ABSTRACT:Since their introduction, modeling tools aimed to architectural design evolved in today's "digital multi-purpose drawing boards" based on enhanced parametric elements able to originate whole buildings within virtual environments. Semantic splitting and elements topology are features that allow objects to be "intelligent" (i.e. self-aware of what kind of element they are and with whom they can interact), representing this way basics of Building Information Modeling (BIM), a coordinated, consistent and always up to date workflow improved in order to reach higher quality, reliability and cost reductions all over the design process. Even if BIM was originally intended for new architectures, its attitude to store semantic inter-related information can be successfully applied to existing buildings as well, especially if they deserve particular care such as Cultural Heritage sites. BIM engines can easily manage simple parametric geometries, collapsing them to standard primitives connected through hierarchical relationships: however, when components are generated by existing morphologies, for example acquiring point clouds by digital photogrammetry or laser scanning equipment, complex abstractions have to be introduced while remodeling elements by hand, since automatic feature extraction in available software is still not effective. In order to introduce a methodology destined to process point cloud data in a BIM environment with high accuracy, this paper describes some experiences on monumental sites documentation, generated through a plug-in written for Autodesk Revit and codenamed GreenSpider after its capability to layout points in space as if they were nodes of an ideal cobweb.
The tremendous improvements in data capturing technologies and in the related processing methodologies are opening more and more possibilities in different fields of applications. In particular the Cultural Heritage field is taking great advantages from the latest reality-based 3D modelling developments. One of the most significant consequences of the introduction of digital 3D modelling in the heritage field is the great opportunity of using 3D models as highly effective and intuitive means of communication or as interfaces to share and visualize information collected e.g. in databases. Unstructured 3D data recorded with photogrammetry or laser scanning techniques are generally converted in polygonal textured 3D models, subdivided and organized using automated and manual methods and finally visualized using web-based tools in order to allow remote access and data retrieval to a wider range of users, with evident advantages in enlarging knowledge and education. The paper presents the state-of-the-art in 3D surveying and modelling, segmentation and web-based access for heritage sites and objects (Fig. 1). The most reliable and practical approaches are presented with references and best practices. Some future perspectives are also addressed.
ABSTRACT:The aim of this contribution is to show the results of evaluations on 3D digitizations performed using different methodologies and technologies. In particular, for surveys conducted at the architectural and urban scale, the recent reduction of costs related to Time of Flight and phase shift laser scanners is actually enhancing the replacement of traditional topographic instruments (i.e. total stations) with range-based technologies for the acquisition of 3D data related to built heritage. If compared to surveys performed using traditional topographic technologies, range-based ones offer a wide range of advantages, but they also require different skills, procedures and times. The present contribution shows the results of a practical application of both approaches on the same case study. Another application was suggested by the recent developments in the photogrammetric field that enhance the improvement of software able to automatically orient uncalibrated cameras and derive dense and accurate 3D point clouds, with evident benefits in reduction of costs required for survey equipment. Therefore, the presented case study constituted the occasion to compare a rangebased survey with a fast 3D acquisition and modelling using a Structure from Motion solution. These survey procedures were adopted at an architectural scale, on a single building, that was surveyed both on the outside and on the inside. Assessments on the quality of the rebuilt information is reported, as far as metric accuracy and reliability is concerned, as well as on time consuming and on skills required during each step of the adopted pipelines. For all approaches, these analysis highlighted advantages and disadvantages that allow to conduct evaluations on the possible convenience of adopting range-based technologies instead of a traditional topographic approach or a photogrammetric one instead of a range based one in case of surveys conducted at an architectural/urban scale.
In the last decade the Cultural Heritage field has deeply benefited from the opportunities of collecting accurate and detailed 3D information of sites and artifacts using both image- and range-based techniques. Since few years ago these technologies were not so extensively used, mainly because they were very expensive, required expertise and the pipeline and procedures related to their use were not straightforward, nor consolidated. But in the last years significant improvements in the digital survey technologies have been reached, with the principal scope of simplifying reality-based survey procedure and providing a series of different solutions that combine the automation of processes with accuracy and resolution performances. In addition to these aspects, the lowering of costs and the consequent widespread use of some survey solutions, such as, for example, range-based, as well as terrestrial and UAV image-based ones, have recently given strong impulse to the widening of use of these technologies in the Cultural Heritage field. As a consequence, this range of possibilities shows that in this field, where case studies have peculiar geometric and radiometric characteristics and survey conditions are often unique, preliminary investigations and evaluations are mandatory in order to define the most suitable solution to adopt.\ud In this context, this paper presents preliminary results from the Santa Maria di Pomposa survey project, with the purpose of starting a deep investigation on the integration of 3D digital technologies and how they can provide complete and multi-scalar information about complex architectures. This purpose is particularly important in case studies where analysis have to be conducted at different scales of complexity. Structural analysis are just an example of the need to easily handle complete and global information that have to be deeply and detailed analyzed, eventually showing the behavior of structures over time. Within the adopted methodology, the comparison of results obtained using different approaches represents an indispensable step in order to evaluate and select the most reliable and suitable solutions to adopt within the final integrations process
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