Accueil > Géographie > Bulletin des Sciences Géographiques > Numéro 23 > Numéro 23

Numéro 23

Articles de cette rubrique

TerraSAR-X and TanDEM-X : Revolution in Spaceborne Radar

Commercially available imagery is and will remain indispensable to civilian and military organizations gathering various types of geo-spatial information. Whether fulfilling international agreements, providing military contingents in international peacekeeping or humanitarian missions, or conducting joint technical exercises with other countries - a reliable access to timely, high resolution remote sensing data is an essential basis for well-informed decision making, particularly in time-critical situations. Today, organizations with those needs customarily resort to high resolution data acquired by optical
sensors - often a lengthy operation. The radar satellite TerraSAR-X, and at a later stage together
with TanDEM-X with it’s complementary near-real time data acquisition capabilities, offer a whole new approach to the use of space-borne datasets for mapping purposes in time-critical situations.

Using Geo-informatics for Development of Rural Roads Under Pradhan Mantri Gram Sadak Yojna

The development of any country depends on the infrastructural facilities available therein. Good road network facilities plays major role here. The developed countries have good road infrastructure not because of the fact that they are wealthy ; instead they become developed because of good road infrastructure. Realizing this fact an ambitious and biggest ever infrastructure development project in
India (expected cost of $26 billion) named as Pradhan Mantri Gram Sadak Yojna (PMGSY) under ministry of Rural Development was conceptualized and launched on 25th December, 2000. The objective was to provide basic access by way of all weather roads to the all habitations having popu-lation « 250 or above in desert and tribal areas » and « 500 or above for the rest of habitations » by year 2007 in phased manner. The role of Rural Roads is very important in a
country like India where majority of the population resides in rural areas and the main source of their earning is based on agriculture products. Rural roads provide the access to basic amenities and means of transporting agricultural products to nearest market centers. The Rural Roads can be classified as Other District Roads (ODR) and Village Roads (VR). ODR are those roads which connects the rural areas to market centers, Block, tehsil/taluka HQ or main roads while VR are those roads which connects
villages and group of villages and each other or to the market place or with the nearest road of higher category (Operation Manual, 2005). PMGSY scheme is becoming very popular among rural areas because of the specifications and quality aspect adopted for construction of roads. Although it is a Rural Road Connectivity Project but it has well
designed working system, clear guidelines and stream lined efficient monitoring and execution strategy.

High Resolution DTM Process to generate accurate River Network for Efficient Water Resource Management

Automated hydrological feature extra-ction using DTM is gaining popularity with the availability of high resolution remote sensing data. The derived hydrological features from DTM are not only accurate but also accelerate the processing speed of modeling of projects like water resource management and flood risk modeling. Including
modeling there are various hydrological application that needs very accurate hydrological feature information. There are serious problems that exist in
the high resolution DTM. They are artifacts and depressions, which increase in number and exacerbate already existing problems with increasing DTM resolution. Secondly, high resolution DTM consumes lot of processing time and resources, especially while dealing with artifacts and depressions. Artifacts are manmade constructions across the rivers and show their dominance in urban location. The natural depressions like pot-holes, sinks-holes play a major role, especially in the derivation of hydrological features like river network and watershed. The presences of artifacts are also create secondary sinks which again lead to further complications. The above mentioned problems are shift the hydrological features spatially from their
actual geographical locations and it also consume lot of resources and time to process. Consequently, the output models give inaccurate results. This paper demonstrates occurrence of artifacts and depressions and their influence over derived river network. It
also describes the techniques attempting to address/resolve such problems, with special focus on high resolution DTMs.

High-Sensitivity GPS - an Availability, Reliability and Accuracy Test

High-Sensitivity GPS receivers shall deliver positions in shadowed areas as well as inside buildings due to their sensitivity with respect to GPS signals with a power ratio below -150 dBm, The paper shows a comparison for three high-sensitivity GPS receivers used in static mode regarding availability, reliability and accuracy in areas with free horizon, in shadowed areas as well as indoor, The investigations show that the availability rate indicates more than 90 % for shadowed areas, Inside buildings with low attenuation and in rooms with windows the availability ranges between more than 70 % and 18 % depending on the receicer type. For free horizon conditions the reproducability standard deviation shows values between 3.75 m and 7.33 m. Inside buildings the respective standard deviation is degraded to more than 80 m. More inside the building, e.g, in a windowless room or a cellar, no GPS signals are received. Additionally kinematic measurements were carried through too. Here the availability reaches values of around 97 `7o for the track including shadowed areas and even tunnels. The reproducability standard deviation indicates values between 4,92 m and 12.22 m. Obviously the kinematic results are more accurate than static results, due to a filter for the positions using a movement model.

Automated 3D modeling of urban environments

The photorealistic modeling of large-scale scenes, such as urban structures, requires a fusion of range sensing technology and traditional digital photography, This paper summarizes the contributions of our group in that area. We present a system that integrates automated 3D-to-3D and 2D-to-3D registration techniques, with multiview geometry for the photorealistic modeling of urban scenes. The 3D range scans are registered using our automated 3D-to-3D registration method that matches 3D features (linear or circular) in the range images, A subset of the 2D photographs are then aligned with the 3D model using our automated 2D-to-3D registration algorithm that matches linear features between the range scans and the photo-graphs. Finally, the 2D photographs are used to generate a second 3D model of the scene that consists of a sparse 3D point cloud, produced by applying a multiview geometry (structure-from-motion) algorithm directly on a sequence of 2D photographs, A novel algorithm for automatically recovering the rotation, scale, and translation that best aligns the dense and sparse models has been developed. This alignment isnecessary to enable the photographs to be optimally texture mapped onto the dense model. Finally, we present a segmentation and modeling algorithm for urban scenes. The contribution of this work is that it merges the benefits of multiview geometry with automated registration of 3D range scans to produce photorealistic models with minimal human interaction. We present results from experiments in large-scale urban scenes.

What do we need laws for ?

In Norway we have found that establishing an SDI on a voluntary basis have worked well. We have had no need so far to establish a legal framework, in the form of new legislation or changes to existing legislation. The government regulates its own activities and other stakeholders have voluntarily joined in, seeing the advantages for themselves. For Europe a different approach is used by the European Union. An SDI is being established with the use of a legal framework, the INSPIRE directive with supplementing regulations. As a supplement for the needs of the private sector, EU has the PSI (re-use) directive. It is interesting to compare these approaches by analysing the need and use of a legal framework for establishing an SDI. It is also interesting to look at what happens when a voluntary solution is about to be replaced by a law reform. Laws and regulations are tools for a purpose and not an end in itself. The question is whether a regulatory approach helps in a way that other tools cannot, It is also a general experience that legislation meant to initiate a fairly large reform in a certain area, needs vigorous follow up for a long time in order to work as expected. The role of the public sector is important in the discussion of how to establish and SDI. In this context, one cannot avoid the issue of funding and the discussion on whether the moving around of money between public organisations serves a purpose. In a global perspective it is interesting to consider how these two approaches, legislation or cooperation will work in other places. There are places where establishing data and services that will work in a modem technological environment are more important than an SDI, because an SDI needs data and data services like a road network needs the roads and the road signs. It is also a consideration that some of the ambitions of an SDI as they have been defined up to now, should be reconsidered when considering the tools for implementing an SDI.

Pollution organique des eaux de l’Oued Seybouse (Plaine alluviale de Guelma, Nord-Est Algérien)

Les eaux de surfaces sont souvent chargées des matières, Un excès de matière présente généralement un risque de contamination pour eaux Les eaux d’irrigation ainsi que pour les eaux souterraines. La pollution organique se produit quand un excès de matière organique, tel qu’engrais ou eaux d’égout, entre dans 1’eau. La plaine alluviale de Guelma, se situe au centre d’une grande région agricole, entourée de montagnes ce qui lui donne le nom de « ville cuvette ». Cette région trouve sa fertilité grâce notamment à l’Oued Seybouse et au grand barrage qui assure un vaste périmètre d’irrigation (12000 ha). Cependant, le développement très rapide de l’activité industrielle, accompagné d’une croissance très poussée de la population ont entraîné une dégradation de la qualité des eaux de surfaces et souterraines. Afin d’évaluer l’impact des rejets des eaux usées sur la qualité des eaux de l’oued Seybouse différents paramètres physico-chimiques ont été mesurés en sept sites répartis le long de l’Oued, Les résultats ont montré une nette détérioration de la qualité des eaux. Cette détérioration se traduit par une diminution de la teneur en oxygène dissous dans l’eau et par une augmentation importante des indicateurs de pollution.

Génération d’un modèle numérique de terrain radar:aplication à la région d’Oran, Algérie

Dans ce travail, nous présentons un processus complet de traitement d’images pour la génération d’un Modèle Numérique de Terrain (MNT) interférométrique en incluant le logiciel développé par l’Université de Delft (Pays Bas), avec pour finalité l’obtention d’un MNT haute résolution à partir d’un couple d’images radar ERS1/2. Ainsi, une fois cet objectif atteint, nous avons été amenés à analyser les résultats obtenus lors de la restitution du relief d’un site test. Nos résultats montrent que le MNT réalisé avec la technique de l’InSAR donne une précision globale de 20 m.

A Framework for the generalization of 3D city models

With a growing availability of detailed 3D city models, an increased demand for the generalization of these models is going to arise, In order to build a useful system for the generalization of highly detailed 3D city models, it is necessary to give the user the opportunity to define the relevance of features on a semantic basis. This requires a high level of semantic information that is often not present in existing models and extremely flexible generalization strategies that allow different algo-rithms with different parameters to be used for the same model. In order to meet these requirements, we propose a framework for the generalization of 3 D city models that supports the definition of custom feature hierarchies and generalization algorithms and offers predefined default features and generalization modules that can be used where the application allows it.

| info visites 9072497

Suivre la vie du site fr  Suivre la vie du site Géographie  Suivre la vie du site Bulletin des Sciences Géographiques  Suivre la vie du site Numéro 23   ?

Creative Commons License