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This site itself consists of a

large pit 400m x 200m x 40m,

surrounding stockpiles, access

roads and tailings ponds.

The aim of the task was to

complete a survey of the entire

site for comparison against a

base survey carried out prior

to excavation to determine

volumes of cut and fill from

the site. Deliverables were to

include volumes for the pit and

stockpiles along with a plan

drawing showing the overall

site layout and cross sections

at specified intervals across

the site. A combination of

survey equipment was used

including Terrestrial Laser

Scanner, GPS and Total Station,to complete the survey in 2

days with just 2 surveyors.

SHorTHiSTorY onTerreSTriaLLaSer

SCanninGTerrestrial Laser Scanning is

a remote sensing technology

first developed in the 1990s as

a means of surveying hugely

complex structures such as oil

refineries. Traditional survey

techniques were not capable

or were far too time consuming

to capture enough information

to draft adequate plans for

such complex pipe networks.

By having millions of measured

points on the pipe networks

full 3D models could be

generated with automatic pipefitting vastly reducing the time

required in the field and greatly

This paper describes Terrestrial Laser Scanningsurveys carried out at the Cavanacaw GoldMine, Omagh, Co Tyrone, Northern Ireland,

owned by Omagh Minerals Ltd (OML), a whollyowned subsidiary of Galantas Gold Corporationto provide the following:

High accuracy geo-referenced 3D CAD Models.

High accuracy volumetric calculations.

Cross sections

Rock Face Profiling.

Visualisations such as flythroughs andwalkthroughs of the site for planningapplications.

Laser Scanning Cavanacaw

Gold Mine, Omagh, Co TyroneA Case Studyby Chstph By BSc aMCistCeS, Gsptl eg

Cavanacaw Gold Mine

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improving the accuracy of thefinal deliverables. The industryhas rapidly developed sincethen and applications for theseinstruments are virtually limitless.

From mining to dam monitoringto reverse engineering,anywhere where rich 3D data isrequired to measure or definecomplex structures, remote ordangerous locations TerrestrialLaser Scanning is withoutcomparison. There are 3 typesof system generally available:Time Of Flight (TOF), PhaseComparison and Triangulation

Time Of Flight (TOF) instrumentsemit a laser beam at theobject and calculate the timeit takes for the laser to reach

the object and return to thesensor to calculate the rangefrom the instrument to theobject. Onboard angle encoderssimilar to those found in TotalStations calculate the horizontaland vertical angles and thusa 3D coordinate for that pointon the object is calculated.This is done in real time at upto 125000 points per second.These types of scanner typicallyhave ranges from 1-2500m withsome instruments capable ofup to 6000m. Accuracies for

these instruments vary but aretypically 10-50mm depending onrange This is the most commontype of instrument for largescale excavation survey work.

Phase Comparison instrumentsemit a stream of light with aknown frequency and phaseand by comparing the emittedphases to the returned phasesthe distance to the objectcan be determined. Theseinstruments tend to have amuch shorter range of 1-100mbut far greater measuring

speed at up to 1,000,000 pintsper second. Because of thisthey lend themselves betterto shorter range applicationssuch as indoor architecturalwork, complicated industrialplant applications or situationswhere access time is verylimited. Accuracies are similarto those for TOF instrumentsover shorter ranges

Triangulation instrumentsutilise two sensors whichsimultaneously record thereflected laser pulse anddetermine the position. Thesetypes of instruments typicallyhave a very short range (>1m) but can achieve submillimetre accuracy. They aremostly used in archaeologyfor recording artefacts and

reverse engineering or

aerospace applications where

tolerances are very tight.

The output from all of these

instruments is the same, a point

cloud, essentially millions or

even billions of individual 3D

points which together form what

looks like a 3D picture of the

survey area. The data can be

viewed in a number of different

ways depending on the users

preference. It can be coloured

by intensity values where thedata is coloured depending on

the intensity of the return signal,

where the surface reflectivity

of the scanned object dictates

its colour. This can be useful for

identifying certain materials from

others such as one type of stone

from another in a stockpile.

The data can be viewed in

greyscale for other applications

or by elevation where the

colour is dictated by elevation

to better display the scale of

an object. Finally the data can

have full colour RGB where high

resolution colour photographs

are draped over the scan data

which gives a real photo realistic

quality to the point cloud data.

This is especially useful for

visualisations such as flythrough

or walkthrough animations.

Some manufactures have

christened the technology High

Definition Surveying due to the

fact that you now have millions

of points where traditionally youhad hundreds recorded with a

Total Station or GPS. It is from

this point cloud that accurate

mesh models, volumes and

cross sections can be produced.

LaSerSCanninGCavanaCawGoLd MineThe Cavanacaw mine has alarge pit which does not lenditself to survey by traditionaltechniques. It is quite deep soacheiving accurate GPS signalsat the bottom of the rock facescan be problematic. It is alsoa dangerous place to workwith a lot of heavy machinerymoving around during the day

transporting raw material upand down the access roadsfrom the vein to the crushingplant. The method chosenwas to laser scan the pit andsupplement the scan data with

GPS data for the stockpiles,tailings ponds and access roads.The laser scanner used was aLeica Scanstation 2, a Time OfFlight instrument which has a

scan speed of up to 50,000 pts/sec and a range of up to 300m.

The scanner was set up at tenpositions along the top of thepit or rock head. The operatorcontrols the scanner via alaptop and using the inbuiltdigital camera is able to seethe instruments field of viewfrom that setup position. Theoperator then chooses the areato scan by fencing off the areaof interest on the laptop andsetting the point resolution orpoint spacing. For Cavanacaw

mine the point resolution wasset at 100x100mm over 300m.That equates to a point every100mm at 300m from thescanner. As much of the pit aspossible was scanned from eachposition to insure good overlapof the data for registration or

joining of the separate scansand also to get into all thenooks and crannies not visiblefrom certain viewpoints. Theinstrument relies on line of sitemeasurement and multiplesetups are usually requiredto fully capture the object.

A number of metal reflectivetargets on tripods wereused to join or register theten different scans togetherTheses targets were positionedaround both sides of the pitand precisely scanned fromeach of the 10 scan positionsproviding accurate commonpoints between the scans.

The scanner processing software

then performed an initialregistration of the 10 scansusing these targets to positionthe scans together to createa fully combined point cloudof the entire pit. The softwareLeica Scanstation 2 Terrestrial

Laser Scanner

The same laser scan data with intensity values above, and full RGB below

Metal target with vertex placed in centreand surrounding pointcloud data

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ProCeSSinG &deLiveraBLeSBack in the office the point

cloud data was cleaned of noise

such as machinery, measuredas the scanner swept its way

across the pit and a solid 3D

mesh of the pit created in

the Leica Cyclone laser scan

software. From here the mesh

was brought into AutoCAD

Civil 3D 2009 and combined

with the line work produced

from the GPS data to provide

a complete picture of the site.

Once combined the various

deliverables including volumes,

cross sections and plan drawings

were produced and comparisonsmade to the base survey.

reSULTSThis modern approach

has proven itself to have

a number of key benefits

over traditional survey

techniques. These include:

SPeedThe entire site including the

large pit was recorded in high

detail in a matter of two days

using just two surveyors. To

achieve this level of detail using

traditional techniques alone

would take up to a week

then analysed the overlapping

scan data and tightened up

the registration using common

areas of overlap between the

separate scans. All 10 scans

were successfully registered

to an accuracy of 7 millimetres

using both targets and cloud

constraints. This was completed

on site to insure full coverage

was achieved. The centre of

the metal targets were also

recorded by reflectoress Total

Station set up over site control,

in this case Irish Grid Northern

Ireland. Recording the position of

the targets in this way allowed

for the Geo-referencing of all

the scan data to site grid during

the registration process.In total over 20 million points

were measured providing a

complete and highly accurate

3D dataset of the pit. The Leica

Scanstation 2 Instrument also

has the ability to overlay high

quality photographs onto the

data providing a real photo

like quality to the dataset

making it easier to visualise

what had been captured.

The second day on site was

used to carry out a GPS survey

of the stockpiles, access roadsand tailings ponds using a Leica

GPS900 base and two rovers

to compliment the scan data

and complete the site survey.

Two separate scans showing target positions and the final registered dataset of the entire pit below

Cross sections comparing the base survey with pit excavation and stockpiles

Highly detailed 3D mesh model coloured by intensity values

aCCUraCY& deTaiLBy using multiple setups with the

laser scanner every last detail of

the pit is recorded. This objective

approach leaves nothing

to chance unlike traditional

subjective techniques which

simply cannot be as accurate or

complete. Far greater accuracy

can be achieved for volumes

due to the sheer number of

points covering the object as no

interpolation is required between

points for the calculations.

SaFeTYThe entre pit was recorded

remotely in high detail

without the need to venture

down into the danger areas.

Attempting to survey an activeexcavation with live plant

machinery constantly on the

move poses obvious dangers

which can be completely

avoided using this approach.

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ConCLUSionSTo date the Cavanacaw gold

mine was successfully surveyed

on two separate occasions.

The laser scan data allows

for excellent visualisation of

changes to the pit over time.

The image below is of the

two laser scan point clouds

Plan drawing in CAD showingcontours and cross section positions

Overlay of two separate surveysshowing movement of pit from thesouth to the north (left to right)

Christopher Byrne, a GeospatialEngineer for Coastway carriedout this survey on behalf

of Cavanacaw Gold MineCoastway were one of thefirst companies in Ireland toadopt this technology and haveused it on countless projects,including infrastructureprojects, archaeology sites,cultural heritage sites, as-builtsurveys and anywhere whereit can be used to supplementtraditional techniques toprovide much improveddeliverables.For more information visitwww.coastway.net or contact:

Mark Hudson FCInstCES MRICSASCS ACIArb MIS MIMQS

Director, Coastway, SurveyHouse, Tougher Business Park,New Hall, Naas, Co. Kildare,Irelandtel: +353 (0)45 435880mob: +353 (0)86 8525108

placed on top of each othershowing how the pit is movingas the excavation follows thevein toward the north. Thisapproach to surveying large

excavations or mines is relativelynew to Ireland but has beenproven for over a decade inAustralia and Canada whereit is routinely used on most ofthe large mining operations formonitoring, volume calculationsand visualisation purposes.

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