Kerberos - 3D undercarriage inspection system

Karel Kosnar, Tomas Krajnık, Libor Preucil

Abstract— The application describes automated laser-basedundercarriage vehicle inspection system developed jointly byCzech Technical University in Prague (CTU) and VOP CZ, s.pcompany. The system in question provides complete recoveryof a full three-dimensional relief of a passing-over vehicle atreasonable driving speed. Its capability incorporates automatedcomparison of the reconstructed undercarriage model to pre-vious scans of the vehicle from a database and identifies anyadditional objects. Unlike other systems, which rely mainly onhigh-resolution cameras, the Kerberos system employs laserrange-finders. Thus this unique solution allows to find and labelobjects even in the cases, these exhibit similar, or the samesurface color and texture as the background they are attachedto. The system solution applies principles based on two-and three-dimensional shape reconstruction and registrationmethods, widely used in mobile robot localization and mapping.The cooperation of the CTU’s Intelligent and Mobile RoboticsLab with the industrial partner VOP CZ, s.p. allowed a smooth,fast and very efficient transfer of the aforementioned state-of-the-art methods into the security/inspection application domainproduct. The vehicle inspection scanner has currently beeninstalled at several safeguarded facilities in Czech Republic.

I. PARTICIPANTS

The Kerberos system is a result of fruitful cooperationof well-established defense engineering company (VOP CZs.p.) and Czech Technical University in Prague (CTU), hereinrepresented by Intelligent and Mobile Robotics Laboratory.The university role was to suggest novel resolution principlesof the given problem and to aid the overall system designand its implementation. Specifically, elaboration of softwarefor data fusion, three-dimensional image reconstruction andadditional foreign object identification has been in the focusof interests. The industrial partner overtook responsibilityfor electromechanical design, system testing and on-siteinstallation.

A. Intelligent and Mobile Robotics group, IMR-CTU

The Czech Technical University in Prague (CTU), foundedin 1707, is one of the oldest technical universities and cur-rently the leading technical university in the Czech Republicwith more than 45.000 of students enrolled in engineeringcourses. With over 1700 members of academic staff, it isalso one of the largest research institutions in the CzechRepublic. The Department of Cybernetics is recognized asan outstanding research center at the CTU. In 2000 thedepartment received the “EU Centre of Excellence” awardand in 2006 the prestigious European IST Prize by the

Authors are with Faculty of Electrical Engineering, Czech Techni-cal University in Prague, Technicka 2, 166 27 Prague, Czech Republic{kosnar,tkrajnik,preucil}@labe.cvut.cz,

European Commission. The Department includes over 80academic staff and researchers, and over 30 Ph.D. students.

The Intelligent and Mobile Robotics group [1] is anintegral part of the Department of Cybernetics [2] of theCTU. The conducted research of Intelligent and MobileRobotics Group (IMR) comprises design and development ofintelligent mobile robots, self-guided vehicles as UGVs andUAVs and advanced approaches to their control. The overalltarget is to advance the robot autonomy, via developmentof highly robust cognitive control systems for this kind ofrobots, or their swarms and to bring novel ideas into partic-ular solutions. Four central topics are considered for the re-search interests of IMR group: Sensing of the environment,sensor data processing and data understanding, all leadingtowards automated world model building and updating.Used knowledge representations of the world are designedand optimized for planning of robot activities and forself-localization and navigation in real environments. Thegroup is currently involved in several international projectswith partners like the GRASP Laboratory, INRIA, KarlsruheInstitute of Technology or Graz Institute of Biology andmany more. The technology transferred into this project hasoriginally been derived from Simultaneous Localization andMapping approaches used in mobile robotics.

B. Military Repair Facilities, VOP CZ

The VOP CZ, s.p. stands for a company that specializesin the field of civil and military equipment engineeringand maintenance, engineering production and development.The company is mainly engaged in maintenance and repairof military and engineering equipment and production ofheavy machinery. Recently, the company’s developmentalactivities are posed into modernization and production ofmilitary equipment and production of civilian engineeringproducts. The VOP CZ, s.p. steadily enhances its engineeringproduction for civilian purposes whose products are marketedon highly competitive international markets. Thanks to theexpertise of its personnel and production capabilities, theVOP manufactures complex welded assemblies as well ascompleted products with high accuracy requirements.

The company is involved in international R&D projectswithin EDA or NATO and takes share in the major procure-ment programs of the Army of the Czech Republic. TheVOP’s principal partners in the field of R&D are the CzechMinistry of Defense, Czech Ministry of Industry and Trade,National Security Authority, Defense and Security IndustryAssociation of Czech Republic, NATO and EDA. It has morethan 700 employees, who together provide a broad portfolioof professional services in the above mentioned areas.

II. MOTIVATION AND GOALS

The safety and security of selected facilities and areasbecome key issues in the nowadays community as activitiesof extremist organizations increase all over the world. Oneof the major treats is unauthorized entrance of persons andvehicles, carrying unauthorized or forbidden items like datastorages, weapons and explosives into a secured area andphysical attacks by e.g. explosives.

The personal security check points are equipped by doorframe metal detectors and baggage x-ray screening deviceswhich help to the increase the speed and reliability of the se-curity check procedures. Practices from various public spacesas airports makes personal security field well researched andmanaged.

The vehicle screening procedures are more complex, sincethey cannot be based on metal detection methods. As itremains simple to attach anything to the undercarriage ofa vehicle during the time it is parked in an area underinsufficient surveillance, such as in public streets or parkinglots at car owner’s home, vehicle inspection procedures focusat foreign object detection. Nevertheless, routine securityscreening of vehicles still remains complicated, unreliableand slow. Present practice stops all the check point passingvehicles and manually/visually inspects the bottom of thevehicle. The undercarriages of vehicles are inspected usinga mirror or a hand camera-monitor system. The manualinspection is slow, requires complete stop of the vehicleand thus does not allow fluent inspection at places withfrequent traffic. Moreover, standard inspection proceduresrequire extra space to buffer the vehicles for inspection. Toremove the aforementioned drawbacks of manual vehicleinspection, automated systems, which capture the vehicleundercarriage image, are used at critical infrastructures.However, the attached objects might be designed to have thesame appearance as the surface they are attached to. Thiswould render them invisible to any camera-based inspectionsystem.

To reduce the major risks of carrying unwanted itemson the vehicle, the Kerberos system has been designed forautomated checking for any changes on the undercarriageof the cars entering regularly safeguarded areas. The sys-tem highlights the changes to the operator for the furtherinspection. The core goal of the herein presented system isto handle the situations, where the majority of the cars enter asecured area on a regular basis, i.e. the cars belong to autho-rized personnel visiting the area frequently. This assumptionallows the inspection process via systemic comparison of thevehicles undercarriage appearance and shape.

The basic design requirements are following:

• The inspected vehicle cannot be stopped.• The average throughput exceeds 10 vehicles per minute.• The system must operate in all-weather conditions.• It has to detect automatically foreign objects even if

they are camouflaged.

III. STATE OF THE ART

Nowadays undercarriage scanning systems are exclusivelybased on high-resolution cameras. However, the capabilitiesof the systems differ significantly. The existing systemscan be sorted into three categories respecting the appliedprincipal approach to capturing the image data and their pro-cessing: streaming video approaches, global image gathering,global image with automatic comparison.

The first and simplest video streaming systems requirefull and uninterrupted attention of the operator. An examplesystem of this class is the TRIGelectronics scanner [3] ,which provides a live video stream of the scanned under-carriage of the inspected car. The LED illumination is usedto acquire clear, noise-free video in sufficient resolution. Thestill image is provided only on request of the operator. TheSecuritex VUC-Scanner improves the streaming functionalityby wireless transfer of the video stream from small andportable scanning head to portable base unit with a CCDdisplay (see Pic. 1).

Fig. 1. Securitex scanning head and portable base station.

The instance of the second category is the VACES-Carscanner [4] which delivers one global image of the wholevehicle. The system provides set of image post-processingfilters to improve quality of the image. However, the imageis distorted and warped by variations of the vehicle velocityand direction. Current and reference image of the samevehicle can be displayed for visual comparison performedby operator. However, the system is not capable to performautomatic comparison of the images.

Automatic comparison capability reduces the chances ofsecurity personnel overlooking potential threats by auto-matically identifying and highlighting any abnormality. Anexample of a system with such capability is the I2Securitysystem [5], which provides undistorted image of undercar-riage regardless of variation in speed. The system, basedon two-dimensional imaging, automatically identifies anydiscrepancies in undercarriage or unauthorized modifica-tions, such as hidden compartments, potentially explosiveadditional devices, etc.. The detected suspicious areas arehighlighted. The iVACS system [6] introduces, besides theembedded and portable solutions, a mobile solution wherethe scanner is carried by a mobile robot (see Pic. 2). Thisallows to scan the stationary vehicles.

One of the most complex and sophisticated systems onthe marked is delivered by Gatekeeper security [7], who

Fig. 2. Scanning mobile robot iVACS.

use either a fish-eye camera to build a global undercarriageimage or a ‘dual view’ scanner, which allows to recoverand automatically compare a ‘virtual 3D’ digital images (seePic. 3). The scanner can be integrated into a complex securitysystem with car recognition, X-ray scanner, explosive detec-tor and biometric access control. The dual view capabilityallows to detect objects hidden hidden on top of an axel ora crossbeam.

Fig. 3. Gatekeeper security dualview scanner and virtual 3D image.

All of the aforementioned systems are based primarily oncameras. Thus, the systems would have problems to detectthe attached objects, which are designed to have the samecolor and texture as the surface they are attached to.

IV. PROJECT APPROACH

The main idea of the solution is to detect foreign objectson the vehicle carriage, which might have the same appear-ance as the chassis parts they are attached to. Such objectsmay easily be invisible to vision-based systems regardless ofthe used principle of object detection. Rather than producinga high-resolution color image, the proposed system createsa three dimensional relief of the vehicle chassis. To identifythe inspected vehicle, the registration plate of is capturedand automatically recognized. Unambiguous identificationof the vehicle then allows comparison of the current reliefwith the reference (or optionally other previous) recordsof the vehicle. Any discrepancies between the previous orreference carriage scans and current shape of the chassisare visually labeled and reported to the system operator.Subsequently, the user can rotate, translate and magnify thethree dimensional surface and decide further on whether thedetected additional object(s) represents a true security threat.

As in other systems, the scanner is part of a more complexsystem securing access to critical facilities. The system as awhole consists of a user-operated gate barrier, a license platerecognition module and the scanner itself. A vehicle-velocityindicator and speed and drive direction limiters assure properpass-over direction and speed of the vehicle at the inspectiontime. The scanner itself comprises of three laser range-finding units - two scanners are buried in the ground andone is placed on the surface, see Picture 4. The undergroundrange-finders have their scanning planes aligned into the

Fig. 4. Scanning unit configuration.

vertical direction and scan the vehicle undercarriage. Theon-surface laser range-finder has its scanning plane alignedparallel 5-9 cm above ground level and is primarily dedicatedto determine approaching vehicle’s position, heading andvelocity.

A. Principle of operation

The placement of individual system components is de-picted in Fig. 5. As the vehicle approaches, its orientation andspeed are delimited mechanically by speed limiting ramps,so it cannot move over the vertical scanner in an undesirabledirection or speed. During the approach to the scanner, thehorizontal scanning unit reads the vehicle speed. To allowvehicle speed adjustment into allowed range, the velocityvalues are provides to the driver via speed display in his/herfield of view. As soon as the vehicle undercarriage reachesthe vertical unit scanning plane, the system starts to gathermeasurements from both the vertical and horizontal scanners.The vertical scanners measure the chassis’ cross sections,which are collected into a three-dimensional point cloud.The horizontal range-finder data is used to determine theexact vehicle pose, which denotes necessary information toproperly align the chassis cross sections within the pointcloud coordinate system. As the vehicle leaves the verticalscanning plane, its license plate image is captured by acamera and the vehicle is identified. The captured point cloudis post-processed to remove various artefacts and re-sampledto achieve uniform spatial resolution of the relief recoveryprocedure. Finally, the system assigns the processed three-dimensional image data to a database together with the vehi-cle ID (recognized license plate) and displays correspondingreports to the system operator.

If the database contains a reference (safe) chassis scanfrom one of the previous vehicle passes, a comparison routineis carried out. In other words, firstly, components of thecurrent scan are registered with the safe three-dimensionalpoint cloud by means of standard 3D registration techniques,as commonly used in mobile robotics domain. Subsequently,the registered to-time scans are searched for differences,which are evaluated by a series of image operations used ina computer vision domain. Finally, suspicious differences ofthe reference (safe) and the current vehicle scan are marked

Fig. 5. System components at the secured gate.

by a distinct color and offered as hypotheses on possiblesecurity threads. The system user can set the viewing angleand zoom in/out both the reconstructed surfaces to obtain aclear, close view of the critical areas and properly undertakethe final decision whether the detected objects truly representa danger.

(a) Current 3D scan with indicated foreign objects.

(b) Safe 3D scan from a previous vehicls pass.

Fig. 6. Threedimensional scan comparison.

Nevertheless, the system does not necessarily requirepermanent and immediate attention and decisions of theoperator. Rather than that, the cases of multiple passes ofvehicles at once (convoys of up to of 20 vehicles) are stackedin a queue within the evaluation system and therefore can beprocessed later on.

V. RESULTS OF RESEARCH AND DEVELOPMENT

Apart from the system itself, the project provided valu-able data regarding long-term, all-season operation of laserrange-finding equipment in outdoor areas. The obtained dataallowed design of extremely robust vehicle position andvelocity estimation methods capable of dealing with harshand adverse weather conditions, such as rain, snow and

even a light fog. Moreover, a novel technique of fast three-dimensional shape registration, which does not completelyrely on the shape rigidity, has been designed and imple-mented. The most suitable data processing methods, whichinfer potentially dangerous objects from the differences inregistered shapes, have also been successfully verified.

Applying the previous methods and tools and speakingin quantitative measures, the Kerberos system achieves thefollowing performance:

• Vehicle inspection speed levels up to 15 km/h withobject resolution in order of few centimeters (whereaslongitude resolution component varies with the vehiclevelocity).

• Threedimensional reconstruction, chassis comparisonand shape visualization in less than two seconds allowsto inspect more than 20 vehicles per minute.

• Reliable operation in adverse weather conditions includ-ing snow and rain.

• Very low failure-rate in terms of either missing aforeign object, or reporting a safe vehicle as occasion-ally dangerous. Achieved values depend on the systemparameters setup for particular application and can beinfluenced by the user.

The aforementioned parameters of the designed system dofully match the intended project goals.

Fig. 7. Kerberos system at VOP CZ facility in Novy Jicın.

Currently, one instance of the system is installed at VOPCZ facility and another few others are used serve safeguard-ing of Czech national security authorities.

VI. ACHIEVED INNOVATION AND COMMERCIAL IMPACT

The result of this project is the only (up to our knowledge)vehicle undercarriage inspection system in the world whichcan automatically detect and suggest hypotheses on foreignobjects even if their surface closely resembles the surfacethey are attached to. This performance has been achieved viareconstructing of full three-dimensional model of the carriagesurface from direct range-measurements. The chosen ap-proach completely cancels out possible performance failuresoriginating from visual similarity of the searched objects withthe carriage background. This capability poses the Kerberossystem supreme to any pre-existing automated inspection

system based on color or monochrome camera sensing. Thecurrent implementation of the three-dimensional reconstruc-tion and foreign object detection algorithm allows to processup to 20 vehicles per minute. Therefore, the processingspeed is sufficient for routine inspection procedures evenat frequently visited areas. Moreover, the system resolution,speed and detection reliability remains fully scalable and itcan easily be fostered by adding more laser range-finders andcameras.

The expected commercial impact correlates with potentialapplication classes.

System’s ability to automatically inspect for likely threat-ening objects disburdens the security personnel from tire-some task of manual checking of passing vehicles. The im-portant related issue is seen also in substantial improvementof the inspection performance (speed) at decreased rate offailures. Generally, the Kerberos system brings new qualityinto vehicle routine inspection at great efficiency and highreliability measures.

Primarily, it can be designed for use applications whereasthe best possible performance is desired to assure pub-lic safety and security. This denotes its use in automatedsafeguarding of critical facilities and infrastructures likeembassies, industrial objects, power and chemical plants,highly exposed public places as airports, congress centers,large hotels and office buildings.

Therefore, the potential impacts are expected in the home-land security and public as well as private property safetydomains.

The industrial partner VOP CZ, s.p. involved in thedescribed technology development and completion aims atposting the Kerberos system on the company’s key productlist. Moreover, further development of the system towardsits customization for particular specific applications (i.e.optimizations on product costs, system mobility, inspectionspeed and resolution improvements, etc.) has already beenlaunched.

VII. HANDLING OF INTELLECTUAL PROPERTY RIGHTS

All the research and development activities concerningcompletion of the Kerberos vehicle carriage inspection sys-tem have been done in a framework of a contract betweenVOP CZ, s.p. and the Czech Technical University in Prague.The agreement in question follows the standard conditionsof Commercial Law of the Czech Republic. By completingthe above agreement, the partners have agreed on transferringall the within contract created intellectual property rights andowner rights onto the VOP CZ, s.p. company. To time, VOPCZ, s.p. company stands for exclusive owner of the currentKerberos system solution.

VIII. COOPERATION AND BENEFIT

Neither of the partners alone would be able to completethe described project successfully. In that terms, CTU repre-sented by Intelligent and Mobile Robotics Group benefitedfrom long-standing experience of VOP CZ, s.p. partner inmachinery design, construction and superb knowledge of

the security and defense market requirements. Moreover, theVOP CZ, s.p. was able to set up an outdoor testing facility,which allowed gather real measurements to develop, test andverify the data processing methods on real world data, toprepare realistic all-whether conditions as well as to performexhaustive testing of the final product before releasing iton the market. The data, which were gathered by VOP attheir facility over a long period of time, proved to be veryvaluable for design of robust localization, reconstruction andregistration methods.

On the other hand, the Czech Technical University partnerbrought up the innovative approach into the solution - not torely on the standard approach using high-resolution cameras,but ground the system on active range-finding technology.The experience with laser range-finding technology allowedfast prototyping of the electromechanical design of the scan-ning unit, depict potential hazards and estimate system oper-ating parameters. Most of the system core software methods,i.e. the data processing, localization of the vehicle, three-dimensional reconstruction and shape registration algorithmswere particularly available at the university partner. There-fore, the core methods did not have to be implemented fromscratch. Rather than that, their reference implementationswere tested with the provided prototype data and potentialmethods candidates were efficiently selected for succeedingtests. This approach assured high efficiency of achieving thedesired solution and allowed to complete the innovation andtechnology transfer within a horizon of 4 months.

Moreover, there were identified certain other side im-pacts for the university partner - the Intelligent and Mo-bile Robotics Group. Execution of the joint academia andindustry development procedure opened a possibility to runlong-term experiments and gathering realistic measurementsin outdoor environment over long periods of time. The accessto real data and the collected measurements represent highlyvaluable testing data-sets and driving force for both, furtherdevelopment of Kerberos system, as well as for academicresearch purposes.

REFERENCES

[1] “Intelligent and Mobile Robotics Group, FEE-CTU,” [Cit: 2013-13-02].[Online]. Available: http://imr.felk.cvut.cz

[2] “Department of Cybernetics, FEE-CTU,” [Cit: 2013-13-02]. [Online].Available: http://cyber.felk.cvut.cz

[3] “TRIGelectronics video streamer,” [Cit: 2013-13-02]. [Online]. Avail-able: http://trigelectronics.com/vehicle-under-carriage-scanner.php/

[4] “VACES-Car,” [Cit: 2013-13-02]. [Online]. Available: http://www.i-secure.sg/vaces.aspx

[5] “I2Security Vehicle Scanning System,” [Cit: 2013-13-02]. [Online]. Available: http://i2securitygroup.com/2012/10/23/undercarriage-vehicle-scanning-system/

[6] “iVACS system,” [Cit: 2013-13-02]. [Online]. Available: http://www.stratechsystems.com/iv ivacs.asp

[7] “Getekeeper security,” [Cit: 2013-13-02]. [Online]. Available: http://www.gatekeepersecurity.com/products/undercarriage inspection