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Theses

Modélisation et calcul parallèle pour le Web SIG 3D

Abstract : This thesis focuses on displaying and manipulating 3D models from Geographic Information Systems (GIS) in interactive time directly in a web browser. Its main contributions are the visualization of high resolution 3D terrains, the simplification of irregular meshes on the GPU, and the creation of a new API for performing heavy and effective computing in the browser (parallelism GP/GPU) without compromising safety. The first approach proposed for the visualization of terrain models is built on recent browsers efforts to become a versatile platform. With the new 3D pluginless APIs, we have created a visualization client for terrain models “streamed” through HTTP. It fits perfectly into the current Web-GIS ecosystem (desktop and mobile) by the use of the standard protocols provided by OGC Open Geospatial Consortium. This prototype is part of an industrial partnership between ATOS Wordline and its GIS customer, and particularly the IGN (French National Geographic Institute) with the Geoportail application (http://www.geoportail.gouv.fr) and its mapping APIs. The 3D embedded in browsers brings its own challenges which are different from what we know in heavy applications: restrictions and constraints from JavaScript but also problems of data transfer. These constraints, detailed in the next paragraph, led us to rethink the standard algorithms for 3D visualization to take into account the browser specificities. Thus, we have taken advantage of network latency to dynamically manage the connections between the different parts of the mesh without significantly impacting the rendering speed. Beyond 3D visualization, and even if the JavaScript language allows task parallelism, data parallelism remains absent from Web browsers. This observation, added to the slowness of JavaScript processing, constituted a major obstacle in our goal to define a complete and powerful GIS platform integrated in the browser. That is why we have designed and developed the WebCLWorkers, a GP/GPU Web API for high performance computing that meets the criteria of simplicity and security inherent to the Web. We tried to find a trade-off for a language close to the script but secure and efficient, based on the OpenCL API at runtime. This approach is opposite to the existing ones, which are either based on precompiled code or disregard performances. Our API proposal interested the Mozilla Foundation which asked us to participate in the development of the WebCL standard by integrating the Khronos Group (Mozilla, Samsung, Nokia, Google, AMD, and so on). Exploiting these new computing resources, we then suggested an algorithm for parallel simplification of irregular meshes. While the state of the art was mainly based on regular grids for parallelism (and did not take into account Web browsers restrictions) or on simplification and kd-tree clustering, no solution could allow both parallel simplification and progressive visualization using irregular grids. Our solution is based on a three-step algorithm using implicit priorities and local minima to achieve simplification, and its degree of parallelism is linearly related to the number of points and triangles in the mesh to process. We have proposed in the thesis an innovative approach for 3D WebGIS pluglinless visualization, offering tools that bring to the browser a comfortable GP/GPU computing power, and designing a method for irregular meshes parallel simplification allowing to visualize level of details directly in Web browsers. Based on these initial results, it becomes possible to carry all the rich functionalities of desktop GIS clients to Web browsers, on PC as well as mobile phones and tablets
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https://tel.archives-ouvertes.fr/tel-02391577
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Submitted on : Tuesday, December 3, 2019 - 3:59:11 PM
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  • HAL Id : tel-02391577, version 1

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Fabien Cellier. Modélisation et calcul parallèle pour le Web SIG 3D. Modélisation et simulation. Université Claude Bernard - Lyon I, 2014. Français. ⟨NNT : 2014LYO10015⟩. ⟨tel-02391577⟩

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