13 Sep 2018

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HERON SUCCESS CASE — STREET EVALUATION AND UNDERGROUND DETECTION


MAPPING AND ANALYSIS OF UNDERGROUND TUNNEL AND UPPER STREETS Aposa underground river, Bologna (Italy)

PDF versione italiana

PROJECT DESCRIPTION

KEYWORDS:  Street evaluation | Urban analysis | Mapping | HERON | Wearable 3D Laser Scanner | Underground city verification



Gexcel, in collaboration with Topcon Italy, College of Surveyors di Bologna and Amici Delle Acque Association, carried out the 3D survey of the underground river Aposa. The ancient tunnels have been mapped and analyzed to verify the level of structural deterioration, dangerous for overlying squares and roads, and to plan possible conservation activities.


HERON outdoor survey of the Aposa river
Fig.1_HERON outdoor survey of the Aposa underground river
Bologna underground tunnel entry
Fig.2_The exit from the city underground tunnel


NEEDS AND GOALS

  • Generate a 3D model of the underground city tunnels
  • Update the existing city map with 3D laser scanner information
  • Obtain a geo-referenced 3D survey
  • Analyze the geometry to prevent collapses or faults and historical monuments deterioration


HERON survey of the Bologna underground tunnel
Fig.3_The Aposa underground tunnels and the HERON surveying 



HERON AC-1 technology has been used to detect approximately one kilometre of route distributed between streets, squares and underground tunnels, without the need for GPS systems. The duration of the survey corresponded to the time taken by the operator to walk. Some spherical targets were placed along the tunnel, noting down their coordinates directly on the HERON Control Unit. In this way, the geo-localization could also be achieved. The many cavities along the tunnel were not a problem and the operator was able to survey even the narrowest of them.  (See Video)


Bologna underground topographic surveying
Fig.4_Topographic surveying of a portion of the Aposa tunnels



The topographic survey was carried out, using 8 control stations and 40 reference points for a high geometric accuracy result. The Topcon GLS2000 static laser scanner survey was necessary for a very old and particularly damaged part of the tunnel. In this way, a high-resolution data was obtained, useful for an accurate analysis of the actual state of the structure.



Bologna 3D underground analysis
Fig.5_Bologna underground tunnell and upper street analysis 

Aposa underground tunnel cross section
Fig.6_The Aposa Underground tunnel cross section



Combining the HERON global survey with high-resolution scans, it was possible to document a significant urban area, obtaining multilevel information and a complete 2D and 3D mapping.
Here some of the HERON technology benefits:

  • Fast mapping of a large area in difficult surveying conditions
  • Fast and frequent update of site’s 3D models' thanks to the automatic geo-localization feature. Operators with basic knowledge in surveying and geo-localization can easily manage it. 
  • Easy integration with colored point clouds from terrestrial laser scanners



RESULTS

  • Detailed technical table
  • Plans, sections, elevations, high-resolution orthophotos and photo plans
  • 3D point cloud model
  • 3D model flythrough movies
  • Topcon terrestrial laser scanner and HERON mobile mapping system joint 3D model


Aposa: Bologna underground 3D model
Fig.7_The joint 3D model visualized in the JRC 3D Reconstructor software



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