Now showing 1 - 10 of 24
  • Publication
    Flying Voxel Method with Delaunay Triangulation Criterion for Façade/Feature Detection for Computation
    (American Society of Civil Engineers, 2012-11) ; ; ;
    A new algorithm is introduced to directly reconstruct geometric models of building façades from terrestrial laser scanning data without using either manual intervention or a third-party, computer-aided design (CAD) package. The algorithm detects building boundaries and features and converts the point cloud data into a solid model appropriate for computational modeling. The algorithm combines a voxel-based technique with a Delaunay triangulation–based criterion. In the first phase, the algorithm detects boundary points of the façade and its features from the raw data. Subsequently, the algorithm determines whether holes are actual openings or data deficits caused by occlusions and then fills unrealistic openings. The algorithm’s second phase creates a solid model using voxels in an octree representation. The algorithm was applied to the façades of three masonry buildings, successfully detected all openings, and correctly reconstructed the façade boundaries. Geometric validation of the models against measured drawings showed overall dimensions correct to 1.2%, most opening areas to 3%, and simulation results within 5% of those predicted by CAD-based models.
      2266Scopus© Citations 43
  • Publication
    Point Cloud Data Conversion into Solid Models via Point-Based Voxelization
    (American Society of Civil Engineers, 2013-05) ; ; ;
    Automated conversion of point cloud data from laser scanning into formats appropriate for structural engineering holds great promise for exploiting increasingly available aerially and terrestrially based pixelized data for a wide range of surveying-related applications from environmental modeling to disaster management. This paper introduces a point-based voxelization method to automatically transform point cloud data into solid models for computational modeling. The fundamental viability of the technique is visually demonstrated for both aerial and terrestrial data. For aerial and terrestrial data, this was achieved in less than 30 s for data sets up to 650,000 points. In all cases, the solid models converged without any user intervention when processed in a commercial finite-element method program.
    Scopus© Citations 80  3054
  • Publication
    Processing of terrestrial laser scanning point cloud data for computational modelling of building facades
    With the rapidly increasing availability of laser scanning data and the growing pressure to use it as the basis for computational models, there has been heighten interest in quickly, cost-effectively, and accurately processing the resulting point cloud data sets so that they are compatible for importation into computational models. This paper presents traditional strategies for solid model generation and examines in detail innovations and continuing limitations of recent patents, newly published research, and some currently available commercial programs for the transformation of laser scanning point cloud data into solid models appropriate for finite element method meshing and various meshing strategies particularly well-suited for point cloud data.
    Scopus© Citations 25  5355
  • Publication
    LiDAR point-cloud mapping of building façades for building energy performance simulation
    Current processes that create Building Energy Performance Simulation (BEPS) models are time consuming and costly, primarily due to the extensive manual inputs required for model population. In particular, generation of geometric inputs for existing building models requires significant manual intervention due to the absence, or outdated nature of available data or digital measurements. Additionally, solutions based on Building Information Modelling (BIM) also require high quality and precise geometrically-based models, which are not typically available for existing buildings. As such, this work introduces a semi-automated BEPS input solution for existing building exteriors that can be integrated with other related technologies (such as BIM or CityGML) and deployed across an entire building stock. Within the overarching approach, a novel sub-process automatically transforms a point cloud obtained from a terrestrial laser scanner into a representation of a building's exterior façade geometry as input data for a BEPS engine. Semantic enrichment is performed manually. This novel solution extends two existing approaches: (1) an angle criterion in boundary detection and (2) a voxelisation representation to improve performance. The use of laser scanning data reduces temporal costs and improves input accuracy for BEPS model generation of existing buildings. The approach is tested herein on two example cases. Vertical and horizontal accuracies of 1% and 7% were generated, respectively, when compared against independently produced, measured drawings. The approach showed variation in accuracy of model generation, particularly for upper floors of the test case buildings. However, the energy impacts resulting from these variations represented less than 1% of the energy consumption for both cases.
    Scopus© Citations 22  380
  • Publication
    Quantitative evaluation strategies for urban 3D model generation from remote sensing data
    Over the last decade, several automatic approaches have been proposed to reconstruct 3D building models from aerial laser scanning (ALS) data. Typically, they have been benchmarked with data sets having densities of less than 25 points/m2. However, these test data sets lack significant geometric points on vertical surfaces. With recent sensor improvements in airborne laser scanners and changes in flight path planning, the quality and density of ALS data have improved significantly. The paper presents quantitative evaluation strategies for building extraction and reconstruction when using dense data sets. The evaluation strategies measure not only the capacity of a method to detect and reconstruct individual buildings but also the quality of the reconstructed building models in terms of shape similarity and positional accuracy.
    Scopus© Citations 46  624
  • Publication
    A Semi-Automatic Member Detection for Metal Bridges
    Terrestrial laser scanners (TLSs) are prominent non-contact instruments for acquiring highly detailed geometries of bridge components in only minutes. A TLS can be a strategic instrument for data collection for bridge inspection and documentation, because it can reduce significantly required field time and auxiliary equipment. To deploy a TLS in this field, a semi-automatic method for post-processing a point cloud for documentation of a historic metal bridge is proposed. In this work, generating 3D model of existing structural members and identifying connection characteristics are mainly of interest. The Guinness Bridge built in 1880s in Dublin, Ireland is presented as a case study for the proposed semi-automatic workflow.
      399
  • Publication
    Combining an Angle Criterion with Voxelization and the Flying Voxel Method in Reconstructing Building Models from LiDAR Data
    Traditional documentation capabilities of laser scanning technology can be further exploited for urban modeling through the transformation of resulting point clouds into solid models compatible for computational analysis. This article introduces such a technique through the combination of an angle criterion and voxelization. As part of that, a k-nearest neighbor (kNN) searching algorithm is implemented using a predefined number of kNN points combined with a maximum radius of the neighborhood, something not previously implemented. From this sample, points are categorized as boundary or interior points based on an angle criterion. Façade features are determined based on underlying vertical and horizontal grid voxels of the feature boundaries by a grid clustering technique. The complete building model involving all full voxels is generated by employing the Flying Voxel method to relabel voxels that are inside openings or outside the façade as empty voxels. Experimental results on three different buildings, using four distinct sampling densities showed successful detection of all openings, reconstruction of all building façades, and automatic filling of all improper holes. The maximum nodal displacement divergence was 1.6% compared to manually generated meshes from measured drawings. This fully automated approach rivals processing times of other techniques with the distinct advantage of extracting more boundary points, especially in less dense data sets (<175 points/m2), which may enable its more rapid exploitation of aerial laser scanning data and ultimately preclude needing a priori knowledge.
    Scopus© Citations 119  767
  • Publication
    Using Terrestrial Laser Scanning for Dynamic Bridge Deflection Measurement
    Heavy vehicular traffic and aggressive environmental conditions can cause unexpected bridge deterioration, thus requiring periodic inspections to identify and assess possible defects. One indicator is the amount of vertical deflection that occurs during loading. Monitoring vertical bridge deflection through traditional surveying typically requires multiple instruments and extensive time in the field, along with their affiliated costs. A terrestrial laser scanner (TLS) can generate a million data points per second with millimeter level accuracy, thus offering the possibility of changing how vertical deflections of bridge girders are checked. This paper presents a preliminary investigation into using TLS to collecting vertical bridge displacements during dynamic loading. In this work, a point-surface based method is proposed to calculate the difference in elevation of a bridge girder at unloaded and loaded conditions. The technique is applied to the Loughbrickland Bridge in Northern Ireland.
      418
  • Publication
    Application of Terrestrial Laser Scanner in Bridge Inspection: Review and an Opportunity
    (International Association for Bridge and Structural Engineering (IABSE), 2014-09-05) ;
    Heavy traffic and aggressive environmental conditions can cause unexpected bridge deterioration. Traditional condition evaluation is expensive. An alternative is Terrestrial laser scanning (TLS) which is a non-contact approach that safe, fast, and applicable to a range of weather conditions. This paper reviews applications of TLS on bridge measurement involving geometric documentation, surface defect determination, and corrosion evaluation, and crack identification. Currently, most post-processing of TLS is manual or within third party software. This paper discusses potential approaches to automatic post-processing.
      1012
  • Publication
    Aerial laser scanning and imagery data fusion for road detection in city scale
    This paper presents a workflow including a novel algorithm for road detection from dense LiDAR fused with high-resolution aerial imagery data. Using a supervised machine learning approach point clouds are firstly classified into one of three groups: building, ground, or unassigned. Ground points are further processed by a novel algorithm to extract a road network. The algorithm exploits the high variance of slope and height of the point data in the direction orthogonal to the road boundaries. Applying the proposed approach on a 40 million point dataset successfully extracted a complex road network with an F-measure of 76.9%.
    Scopus© Citations 17  809