Visualization Of The Geomagnetic Field Spatial Structure And Intensity Distribution

The geomagnetic field is closely related to human’s life. To study the geomagnetic field has great significance in both theory and practice. The scientific visualization is an important method to study the geomagnetic field. Scientific visualization technology provides a wide variety of forms for geomagnetic field visualization, and the magnetic field line and geomagnetic shell is two common forms. In this paper, the spatial structure and intensity distribution of the geomagnetic field have been visualized by the forms of magnetic field line and geomagnetic shell with geomagnetic internal field model and external field model.Seed point selecting and the magnetic field line tracking are two main steps to visualize the geomagnetic field line. Seed point selecting is mainly to generate the first point on the magnetic field line for tracing magnetic field line, and the magnetic field line tracing is product the remaining points on the magnetic field line. An effective magnetic field line visualization should be able to show the physical characteristics of the geomagnetic field. In the physical meaning of magnetic field line, the greater the magnetic field intensity is, the greater the magnetic flux within the unit area is, and the magnetic field line distribution should be denser. On the contrary,the smaller the magnetic field intensity is, the smaller the magnetic flux within the unit area is,and the magnetic field line distribution should be sparser. So the correlation between the magnetic field line density and magnetic field intensity spatial distribution can be a key factor to evaluate the effect of the visualization. Every seed point can generate a magnetic field line, so the space distribution of seed points directly determines the density of magnetic field lines. Seed points which can reflect space distribution of geomagnetic intensity will improve the effectiveness of the geomagnetic field line visualization.The traditional algorithms that select seed points with uniform angles on geomagnetic meridian circles cannot objectively reflect the spatial distribution of geomagnetic field intensity. This paper proposes an algorithm of selecting seed points with equal line integral of magnetic field intensity. Using the algorithm, the geomagnetic internal field and external field are depicted from the data of IGRF model and T96 model. The magnetic field line is traced by fifth order Runge Kutta method. The redundant magnetic field lines existing in the result are removed by three methods including same area seed remained method, magnetic equator devided method and magnetic field line gap evaluated method. All three methods have obvious effect. The experimental results analyzed statistically shows that there is obvious correlation between the magnetic field line density and magnetic field intensity spatial distribution. This indicates that the seed algorithm can better realize the visualization of geomagnetic field, and the density of magnetic field line can effectively reflect the spatial distribution of the geomagnetic fieldintensity.Geomagnetic shell constructing and rendering are two key issues to visualize the geomagnetic shell. Geomagnetic shell constructing is to shape of the geomagnetic shell in the three-dimensional space, and geomagnetic shell rendering is improve the visual effect by some method such as perspective effect, color mapping and illumination. This paper expresses the geomagnetic field spatial structure with multi-shell combine with perspective effect, color mapping. In order to generate the multi-shell, select seed points evenly on the latitude circle on the geomanetic equatorial plane. The magnetic field line is also traced with a fifth order Runge Kutta method. Use the shortest diagonal method and the maximum vertex angle method separately to construct triangle surfaces between adjacent magnetic field lines. Changing the geomagnetic shell parameter will generate other geomagnetic shells. Render the geomagnetic shell by setting perspective effect with VTK and depth Peeling technique, and using the pseudo color algorithm to color the magnetic shells. In order to estimate the effect of rendering, the discrimination of different geomagnetic shell is used to evaluation perspective effect and the color distribution is used to evaluate the color mapping effect. The results show that different geomagnetic shells have a good distinction, and the color of the geomagnetic shell is rich, and the color distribution is even. The final result presents clear and beautiful visual effect.