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