Research On 3D Modeling And Volume Rendering Of Electromagnetic Environment Based On Geographic Coordinate System

With the increase of electromagnetic equipment and the increasingly complex electromagnetic environment,many facilities and equipment will be affected by the electromagnetic environment.The simulation of the electromagnetic environment is the basis of evaluating the electromagnetic impact.Because the electromagnetic environment cannot be seen or touched,it is urgent to find a method to describe the radiation ability of electromagnetic equipment and the distribution of electromagnetic environment scientifically,accurately and intuitively.The core of this problem is the construction of electromagnetic environment computing model and the visualization of space electromagnetic environment.The main research work of this paper is on the three-dimensional digital earth,the construction of multi radiation sources three-dimensional electromagnetic environment model based on radio wave propagation model in geographic coordinate system,the direct volume rendering of spherical regular grid electromagnetic environment data in geographic coordinate system and related optimization methods.Specifically speaking,there are the following four aspects:1)Aiming at the modeling of electromagnetic environment on three-dimensional digital earth,firstly,this paper organizes electromagnetic field data in geographic coordinate system,i.e.sampling spatial electromagnetic environment at equal intervals along longitude,latitude and height,and forms the data organization form of spherical regular grid.Secondly,based on the ITM radio propagation model,the electromagnetic environment calculation model of multi radiation sources is designed.On this basis,the terrain reuse method in the traditional Cartesian coordinate system is improved.This paper calls it the terrain reuse algorithm of spherical regular grid data,which not only reduces the redundancy calculation of terrain extraction,and realizes the accelerated calculation of electromagnetic field data,but also takes into account the influence of earth curvature.The calculation results are more accurate.Finally,aiming at the low computational efficiency of multi-source electromagnetic field data in a single PC,a parallel sampling method for multi radiation sources is proposed,which combines the terrain reuse algorithm of spherical regular grid data to realize the fast calculation of multi-source electromagnetic field data.2)The bounding box of traditional GPU ray casting volume rendering algorithm is a cube,which cannot be directly used to render spherical regular grid data in geographic coordinates.A GPU ray casting algorithm based on dome bounding box is proposed.The construction process of spherical regular grid data bounding box(called dome bounding box in this paper)is described in detail.At the same time,in order to obtain the correct optical properties of resampling points,a coordinate conversion algorithm in shader is designed to realize volume rendering of spherical regular grid data.In order to accelerate the reconstruction of electromagnetic environment,octree partitioning is carried out in geographic coordinate system,and compact bounding box of volume data is constructed.As a result,empty voxels are eliminated,the amount of volume data of rendering and the number of light resampling are reduced,and rendering efficiency is improved.3)For large-scale spherical regular grid electromagnetic field data,it cannot be loaded from external memory to system memory and texture memory for rendering at one time.Based on the storage structure of depth octree and combined with the multi-resolution analysis characteristics of wavelet transform,volume data is regarded as three-dimensional discrete signal,and a multi-resolution hierarchical block data model based on depth octree and three-dimensional wavelet transform is constructed.According to the view position,the multi-resolution data models with different resolutions are dynamically scheduled.4)A subsystem of three-dimensional modeling and visualization of electromagnetic environment is designed.It verifies the related technologies of three-dimensional modeling and visualization of electromagnetic environment.The subsystem is integrated on the VBF(Virtual Battle Field)platform.