HIGH-DEFINIT ION SUR VEYING: 3D LASER SCANNING

The use of high-definition survey-ing/laser scanning for transport-ation-related projects is one ofthe “sweet spots” for this tech-

nology. This article takes a closer look atthe latest trends and the specific applica-tions and benefits that this technologybrings to transportation projects today.

Trends

Laser scanning technology is beingused at a rapidly increasing rate fortransportation-related surveys. This isevident based on discussions with nu-merous surveying organizations thathave scanning capabilities and provideservices to transportation clients. It’s al-so evident based on the growing num-ber of transportation agencies that haveacquired laser scanning systems or havestarted to require subcontractors tohave suitable scanning capabilities inorder to bid on certain contracts.

There are two primary drivers behindthis trend. First, transportation project“clients” or end-users are becoming in-creasingly educated about the benefitsof the technology. As a result, end usersare increasingly open to its use and, infact, many are requiring its use for cer-tain types of projects.

The second driver is simply econom-ics. Experienced service providers, arm-ed with the latest round of full field-of-view high-definition surveying systemsand surveyor-friendly office processingsolutions, have sharply driven down thecost of scanning-based transportationsurveys. Field costs have been drivendown sharply by full field-of-view scan-ners that minimize the number of scan-ner setups and target placements. Of-fice costs have been driven down bynew surveyor-friendly software and

workflows, along with more featuresthat automate processing point cloudsinto final deliverables.

For many transportation surveys,scanning-based surveys today cost lessthan or the same as traditional surveys.Even at an equal cost, scanning providesmany added-value benefits that have of-ten made it the method of choice: im-proved safety, faster turnaround, andmore complete and accurate survey data.

In the early days of laser scanningtechnology, its “ancillary cost savings”were a key economic driver. For exam-ple, end-users could deploy scanningto eliminate the cost of lane closureservices, which can be as costly as field

surveys. In these early days, the cost ofa laser scan survey was often only com-petitive with traditional methods forsurveying objects/sites that were hardto reach (e.g., bridges or rock faces) orthat contained lots of detail. Today,however, the pure productivity advan-tage of the technology for everydaytransportation surveys has led to thesharply increased use of scanning. Forexample, a proper scanning system andits crew can survey many roadways 20-30% faster than a conventional crew.Moreover, for the same task, the size ofa scanning crew is typically smallerthan the size of a corresponding con-ventional crew.

Point cloud withtrue color overlayfor analyzingpavement problem. Imagecourtesy: ESPAssociates

Geoff Jacobs

3D MicroStation model created from laser scan data. Image courtesy: SAM Inc.

Uses inTransportation

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HIGH-DEFINIT ION SUR VEYING: 3D LASER SCANNING

Roadways

High-definition surveying is used formany types of road-related surveys. A ma-jor advantage of the technology is theability to perform many road surveys with-out lane closures and/or to conduct themat night. Safety is another key benefit.

• Road topo for design—common formulti-lane roads, such as highwaywidening projects, when engineering-grade accuracy is required.

• Intersections—many intersection sur-veys involve collecting detail, a taskfor which scanning is well-suited.

Scanning is also often used at busy in-tersections where lane closures wouldbe problematic.

• Pavement QA—surfaces and profilescan be collected very cost-effectivelywith a greater level of detail. This is acommon use for scanning.

• Road topo for problem analysis—many high-definition surveys havebeen done on pavement where watergathers and can cause vehicles to hy-dro-plane. Scanning has also beenused to monitor roads suspected ofsubsidence.

• Paving volumes—the technology isregularly used for calculating actualvolumes of materials applied.

• Input to road milling—the detaileddata from a high-definition surveyprovides accurate guidance for whereand how much to mill surfaces thathave been paved too thick.

• Accident investigation and analysis

—the completeness of high-definitionsurvey data, the accuracy of the data,and the ability to capture data withoutdisturbing the scene are all advantages.

• Slope stability and retaining wall

surveys—some roadways are cut intothe sides of steep hillsides. Many aresubject to falling rocks or landsliderisk. High-definition surveys are high-ly cost effective for monitoring and as-sessing slopes and retaining walls ad-jacent to roadways. Slope terrain isdifficult to access; aerial surveys areproblematic for highly sloping sur-faces; and, geometry is complex.Scanning is an attractive solution,

Scanning is used to survey busy intersections without closing lanes. Image courtesy: Precision Measurements Inc. (PMI)

A high-definition survey was used to assess the sag of traffic light structure installed aftera Florida hurricane. Image courtesy: Consul-Tech

Scanning is used extensively for toll plazaas-buit surveys. Image courtesy:American Surveying Consultants

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provided that a scanner can be locat-ed with a good line-of-sight to theslope and the surface is within theuseful range of the scanning system.

• Toll plazas—many plazas are beingupgraded to include automatic tollcollection. Designing the toll plaza up-grades requires accurate, completeas-builts. For these surveys, scanningis often used in conjunction with con-ventional methods. The fully roboticcapability of scanning allows fieldstaff to also support conventional sur-vey tasks while the scanner is auto-matically scanning. The combinationtypically provides overall productivitygains greater than 30% compared toconventional methods only; plus,there’s no need to close lanes.

Bridges and Elevated Roads

Bridge surveys represented some of thefirst successful transportation applications

of high-definition surveying years ago. To-day, the technology is used as an almostde facto standard in many areas. Inacces-sibility to parts of the bridge, the ability tocapture surfaces without lane closures,and the trustworthiness of the data for ar-eas that are hard to reach are advantages.Overall, the cost of doing a bridge surveywith suitable scanning solutions is often

HIGH-DEFINIT ION SUR VEYING: 3D LASER SCANNING

Scanning was used to survey the approaches, bridge deck, and underside of James Creekbridge. Image courtesy: B.H. Mulkey Engineering Inc.

High-definitionsurvey of

bridge damagecaused by atruck. Image

courtesy: ESPAssociates

less than half of the cost of doing thesesurveys conventionally.• Design as-builts—decks, undersides,

piers, abutments, caps, railings, and

Stairway connecting an elevated highwaywas scanned for accurate design as-builts. Image courtesy: M.J. Engineeringand Land Surveying, P.C.

structural elements are common con-tent for scanning-based surveys.

• Clearances—a high-definition surveygives users the ability to locate thetrue minimum clearance both vertical-ly and horizontally, again without hav-ing to occupy the roadway.

• Topo for problem analysis—scanningis often used to analyze structuraldamage or causal circumstanceswhen a truck has hit a bridge (i.e., itsheight or width exceeded the actualclearance).

• Heritage—many old bridges are con-sidered heritage landmarks. Scanningis used both for historical archive(e.g., HABS & HAERS) and for retro-fit/modification projects. On rehabprojects it is important to preservemany façade and ornamental fea-tures. The detail of a high-definitionsurvey is well-suited to this task.

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Scan of heritage bridge in Chicago. Image courtesy: Dynasty Group

HIGH-DEFINIT ION SUR VEYING: 3D LASER SCANNING

Tunnels

Tunnel surveys (both road and rail) al-so represented some of the first success-ful uses of high-definition surveying fortransportation projects. Here, the inac-cessibility of tunnel ceilings and high-walls, the need for detailed profile geom-etry, and the need to perform data cap-ture quickly are all major reasons for thesuccess of laser scanning in this applica-tion. Over the last few years, access hasbeen severely restricted to many tunnelsin view of possible terrorist threats, mak-ing the challenge of surveying tunnelsthat much greater. Just as for bridge sur-veys, scanning has proven to be highlycost-effective when compared to tradi-tional methods.

• Profiles—High-definition surveys cap-ture profile details that traditionalsurveys may miss. The ability to slicethe tunnel scan at any interval andcreate more closely spaced profiles isalso a plus. Scan-based surveys areregularly performed on finished

tunnels as well as tunnels that are be-ing newly bored.

• Paving QA & quantities—like roadsurveys, tunnel walls also go througha process of layered construction.Scanning is cost effective for QA andfor quantity estimations.

• Clearances—just as with bridges, ver-tical and horizontal clearances arevery important. High-definition sur-veys can readily provide true mini-mum clearances cost-effectively.When “time windows” for capturing

data are severely restricted and thespeed of data capture is critical, phase-based laser scanners are often the toolsof choice. They can capture several hun-dred thousand points/sec and their oth-erwise limited range is not a constraintfor profiling narrow tunnels.

Airports

High-definition surveying is common-ly used for airport-related surveys. Keyadvantages of scanning are fast datacapture (especially for runways that are

only accessible for short periods atnight); complete and accurate as-builtsof facilities and baggage handling areas;and the ability to easily and accuratelycapture hard-to-reach ceilings, terminalstructures, towers, and antennas. Inter-national airports, regional airports andmilitary air bases have all taken advan-tage of the technology.• Runway pavement QA & quantities —

this is a common application for scan-ning, as high-speed data capture, theability to survey remotely, and theability to survey at night represent real advantages.

• Baggage handling areas—many areasare being updated with the latest bag-gage inspection equipment. These ar-eas are often already densely populat-ed with utilities, support structures,conveyors, and other physical ele-ments that make inserting new bag-gage inspection equipment challeng-ing. Scanning has been used for cost-effective as-builts that are needed fordesign and construction planning.

• Terminal transport structures—scan-ning is used for surveying roadways,ramps, and inter-terminal infrastruc-ture when changes are being plannedto these parts of an airport. The infor-mation is used both for design and forconstruction planning, such as deter-mining optimal crane locations. Re-mote data capture and the ability toeasily capture complex geometry arepluses for scanning.

• Exterior envelope for landing pat-

terns—3D models have been createdusing laser scanning for the purpose

High-definition surveying has been used extensively for tunnel pavement surveyson Boston’s BigDig project. Image courtesy: BSC/Cullinan and the Central Artery/Tunnel agency

Airport runwaysurveys benefitfrom fast, remotedata capture atnight. Imagecourtesy: PrecisionMeasurements Inc.(PMI)

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HIGH-DEFINIT ION SUR VEYING: 3D LASER SCANNING

of updating key flight path informa-tion. Scanning can capture the geom-etry of large structures without havingto use scaffolding or man-lifts.

• Construction as-builts—for hard-to-reach structures, scanning is oftenvery cost effective.

One application that has been prob-lematic for scanning at airports has beenparking garages. Because scanning isline-of-sight to the surfaces being cap-tured, parked cars can pose a significantproblem for scanning pavement. Parkinggarages and parking lots, in general, are

Many airport structures and overhead ceilings are hard to capture with conventionalsurvey methods. Image courtesy: AZTEC Engineers

Model of Sea-Tac airport baggage handling area created from a high-definition survey.Image courtesy: David Evans and Associates

only suited to scanning if they are prac-tically empty of cars during the survey.

Rail

Rail applications are similar to tunnelapplications in that it can be difficult togain permits and access for conductingsurveys on a live track. Scanning can of-ten be conducted from outside the railright-of-way, which makes it a good op-tion for open track surveys. This is par-ticularly useful when lengths of trackhave to be surveyed at road/rail inter-sections.• Track—scanning is used for limited

lengths of track. Research is beingconducted with high-speed phasescanners for use on moving platformsin which the complete, immediate en-virons of the track can be captured byscanning. This will be beneficial foridentifying overhanging foliage.

• Signaling—the ability to remotelycapture signaling in rail yards is an ad-vantage of scanning.

• Platforms—many parts of a rail station orplatform are often hard-to-reach and maycontain complex geometry and structuraldetails. High-definition surveys can effec-tively address these challenges.

• Utilities—like signaling, utilities at railfacilities can be difficult to capture.

• Clearances—for overhead and hori-zontal structures, rail clearances arecritical. The high density of scanningcan be an aid in identifying true mini-mum clearances.

Ports and Harbors, Canals

Although terrestrial laser scanning isnot suitable to survey underwater terrain,it is successfully used on related struc-tures, such as port and harbor facilities.In many cases these structures are diffi-cult to physically access, therefore scan-ning’s remote measurement capabilitiesare beneficial. The U.S. Army Corps of En-gineers, for example, has deployed laserscanning on a wide variety of as-built sur-veys. Many of these have been conduct-ed for the purpose of assessing structur-al deformations or damage.

Summary

Many types of transportation-relat-ed as-built surveys are good candidates

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HIGH-DEFINIT ION SUR VEYING: 3D LASER SCANNING

Scanning has quickly become astandard for rail tunnel surveys.Image courtesy: American Surveying Consultants

for taking advantage of thebenefits and cost advantages oflaser scanning. Recent trends inscanning have reduced thecosts of scan-based surveys tobe highly competitive with con-ventional surveys for a wide va-riety of such projects. Laserscanning’s capabilities for re-mote and overhead measure-ment, as-built detail, and fastdata capture lend themselveswell to transportation surveyswhere occupying the trans-portation structure itself is of-ten problematic.

Geoff Jacobs hasbeen employed byLeica Geosystems,HDS, Inc. (former-ly Cyra Technolo-gies Inc.) since1998. He currentlyacts as SeniorVice President, Strategic Market-ing. He is also a contributingwriter for the magazine.

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