1,354,334 research outputs found
The added value of contextual information in natural areas : Measuring impacts of mobile environmental information
No full textScholten, H.J. [Promotor]Rietveld, P. [Promotor]Camara, A. [Copromotor]Beinat, E. [Copromotor
An Automatic Analytical Procedure for Searching Corresponding Feature Points in a Cadastral Map - TS28.5
No full textIn some recent papers Beinat and Crosilla (2003a, 2003b) have illustrated a new direct procedure, based on Procrustes analysis techniques, for the least squares adjustment of digital cadastral map features. The method has been successfully applied to simultaneously fit a series of fiducial point networks (polygons), each one connecting at least three points measured in the field by professional surveyors, strictly preserving their geometrical shape and linking the whole polygon set to a limited number of fixed points. The proposed procedure considers the various partially or totally overlapping measured polygons as unitary component parts of the general network of fiducial cadastral points to be adjusted. Direct and independent similarity transformation models are applied to each polygon – i.e., the so called Procrustes adjustment model – so to minimise a measure of discrepancy among the various polygons. As well as for the fiducial point network, the same technique can also correctly perform the conformal mosaicking of the new surveyed cadastral parcels with those ones obtained by digitisation of the original map, satisfying further possible geometrical constraints of the map entities like alignments, orthogonality and so on. To achieve the conformal parcel mosaicking in the absence of any topological or structural information, a specific procedure is needed to automatically identify the point-to-point correspondences between the various geometric entities to be connected. Several methods to detect possible correspondences between two sets of equal number of unlabeled points have been developed and investigated. Among these, we report the Umeyama's method (1988) developed to compute the permutation that maximises the agreement between two weighted graphs by way of a singular value decomposition of the relative adjacency matrix product. Another original direct solution, based on pure geometric rules, has been implemented and successively described. For the more general problem of detecting a geometric entity entirely contained within a more complex configuration, e.g. a measured parcel belonging to a cadastral map, a "kernel growing" geometric approach has been developed. The method explained in the paper is based on the analysis and segmentation of the adjacency matrices relative to the specific parcel and to the entire map vertex coordinates, and on the computation and validation of transformation parameters performed by Procrustes analysis techniques. In addition to the cadastral cartographic purposes, the procedure seems suitable for a wider range of possible applications, spacing from the Geographic Information Systems to the industrial and civil engineering design
Fifty years of the Friuli Venezia Giulia regional technical map: a best practice in the Italian cartographic context
No full textFifty years have already passed away from the production start-up of the regional technical map of the Italian Friuli Venezia Giulia region. On this occasion, the part of the new regional topographic database (DBT), relating to the Trieste province, is now available. This is a new digital product that represents a significant technological evolution of the well-known “Carta Tecnica Regionale Numerica.” In conjunction with this important event, before the time would definitely delete the memory of the origins, this paper gives a synthetic excursus of the various phases of design, realization and use of the Friuli Venezia Giulia regional technical map (CTR) and of its subsequent digital version (CTRN). The beginning of that development period was marked by a catastrophic event: the 1976 earthquake, and also by the following reconstruction phase that transformed the region. In correspondence, the new digital cartography had been an essential tool for developing and managing the territory. Furthermore, the main characteristics of the now partially available Topographic Database (DBT) will be described. At last, this paper is aimed to remind the various professional figures that have contributed to realize these important cartographic tools
FEASIBILITY AND ACCURACY OF AS-BUILT MODELLING FROM SLAM-BASED POINT CLOUDS: PRELIMINARY RESULTS
No full textNowadays, portable Mobile Mapping Systems (MMSs) and robotic mapping platforms leveraging on Simultaneous Localization and Mapping (SLAM) methods are gaining increasing attention for architectural and construction surveying, representing an efficient solution for geometric data acquisition for scan-to-BIM purposes. However, the applicability of standard modelling workflows and the accuracy of Building Information Models (BIM) that can be obtained from SLAM-based point clouds is still an open question. In this paper, we propose a preliminary evaluation on the feasibility of extracting as-built BIM from (i) a point cloud acquired with a commercial portable MMS, and (ii) a point cloud obtained through an open-source SLAM algorithm, surveying the environment with an autonomous mobile robotic platform. In both cases, the main structural elements of the test site are accurately generated, thus showing promising results. On the other hand, the experiment highlights also the need for SLAM systems capable of providing less noisy point clouds, in order to capture and model architectural details
Performance Investigation and Repeatability Assessment of a Mobile Robotic System for 3D Mapping
No full textIn this paper, we present a quantitative performance investigation and repeatability assessment of a mobile robotic system for 3D mapping. With the aim of a more efficient and automatic data acquisition process with respect to well-established manual topographic operations, a 3D laser scanner coupled with an inertial measurement unit is installed on a mobile platform and used to perform a high-resolution mapping of the surrounding environment. Point clouds obtained with the use of a mobile robot are compared with those acquired with the device carried manually as well as with a terrestrial laser scanner survey that serves as a ground truth. Experimental results show that both mapping modes provide similar accuracy and repeatability, whereas the robotic system compares favorably with respect to the handheld modality in terms of noise level and point distribution. The outcomes demonstrate the feasibility of the mobile robotic platform as a promising technology for automatic and accurate 3D mapping
Shadow detection and removal in RGB VHR images for land use unsupervised classification
No full textNowadays, high resolution aerial images are widely available thanks to the diffusion of advanced technologies such as UAVs (Unmanned Aerial Vehicles) and new satellite missions. Although these developments offer new opportunities for accurate land use analysis and change detection, cloud and terrain shadows actually limit benefits and possibilities of modern sensors.Focusing on the problem of shadow detection and removal in VHR color images, the paper proposes new solutions and analyses how they can enhance common unsupervised classification procedures for identifying land use classes related to the CO2 absorption.To this aim, an improved fully automatic procedure has been developed for detecting image shadows using exclusively RGB color information, and avoiding user interaction. Results show a significant accuracy enhancement with respect to similar methods using RGB based indexes.Furthermore, novel solutions derived from Procrustes analysis have been applied to remove shadows and restore brightness in the images. In particular, two methods implementing the so called "anisotropic Procrustes" and the "not-centered oblique Procrustes" algorithms have been developed and compared with the linear correlation correction method based on the Cholesky decomposition.To assess how shadow removal can enhance unsupervised classifications, results obtained with classical methods such as k-means, maximum likelihood, and self-organizing maps, have been compared to each other and with a supervised clustering procedure. © 2016 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS)
A Generalized Factored Stochastic Model for Optimal Registration of LIDAR Range Images
No full textSurveying complex shapes or very large entities by laser scanners often requires the registration of a sufficient number of partial 3-D range images in order to completely reproduce the model of the real object. If redundancy exists among the partial models composing the measured entity, a global adjustment of the model components improves the final accuracy with respect to a simple pairwise registration.
To this regard, a new solution for the optimal least squares registration of range images, based on the Generalised Procrustes Analysis techniques, has been recently developed by the authors and can be found in the literature. The method, using the classical tie point correspondence, has proven to be very efficient since it does not require any prior information of the geometrical relationship existing among the particular reference frames in which the different partial 3-D models are expressed. Considering its computational
advantages, it does not involve linearisation of equation systems nor matrix inversions, the only requirement is the singular value decomposition (SVD) of matrices of order 3 x 3.
In this paper a significant analytical enhancement of the Procrustean method is presented, to manage the stochastic properties of the tie point coordinates in a more complete and exhaustive way. In the previous formulation the possibility to assign a different isotropic weighting factor to the single tie points, according to their specific accuracy, was considered. With the new proposed method, also the positional components, i.e. each coordinate, can be weighted separately. In this way a complete anisotropic and inhomogeneous factored stochastic model can be introduced in the Procrustes procedure.
The generalisation of the stochastic model is recommended for certain practical applications, particularly for joining aerial laserscanners strips produced with low sampling density. In these cases, matching correspondence points of low resolution range images
generates poorly accurate tie point coordinate estimation. Indeed, this event introduces an uncertainty in the 3-D position that must be considered anisotropic, i.e. not affecting the three components of the same amount. In fact, considering one tie-point laying on a surface perpendicular to the laser beam, the effective position of the laser footprint on the correspondence element affects the planimetric position more than the related altimetric component. In these situations, the different quality of the tie points position
components must be correctly and advantageously preserved, performing the global registration adopting the anisotropic model here presented.
A suitable application is discussed in the paper to illustrate the registration problem and the expected advantages of the method proposed
Global registration of multiple point clouds embedding the Generalized Procrustes Analysis into an ICP framework
No full textA new proposal for the global and optimal conformal updating of a cadastral digital mapping
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