In our paper we will present results of an on-going project connected with monitoring the condition of 12 fragments of the Museum of King Jan III’s Palace at Wilanów (Warsaw, Poland) building façade by 3D structured-light scanning method. During 30 months, 7 series of three-dimensional measurements have been planned. In each of the twelve elevation fragments, chosen by the conservation and architecture departments as particularly interesting, an area of 120 mm x 120 mm was scanned with 2500 points/mm<sup>2</sup> resolution. This article describes the methodology of the measurement process, the hardware setup developed especially for this purpose, as well as the data processing path and analysis algorithms. In addition to having such accurate measurement data, we must still be able to match the measurements carried out in the same place at intervals of several months. For this purpose the areas of interest were marked with special aluminum targets, embedded with three intersecting planes. The algorithm of their detection, analysis and use for aligning data from subsequent measurement series is discussed. A portable SLS 3D-measurement head with two cameras, integrated with linear drive has been developed for scanning purposes and adopted to use in outdoor condition. The 3D scanner has a measurement volume limited to 45 mm x 50 mm x 10 mm for a single scan, due to high-resolution requirements. In less than 25 minutes, 40 measurements are acquired at various positions, covering the entire area, with the support of a controlled linear stage stand. Individual scans are pre-aligned with limited accuracy and then fitted using the Iterative Closest Point algorithm. The final representation of each fragment is a cloud of points with color containing more than 200 million 3D measurement points. We present the results of 3D measurements and a proposition of a monitoring procedure for assessing the change in 3D surfaces over time.
The pace of development of information systems nowadays demonstrates the magnitude of the demand for digitization of all aspects of our lives, such as medicine, industry, and documentation of cultural heritage. Digitization is the process of converting objects from the real world into their digital representations. In order to acquire complete and detailed information about the whole surface of an object, several 3D scans have to be taken from different perspectives. The resulting 3D object can be acquired in a form of a numerous amount of 3D point clouds overlaying each other. Sometimes, depending on a quality of a 3D scanner and surface properties, the point clouds can represent a noisy geometrical surface and an incorrect colour. Moreover, the directional point clouds are not perfectly aligned and a registration between them must be applied. The registration of the point clouds is a complex task which is not always possible to automate. Usually, the entire process of registration has to be supervised by a skilled operator. The registration is usually divided into two parts: initial and final matching. Initial matching is a more complex one and in this scenario, it is supported by the known system calibration, which includes, e.g., robotic arm, head of the scanner, sources of lights. Using ICP based algorithms afterward is usually enough to get appropriate final matching. The difficulty of point cloud registration increase accordingly to the number of directional clouds of points to integrate. The aim of this paper is to propose a methodology to decrease or even fully eliminate some of the presented registration issues encountered during the reconstruction of Museum of King Jan III’s Palace at Wilanów.
As forensic science technologies progress, digital photography in the crime scene documentation is being replaced in favor of high-precision 3D measurements. Three-dimensional documentation presents every object in the context of the entire crime scene and allows accurate measurements between potentially important traces, like bloodstains or weapons. These and other advanced 3D documentation and analysis tools have improved the possibilities of investigation to a previously unattainable level. We present a novel solution for detailed 3D documentation, which overcomes the limitations of commonly used 3D measurement techniques, e.g. highly accurate Structured Light Scanning or convenient to use Structure from Motion. Our solution, called active-SfM, involves the use of special projection devices to project a random pattern on the part of the scene under measurement. This modification makes the measurement process robust and reliable, even when measuring featureless surfaces. The reconstructed 3D model has better quality and surface uniformity than the result of standard Structure from Motion measurements. Moreover, the acquisition process remains as quick and easy to use as before the modifications.<p> </p> We present newly developed equipment: wireless projection devices and controllers, that were designed especially to be used by forensic technicians on crime scenes and that are compatible with stock cameras used by them in everyday practice. We also present a full set of developed algorithms that transform input images into the final 3D model.<p> </p> The proposed solution complements the hierarchical, three-dimensional measurement system developed in recent years by Polish Central Forensic Laboratory of the Police, CYBID Ltd., and Warsaw University of Technology, designed especially for crime scene documentation. The whole documentation process is supervised by a specialized CrimeView3D application, a software platform for measurement management and data visualization. We also present the outcome of measurement sessions that were conducted on both simulated and real crime scenes with the cooperation of Technicians from Central Forensic Laboratory of Police.
Three dimensional measurements (such as photogrammetry, Time of Flight, Structure from Motion or Structured Light techniques) are becoming a standard in the crime scene documentation process. The usage of 3D measurement techniques provide an opportunity to prepare more insightful investigation and helps to show every trace in the context of the entire crime scene. In this paper we would like to present a hierarchical, three-dimensional measurement system that is designed for crime scenes documentation process. Our system reflects the actual standards in crime scene documentation process – it is designed to perform measurement in two stages. First stage of documentation, the most general, is prepared with a scanner with relatively low spatial resolution but also big measuring volume – it is used for the whole scene documentation. Second stage is much more detailed: high resolution but smaller size of measuring volume for areas that required more detailed approach. The documentation process is supervised by a specialised application CrimeView3D, that is a software platform for measurements management (connecting with scanners and carrying out measurements, automatic or semi-automatic data registration in the real time) and data visualisation (3D visualisation of documented scenes). It also provides a series of useful tools for forensic technicians: virtual measuring tape, searching for sources of blood spatter, virtual walk on the crime scene and many others. In this paper we present our measuring system and the developed software. We also provide an outcome from research on metrological validation of scanners that was performed according to VDI/VDE standard. We present a CrimeView3D – a software-platform that was developed to manage the crime scene documentation process. We also present an outcome from measurement sessions that were conducted on real crime scenes with cooperation with Technicians from Central Forensic Laboratory of Police.
This paper presents a surface shape measurement system based on laser deflectometry. System’s design aims at application in documentation of objects of cultural heritage. The system is composed of a semiconductor laser, a CCD camera and imaging optics. The principle of measurement involves ray tracing of the laser beam calculated from two positions of the detector along the optical axis to determine the angle of inclination of the measured surface. The object is scanned with the designed system and resulting surface normal vectors are integrated to form the output surface. Exemplary measurement results are presented and discussed.
In this paper, a fully automated 3D digitization system for documentation of paintings is presented. It consists of a specially designed frame system for secure fixing of painting, a custom designed, structured light-based, high-resolution measurement head with no IR and UV emission. This device is automatically positioned in two axes (parallel to the surface of digitized painting) with additional manual positioning in third, perpendicular axis. Manual change of observation angle is also possible around two axes to re-measure even partially shadowed areas. The whole system is built in a way which provides full protection of digitized object (moving elements cannot reach its vicinity) and is driven by computer-controlled, highly precise servomechanisms. It can be used for automatic (without any user attention) and fast measurement of the paintings with some limitation to their properties: maximum size of the picture is 2000mm x 2000mm (with deviation of flatness smaller than 20mm) Measurement head is automatically calibrated by the system and its possible working volume starts from 50mm x 50mm x 20mm (10000 points per square mm) and ends at 120mm x 80mm x 60mm (2500 points per square mm). The directional measurements obtained with this system are automatically initially aligned due to the measurement head’s position coordinates known from servomechanisms. After the whole painting is digitized, the measurements are fine-aligned with color-based ICP algorithm to remove any influence of possible inaccuracy of positioning devices.
We present exemplary digitization results along with the discussion about the opportunities of analysis which appear for such high-resolution, 3D computer models of paintings.
Faulty postures, scoliosis and sagittal plane deformities should be detected as early as possible to apply preventive and treatment measures against major clinical consequences. To support documentation of the severity of deformity and diminish x-ray exposures, several solutions utilizing analysis of back surface topography data were introduced. A novel approach to automatic recognition and localization of anatomical landmarks of the human back is presented that may provide more repeatable results and speed up the whole procedure. The algorithm was designed as a two-step process involving a statistical model built upon expert knowledge and analysis of three-dimensional back surface shape data. Voronoi diagram is used to connect mean geometric relations, which provide a first approximation of the positions, with surface curvature distribution, which further guides the recognition process and gives final locations of landmarks. Positions obtained using the developed algorithms are validated with respect to accuracy of manual landmark indication by experts. Preliminary validation proved that the landmarks were localized correctly, with accuracy depending mostly on the characteristics of a given structure. It was concluded that recognition should mainly take into account the shape of the back surface, putting as little emphasis on the statistical approximation as possible.
Currently, a lot of different 3D scanning devices are used for 3D acquisition of art artifact surface shape and color.
Each of them has different technical parameters starting from measurement principle (structured light, laser
triangulation, interferometry, holography) and ending on parameters like measurement volume size, spatial resolution
and precision of output data and color information. Some of the 3D scanners can grab additional information like
surface normal vectors, BRDF distribution, multispectral color. In this paper, we plan to present results of the
measurements with selected sampling densities together with discussion of the problem of recognition and assessment
of the aging process. We focus our interest on features that are important for the art conservators to define state of
preservation of the object as well as to assess changes on the surface from last and previous measurement. Also
different materials and finishing techniques requires different algorithms for detection and localization of aging
changes. In this paper we consider exemplary stone samples to visualize what object features can be detected and
tracked during aging process. The changes in sandstone surface shape, affected by salt weathering, will be presented as
well as possibilities of identification of surface degradation on real object (garden relief made in sandstone).
Currently, a lot of different 3D scanning devices are used for 3D acquisition of art artifact surface shape and color. Each
of them has different technical parameters starting from measurement principle (structured light, laser triangulation,
interferometry, holography) and ending on parameters like measurement volume size, spatial resolution and precision of
output data and color information. Some of the 3D scanners can grab additional information like surface normal vectors,
BRDF distribution, multispectral color. In this paper, the problem of establishing of threshold for technical parameters of
3D scanning process as a function of required information about the object is discussed. Only two main technical
parameters are under consideration, in order to cover as many different 3D scanning devices as possible - measurement
sampling density (MSD - represented by number of points per square millimeter) and measurement uncertainty (MU - directly influencing final data accuracy). Also different materials and finishing techniques require different thresholds of MSD and MU parameters to collect similar documentation (for example documentation of object state for art conservation department) of different objects. In this paper we consider exemplary painting on canvas, wallpainting, graphics prints and stone samples to visualize what object features can be observed within different values of MSD and MU parameters.