University of Brescia - ITALY DAMAGED ROAD TUNNEL LASER SCANNER SURVEY Prof. Giorgio Vassena giorgio.vassena@unibs.it
WORKFLOW - Demand analysis - Instruments choice - On field operations planning - Laser Measuring session - Georeferencing the scans - Data processing - Extraction of geometrical information - Graphic elaboration
CASE STUDY ROAD TUNNEL: - 10 meters inside diameter - Structural collapsing of concrete coating and overhanging rock mass detachment in the roadside rest area
DEMAND ANALYSIS ACQUIRED DATA FEATURE EXTRACTION PURPOSES DEMAND COMPLETE GEOMETRY EXTRACT MORPHOLOGICAL INFORMATION GRAPHICS REPRESENTATION 3D MODEL PLANS SECTIONS REFLACTANCE VALUES DIGITAL IMAGES LOCALIZE INTERESTING ZONES POSITIONING DIFFERENT MATERIALS CONSTR. PARTICULAR RED FAULT - STEEL BARS POSITION
- Instruments choice LASER SCANNER For this kind of application a phase shift laser scanner, with a fast rate of point acquisition combined by a good accuracy and resolution is suggested. In this application the characteristics of the hardware are as follow: Phase shift laser scanner - Range: 53 m - Field of view: 360 x 310 degrees - Speed: up to 500,000 pts/sec - Resolution: 350 micro-radians min. angular step
- Instruments choice TOTAL STATION As total station, to measure the target point, we suggest an instruments with a RL (reflector less) distanziometer. The total station must have at least an accuracy of 1,5 mgon in angle and 2+2 ppm in distance accuracy.
- Software choice SOFTWARE - Laser control To manage the laser scanner data the software Reconstructor developed by the JRC (Joint Research Centre of the European Commission) has been used - Pre-processing - Registration - Meshing/Integration -Texture/Texture Mapping - Inspection - File view
On field operations planning COLLAPSED ZONE PLANNING THE SCAN POSITIONS ON A NOT COLLAPSED ZONE 38 m 1 2 3 5 4
On field operations planning PLANNING THE SCAN POSITIONS ON A NOT COLLAPSED ZONE UNDAMAGED ZONE 38 m 1 2
Laser Measuring session CHARACTERISTICS OF ACQUIRED CLOUDS OF POINTS POINT CLOUD RESOLUTION: The obtained point clouds have around 7mm points spacing Small Elements are observable and can be measured 7mm at 6 m
Georeferencing the scans GEOREFERENCING THE ACQUIRED POINT CLOUDS The clouds of points are placed in a local or cartographic reference system The best fitting of the different scans is optimized thanks to the ICP (automatic registration)
Data processing 3D JRC Reconstructor DATA PROCESSING WITH RECONSTRUCTOR 1/2 Besides their georeferencing and mutual registration, the point clouds of the scans have been processed according to the following operations: 1. Normal computation: the local surface normal is computed 2. Confidence computation: calculate the reliability for each single measured point. 3. Edge detection: angular and distance discontinuity have been computed and represented with edges. 4. Noise reduction: this operation has been needful to reduce the presence of noise in the scan range using filters.
Data processing 3D JRC Reconstructor DATA PROCESSING WITH RECONSTRUCTOR 2/2 5. Data clustering: the creation of a hierarchical structures has been performed. 6. Integration: during this phase the processing software has to remove the redundancy introduced through overlapping scans. 7. Meshing: this process has finally converted the set of raw 3D points into a continuous surface. 8. Texture Processing: the integration of the 3D measurements from the laser scanner with 2D information taken with an external camera has been carried out.
Extraction of geometrical information EXTRACTION OF GEOMETRICAL INFORMATION Realisation of cross-sections a) In this case study the extraction of the DWG files has been carried on by the surveyor. b) The University of Brescia has also tested its own developed software 3D Manager. The research is going in the way to permit to the final user, not to expert in 3D laser scanning data, to extract by himself the information from the 3D model. In this way the 3D model can be really used not only by the laser scanner expert but also by civil engineers, geologists, architects, that means by what can be called the final user of the survey.
Extraction of geometrical information EXTRACTION OF GEOMETRICAL INFORMATION Realisation of cross-sections Sectioning planes are defined by their geometrical position specifying n : the normal unit vector. n
Extraction of geometrical information EXTRACTION OF GEOMETRICAL INFORMATION Realisation of the plans
Extraction of geometrical information EXTRACTION OF GEOMETRICAL INFORMATION Positioning the main steel bars and the red fault Steel bars position (x,y,z) Red fault contour
CONCLUSIONS immediate structures restoring acquisition of all the considerable geometric features Possibility to survey and represent quickly complex geometry situations: provides to associate the geometry to the visual information precise surveying of the main geological and structural units can be conveniently adopted in road and rail tunnels in order to minimize the influence on the regular traffic
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