Study And Development Of Virtual-Reality And3D-Visualization Ocean Engine

Ocean is a complicated dynamic time-varying system with many factors andprocesses interacting. China is a large maritime country and increasinglydependents on the ocean because of the development of society and economy."Digital Ocean" is an ocean information system consisting of vast,multi-resolution, multi-time phase, multi-type data and its correspondingalgorithm. China has already put “Digital Ocean” into the developmentprogramme of marine science and technology as a long-term strategy. As theproceeding of this programme, the task of digitalized management, analysis andexpression of marine data has become increasingly pressing.In this paper, a virtual-reality and3D-visualization engine of ocean, i4Ocean,is designed for the applications oriented to “Digital Ocean”. The word i4means4Is:“Immersion”,”Interactivity”,”Imagination” and”Intelligence”. i4Oceanprovides a marine space-time data model for marine data management. Thismodel can well express marine space-time data and somecharacteristic patterns.The engine of this model employs the programmable effect files to manage andrealize the complicated visualization effects such as shadows. i4Ocean contains4main modules, which correspond4different functions of management. They areresource management module, scene management module, renderingmanagement module and interactivity management module. They can help usersand developers to build a real-time interactive3D environment of virtual oceanand realize the basic functions of marine data visualization. Based on this engine,users and developers can also build an ocean digital platform efficiently andextend their functions for some special use. In the last, two application cases arerealized based on this engine. The first case is the simulation of oil spilling in theocean. In this case, the whole diffusing and drifting process of the oil particlesunder the influences of wind and flow field is emulated and visualized. The other case is constructing a visualization system of hydrologic environment. And in thiscase, this system realizes the spherical3D visualization of scalar and vector datalocated at Chinese East Sea.The main contributions of this paper are:1. Design and realization of a virtual-reality and3D-visualization engine ofocean, i4Ocean. In this paper, an improved Model-View-Adapter-Effect frame isemployed to build the underlying architecture of the engine so that the integrationof interface, interactivity, function and effect is realized. The connections amongthese4parts are reduced, which realizes the weak coupling. The layers of viewand operation are isolated, so the codes in view layer can be edited withoutre-compiling codes of model and adapter. Meanwhile, the engine providesexpanded ports of data, interactivity, function and effect for developers. i4Oceanpackages and realizes the visualization and emulation of the ocean. Base on thisengine, users and developers can also build digital ocean platforms of differenttypes efficiently.2. A sphere-based volume rendering method, which is suitable for theexpression of ocean data, is proposed. The traditional ray-casting method ofvolume rendering is realized in a cube. However, for topographic data of largespatial scale, cube-based volume rendering cannot precisely reveal the geographicposition on the earth because of the influence of the earth’s curvature. So it willcause a lot error when displaying large-scale oceanic data. In GPU-acceleratingsphere-based volume rendering method, spheroidal coordinates are employed inthe process of coordinate transformation. Volume rendering in a sphere can betterexpress patterns and variations of marine data.3. A self-adapting noise-sampling volume rendering method of vector data isput forward. The traditional Line Integral Convolution (LIC) method selects thenoise texture as the input, and uses line integral to convolute the output data.Then every value of pixel of the output texture can be obtained. This method usesthe noise texture with a fixed spatial resolution and the sampling frequency of thismethod is also fixed regardless of the distance of the view point. In this paper, a self-adapting method of setting sampling resolution considering the distance ofthe view point is used. The new real-time noise texture is sent to GPU forgenerating the convolution of flow line. Using this method, a Level-Of-Detail(LOD) effect, the amount of the flow line vitiating with the distance of the viewpoint, is realized.