After a short introduction into the young history of Laser Scanning special attention will be given the determination of subterranean structures. Until now the determination of the topography of subterranean excavations (Like gullies, sinks, sewers, etc.) is costly and time-consuming. Very often huge Hidden-Point-Poles are used in conjunction with Total Stations. A new measurement concept is developed with as much standard products as possible: The main component is a Laser Scanner (Here IMAGER 5006i from ZOLLER + FROHLICH, Germany) used in an upside-down-mode in combination with a special pendulum-tripod. The first investigations are very promising. The concept can be transformed to all laser scanners which can be used in the upside-down-orientation. The big advantage of this method compared to the existing ones: the data collection on site is faster and there is much more information. The time-consuming data processing is realized later on in the office.

Анотація наукової статті за медичними технологіями, автор наукової роботи - Staiger Rudolf


Область наук:

  • Медичні технології

  • Рік видавництва: 2011


    Журнал: Інтерекспо Гео-Сибір


    Наукова стаття на тему '10 years of terrestrial Laser Scanning technology, systems and applications '

    Текст наукової роботи на тему «10 years of terrestrial Laser Scanning technology, systems and applications»

    ?УДК 528

    Рудольф Штайгер Віце-президент МФГ Німеччина

    Email: rudolf. staiger @ hs-bochum. de

    10 РОКІВ наземних лазерного сканування - ТЕХНОЛОГІЯ, СИСТЕМИ І ЗАСТОСУВАННЯ

    Після короткого вступу в історію лазерного сканування, яка є досить молодий технологій, особлива увага приділяється визначенню підземних споруд. До теперішнього часу визначення рельєфу підземних земляних робіт (наприклад, водостічні колодязі, водостоки, колектори, і т.д.) вважалося дорогим і вимагає багато часу. Дуже часто використовуються величезні рейки і електроннітахеометри. Розробляється нова концепція вимірювань стосовно до багатьох стандартним технічним засобам. Головним компонентом є лазерний сканер (в даному випадку IMAGER 5006i фірми ZOLLER + FROHLICH, Німеччина), який використовується в перевернутому стані і прикріпленим на штативі зі спеціальним схилом. Перші дослідження виявилися багатообіцяючими. Цю концепцію застосували до всіх лазерним сканерів, яких можна було використовувати в перевернутому стані. Головні переваги такого методу в порівнянні з існуючими -швидкий збір даних і наявність більшої кількості інформації. Камеральна обробка даних виконується після проведення робіт і не вимагає багато часу.

    Rudolf Staiger Vice-President of FIG Germany

    10 YEARS OF TERRESTRIAL LASER SCANNING - TECHNOLOGY, SYSTEMS AND APPLICATIONS

    Key words: Laser scanner, Topography of subterranean excavations, IMAGER 5006, Scanner in Upside-down-mode, Hidden Point poles, special pendulum tripod.

    SUMMARY

    After a short introduction into the young history of Laser Scanning special attention will be given the determination of subterranean structures. Until now the determination of the topography of subterranean excavations (like gullies, sinks, sewers, etc.) is costly and time-consuming. Very often huge Hidden-Point-Poles are used in conjunction with Total Stations. A new measurement concept is developed

    with as much standard products as possible: The main component is a Laser Scanner (here IMAGER 5006i from ZOLLER + FROHLICH, Germany) used in an upside-down-mode in combination with a special pendulum-tripod. The first investigations are very promising. The concept can be transformed to all laser scanners which can be used in the upside-down-orientation. The big advantage of this method compared to the existing ones: the data collection on site is faster and there is much more information. The time-consuming data processing is realized later on in the office.

    ZUSAMMENFASSUNG

    Nach einem kurzen Uberblick uber die Entwicklung und Technologie des terrestrischen Laser Scanning wird eine spezielle Anwendung vorgestellt und naher untersucht: Die Erfassung kleinraumiger unterirdischer Hohlraume:

    Zur geometrisch gesamthaften Erfassung kleiner unterirdischer Schachtanlagen wurde ein Messsystem, das aus moglichst serienma? Igen Komponenten bestehen soll, bis zur Serien-reife entwickelt. Hauptbestandteil ist ein Panoramascanner im "Uberkopfbetrieb" in Kombination mit einem spez. Pendelstativ. Die Versuche wurden mit einem Z + F IMAGER® 5006i von Zoller + Frohlich durchgefuhrt. Das Messkonzept ist jedoch grundsatzlich auf alle Scanner dieses Typs ubertragbar, sofern ein Uberkopfbetrieb moglich ist. Nach der Beschreibung der grundsatzlichen Ausgangssituation, werden das Messkonzept sowie die Ergebnisse erster Testmessungen vorgestellt.

    Zur geometrisch gesamthaften Erfassung kleiner unterirdischer Schachtanlagen wurde ein Messsystem, das aus moglichst serienma? Igen Komponenten bestehen soll, bis zur Serien-reife entwickelt. Hauptbestandteil ist ein Panoramascanner im "Uberkopfbetrieb" in Kombination mit einem spez. Pendelstativ. Die Versuche wurden mit einem Z + F IMAGER® 5006i von Zoller + Frohlich durchgefuhrt. Das Messkonzept ist jedoch grundsatzlich auf alle Scanner dieses Typs ubertragbar, sofern ein Uberkopfbetrieb moglich ist. Nach der Beschreibung der grundsatzlichen Ausgangssituation, werden das Messkonzept sowie die Ergebnisse erster Testmessungen vorgestellt.

    Terrestrial Laser Scanner - History, Types and Methods

    The first Laser Scanners appeared on the market about 15 years ago. The company who was first on the market can not be determined exactly. RIEGL (Austria) and CYRAX (USA) were certainly two pioneers in the field of terrestrial Laser Scanning.

    Fig. 1a: The first CYRAX-Scanner Fig. 1b: The first RIEGL Scanner LMS Z

    210

    Classification of Terrestrial Laser Scanner

    Until now Laser Scanner are classified in two different ways:

    а) The Distance Measurement Technique. Very similar to Total Stations the Scanners are using phase based methods and pulse based methods in order to determine the distance to the object without an artificial reflector. Pulse based systems assure a wide measurement range, but they are compared to phase based instruments much slower. In contradiction the phase based techniques do allow a high measurement frequency but are limited in the range (distance to object).

    б) The Type of Beam Deflection. Each laser Scanner has an individual Beam deflection system. There are three different types, leading to Camera, Hybrid- and Panorama-Scanners (Fig. 2). The Panorama-Type has the biggest Field-of-View (FOV) which is especially useful for indoor situations.

    With the current generation of Laser Scanners the difference in "measurement frequency versus range" between the two types (a) are becoming smaller. Pulse based instruments are nowadays fast (100 kHz), while the achievable range of phase based systems is close to 200m.

    Camera-Scanner Hybrid-Scanner Panorama-Scanner

    Fig. 2: Classification of Terrestrial Laser Scanner by the type of beam deflection

    Historical Development of Terrestrial Laser Scanner (TLS)

    Since the appearance of the first Laser scanners on the market, dramatic improvements in terms of measurement speed, accuracy and general usability can be observed during the last 10 years. This process of technical progress will certainly continue during the upcoming years. At the same time all systems became smaller, easier to handle and less expensive. Although the existing systems are already very well engineered and real world solutions, the technical progress will nevertheless be continued. The development as such can be roughly categorized into 4 phases or generations:

    - 1st generation (from 1997): The instruments are bulky, look like prototypes and the data storage and the power supply were external. The measurement frequency is between 1 and 5 kHz within a range of 50 to 200m. All systems are pulse based. Typical representatives are: CYRAX 2200, RIEGL LMS Z210.

    - 2nd generation (from 2002): The data storage and the power supply are still outside of the instrument, but the systems become faster. The first phase based systems appear on the market. Typical representatives are: CALLIDUS, CYRAX 2500, ZOLLER + FROHLICH IMAGER 5003.

    rA

    - 3 generation (from 2007): The manufacturers start integrating the data storage and the power supply into the instrument. The range and the measurement speed are improved. Digital images are more and more combined with point clouds. Forced centering systems and reflectors or GNSS-antennas on top of the instruments show a closer cooperation with traditional surveying methods. Typical representatives are: FARO PHOTON, ISITE 4400, LEICA SCAN STATION, RIEGL LMS Z-420i, ZOLLER + FROHLICH IMAGER 5006.

    - 4th generation (from 2009): The data storage and the power are fully integrated. The camera is also part of the acquisition and data treatment process. RIEGL introduced the Full-Wave-Form-Analysis, allowing the detection of multiple echoes in one measurement. In addition the performance in terms of measurement speed and range is again improved. Typical representatives are: FARO FOCUS, RIEGL, VZ 400, ZOLLER + FROHLICH IMAGER 5010.

    THE DETERMINATION OF SUBTERRANEAN STRUCTURES

    In Germany there are millions of small sized sewers, embedded in the urban road system, mainly for waste and rain water purposes. There is an increasing demand for geometrical information about these buildings, because of their age there is a general need for refurbishment. Until now the geometry of these excavations are measured from inside or from outside with a Total Station and a huge hidden point bar. The effort is big and the final results are just some representative points with mediocre accuracy.

    In this publication we will develop a new method, which is replacing the existing one with a surface sweeping method. Instead of some representative points we obtain by the data acquisition with a Laser Scanner a huge amount of geometrical information..

    What is needed?

    Description of the Measurement Task: sewers typical for roads and canals (horizontal dimensions: 10 x 10m, depth 5 to 10 m). The sewer is accessible very often by a hole, which is typically round with a diameter of about 60-80 cm. The general requirements are:

    1. The measurement should be executed from "above" or in other words: the personnel should not climb into the cavern.

    2. The time for data acquisition should be not longer than 30 Minutes per hole.

    3. The equipment should be robust, easy to transport and not expensive.

    4. The data acquisition should be done by 1 person

    Such a system would have several advantages compared to the existing method

    1. The risk of personal damages (pit falls, poisoning gas, ...) is small.

    2. There is no need for special security personnel when there is no need to climb into the building.

    3. The information we can acquire is much more detailed.

    4. The data processing can be realized later in the office in a save and more comfortable environment.

    5. The data processing can be performed in different steps of density (scalable effort) without any loss of information.

    THE CONCEPT OF THE MEASUREMENT SYSTEM

    The sewer will be digitized with a Laser Scanner. The resulting point cloud should be transformed afterwards into the known reference coordinate system from over ground. There-fore the position and orientation of the laser scanner is needed for the measurement time. Analyzing the entire task it becomes clear, that this process of Georeferencing (= transformation into the given coordinate system) is the most critical part of the entire task.

    Georeferencing of the Scanner in the manhole

    The Swiss Federal Institute of Zurich (Switzerland) developed a special Scanner (KMS) for the acquisition of sewers (manholes, shafts, ...). The main components are a line scanner LMS 200 (SICK, Germany) combined with a rotating module, which was designed and built by the Institute itself. This prototype allows the generation of 3D point clouds. In conjunction with this measurement system two different strategies for the Georeferencing were followed.

    1. The scanner hangs under a rigid pendulum tripod, which is on the upper side attached to a horizontal bar, which is equipped with two reflectors (comparable to a subtense bar). The 3D position of the two reflectors is known relative to the position and orientation of the scanner. This means: If the positions of the reflectors are determined with a Total Station, the position and orientation of the scanner in the given coordinate system is also known.

    2. If there are prior information about the horizontal orientation of parts of the sewer (like the horizontal orientation of a drain or sluice, the Georeferencing of the point cloud can be realized without additional measurements.

    Fig. 3a: Scan position over Fig. 3b: Scan position

    ground underground

    Here a third method is suggested and proposed:

    3. The scanner hangs in a "upside-down position" under a free pendulum which is fixed by a traditional tripod (Fig. 5).

    In a first step a scan over ground is performed. When there known points (targets) in the point cloud (Fig. 3a), the Position and Orientation of the instrument can be determined. In addition the horizontal orientation of the scanner is fixed with the means of a special Laser pointer (Fig. 4). Before the scan the Laser pointer is oriented towards a vertical reference line, like the vertical line defined by the corner of a house.

    After the lowering of the scanner into the sewer, the horizontal orientation is reestablished by pointing with the laser pointer to the same vertical line. In this case both scans have the same horizontal orientation and position. The height difference of the two points of views can be detected directly in the corresponding point clouds.

    Measurement Equipment

    The measurement equipment consists of a simple laser pointer (special construction, Fig. 4), a Laser scanner IMAGER 5006 from ZOLLER + FROHLICH and a special pendulum tripod (Fig. 5), which is until now a prototype from Gottlieb NESTLE (Germany).

    Fig. 4a: Laser pointer on the Fig. 4b: Laser pointer with a mechanical top of the tube elements fixation for the inclination angle

    Principal Sequence of a Measurement

    In most of the cases the acquired point clouds should be georeferenced. Therefore a scan over ground is necessary, including some known points (targets). After the scan over ground - also executed in the up-side down mode - the scanner is lowered into the underground position (Fig. 7). The lowering itself can be handled with a mechanical or electrical crank.

    Fig. 5b: Elevation component of the tripod

    Fig. 5c: Adapter plate for the Scanner

    The horizontal position and the horizontal orientation of the scanner do not change between the over ground and underground position. The only remaining unknown value is the height difference between both scans: it will be determined later on during the data processing via a direct comparison of the z-component in the two point clouds. The result is a georeferenced point cloud of the sewer.

    PRELIMINARY INVESTIGATIONS

    First of all this method was evaluated in terms of functionality and accuracy. Several tests were made at the University of Applied Sciences Bochum, by simulating the manhole-situation.

    Feasibility Study - Outdoor

    Directly in front of the Laboratory for Laser Scanning a hole was made into the balcony in order to simulate the manhole. This allowed simulations up to a height difference of about 4m (Fig. 6).

    Fig. 6: Measurement of the rotation of the scanner with auto collimation

    The biggest advantage of this simulation is the combination of the over ground and underground scans by identical targets. This is in the real situation not possible. Here it is the key element for an independent evaluation of the real budget of measurement uncertainties.

    Scans in three different depths were performed. During the scans the scanner position was continuously determined with a Laser Tracker (T3 from API, USA). The accuracy of the determination was better than 0.1mm (1 a).

    Fig. 7: Sequence of a measurement - the sewer is simulated by a hole in

    the balcony

    Fig. 8: Stability of the position of the Laser Scanner during the scans

    The changes in position show a magnitude of 10 millimeters. For the height there are nearly no variations.

    The horizontal (X) and vertical (Y) rotations were additionally observed during the scans with an auto collimator (ELCOMAT 2000, MOLLER-WEDEL, Germany). The results are displayed in Fig. 9.

    Fig. 9: Rotation angles during 1 Scan - observed with autocollimator ELCOMAT

    2000.

    The rotations about the vertical axis (horizontal changes) were very small, compared to the rotations about the horizontal axes.

    In Fig. 10 two images of the same target in the object space are shown. Fig. 8a shows a geometrically stable point cloud from the over ground position. In contradiction Fig. 10b: The dark and bright segments of the targets are separated in reality by straight lines. The undulated lines indicate periodic rotations of the scanner during the data acquisition.

    Fig. 10a: from over ground position Fig. 10b: from lowest underground

    position

    As a first result we can conclude: in principle the scanner is working in the upside-down mode and also in conjunction with the special tripod. The underground positions of the scanner are not stable enough during the scans. As a consequence it was decided to make a second test in an indoor environment.

    Feasibility Study - Indoor

    The second feasibility study was conducted in an indoor environment. The situation was simulated again with an artificial hole in the balcony of one of our laboratories (Fig. 7). In this environment 25 Auto-targets from ZOLLER + FROHLICH were used for the independent accuracy estimation.

    Fig. 11: Proper movement of the scanner in a depth of 3.7m

    The proper movements of the scanner were much smaller compared to the first outdoor study. Fig. 11 shows the position displacement during several scans. One important result is: The movements in the lowest position show - after a period of initial damping - residuals of some Millimeters. The asymmetric behavior during the real data acquisition can be caused by a slightly asymmetric mass distribution in the scanner itself.

    Fig. 12: Horizontal displacements of the scanner during 1 scan (3m19s).

    Fig. 12 is representing the horizontal displacements during one active scan (3m19s). On a first view the displacements are looking dramatic, but the magnitude of the variations is overall smaller than 2 mm for each direction.

    rr 110

    ^ 108

    .E 106 c

    .2 104

    102

    ~ 100

    oo

    98

    96

    94

    • over ground • underground 1-

    - V ^ 1 \

    \ 1

    X \

    /

    / / / 1

    «r

    92 94 96 98 100 102 104 106 108 110 112

    Changes in position X [mm]

    Fig. 13: Deviations of the horizontal orientation as vector plot between the 2 scans.

    In order to investigate the quality of the horizontal orientation a real registration was compared with the known nominal values. The plot of vectors shows the results (Fig. 13).

    CONCLUSIONS

    With this method we can measure and determine the geometry of small sized subterranean structures, like manholes, sewers, shafts, etc. without climbing into the building. An accuracy of 1 to 3cm horizontal and vertical is achievable. The significant differences in the quality and accuracy of the measurements between the indoor and the outdoor study were mainly caused by wind during the outdoor experiments.

    REFERENCES

    FUSS, Marcel (2011) "Die Aufmessung unterirdischer Schachtanlagenmit einem Laserscanner.- Entwicklung und Erprobung eines Messkonzepts", Bachelor Thesis University of Applied Sciences Bochum, unpublished.

    FUSS, Marcel; STAIGER, Rudolf (2011) "Die Erfassung unterirdischer Schachtanlagen mittels Laserscanning", Allgemeine Vermessungsnachrichten; in print.

    ZOGG, Hans-Martin (2008): "Terrestrisches Laserscanning zur Aufnahme von technischen Bauwerken am Beispiel von Schachtkammern" 74. DVW-Seminar "Terrestrisches Laserscanning - Ein Messverfahren erobert den Raum" 2007. Schriftenreihe des DVW, Volume 53, P. 187 - 200

    CONTACT Prof. Dr.-Ing. Rudolf Staiger Vice-President of FIG University of Applied Sciences Bochum Lennershofstrasse 140 44801 Bochum GERMANY Tel. + 49-234-32-10547 Email: Ця електронна адреса захищена від спам-ботів. Вам потрібно увімкнути JavaScript, щоб побачити її. Website: www.hs-bochum.de

    © R. Staiger, 2011


    Ключові слова: LASER SCANNER /TOPOGRAPHY OF SUBTERRANEAN EXCAVATIONS /IMAGER 5006 /SCANNER IN UPSIDE-DOWN-MODE /HIDDEN POINT POLES /SPECIAL PENDULUM TRIPOD

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