Terrestrial Laser Escaner (English)

8/9/2019 Terrestrial Laser Escaner (English)

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Tratamiento y Gestin de Datos 3D

Terrestrial Laser Scanning

Tasca Adrian UPV 27.01.2015

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Table of Contents

Abstract......................................................................................................................................................... 3

Theoretical introduction of the method.........................................................................................................3

Introduction................................................................................................................................................... 3

Lasers ............................................................................................................................................................ 3

Definition ...................................................................................................................................................... 3

First working laser ........................................................................................................................................ 4

Common laser technology ............................................................................................................................4

Important properties of laser light.................................................................................................................5

Laser Safety .................................................................................................................................................. 5

Static and dynamic laser scanning ................................................................................................................6

Static laser scanning................................................................................................................................ ...... 6

Dynamic laser scanning ................................................................................................................................ 7

3D Scanner .................................................................................................................................................... 7

Functionality of a 3D Scanner ...................................................................................................................... 7

3D Laser Technology................................................................................................ .................................... 8

Measuring using light ...................................................................................................................................8

Passive scanners................................................................................................................................ ............ 9

Active scanners .............................................................................................................................................9

Triangulation based measurement .............................................................................................................. 10

Structured light based measurement ...........................................................................................................10Time-based measurement ...........................................................................................................................11

Puse-based scanners ................................................................................................................................ .... 11

Phase-based scanners ..................................................................................................................................13

Instruments of this technology existing on the market ...............................................................................16

Laser rangefinder (Laser Instrument) .........................................................................................................16

Actual and future applications ....................................................................................................................22

Actual applications................................ ...................................................................................................... 23

Future applications...................................................................................................................................... 25

References................................................................................................................................................... 28


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Abstract

In this document I elected to describe an common technics for a terrestrial laser scanning that is

more tangent to my domain of studies and my future surveying career.Terrestrial laser scanning systems have been available for about ten years and in the last five years

laser scanning has been seen to be on the way to becoming accepted as a standard method of 3D

data acquisition, taking its place beside established methods such as tacheometry, photogrammetry

and GPS. In particular, industrial as-built-documentation terrestrial laser scanning systems haveplayed an important role since their first availability as commercial systems. The major advantage

of this measuring system is the complete and detailed 3D data acquisition of objects for many

different applications. Specifically, the use of terrestrial laser scanning for 3D modeling,deformation measurements, monitoring and analysis has increased over the past years.

Theoretical introduction of the methodIntroduction

In modern engineering, the term laser scanning is used with two related, but separate meanings:

The first, more general, meaning is the controlled deflection of laser beams, visible or invisible.Scanned laser beams are used in stereolithography machines, in rapid prototyping, in machines for

material processing, in laser engraving machines, in ophtalmological laser systems for the

treatment of presbyopia, in confocal microscopy, in laser printers, in laser shows, in Laser TV,in LIDAR, and in barcode scanners.

The second, more specific, meaning is the controlled steering of laser beams followed by a distance

measurement at every pointing direction. This method, often called 3D object scanning or 3D laserscanning, is used to rapidly capture shapes of objects, buildings and landscapes.

A laser rangefinder is a device which uses a laser beam to determine the distance to an object.

Laser Scanning describes a method where a surface is sampled or scanned using laser technology.

It analyzes a real-world or object environment to collect data on its shape and possibly its

appearance (e.g. colour). The collected data can then be used to construct digital, two-dimensionaldrawings or three-dimensional models useful for a wide variety of applications.

The advantage of laser scanning is the fact that it can record huge numbers of points with high

accuracy in a relatively short period of time.

Lasers

Definition

Laser is a device that is able to generate a wave of light using only a very narrow band of the spectrumiscalled a laser. The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation.A typical laser emits light in a narrow, low-divergence beam with a well-defined wavelength

(corresponding to a particular color if the laser is operating in the visible spectrum).


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Many engineering applications, such as topography require positioning the focus of a laser beam in threedimensions. This is achieved by a servo-controlled lens system, usually called a focus shifter or z-

shifter.

Many laser scanners further allow changing the laser intensity. The most common way to move mirrors is,

as mentioned, the use of an electric motor or of a galvanometer. However, piezoelectricactuators or magnetostrictive actuators are alternative options. They offer higher achievable angular speeds,

but often at the expense of smaller achievable maximum angles.

Important properties of laser light

Laser light is simply light generated with a laser device. Such light has some very special

properties, which distinguishes it from light from other origins:

Laser light may be visible, but most lasers actually emit in other spectral regions, in particularthe near infrared region, which human eyes cannot perceive. Laser light is not always continuous, but may

be delivered in the form of short or ultra short pulses. As a consequence, the peak power can be extremelyhigh. In most cases, laser light is linearly polarized. This means that the electric field oscillates in a

particular spatial direction.

Laser light is generated in the form of a laser beam. Such a laser beam has a high(sometimes extremely high) degree of spatial coherence, therefore it propagates dominantly

in a well defined direction with moderate beam divergence. The term coherence means thatthe electric signal at different locations across the beam profile oscillates with a rigid phaserelationship. This coherence is the reason why a laser beam can propagate over long distances and can befocused to very small spots. Because of its coherence properties, laser beams stay in focus when projectedon a distant scene. Another fundamental property of laser light waves is their velocity of propagation. Light

waves travel with a finite and constant velocity in a certain medium. Because of these properties, laser light

is highly suited to the measurement of objects.

Laser Safety

Lasers are used in a wide variety of applications including, scientific, military, medical, and

commercial fields. The coherency, high monochromaticy, and ability to reach extreme powers are allproperties which allow for these specialized applications. Therefore, laser light should be handled withextreme caution and understanding of laser types becomes necessary. All lasers and devices that use lasers

are labelled with a classification, depending on the wavelength and power of the energy the laser produces.


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For example, the European Standard provides information on laser classes and precautions. It outlines sevenclasses of lasers:

1. Class 1 lasers are safe under reasonably foreseeable conditions of operation, including the use of

optical instruments for intra-beam viewing.2. Class 1M lasers are safe under reasonably foreseeable conditions of operation, but may behazardous if optics are employed within the beam.

3. Class 2 lasers normally evoke a blink reflex that protects the eye; this reaction is expected to provideadequate protection under reasonably foreseeable conditions, including the use of opticalinstruments for intra-beam viewing.

4. Class 2M lasers normally evoke a blink reflex that protects the eye, this reaction is expected to

provide adequate protection under reasonably foreseeable conditions. However, viewing of theoutput may be more hazardous if the user employs optics within the beam.

5. Class 3R lasers are potentially hazardous where direct intra-beam viewing is involved, althoughthe risk is lower than that for Class 3B lasers.

6. Class 3B lasers are normally hazardous when direct intra-beam exposure occurs, although viewing

diffuse reflections is normally safe. This class of laser is generally not suited for surveyapplications.7. Class 4 lasers will cause eye or skin damage if viewed directly. Lasers of this class are also capable

of producing hazardous reflections. This class of laser is not suited for survey applications.

Static and dynamic laser scanning

Current laser scanner technology can be divided into 2 categories: static and dynamic.

Static laser scanning

When the scanner is kept in a fixed position during the data

acquisition, it is called static laser scanning. The advantages of usingthis method are the high precision and its relatively high pointdensity. All static laser scanning can be seen as terrestrial laser

scanning, however not all terrestrial laser scanning can be categorizedas being static laser scanning.

Figure Static Laser Scanner Leica ScanStation 2


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Dynamic laser scanning

In cases of dynamic laser scanning, the scanner is mounted on a mobile platform. These

systems require additional positioning systems such as INS and GPS which makes the systemmore complex and expensive. Examples of dynamic laser scanning are scanning from anairplane (airborne laser scanning), scanning from a moving car or from an unmanned aerialvehicle (UAV).

Figure Laser Scanner on Vehicle Board

Note: I elected to introduce and to describe more the static type of laser scanning because this process is

using a cheap laser equipment from economic point of view and is more applied in different engineering

and scientific applications.

3D Scanner

A 3D scanner is a device that analyses a real-world object or environment to collect data on its shape and

possibly its appearance (e.g. colour). The collected data can then be used to construct digital three-dimensional models. Many different technologies can be used to build these 3D-scanning devices; eachtechnology comes with its own limitations, advantages and costs. Many limitations in the kind of objectsthat can be digitised are still present, for example, optical technologies encounter many difficulties withshiny, mirroring or transparent objects.

Functionality of a 3D ScannerThe purpose of a 3D scanner is usually to create a point cloud of geometric samples on the surface of thesubject. These points can then be used to extrapolate the shape of the subject If colour information iscollected at each point, then the colours on the surface of the subject can also be determined.


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Figure: Types of Laser Scanners That are Using Light

Passive scanners

Passive scanners do not emit any kind of radiation themselves, but instead rely on detecting

reflected ambient radiation. Most scanners of this type detect visible light because it is a readily

available ambient radiation. Other types of radiation, such as infrared could also be used.

Passive methods can be very cheap because in most cases they do not need particular

hardware other than a digital camera. The problem with these techniques is that they rely on

finding correspondences between 2D images, which do not always have unique solutions. For

example, repetitive patterns tend to fool the measurement method. The accuracy of these

methods depends mostly on the resolution of the imaging system and the density of identifiable

features in the image.

Active scanners

Active scanners emit some kind of controlled radiation and detect its reflection in order to probe an objector environment. Possible types of radiation used include light, ultrasound or x-ray. Since these active

measurement techniques require a laser transmitter and a receiver, they are mechanically more complexthen passive techniques.


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Popular types of measurements using active scanners:

Triangulation based measurement

Triangles are the basis of many measurement techniques.Triangulation based 3D laser scanners are scanners that use laser

light to probe the environment. With respect to time-of-flight 3Dlaser scanner, the triangulation laser shines a laser on the subject

and exploits a camera to look for the location of the laser dot.

The laser emitter and the camera are setup under a constant angle,creating a triangle between them and the laser projection on the

object, hence the name triangulation.

Because of this configuration, the laser projection changes in thecameras field of view depending on the distance to the camera.

Figure: Triangulation Principle in 3D Scanning

Structured light based measurement

Structured-light 3D scanners project a pattern of light on the subject and look at the deformation of thepattern on the subject. The pattern is projected onto the subject using either an LCD projectoror other stable

light source. A camera, offset slightly from the pattern projector, looks at the shape of the pattern andcalculates the distance of every point in the field of view. The advantage of structured-light 3D scanners isspeed and precision. Instead of scanning one point at a time, structured light scanners scan multiple points

or the entire field of view at once.

Figure: Structured Light 3D Scanning Principle


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The main methods and technical dispositive that I selected for this short project is Time-basedmeasurements which will be listed and shown in more detailed form in next paragraphs

Time-based measurementTime-based scanners are active scanners that measure a time frame between two events. In

general we have two time-based scanning principles: Pulse based (Time-of-Flight) and Phase

based scanners.

Puse-based scanners

Time-of-flight (TOF) scanners utilize a "pulse" of laser light. This pulse is sent to the object and the timeis measured from when it was emitted to the time it returns. The time and the encoder reference angles andthen compute an x, y, z point, along with a reflectance value. TOF scanners are mainly used for long-range(100m +) measurement applications like topographic surveys.

How its known, light waves travel with a finite and constant velocity in a certain medium Therefore, when

the time delay created by light travelling from a source to a reflective target surface and back to the source(round trip) can be measured, the distance to that surface can be evaluated using the following formula:

With c= speed of light in air

t= time between sending and receiving the signal

Figure: Time-of-flight Laser Scanner Principle


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The current accepted value for the speed of light in a vacuum is exactly c= 299,792,458 m/s. If

the light waves travel in air then a correction factor equal to the refraction index (depending on

the air density) must be applied to c. Taking into account this speed of light, one can calculate it

takes 3.33 nanoseconds to travel 1 meter. Therefore, to reach a point accuracy of 1 mm, we

need to be able to measure a time delay of about 3.33 picoseconds.

Pulsed time-of-flight scanners do not use continuous laser beams, but make use of laser pulses.

They scan their entire field of view one point at a time by changing the range finders direction.

The view direction of the laser range finder is changed by a deflection unit.

Figure: Laser Pulse Measurement Principle

Note: For a non-ambiguous measurement, the time measured (t) should be greater than the pulse width,Tpulse.

Thus or

Setting Tpulse to be 10ps, implies that the maximum accuracy that can be achieved will be

d = 1.5mm. Most commercial mid and long-range systems provide an accuracy of about 6 to 10 mm.Because the accuracy depends on the clocking mechanism, the error of a time-of-flight scanner is almostindependent of the distance itself. It is important to notice that the time derivation method for measuringthe return pulse depends on the desired time resolution, the counting rate and the required dynamic range

of the pulse.

In a pulsed time-of-flight system, the maximum pulse repetition frequency is dictated by the fact

that the transmitter cannot send another pulse until the echo from the previous one has been

received. Typical time-of-flight 3D laser scanners can measure the distance of 10,000~100,000 points everysecond.


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Major factors govern the accuracy of a pulsed ranging system

Ability to select the same relative position on the transmitted and received pulse to measure thetime interval. This is limited by noise, time jitter, signal strength and sensitivity of the threshold

detector, and shortness and reproducibility of the transmitter pulse.

The accuracy with which fixed time delays in the system are known.

The accuracy of the time interval measurement instrumentation.

Advantages

High concentration of transmitted laser power. This power makes it possible to achieve the required

SNR (signal to noise ratio) needed for high accuracy measurements at long ranges.

The advantage of time-of-flight range finders is that they are capable of operating over very longdistances, on the order of kilometers.

At a rate of 10,000 sample points per second, low resolution scans can take less than a second.

Disadvantages

The problem of detecting the exact arrival time of the backscattered laser pulse

due to the changeable nature of the optical threshold and atmospheric attenuation.

Time-of-flight scanners accuracy can be lost when the laser hits the edge of an object because the

information that is sent back to the scanner is from two different locations for one laser pulse.

The disadvantage of time-of-flight range finders is their accuracy.

The distance accuracy is relatively low, of the order of millimeters.

Phase-based scanners

Another time-based measuring principle avoids using high precision clocks by modulating the power of thelaser beam. Phase-based scanners utilize a "continuous wave" of laser light. System brands vary, but ingeneral, the light is emitted at varying frequencies in a steady stream vs. a pulse. The different frequencies

help the scanner cover different distances; a low frequency travels long distances and short frequenciesserve well for close range, very similar to sound waves. The scanner receives the return waves and measures

the "phase-shift" of the wave compared to when it returned. This shift calculates the distance from thescanner and, along with encoder references and inclinometer, calculates an x, y, and z value along withreflectance.


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Figure: Phase-based laser scanner principle

Typical phase-based scanners modulate their signal using sinusoidal modulation, amplitudebased (AM) or frequency based (FM) modulation, pseudo-noise or polarization modulation.

In case of a sinusoidal modulated signal, the reflected light is demodulated by means of foursampling points that are triggered to the emitted wave. Out of the four measurements c(0),c(1), c(2) and c(3) the phase shift, the offsetB and the amplitudeA can be calculated:

This phase difference can be related to a time delay similar to that measured in the pulse-based

scanners. The relationship between phase difference (), modulation frequency (fmodulated),and time delay (t), is:


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Then, according to the distance measuring equation of the time-of-flight scanner, the distance to

the target is given by:

Again numbers may be inserted to get a better feel for these entities. With a frequency of 10MHz and aphase resolution of 0.01 degree (not too difficult with standard electronics), we get a resolution inzof about

0.5 mm.

Continuous beam-modulation scanners also have a maximum unambiguous range, similar to pulsed time-of-flight systems. For these systems the range is limited to that which causes a phase delay in the sine wave

of one complete cycle. The equation for maximum unambiguous range in a continuous wave system that isgiven by:

In the example above, the interval is about 15 m (frequency 10MHz). The range measurementuncertainty is proportional toZamb and inversely proportional to the Signal-to-Noise Ratio (SNR).To get around the inconvenience of a range ambiguity interval, one can use multiple frequency

waveforms in which the target is localized at low frequency (long wavelength) and then accuratemeasurement is performed at high frequency.

In the latest generation of phase based scanners, 2 or even 3 waves with different wavelengths are

superimposed. The longest wavelength defines the uniqueness range and the shortest wavelength definesthe precision that can be obtained.


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RIEGL VZ-2000

Request information:

RIEGLs unique V-Line technology,based on echo digitization, onlinewaveform processing, and multiple-time-around processing is the key to

enabling such high speed, long range,high accuracy measurements even in

poor visibility and demanding multitarget situations caused by dust, haze,rain, snow, etc.

RIEGL VZ-2000Type Echo digitization and online waveform processing

Range 2,000 m

Measurement400,000 meas./sec

240 scan lines/sec

Eye safe Laser Class 1

Field of view 100 x 360

Precision 5 mm

Accuracy 8 mm

Laser wavelength Near InfraredWeight approx. 9,9 kg

Dimensions 196x203x308 mm

Camera option Enables the integration of an optional DSLR camera

ReceiverIntegrated L1 GPS receiver with antenna

Interface for external GNSS receiver

Other features:

Integrated compass

Laser plummet

Various interfaces (LAN, WLAN, USB 2.0)

Internal data storage

Main

Applications

Archaeology & Cultural Heritage

Civil Engineering

Measurement of Bulk Material

Surveying in Open-Pit Mining

Mobile Laser Scanning

Topography & Mining

Software

PackagesRiSCAN PRO, RiMINING, RiANALYZE, RiPROCESS, etc


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Optech ILRIS Terrestrial Laser Scanner


ILRIS is a fully portable, laser-based

ranging and imaging system for thecommercial survey, engineering,mining and industrial markets.ILRIS is an industry-leading solutionthat addresses the needs of

commercial users. It is field-readyand requires no specialized trainingfor deployment. ILRIS is packagedfor several applications, including

automated monitoring and long-range scanning.

ILRIS-LR (Long Range)

Type Laser-based ranging (Pulse-based)Range Up to 3000 m (80% reflectivity)

Measurement Up to 10,000 points/s

Eye safe Laser class 3

Field of view 40 40

Precision 1 mm

Accuracy 4-8 mm at 100 m

Laser wavelength 808 nm (invisible) / 658 (visible)

Weight 14 kg

Dimensions 320 320 240 mm

Camera option 3.1 MP Integrated Camera

ReceiverInterface for external GPS receiver

Enables GPS timestamping (from INS system)

Other features:

2.0-GB USB memory drive

Cold-weather jacket

Rugged carrying case

Software to generate user-selectable file formats

Main Applications

Industrial design

Building Information Modeling (BIM)

Civil Engineering

Rail

Forestry

Geology, Mining & Geotechnical

Software

Packages

Optech FMS

Optech LMS Pro

Optech HidroFusion

Optech ILRIS Scan


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FARO Laser Scanner Focus3DX Series


The smallest and lightest laserscanners on the market - Focus3D XSeries are tools for indoor and outdoor

applications. The FARO Focus3D X330 is specially designed for outdoor

applications due its small size, lightweight, extra long range, extendedscanning possibilities even in direct

sunlight and easy positioning with tothe integrated GPS receiver.


Type Phase based ranging

Range 0.6 330m

MeasurementUp to 976,000 points/second


Field of view 40 40

Precision 1 mm

Accuracy 2mm

Weight 5,2kg

Dimensions 240 x 200 x 100mm

Camera option 70 MioP Integrated Colour Camera

ReceiverInterface for external GPS receiver

Dual Axis Compensator

Other features:

Compass

Height Sensor

High level of simplicity

Scanner control: via touchscreen display and WLAN

Main

Applications

Industrial design


Civil Engineering

Reverse Engineering

Forensic Animations

Documenting As-Built Conditions

Software

Packages

FARO CAD Zone

FARO CAM2 Measure 10

FARO CAM2 SmartInspect

FARO SCENE


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Trimble TX8 Laser Scanner


High speed- with a typical scan time of

only 3 minutes the Trimble TX8allows to capture more stations and

complete projects very fast. Intuitiveand easy to operate- the intuitiveonboard software of the Trimble TX8

makes it easy to learn and get up tospeed capturing data.

Trimble TX8

Type Ultra-high speed time-of-flight powered

Range120 m on most surfaces

340 m with optional upgrade

MeasurementUp to 976,000 points/second


Field of view 360x317

Precision


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Leica ScanStation P20


Ultra-high speed scanners (up to 1million points/second) are known for

their ultra-fast scan speeds and oftenhigher level of detail. To this, the

break-through, compact LeicaScanStation P20 also bringsunprecedented data quality at range

(120m, max), plus outstandingenvironmental capabilities, survey-

grade tilt compensation, and anindustry first "Check & Adjust"capability.

Leica ScanStation P20

Type Speed phase laser (phase-based)

Range Up to 120 m

Measurement Up to 1000000 points/s


Field of view Horizontal: 360, Vertical: 270

Precision 1 mm

Accuracy 3 mm at 50 m; 6 mm at 100 m

Laser wavelength 808 nm (invisible) / 658 (visible)

Weight 11.9 kgDimensions 238 mm x 358 mm x 395 mm

Camera optionAuto-adjusting, integrated high-resolution digital

camera with zoom video, 5 megapixels ( 17 x 17)

ReceiverGNSS SmartAntenna

Internal Battery with GPS Antenna on top

Other features:

256 GB onboard solid-state drive (SSD) or external

USB device

Upside down mounting adapter

Integrated compass

Laser plummet

Main Applications

Industrial design


Crime Scene

Heritage

Architecture

Accident documentation

Software Packages

CD-ROM Cyclone, CloudWorx & TruView

Leica CloudWorks for 3ds Max

Leica CloudWorks for AutoCAD

Leica CloudWorks for Revit


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Actual and future applications

Collected 3D data is useful for a wide variety of applications. These devices are used extensively by the

entertainment industry in the production of movies and video games. Other common applications of thistechnology include industrial design, orthotics and prosthetics, reverse engineering and prototyping, qualitycontrol or inspection and documentation of cultural artifacts.

The purpose of a 3D scanner is usually to create a point cloud of geometric samples on the surface of thesubject. These points can then be used to extrapolate the shape of the subject (a process calledreconstruction).

Figure: 3D Laser Scanner Applications


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Actual applications

Quality assurance and industrial metrology

The digitalisation of real-world objects is of vital importance in various application domains. This methodis especially applied in industrial quality assurance to measure the geometric dimension accuracy. Industrial

processes such as assembly are complex, highly automated and typically based on CAD (Computer AidedDesign) data. The problem is that the same degree of automation is also required for quality assurance. Itis, for example, a very complex task to assemble a modern installation, since it consists of many parts thatmust fit together at the very end of the production line. The optimal performance of this process isguaranteed by quality assurance systems.

Figure: Industry Laser Scanning and Metrology

Especially the geometry of the metal parts must be checked in order to assure that they have the correctdimensions, fit together and finally work reliably.

Within highly automated processes, the resulting geometric measures are transferred to machines thatmanufacture the desired objects. Due to mechanical uncertainties and abrasions, the result may differ fromits digital nominal. In order to automatically capture and evaluate these deviations, the manufactured part

must be digitized as well. For this purpose, 3D scanners are applied to generate point samples from theobjects surface which are finally compared against the nominal data.

The process of comparing 3D data against a CAD model is referred to as CAD-Compare, and can be a

useful technique for applications such as determining wear patterns on moulds and tooling, determiningaccuracy of final build, analysing gap and flush, or analysing highly complex sculpted surfaces. At present,contact scanning are the predominant technologies employed for industrial purposes, with contact scanningremaining the slowest, but overall most accurate option.


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Reverse engineering

Reverse engineering of a mechanical component requires a precisedigital model of the objects to be reproduced. Rather than a set of

points a precise digital model can be represented by a polygon mesh, aset of flat or curved NURBS surfaces, or ideally for mechanicalcomponents, a CAD solid model. A 3D scanner can be used to digitisefree-form or gradually changing shaped components as well as

prismatic geometries whereas a coordinate measuring machine is

usually used only to determine simple dimensions of a highly prismaticmodel. These data points are then processed to create a usable digitalmodel, usually using specialized reverse engineering software.

Figure: 3D Installation Model

Cultural Heritage Scanning

Cultural Heritage can be defined as monuments, buildings, or landscapes of "outstanding universal value

from the point of view of history, art or science." These sites are often under threat from environmentalconditions, structural instability, increased tourism and development, and they are most likely under-funded, and hence, inadequately documented and maintained. Laser scanning, in combination with other

digital documentation techniques and traditional survey, provides an extremely useful way to document thespatial characteristics of these sites. This spatial information forms not only an accurate record of these

rapidly deteriorating sites, which can be saved for posterity, but also provides a comprehensive base datasetby which site managers, archaeologists, and conservators can monitor sites and perform necessaryrestoration work to ensure their physical integrity. A digital record of these sites also facilitates their

accessibility to a broader audience via the Internet.

Figure: 3D Model of Chichn Itz (Mexico)


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Tunnel and Rail Scanning

In recent years, the requirements and high standardsof quality, safety, environment or cost-effectiveness

placed upon public construction have grownsignificantly. For clients, designers and contractors,

the right information at the right time is the key tosuccess. Laser Scanning in railways and tunnels is

being used at a rapidly-increasing rate and becomingthe quickest, safest and most accurate approach todocument valuable 3D information for

transportation-related surveys. Laser scanningproviding 3D precision measurement for theacquisition, analysis and provision of valuableinformation for railway track and tunnels for newconstruction, refurbishment or monitoring.

Future applications


Building information modeling (BIM) is a process involving

the generation and management of digital representations ofphysical and functional characteristics of places. Building

information models (BIMs) are files (often but not always inproprietary formats and containing proprietary data) which canbe exchanged or networked to support decision-making abouta place. Current BIM software is used by individuals,

businesses and government agencies who plan, design,construct, operate and maintain diverse physical

infrastructures, such as water, wastewater, electricity, gas,refuse and communication utilities, roads, bridges and ports,

houses, apartments, schools and shops, offices, factories,warehouses and prisons.

Scanning for building construction is being applied most oftento existing structures, but is also seeing an advent of

applications relating to new construction work. Scanningtechnology is becoming a critical function necessary to

complete the integrated BIM cycle and provides a clear value-add for the integrated BIM workflow.


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3D SCANNING AND RECONSTRUCTION OF CRASH SCENES

Police (for example in England) will soondeploy 3D laser scanners to the scene of car

crashes, saving time and allowing wreckageto be cleared from roadways more quickly.

The 3D accident reconstruction will also bemore accurate than human-generated reports.The laser scanner will capture a 360-degree

image of a crash scene. Mounted on a tripod,a laser scans the horizon and records up to 30

million separate data points, down to sub-millimeter resolution. Each sweep takes fourminutes, and investigators will typically

make four sweeps. The image can then beprocessed into a 3D computer model,

allowing investigators to see where thevehicles are located relative to each other,

tire skid marks, and other evidence.

Conclusion

Why laser scanning?

Laser scanning technology is one of the latest techniques that has improved three-dimensional surveying.

The major advantage of this surveying technique is that it facilitates complete and detailed threedimensional (3D) data acquisition of objects rapidly and at minimum cost for use in many applications,including civil engineering. Also scanning takes not as much time as the traditional technologies. Resultsare high detailed scans with huge point clouds and a lot of information.

Pulse-based or Phase-based scanner?

However, when considering pulse-based and phase-based laser scanners, there are important differencesthat have an influence on the choice of the most suited type of laser scanner, depending on the projects

specifications and the accuracy requirements. Aspects that can be assessed are the horizontal and verticalangle error, range error, noise on the distance measurement, spot size, achievable point resolution etc.Moreover, the reflectance properties of the objects material also have an important influence on theaccuracy of the resulting point cloud. When including a more economical factor, the field of view, thescanning speed and maximal range play a significant role. Several uniform methodologies to assess the

accuracy of different types of laser scanners already exist, but most of these methodologies are based onlaboratory measurements, providing no answer to the question how the measurement instrument will

perform in actual field conditions.


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For the comparison, measurements with a phase-based laser scanner, a pulse-based laser scanner are used.Not only the accuracy, but also the edge effects and the achievable resolution are assessed. Furthermore,

the influence of different types of commonly used construction materials on the accuracy is compared.Based on the measurements of several flat reference targets, the results indicate no significant difference in

3D accuracy between the tested pulse-based and phase-based laser scanners. When using spherical targets,significant differences can be observed. The phase-based laser scanner results in a finer achievableresolution at short distances, where the pulse-based laser scanner delivers better results at longer distances.

The tested edge effects show no significant differences between both types of laser scanners. Furthermore,the measurements indicate that the pulse-based laser scanner results in lower noise levels for the differenttested construction materials.

References

Methods for Geometric Accuracy Investigations of Terrestrial Laser Scanning Systems

www.schweizerbart.de/content/papers_preview/download/73792

Laser light properties: Theory and practice on Terrestrial Laser Scanninghttps://lirias.kuleuven.be/bitstream/123456789/201130/2/Leonardo_Tutorial_Final_vers5_ENGLISH.pdf

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RIEGL VZ-2000

http://www.riegl.com/nc/products/terrestrialscanning/produktdetail/product/scanner/45/


http://www.faro.com/products/3d-surveying/laser-scanner-faro-focus-3d/overview

Quality assurance and industrial metrologyhttp://en.wikipedia.org/wiki/3D_scanner#Quality_assurance_and_industrial_metrology

3DScanning and reconstruction of crash scenes

http://www.popsci.com/cars/article/2011-07/3-d-crash-scene-reconstruction-lasers-will-save-cops-

time-and-money

Laser scanner http://en.wikipedia.org/wiki/Laser_scanning

The first laser http://laserfest.org/lasers/history/early.cfm

Laser safety https://www.lia.org/subscriptions/safety_bulletin/laser_safety_information

Common laser technologyhttp://en.wikipedia.org/wiki/Laser_scanning#Scanning_mirrors

Types of laser scanning http://www.arrival3d.com/laser-scanning-what-is-laser-scanning.php

Heritage scanning in Warsaw http://www.3deling.com/art-nouveau-cultural-heritage/

Optech ILRIS Laser Scanner http://www.optech.com/index.php/product/optech-ilris/

Terrestrial Laser Escaner (English)

Documents

Transcript of Terrestrial Laser Escaner (English)