Tania Landes

Automatic Extraction of Planar Clusters and Their Contours on Building Façades Recorded by Terrestrial Laser Scanner

Since 3D city models need to be realistic not only from a birds point of view, but also from a pedestrians point of view, the interest in the generation of 3D façade models is increasing. This paper presents two successive algorithms for automatically segmenting building façades scanned by Terrestrial Laser Scanner (TLS) into planar clusters and extracting their contours. Since majority of façade components are planes, the topic of automatic extraction of planar features has been studied. The RANSAC algorithm has been chosen among numerous methods. It is a robust estimator frequently used to compute model parameters from a dataset containing outliers, as it occurs in TLS data. Nevertheless, the RANSAC algorithm has been improved in order to extract the most significant planar clusters describing the main features composing the building façades. Subsequently, a second algorithm has been developed for extracting the contours of these features. The innovative idea presented in this paper is the efficient way to detect the points composing the contours. In order to evaluate the performances of both algorithms, they have successively been applied on samples with different characteristics, i.e. densities, types of façades and size of architectural details. Finally, a quality evaluation based on the comparison of planar clusters and contours obtained manually has been carried out. The results prove that the proposed algorithms deliver qualitative as well as quantitative satisfactory results and confirm that both algorithms are reliable for the forthcoming 3D modelling of building façades.

Combining Airborne Photographs and Spaceborne SAR Data to Monitor Temperate Glaciers: Potentials and Limits

Monitoring temperate glacier activity has become more and more necessary for economical and security reasons and as an indicator of the local effects of global climate change. Remote sensing data provide useful information on such complex geophysical objects, but they require specific processing techniques to cope with the difficult context of moving and changing features in high-relief areas. This paper presents the first results of a project involving four laboratories developing and combining specific methods to extract information from optical and synthetic aperture radar (SAR) data. Two different information sources are processed, namely: 1) airborne photography and 2) spaceborne C-band SAR interferometry. The difficulties and limitations of their processing in the context of Alpine glaciers are discussed and illustrated on two glaciers located in the Mont-Blanc area. The results obtained by aerial triangulation techniques provide digital terrain models with an accuracy that is better than 30 cm, which is compatible with the computation of volume balance and useful for precise georeferencing and slope measurement updating. The results obtained by SAR differential interferometry using European Remote Sensing Satellite images show that it is possible to measure temperate glacier surface velocity fields from October to April in one-day interferograms with approximately 20-m ground sampling. This allows to derive ice surface strain rate fields required to model the glacier flow. These different measurements are complementary to results obtained during the summer from satellite optical data and ground measurements that are available only in few accessible points

Assessment and Calibration of a RGB-D Camera (Kinect v2 Sensor) Towards a Potential Use for Close-Range 3D Modeling

In the last decade, RGB-D cameras - also called range imaging cameras - have known a permanent evolution. Because of their limited cost and their ability to measure distances at a high frame rate, such sensors are especially appreciated for applications in robotics or computer vision. The Kinect v1 (Microsoft) release in November 2010 promoted the use of RGB-D cameras, so that a second version of the sensor arrived on the market in July 2014. Since it is possible to obtain point clouds of an observed scene with a high frequency, one could imagine applying this type of sensors to answer to the need for 3D acquisition. However, due to the technology involved, some questions have to be considered such as, for example, the suitability and accuracy of RGB-D cameras for close range 3D modeling. In that way, the quality of the acquired data represents a major axis. In this paper, the use of a recent Kinect v2 sensor to reconstruct small objects in three dimensions has been investigated. To achieve this goal, a survey of the sensor characteristics as well as a calibration approach are relevant. After an accuracy assessment of the produced models, the benefits and drawbacks of Kinect v2 compared to the first version of the sensor and then to photogrammetry are discussed.

High-Resolution SAR Interferometry: Estimation of Local Frequencies in the Context of Alpine Glaciers

Synthetic aperture radar (SAR) interferometric data offer the opportunity to measure temperate glacier surface topography and displacement. The increase of the resolution provided by the most recent SAR systems has some critical implications. For instance, a reliable estimate of the phase gradient can only be achieved by using interferogram local frequencies. In this paper, an original two-step method for estimating local frequencies is proposed. The 2-D phase signal is considered to have two deterministic components corresponding to low-resolution (LR) fringes and high-resolution (HR) patterns due to the local microrelief, respectively. The first step of the proposed algorithm consists in the LR phase flattening. In the second step, the local HR frequencies are estimated from the phase 2-D autocorrelation function computed on adaptive neighborhoods. This neighborhood is the set of connected pixels belonging to the same HR spatial feature and respecting the ldquolocal stationarityrdquo hypothesis. Results with both simulated TerraSAR-X interferograms and real airborne E-SAR images are presented to illustrate the potential of the proposed method.

From laser data to parametric models: towards an automatic method for building façade modelling

The interest in the generation of 3D facade models is increasing more and more. TLS data have introduced other visions to deal with this topic. This paper proposes a new approach to facade modelling using TLS data. Geometric relevant features of facades are first extracted via a segmentation algorithm. Then, based on the segmentation results, the automatic extraction of edges has been carried out. Afterwards, the edges are decomposed into straight segments and arcs, based on the criterion of the collinearity of points. Then, the intersection points are calculated based on the study of their geometric characteristics, as well as their topological relationships. These points allow us to construct the parametric objects that can be correctly sized and completed via an interactive graphical user interface.

Joint combination of point cloud and DSM for 3D building reconstruction using airborne laser scanner data

More and more cities are looking for service providers able to deliver 3D city models in a short time. Airborne laser scanning techniques make it possible to acquire a three-dimensional point cloud leading almost instantaneously to digital surface models (DSM), but these models are far from a topological 3D model needed by geographers or land surveyors. The aim of this paper is to present the pertinence and advantages of combining simultaneously the point cloud and the normalized DSM (nDSM) in the main steps of a building reconstruction approach. This approach has been implemented in order to exempt any additional data and to automate the process. The proposed workflow firstly extracts the off-terrain mask based on DSM. Then, it combines the point cloud and the DSM for extracting a building mask from the off-terrain. At last, based on the previously extracted building mask, the reconstruction of 3D flat roof models is carried out and analyzed.

Monitoring temperate glaciers by high resolution Pol-InSAR data: First analysis of Argentière E-SAR acquisitions and in-situ measurements

This paper highlights the potential to measure temperate glacier velocities and surface characteristics by airborne interferometric and polarimetric SAR remote sensing. Indeed, a novel SAR airborne campaign took place in October 2006 over two Alpine glaciers. Simultaneously to the acquisition of repeat pass interferometric, polarimetric and multi-band data, in-situ measurements were carried out to provide useful information for the SAR synthesis, for backscattering analysis and for performance assessment. Analysis of the experimental data as well as early PolInSAR processing results regarding information extraction are presented.

Combining optical and SAR data to monitor temperate glaciers

Monitoring temperate glaciers activity becomes more and more necessary for economical and security reasons and as an indicator of the local effects of global changes. This paper presents the beginning of a three year project which regroups four laboratories to develop and combine specific methods to extract information from optical and radar remote sensing data. Preliminary results are presented on three different information sources: airborne photography, space-borne multi-spectral images and SAR interferometry, which respectively allow the compution of high resolution DTM, the detection of glacial lakes and the measurement of glacier surface velocity. Results obtained on two glaciers located in the French Alps are compared and validated with ground measurments.

Semi-automatic Segmentation and Modelling from Point Clouds towards Historical Building Information Modelling

This paper presents a semi-automatic approach for creating a 3D model from point clouds. The proposed approach consists in the development of two successive algorithms. First, the segmentation of the point cloud in geometric primitives is made based on RANSAC paradigm. Then, in a modelling step, the geometric primitives are used for either surface modelling or boundaries extraction and more particularly sectional view extraction. Regarding the results analysis, the developed approach is promising despite some limitations. Not only the limitations, but also potential improvements of our processing chain are discussed. Finally, a bridge towards HBIM is considered.

Assessment of the accuracy of 3D models obtained with DSLR camera and Kinect v2

3D modeling of objects such as statues, moldings or ornaments, answers to a need of documentation and analysis in the field of cultural heritage. Several sensors based on different technologies are used to obtain information on the geometry of an object in form of point clouds: laser scanners, digital cameras or more recently RGB-D cameras. Among them, the recent Kinect v2 sensor looks promising and therefore its use has been studied in this paper. The aim of this paper is to compare two methodologies for 3D models acquisition: photogrammetry-based models and models obtained using a RGB-D camera. Since the quality of the meshed models is obviously correlated to the quality of the point cloud, the result will be more or less faithful to reality. To quantify this reliability, several comparisons to a reference model have been carried out. Regarding the results of the comparisons, we will be able to conclude about the strengths and weaknesses of photogrammetry and RGB-D cameras for 3D modeling of complex objects.