Visualisation technical 3D mapping the Tower of

Compiled by Clare van Zwieten, EE Publishers

Australian researchers have created the first ever interior 3D map of ’s Leaning Tower of Pisa by using a breakthrough mobile laser mapping system, the ZEB 1. This detailed record will be of great assistance in preserving the cultural heritage of the site.

he Leaning Tower of Pisa is the freestanding bell tower, Tof the of the Italian city of Pisa, known worldwide for its unintended tilt to one side. It is situated behind the Cathedral and is the third oldest structure in Pisa's Cathedral Square (Piazza del Duomo) after the Cathedral and the Baptistry. In 1987 the tower was declared as part of the Piazza del Duomo UNESCO World Heritage Site. The leaning Tower of Pisa was designed as a circular bell tower and is constructed of white marble. It consists of eight stories, including the chamber for the bells. The bottom story has 15 marble arches and each of the next six stories contain 30 arches that surround the tower. The top story is the bell chamber,

which has 16 arches. There is a 297 Fig. 1: Dr. Jonathan Roberts, Program Leader for CSIRO's Computational Informatics Division step spiral staircase inside the tower scanning the Leaning Tower of Pisa with the new Zebedee technology. leading to the top. The height of the tower is 55,86 m from the ground on the low side and 55,70 m on the high side. The width of the walls at the base is 4,09 m and at the top 2,48 m. Its weight is estimated at 14 500 metric tons.

Construction Construction of the tower occurred in three stages across 199 years. Work on the ground floor of the white marble campanile began in 1173, during a period of military success and prosperity. This ground floor is a blind arcade articulated by engaged columns with classical Corinthian capitals. The tower began to sink after construction had progressed to the second floor in 1178. This was due to a mere 3 m foundation, set in weak, unstable subsoil. Construction was subsequently halted for almost Fig. 2: Lead counterweights are used to stabilise the tower. (Credit: Rolf Gebhardt.)

52 PositionIT – October 2013 VISUALISATION technical

in combination with the softer foundations on the lower side. Many methods were proposed to stabilise the tower, including the addition of 800 tonnes of lead counterweights to the raised end of the base (see Fig. 2). In January 1990, after over two decades of stabilisation studies, the tower was closed to the public. The bells were removed to relieve some weight, and cables were cinched around the third level and anchored several hundred metres away. Apartments and houses in the path of the tower were vacated for safety. The final solution to prevent the collapse of the tower was to slightly straighten the tower to a safer angle, by removing 38 cubic metres of soil Fig. 3: Display of final Zebedee 3D map of the Leaning Tower of Pisa. from underneath the raised end. The tower was straightened by 45 cm, returning to its 1838 position. After a decade of corrective reconstruction and stabilisation efforts, the tower was reopened to the public in December 2001. In May 2008, another 70 metric tons of ground was removed, and engineers announced that the tower had been stabilised.

3D laser scan In September 2013 Australian researchers created the first ever interior 3D map of the tower using Zebedee technology. Developed by the CSIRO, Australia's national science agency, the Zebedee system consists of a handheld 3D mapping system incorporating a laser scanner that sways on a spring to capture millions of detailed measurements of a site as fast as an operator can walk through it. The primary sensing technology utilised is lidar, in which an infrared laser measures ranges to surfaces in the environment. The Fig. 4: Screenshot of the 3D point cloud created from the scan of the Leaning Tower of system produces a 3D map of the Pisa. environment as well as an accurate record of the trajectory followed. The distinguishing feature of a century, because the Republic of Stabilising Zebedee's design is that the laser Pisa was almost continually engaged In 1964, the government of Italy scanner is mounted on a spring, in battles. This allowed time for the requested aid in preventing the which provides a lightweight solution underlying soil to settle. tower from toppling. It was, however, for ensuring a wide scanning field of In 1272 construction resumed and in considered important to retain the view. The spring converts the natural an effort to compensate for the tilt, the current tilt, due to the role that this motions of the operator into a suitable engineers built upper floors with one element played in promoting the sweeping motion of the scanner. side taller than the other. Construction tourism industry of Pisa. A low-cost inertial sensor provides was halted again in 1284, when the A multinational task force of rough measurements of the spring’s Pisans were defeated by the Genoans engineers, mathematicians, and rotations. Specially designed software in the Battle of Meloria. The seventh historians gathered to discuss is able to convert the raw range and floor was completed in 1319 and the stabilisation methods. It was inertial measurements into a 3D map bellchamber was finally added in 1372. found that the tilt was increasing in less time than it takes to collect the

PositionIT – October 2013 53 VISUALISATION technical

data. The 3D maps are represented as composition, including small details in solutions to commercialise the point clouds, which consist of millions the stairs and stonework. Zebedee research into the ZEB1 of points expressed in a common During “Project Pisa”, CSIRO also product. As well as its applications in coordinate frame. collaborated with local Italian cultural heritage, ZEB1 is also being While the tower's cramped stairs and scientists from Scuola Superiore used to increase efficiencies and complex architecture have prevented Sant'Anna (SSSA) who believe the improve productivity in a number of previous mapping technologies from research will have significant impact different industries. For example, the capturing its interior, Zebedee has on preserving the cultural heritage of technology is already assisting mining enabled the researchers to finally the site. companies to better manage their create the first comprehensive 3D Franco Tecchia, Assistant Professor at operations and helping security forces map of the entire building. the PERCRO – Perceptual Robotics lab, to quickly scan crime scenes. Dr. Jonathan Roberts, Research says that this detailed record of the CSIRO's Zebedee research was Program Leader at CSIRO’s Leaning Tower of Pisa may one day recently awarded a 2013 Eureka Prize, Computational Informatics Division be critical in being able to reconstruct often referred to as an "Australian says that the technology is ideal for the site if it was to suffer catastrophic Oscar of Science", for Innovative Use cultural heritage mapping, which is damage due to natural disasters such of Technology. The Australian national usually very time consuming and as a fire or an . Having science agency's breakthrough 3D labour intensive. It can often take a detailed 3D model of the world’s mapping system was also recently a whole research team a number of most significant cultural heritage sites days or weeks to map a site with the recognised as the winner of the accuracy and detail of what we can could also be used to allow people Research and Development category produce in a few hours. who cannot physically visit these sites at the iAwards, Australia's premier to better understand and appreciate ICT awards program. Within 20 minutes the researchers their history and architecture. were able to use Zebedee to complete References an entire scan of the building’s In 2012, CSIRO through its Digital interior. This allowed them to create a Productivity and Services Flagship [1] Wikipedia: http://en.wikipedia.org/wiki/ uniquely comprehensive and accurate worked with 3D Laser Mapping, a Leaning_Tower_of_Pisa 3D map of the tower's structure and global developer of laser scanning [2] CISRO: www.csiro.au 

54 PositionIT – October 2013