Systems for data processing, anaylsis and representation

Allam, Mosaad; Plunkett, Gordon

Bibliographic data

Monograph

Persistent identifier:: 1067490280

Title:: Systems for data processing, anaylsis and representation

Sub title:: ISPRS Commission II Symposium : June 6 - 10, Ottawa, Canada

Scope:: 1 Online-Ressource (XX, 530 Seiten)

Year of publication:: 1994

Place of publication:: Ottawa

Publisher of the original:: The Surveys, Mapping and Remote Sensing, Natural Resources Canada

Identifier (digital):: 1067490280

Illustration:: Illustrationen

Signature of the source:: ZS 312(30,2)

Language:: English

Additional Notes:: Erscheinungsdatum des Originals ist aus dem Copyrightjahr ermittelt.

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Allam, Mosaad; Plunkett, Gordon

Corporations:: Symposium Systems for Data Processing, Analysis and Representation, 1994, Ottawa; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis; Kanada, Surveys, Mapping and Remote Sensing Sector

Adapter:: Symposium Systems for Data Processing, Analysis and Representation, 1994, Ottawa; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis; Kanada, Surveys, Mapping and Remote Sensing Sector

Founder of work:: Symposium Systems for Data Processing, Analysis and Representation, 1994, Ottawa; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis; Kanada, Surveys, Mapping and Remote Sensing Sector

Other corporate:: Symposium Systems for Data Processing, Analysis and Representation, 1994, Ottawa; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis; Kanada, Surveys, Mapping and Remote Sensing Sector

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2019

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: [Friday, June 10, 1994]

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: [Session L-1 WG II/1 - Real-Time Mapping Technologies - Algorithmic Aspects]

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: LASER RANGE SCANNER SUPPORTING 3-D RANGE AND 2-D GREY LEVEL IMAGES FOR TUNNEL SURFACE INSPECTION C. Fröhlich, M. Mettenleiter and G. Schmidt

Document type:: Monograph

Structure type:: Chapter

highly reliable range measurements are necessary for geome- tric inspection of tunnel tubes. Gap-less inspection of tunnel tubes requires a range of up to 10 m, a spatial resolution of 2500 pixels per 360° profile, and a distance between two consecutive measured profiles of less than 2.5 cm. Due to sooty walls and metallic objects in the tunnel, the sensor system has to handle high dynamic range re- flectances of the objects. Furthermore, the sensor system must be robust when dealing with environmental influences such as temperature or humidity as well as varying illumination conditions (dark, ambient light, lamps, etc) as they are typical for tunnel tubes. Safe operation with respect to people is re- quired all times. Only non-tactile sensors are suited for covering these de- mands. Non-tactile range measurement techniques may be classified as either active techniques, directing visible or infra- red (IR) light, ultrasonic [16] or radar [17] pulses to the sur- face to be measured, or as passive techniques based on vision. A rich variety of passive vision techniques produce three- dimensional information. Traditionally they have lacked ro- bustness with changing illumination conditions and generality, and have not proven themselves effective in practice. Passive stereo or motion stereo vision [18,19] are particullary pro- mising sources of range information, but require substantial data processing to match images with each other in order to determine range by triangulation and, therefore, are not well suited for real-time tunnel surface inspection. For these reasons we have selected an active range measure- ment technique which directly determines "range" data with a minimum computation time. To achieve high spatial réso- lution, only an active technique emitting collimated laser light is suitable. The collimated laser beam is directed to the target to be measured and the back scattered light is sensed. In ad- dition to "range" measurement, evaluation of the magnitude of the back-scattered light provides an "active grey level" which is similar to the grey level information of a video camera. Both range and grey level data of a target point are registered at the same time and correspond to a single target point defined by the laser beam direction. Due to emitted laser energy, both informations, range, and grey level data are near- ly independent from environmental influences and illumina- tion conditions. In order to achieve profile data the range measuring system is combined with a one-dimensional scanner for 360? beam deflection. For longitudinal inspection of the tube, the system is mounted on a special vehicle (or train) navigating at a maxi- mum speed of 5 m/s through the tunnel. Resulting spiral pro- files are combined with respect to the corresponding sensor positions. The final range image reflects geometric dimensions of the tunnel tube whereas the grey level image is used for vi- sual inspection, surface classification, and documentation pur- poses. 2.2 The two-frequency phase-shift method Because of the requirements for high-precision range mea- surement within a range of up to 10 meters, evaluation of the phase-shift (Fig. 1) between a reference laser beam and the back scattered laser light is more suitable than measuring the light's extremely short time of flight. The amplitude P, of the emitted continuous-wave laser signal is simultaneously intensity modulated (am-cw) with two fre- quencies Q, and o». Laser light back scattered from a target is collected by an avalanche photodiode. The amplitudes Py are fairly small. Due to the time-of-flight, the received sine- shaped signals are phase-shifted in relation to their reference in the transmitted signal. Phase shifts ¢, and ¢, are propor- tional to the range d and the modulation frequencies. Since phase shifts are only unique modulo 2m, the modulation fre- quencies ®; and ®, are selected to provide a sufficient mea- surement range with an appropriate range resolution. A low- frequency signal (LFS: o, = 10 MHz) guarantees a coarse but absolute measurement range of s, (s, 2 15 m), whereas the high-frequency component (HFS: ®, = 80 MHz) provides a fine (s 2 1.875 m) but ambiguous range information over $,. Correct combination of the phase shifts ©, and ©, of both fre- quencies provides absolute and accurate range measurements within the specified range. R- CD NO Target Fig. 1: The two-frequency phase-shift method 3. THE LASER RANGE SCANNER Hardware of the laser range scanner (Fig. 2) consists of two major components: the range measuring system and the beam deflection system. Both components operate independently from each other. They are connected via a control and moni- toring system. emitted ' L: avalanche laser light photodiode ' * | receiver v received | laser light E rr > optics a a Wa LU ue = + id Fig. 2: Mechanical design of the range scanner Deviations from the continuously monitored eyesafe operation level or any deviations from the normal operation mode of the scanner, causes the camera to be shut off automatically. High- 472 speed da compute; The rang laser ran; cy unit ai sing. Laser H« The laser infrared ( tered froi micro-me The laser that emit Varying | modulate: 60825) is of a grey: power rec as well as forms the with smal reflected optical pa f = 50 mr todiode as tral noise reflectanc High freq The high | laser diod quency-se light. For modul the frequei In order tc single 80 1 ates modu current mc eliminatin; oscillator a The back-: tered in or channels, : ture mixer dynamic r2 quadrature quadrature In-phase (F complex m tional to m guity inter dicates inte

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