This is possible thanks to the hardware and software growth. Today hardware allows to scan with precision both underwater objects, e.g. with interferometric bathymetry, and objects above sea-level, with laser scanning systems. It is then possible to register the two scan types, making them effectively usable without distinction.

On the other side, even software has developed and today it is possible to model directly in three-dimensions on the point clouds acquired by laser scanning and/or interferometric bathymetry and than extract, easily and quickly, from the model the necessary dimensional information.

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Hardware: Integrated Laser Scanning, Interferometric Bathymetry and Side Scan Sonar

Laser scanning and underwater interferometry are the state of art of technology applied on environmental survey. For such reason Codevintec (Italian reseller company of Optech and SEA instruments) and its partners wanted to test the integration between the two technologies carrying out precision surveys on the river Po and some Italian ports (Venice, La Spezia, Monopoli and Livorno).
The present paper deals with the survey of Livorno port where the seabed was surveyed with interferometric system, producing the point cloud with signal intensity, bathymetry DTM and side scan images. The scanning of the areas above sea-level was carried out with the laser scanner Ilris 3D.
The multibeam survey was performed aboard a boat, thanks to the precision positioning obtained with an inertial platform and connection with the GPS (Global Positioning System) satellite system, necessary for georeferencing instantaneously the point clouds acquired with the two different instruments. On the contrary, the laser survey was performed on land. In particular the castle was surveyed from three different points, then the clouds were registered and georeferenced. Technology has evolved further on since the time in which such survey was performed and now it is possible to directly interface the laser scanner with the inertial platform. In this way it will be possible to carry out at the same time bathymetric and laser investigations directly aboard a boat. For such reasons, Codevintec and its partners are planning some surveys to be performed within autumn 2008.

Survey Technical Data

• The underwater parts survey has been performed by a SEA SWATHplusII Interferometric Multibeam.
• The position adjustment was performed with positioning system and motion compensation CodaOctopus F-180. In some cases they were used the positioning systems already available aboard the lodging boats and used with traditional multibeam systems.
• The areas above sea-level were surveyed by Optech ILRIS-3D Terrestrial Laser Scanner.

Software: 3D Modelling and Dimensional Enquiries

Using CloudCUBE 2008, an AutoCAD integrated software developed by Virtualgeo s.r.l. (Italian multidisciplinary company with a 20-year experience in the survey field), it was realized a 3D model starting from the registered point clouds. The point cloud resulting from the registration of the castle walls (scanned with terrestrial laser scanner) and the surrounding seabed (acquired with interferometric bathymetry) counts 5.791.547 non coloured points. The Ilris 3D laser scanner is equipped with high resolution camera to produce RGB coloured point clouds.
Once the modelling process was completed, performed applying a surface (a 0.50x0.50 m step quadrangular grid for the structure of the fortress and a 1.00x1.00 m step quadrangular grid for the seabed), 39.727 triangles were obtained.
In such way it was possible to interpret the surveyed data according to the specific case requirements, producing a “light” final output including all and only the required dimensional information and which can be “studied” quickly and simply by the experts of the field.
The modelling process was completed in 7 hours. It included the following main phases:

1. point cloud analysis, highlighting the main elements and deciding the level of the finishing to be used for modelling;
2. segmentation process: dividing clouds into parts and sub-parts to make the modelling and representation processes easier;
3. modelling of the several sub-clouds, resulting from the segmentation process, using the most appropriate modelling techniques: surface (quadrangular grid with variable step according to the final detail);
4. joint of the several parts of the model, the structure of the fortress and the seabed, thus obtaining a single final model.

Conclusion

Thanks to the new available technologies, both software and hardware, nowadays it is possible to generate digital three-dimensional supports, rapidly and with a level of detail unimaginable for the old techniques and technologies, which allow to refine and improve the study, monitoring and planning activities. Such advancement is a remarkable important resource to manage and govern better both the natural and anthropic transformations of lands and seas.