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Following the violent earthquake that hit Valle del Belìce (Italy) in 1968, the ruins of the old town centre of Gibellina, Sicily have been compacted inside Alberto Burri’s 'Grande Cretto'. At 12 hectares (29 acres), it is currently the largest open-space contemporary work of art in the world.
Like a white sudarium, the 'cretto' veils the wreckage of a past and the town that was suddenly swept away. It lies on the ruins with 2-3m large cracks and blocks of 20-30m in size. The work of art is actually not completed yet, even though the project started in 1985 and finished in 1989. It will finally be an irregular quadrilateral.
The mapping study is a kinematic analysis, carried out both on trajectory and mountain-bike, of the cycle lanes within the work of art. The experiment aimed at defining the accuracy of the surveying system that compares coordinates of specific points, on the "Grande Cretto", surveyed both on mountainbike and calculated using traditional RTK survey. At first, nine calibration points were surveyed: the points that are located at the border of the work of art, which were used to create the survey framework for the following survey phases.
In this phase the GNSS RTK survey was performed on all the blocks that form the work of art, in total, surveying more than 2150 points. Finally, the RTK survey on mountainbike was carried out: to overcome the difference of level that portrays the morphology of the "Grande Cretto", a path of more than 250 meters (820 ft) was located (passing through its highest point on the west side to its lowest point on the east side) and a further 170 positions were surveyed going along the mean line of the route.
The University of Palermo provided the GNSS equipment used during the surveying phases: a Topcon HiPer Pro receiver for the calibration points, whilst a Topcon GRS-1 receiver with PG-A2 antenna was used for both traditional RTK survey and for the kinematic survey on mountainbike. The external antenna was connected to the mountainbike through a special customised aluminium alloy bracket and provided with lateral metal screws.
The nine calibration points were used to overlay the traditional survey of Gibellina's "Grande Cretto" on the geo-referenced mapping of the old town centre at a set scale. It was then possible to observe how the work of art corresponds in its geometry to the concept of Master Burri to recall the original street asset of the town centre destroyed by the 1968 earthquake. There were many similarities found with the main streets of the old town centre, as well as the geographical correspondence to the ancient streets and urban perimeter.
As far as the traditional survey of the "Grande Cretto" is concerned, the results obtained were very encouraging; in fact, the data related to the values of the standard deviation indicate a centimetre precision. It can be therefore considered a reliable survey, allowing for an "updated state of the art of the Grande Cretto"! This is also useful for the municipal administration of Gibellina, which is currently carrying out a project to get the work of art completed.
As for the RTK survey on mountainbike, this provided the opportunity to test the usefulness of the receiver in an unusual scenario. The comparison between the points' coordinates of the mean trajectory surveyed on mountainbike and those collected with the traditional survey of the "Grande Cretto" has also provided standard deviation's values with centimetre precision.
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