New instruments and technologies for Cultural Heritage survey: full integration between point clouds and digital photogrammetry

In the last years the Geomatic Research Group of the Politecnico di Torino faced some new research topics about new instruments for point cloud generation (e.g. Time of Flight cameras) and strong integration between multi-image matching techniques and 3D Point Cloud information in order to solve the ambiguities of the already known matching algorithms. ToF cameras can be a good low cost alternative to LiDAR instruments for the generation of precise and accurate point clouds: up to now the application range is still limited but in a near future they will be able to satisfy the most part of the Cultural Heritage metric survey requirements. On the other hand multi-image matching techniques with a correct and deep integration of the point cloud information can give the correct solution for an "intelligent" survey of the geometric object break-lines, which are the correct starting point for a complete survey. These two research topics are strictly connected to a modern Cultural Heritage 3D survey approach. In this paper after a short analysis of the achieved results, an alternative possible scenario for the development of the metric survey approach inside the wider topic of Cultural Heritage Documentation is reporte

Integration of range and image data for building reconstruction

The extraction of information from image and range data is one of the main research topics. In literature, several papers dealing with this topic has been already presented. In particular, several authors have suggested an integrated use of both range and image information in order to increase the reliability and the completeness of the results exploiting their complementary nature. In this paper, an integration between range and image data for the geometric reconstruction of man-made object is presented. The focus is on the edge extraction procedure performed in an integrated way exploiting both the from range and image data. Both terrestrial and aerial applications have been analysed for the faade extraction in terrestrial acquisitions and the roof outline extraction from aerial data. The algorithm and the achieved results will be described and discussed in detail

Integration between calibrated time-of-flight camera data and multi-image matching approach for architectural survey

In this work, the integration between data provided by Time-of-Flight cameras and a multi-image matching technique for metric surveys of architectural elements is presented. The main advantage is given by the quickness in the data acquisition (few minutes) and the reduced cost of the instruments. The goal of this approach is the automatic extraction of the object breaklines in a 3D environment using a photogrammetric process, which is helpful for the final user exigencies for the reduction of the time needed for the drawing production. The results of the performed tests on some architectural elements will be reported in this paper

Multi-image matching: an "old and new" photogrammetric answer to lidar techniques

Over the last decade, LIDAR techniques have replaced traditional photogrammetric techniques in many applications because of their speed in point cloud generation. However, these laser scanning techniques have non-negligible limits and, for this reason, many researchers have decided to focus on improving the performances of matching technique in order to generate dense point clouds from images.The first tests carried out at the Politecnico di Torino on the first fully-automated multi-image matching commercial software, the ZScan Menci Software, are described in this paper. This instrument was first devised to allow inexperienced users to generate very dense point clouds from image triplets; a customized calibrated bar (0,90 m length) is used for image acquisition. Recently a new version of ZScan has been created in order to elaborate triplets of oriented aerial images and generate DSM: the first results obtained in this way are presented in this paper. Several tests have been performed on the ZScan performances analysing different geometrical configurations (base-to-height ratio) and textures. The evaluation of the geometric precision obtained by this software in point cloud generation may help to understand which performances can be achieved with a fully automated multi-image matching. The evaluation concerns what the most critical aspects of these techniques are and what improvements will be possible in the future. Furthermore a possible new research project is described which has the aim of transferring useful information about breakline location from images to point clouds in order to derive automatically the segmentation algorithms

THE SEMANTIC INFORMATION OF IMAGES ACQUIRED BY AERIAL DIGITAL SENSORS IN CARTOGRAPHIC AND ENVIRONMENTAL APPLICATIONS

Aerial digital cameras were first presented on the occasion of the ISPRS International Symposium in 2000. Since then, several papers that analyse the geometrical accuracy of digital camera have been presented. These works have underlined the fact that the geometric accuracy obtainable with the digital sensor is significantly higher than the accuracy achieved with scanned analogue cameras. Nevertheless, this accuracy is usually obtained considering predefined markers which allow higher geometric precision than the other points required in the Technical Specifications at a certain map scale, whereas precision (during tests) in map productions is focused on common map entities required in Technical Specifications. Furthermore, good geometric precision in triangulation does not guarantee easy stereoplotting of all the map entities with the required precision. However, it is obviously wrong (and simplistic) to consider, without any logical proof, that digital camera products are comparable, from a semantic point of view, with traditional photogrammetric camera products acquired approximately at the same nominal scale. The semantic information of digital images is accurately analyzed in this paper, and the geometrical aspect is neglected. In particular, the semantic information is considered both from a qualitative and quantitative point of view and the image quality and information content of several digital sensors (ADS40 Leica Geosystems 1st and 2nd Generation, DMC Intergraph Z/I, UltraCamD Vexcel Corp., 3-Das-1 Wehrli & Associates), which are commonly employed in the map production at different scales, are evaluated. In this analysis, particular attention is paid to the handiness of the interpretation of the entities that are requested in modern technical specifications (at several scales) for map productio