Two innovative laser scanning prototypes have been developed at ENEA for diagnostics of large surfaces relevant to
monumental cultural heritage. The first, based on amplitude modulation technique in the visible, is a trichromatic (Red
/Green /Blue) imaging topologic radar (RGB-ITR) specialized to collect high resolution 3D models. After proper color
calibration, it allows for hyper-realistic rendering of colored features on painted surfaces and for precise localization of
irregularities.
The second is a line scanning system, working either in reflectance or laser induced fluorescence mode, capable of fast
2D monochromatic images acquisition on up to 90 different spectral channels in the visible/UV range, which was
developed to investigate the presence of different substances onto the painted surface.
Data collected during former field campaigns on frescos by means each scanning system will be reported and discussed
extracting information of interest to conservators by means of specific data processing methodologies and respective
software tools.
Recent results relevant to paints of the Assumption on slate and canvas by Scipione Pulzone named “il Gaetano”
collected in two churches in Rome (San Silvestro al Quirinale, Bandini chapel; Santa Caterina dei Funari, Solano della
Vetera Chapel) from the late XVI century are presented in order to demonstrate the increased diagnostic capabilities
coming from data integration. From combination of reflectance data from both instruments, the first true remote
differential colorimetry has been implemented, giving a chance to test the color quality in the future from the archived
images.
KEYWORDS: Laser scanners, Calibration, Modulation, 3D scanning, Signal detection, Distance measurement, Laser sources, 3D modeling, Sensors, Cultural heritage
Since several years our laboratory in ENEA Frascati Research Center is involved in development of laser scanners for
Cultural Heritage investigation problems. Actually the best result obtained in this field by our laboratory is a 3D Red
Green Blue Laser scanner, called RGB-ITR: the main feature of this scanner, further then measuring distances (up to
20m with a sub-millimetric resolution), is the ability to capture remotely color information by three calibrated laser
sources: this information is collected for each point sampled by the instrument and is not affected by external light
sources' influence. Moreover the ability to acquire color and distance information at the same time and for each point
decrease drastically the post-production pipeline of a complete mesh. In this work the results of a complete scan of S.
Peter Martyr in Rieti are shown, highlighting the efficiency and robustness of color calibration algorithms introduced for
a correct color representation.
KEYWORDS: RGB color model, 3D image processing, Sensors, Laser scanners, Signal to noise ratio, LIDAR, Reflectivity, 3D modeling, Modulation, Signal detection
We present a new color (RGB) imaging 3D laser scanner prototype recently developed in ENEA (Italy). The sensor is
based on AM range finding technique and uses three distinct beams (650nm, 532nm and 450nm respectively) in
monostatic configuration. During a scan the laser beams are simultaneously swept over the target, yielding range and
three separated channels (R, G and B) of reflectance information for each sampled point. This information, organized in
range and reflectance images, is then elaborated to produce very high definition color pictures and faithful, natively
colored 3D models. Notable characteristics of the system are the absence of shadows in the acquired reflectance images -
due to the system's monostatic setup and intrinsic self-illumination capability - and high noise rejection, achieved by
using a narrow field of view and interferential filters. The system is also very accurate in range determination (accuracy
better than 10-4) at distances up to several meters. These unprecedented features make the system particularly suited to
applications in the domain of cultural heritage preservation, where it could be used by conservators for examining in
detail the status of degradation of frescoed walls, monuments and paintings, even at several meters of distance and in
hardly accessible locations.
After providing some theoretical background, we describe the general architecture and operation modes of the color 3D
laser scanner, by reporting and discussing first experimental results and comparing high-definition color images
produced by the instrument with photographs of the same subjects taken with a Nikon D70 digital camera.
The propagation of polarized laser beams in turbid water is a subject of relevant interest in the field of underwater
quantitative visualization with active sensors like amplitude modulated laser systems. In such devices, target range
determination is based on the measurement of the phase difference ΔΦ between the fraction of the amplitude modulated
laser beam reflected by the target and a reference signal. As water turbidity increases, the laser radiation backscattered
from the water column shined by the sounding laser beam gives rise to an optical background with detrimental effects on
the accuracy of range measurement. In this paper we analyze the possibility to increase the apparatus accuracy with a
polarimetric technique based on the adoption of polarized laser radiation and polarization selective detection scheme for
improving the underwater imaging of real scenes (e.g. archaeological sites). The method fully takes advantages of the
different polarization properties of the laser radiation backscattered by turbid water and of the Lambertian component
diffusively reflected by the target as described by the associated Mueller matrices. Measurements have been performed
by adopting both a co-polarized and cross-polarized detection scheme with linearly and circularly polarized laser
radiation. Various degrees of turbidity were realized by adding, as diffusive element, skim milk to water in order to
obtain different scattering conditions. The effect of the transition from Rayleigh to Mie scattering regime on phase
accuracy determination has been investigated together with the role played by high order scatterings as the medium
approaches the optical thickness condition.
KEYWORDS: 3D modeling, Sensors, Signal to noise ratio, Radar, Cultural heritage, Radar imaging, Image resolution, Modulation, Software development, Data modeling
We present the last results obtained by using our Imaging Topological Radar (ITR), an high resolution laser scanner aimed at reconstruction 3D digital models of real targets, either single objects or complex scenes. The system, based on amplitude modulation ranging technique, enables to obtain simultaneously a shade-free, high resolution, photographic-like picture and accurate range data in the form of a range image, with resolution depending mainly on the laser modulation frequency (current best performance are ~100μm). The complete target surface is reconstructed from sampled points by using specifically developed software tools. The system has been successfully applied to scan different types of real surfaces (stone, wood, alloy, bones) and is suitable of relevant applications in different fields, ranging from industrial machining to medical diagnostics. We present some relevant examples of 3D reconstruction in the heritage field. Such results were obtained during recent campaigns carried out in situ in various Italian historical and archaeological sites (S. Maria Antiqua in Roman Forum, "Grotta dei cervi" Porto Badisco - Lecce, South Italy). The presented 3D models will be used by cultural heritage conservation authorities for restoration purpose and will available on the Internet for remote inspection.
A high resolution Amplitude Modulated Imaging Laser Radar (AM-LR) sensor has recently been developed, aimed to accurately reconstructing 3D digital models of real targets - either single objects or large amplitude complex scenes. The system sounding beam can be swept linearly across the object or circularly around it, by placing the object on a controlled rotating platform. Both intensity and phase shift of the back-scattered light are then collected and processed, providing respectively a shade-free photographic-like picture and accurate range data in the form of a range or depth image, with accuracy depending mainly on the laser modulation frequency. The development of software, suitable for simultaneous 3D rendering of the intensity and absolute distance data collected by the ITR, constitutes one of the main objectives of the research activity, whatever is the application pursued. In fact, high resolution AM-LR systems have a great interest for their potentials in accurate 3D imaging of valuable objects which must be preserved in digital archives. Examples range from artwork monitoring, cataloguing and restoration from sparse fragments, to medicine for non-hazardous diagnostics and fast design of bio-compatible prostheses, to microtechnology in the miniaturization of macro-components (plastic prototypes, quality control). Several meaningful results of measurements executed in various important European archaeological sites, in particular Santa Maria Antiqua church situated in Fori Imperiali area in Rome and Costanza (Romania), involving 3D color mapped representation are also presented.
KEYWORDS: 3D modeling, Data modeling, Laser induced fluorescence, Modulation, Sensors, Data integration, Cultural heritage, Thermal modeling, Software development, Stereoscopy
A high performance Amplitude Modulated Laser Rangefinder (AM-LR) is presented, aimed at accurately reconstructing 3D digital models of real targets, either single objects or complex scenes. The scanning system enables to sweep the sounding beam either linearly across the object or circularly around it, by placing the object on a controlled rotating platform. Both phase shift and amplitude of the modulating wave of back-scattered light are collected and processed, resulting respectively in an accurate range image and a shade-free, high resolution, photographic-like intensity image. The best performances obtained in terms of range resolution are ~100 μm. Resolution itself can be made to depend mainly on the laser modulation frequency, provided that the power of the backscattered light reaching the detector is at least a few nW. 3D models are reconstructed from sampled points by using specifically developed software tools, optimized so as to take advantage of the system peculiarities. Special procedures have also been implemented to perform precise matching of data acquired independently with different sensors (LIF laser sensors, thermographic cameras, etc.) onto the 3D models generated using the AM-LR. The system has been used to scan different types of real surfaces (stone, wood, alloys, bones) and ca be applied in various fields, ranging from industrial machining to medical diagnostics, vision in hostile environments cultural heritage conservation and restoration. The relevance of this technology in cultural heritage applications is discussed in special detail, by providing results obtained in different campaigns with an emphasis on the system's multi-sensor data integration capabilities.
KEYWORDS: 3D modeling, Sensors, Modulation, Reverse modeling, Cultural heritage, 3D image processing, Data modeling, Reflectivity, LIDAR, 3D image reconstruction
A high resolution Amplitude Modulated Laser Radar (AM-LR) sensor has recently been developed, aimed at accurately reconstructing 3D digital models of real targets, either single objects or complex scenes. The sensor sounding beam can be swept linearly across the object or circularly around it, by placing the object on a controlled rotating platform, enabling to obtain respectively linear and cylindrical range maps. Both amplitude and phase shift of the modulating wave of back-scattered light are collected and processed, providing respectively a shade-free, high resolution, photographic-like picture and accurate range data in the form of a range image. The resolution of range measurements depends mainly on the laser modulation frequency, provided that the power of the backscattered light reaching the detector is at least a few nW (current best performances are ~100 µm). The complete object surface can be reconstructed from the sampled points by using specifically developed software tools. The system has been successfully applied to scan different types of real surfaces (stone, wood, alloys, bones), with relevant applications in different fields, ranging from industrial machining to medical diagnostics, to vision in hostile environments. Examples of artwork reconstructed models (pottery, marble statues) are presented and the relevance of this technology for reverse engineering applied to cultural heritage conservation and restoration are discussed. Final 3D models can be passed to numeric control machines for rapid-prototyping, exported in standard formats for CAD/CAM purposes and made available on the Internet by adopting a virtual museum paradigm, thus possibly enabling specialists to perform remote inspections on high resolution digital reproductions of hardly accessible masterpieces.
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