LABORATORY: CNR ISPC

                                                                    

NAME OF THE INSTRUMENT

Cameras and several lenses, UAS), laser scanning systems (TOF and phase-based), topographic systems (differential GPS and total station)

 

GENERAL DESCRIPTION

The CNR ISPC laboratories have a strong know-how in survey methodologies and techniques integrating image-based e range-based solutions aimed at surveying Cultural Heritage, documentation, and scientific visualization. The laboratories are equipped with instrumentation and active and passive sensors for the 2D and 3D digitization of monuments and archaeological sites. The institute's instrumentation mainly consists of terrestrial and aerial photogrammetric systems (high-resolution photographic cameras and several lenses, UAS), laser scanning systems (TOF and phase-based), topographic systems such as the differential GPS, for the positioning of points on the territory, intended both as points of fixed stations for the constitution of polygonal, and points for the determination of the shape of the territory, which can be loaded directly on the most common GIS platforms (QGIS), and total station. In the context of a 3D survey project, CNR ISPC can offer its scientific collaboration for the planning, survey, processing, interpretation, and visualization of the surveyed data.

 

TECHNICAL DESCRIPTION

Although laser scanner and photogrammetric systems are independent, they often require a topographic survey to support orientation and to avoid rotation and propagation errors. Given that, surveying activities on the territory or in the archaeological/architectural field are always carried out with the following instrumentation: Total Station (TS) and Global Navigation Satellite System (GNSS).

a)   The stazione totale can be considered the descendant of to the theodolite and is still a useful tool for topographic work in the archaeological field. Starting from different stations, defined by the topographer, it is possible to acquire coordinates of points in space, in a local reference system established a priori (x,y,z). In the past, this technique has made it possible to acquire numerical data in photo-rectification processes for the representation of the facades of historical buildings in the architectural field. Recently, it is a fundamental tool for every photogrammetric application. Indeed, topographic survey of ground control points is always required to improve photo alignment during image-processing and to scale and geo-reference 3D models obtained.

b)     GPS/GNSS (Global Positioning System/Global Navigation Satellite System) systems are measuring instruments used to gather and manage spatial data. This technology was developed at the end of the 1980s with the GPS constellation derived from military know-how . Currently, GNSS systems have achieved high accuracy in the field of topographic surveying by exploiting other constellations, such as GLONASS and COMPASS. The main advantage of this technology is the possibility to relate spatial data within a single (global) reference system.

GPS determines the coordinates of a point based on information received from at least 4 satellites, using the geometric principle of space forward intersection. A single GPS receiver has positioning error between 10 m and 30 m. This uncertainty depends mainly on the signal but also on other variables such as the geometric arrangement of the satellites. To achieve centimetre accuracy, it is necessary to use two receivers in differential mode. This mode, called D-GPS (Differential Global Positioning System), allows twin receivers (with the same characteristics) to receive the same information from the satellites at two different times during the measurement, improving final accuracy.

 

Referents:
Daniele Ferdani daniele.ferdani@cnr.it
Andrea Angelini andrea.angelini@cnr.it

 

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