)
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.
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 ????
Yordas Cave, Yorkshire
First trial laser scan for caves QuarrymanPro Laser Scanner used on
Tripod 3 Setups, 5 hours scanning
Reads Cavern, Mendips
Cave Electronics and Radio Group 19-20 April 2008
Demonstration of QuarrymanPro Laser Scanner 2 Setups, 2 hours scanning
OFD2, Wales
Main Chamber and Top Entrance Series QuarrymanPro Laser Scanner on Tripod 11 Setups, 8 hours scanning
OFD2 TBCNTE
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
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
GG Mud Hall
GG From West to East
GG Revolution
GG Heights for 2008
GG Jumbo x 2
Cave Scanning in the News
Yorkshire Post 27 Aug 2008
Yorkshire Dalesman Oct 2008
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
Titan Side Elevation
Scans so far
Titan Revolution
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 !!
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
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 ??
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
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 =
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 =
Handheld Lasers
None Are Waterproof
Only 2 have Tilt and Compass
Make Model Water Size (mm) Weight Range Accuracy Visible Tilt Mag Mem Connect Power PriceStanley TLM 100 Low 30m 6mm Yes No No 1x9V £103Bosch DLE50 IP54 100x58x32 175g 50m 1.5mm Yes No No 4xAAA £119Leica D3 IP54 125x45x24 110g 100m 1mm Yes Yes No 20 2xAAA £229Hilti PD38 IP54 120x65x28 230g 70m 1.5mm Yes No No BlueTooth 2xAA £450
LTI TruePulse 360B IP54 120x50x90 220g 1000m 300mm No Yes YesSerial orBlueTooth 2xAA £1,325
MDL LaserAce 150 IP63 110x100x50 400g 150m 50mm No Yes Soon 2000 BlueTooth Camcorder £1,145