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The preservation of heritage buildings is essential in a modern society that understands the importance of architecture, culture, and history. The lack of reconstruction funds or the vision of the decision-makers can delay the realization of the works to protect these buildings. The digital conservation of these buildings can be a solution for a later reconstruction or for the creation of a realistic virtual museum. The article presents the rigorous setup and calibration of an airborne side scanner mounted on a UAV platform. Acquiring fine architectural details involves the use of more precise scanning sensors, with substantially higher costs, leading to delays. The present study shows that medium precision scanning sensors can also be used for digitizing architectural details. The side scan solution can be applied successfully in the digital preservation of buildings with a medium degree of detail, but it can also be useful in complex cases. Using optimal processing methods greatly improves the internal accuracy of the modelling with little loss in accuracy. The proposed methodology can be applied even when using superior sensors, leading to exceptional results. [ABSTRACT FROM AUTHOR]

The current research presents the way to obtain direct georeferencing of photogrammetric imagery and to obtain rigorously georeferenced orthophoto plans without using ground control points. The direct georeferencing procedure is studied in Romania's atypical coordinate systems (planimetric system based on an ellipsoid different than GRS80 and a vertical system of normal elevations, different than the ellipsoidal elevations used in GNSS technology), but it can also be applied to other systems of coordinates. To generate superior photogrammetric products, an innovative orthorectification methodology based on LIDAR data acquired simultaneously with photogrammetric images is presented. LIDAR data is also acquired by a direct georeferencing procedure and transformed with high precision using an application designed for this purpose. Therefore, a much faster way to generate orthophoto plans is presented, with lower production costs, without a substantial loss of the positional quality of the final product. Finally, there is presented the first stereo restitution project in Romania using small size images, acquired with a UAV system by direct georeferencing. The focus on the atypical case of Romania underlines the innovative features of this research. [ABSTRACT FROM AUTHOR]

The paper aimed to present the advantages of realistic representation of a geographic area by combining optical and LiDAR data captured with UAVs. LiDAR data and aerial images, both captured with an UAV, have their own unique advantages and disadvantages and it is natural to integrate those two data sets for a good realistic representation of a geographic area in terms of horizontal and vertical accuracy. Compared with aerial images, LIDAR data provide more accurate height information but less accurate boundaries. Aerial images provide more extensive planimetric information such as high-resolution texture and colour information. Although 3D height information can be estimated from one or several images by the use of several photogrammetric methods, the height information extracted from aerial images is still relatively less accurate. The realistic representation of a geographic area in the virtual environment, was verified for validation in the Cernica Dam area, checking the spatial data sets used (LiDAR and optical). We used for data validation, the ground truth, given by GNSS measurements in the field, and the experimental results indicate that this combination improves the overall accuracy from 94% to 97%. [ABSTRACT FROM AUTHOR]

The paper presents how the use of multispectral LiDAR intensity data for classification has high potentials to increase land classification accuracy. Traditionally, classification of LiDAR data refers to the separation of terrain from other objects based on elevations (range data). Up to about 70% of overall accuracy can be achieved using intensity data only. Land classification accuracy, of about 80%, can be achieved by incorporating both the geometric and radiometric record of LiDAR data. Range and scan/incidence angle have prominent effect on the radiometric correction of intensity data. Radiometric correction of LiDAR intensity data is required for potential use of the LiDAR intensity in land cover classification and radiometric correction can be achieved day or night with similar good results. Current research involves the use of image segmentation and object oriented classification techniques to improve the classification results. The increased number of wavelengths in a sensor has the effect of increasing the information content that can be derived from the target surface and allowing surveying professionals to address many more applications using a single-sensor solution. The complementary information of multispectral LiDAR data may greatly improve the classification performance, especially in the complex urban areas. Use of a minimum of three intensity images from a multi-wavelength laser scanner and 3D information included in the digital surface model (DSM) has the potential for land cover and land use classification. Over 90% of overall accuracy is achieved via using multispectral LiDAR point clouds for 3D land cover classification. [ABSTRACT FROM AUTHOR]