Research And Implementation On Key Technologies Of 3D Visualization Of Ocean Field Data

The rich ocean contains abundant resources,including energy,mineral,fishery and so on,which are the guarantee for human survival.China is a big ocean country with a "blue territory" of 3 million square kilometers.The importance of the ocean to our economy,national defense and military is self-evident.With the exploration of the oceans and the exploitation and utilization of marine resources,human activities for ocean scientific research are increasing day by day.And at the same time,the oceanographic information data obtained is also increasing at the speed of geometric series.How to effectively use these data and intuitively display the useful information hidden inside the data is an important research content of ocean visualization.In this thesis,the key technology of 3D visualization of ocean field data is studied.This article introduced the basic principles of particle systems,ray casting algorithms,and multi-level visualization methods.Taking the ocean current and temperature field data as examples,this thesis realized the ocean current particle system,temperature ray projection volume rendering,and ocean current multi-level visualization.Finally,we designed and developed the ocean 3D visualization verification system to verify the visualization methods in this thesis.The main work of this thesis includes the following aspects:(1)The implementation of ocean current particle system: The overall change strend of ocean currents is reflected by the change of a large number of particles.The five-step realization process of ocean current particle,generation,attribute initialization,movement,extinction and drawing is described.Finally,the three-dimensional dynamic visualization of ocean current based on particle system is realized.(2)Improvement and implementation of the ray casting algorithm: Based on the analysis of the existing methods of volume data organization,we propose the pseudo-octree model for data organization.The model suitable for field data which are non-equidistantly sampled in the depth direction.According to the relative positions of the incident and exit points of the projected light through the volume data,different interpolation methods and sampling methods are adopted.And combing with the early termination,the drawing efficiency of the ray casting algorithm is improved by reducing the resampling point and the calculation amount.(3)The realization of multi-level visualization: Multi-level visualization needs to consider drawing efficiency and the display position of each layer.Taking into account the characteristics of non-equidistant sampling data layer,in the construction of the coordinate system,logarithmic coordinate is used in the depth direction to reduce the interval between layers.The quadtree group model is used to organize data to achieve the purpose of data cutting,which can speed up data access speed.The data scheduling thread and the data rendering thread are created to separate the data scheduling and rendering tasks.We take use of multi-thread parallelism,and perform visualized rendering of each layer of processed data,thereby achieving multi-level visualization acceleration.Taking ocean currents as an example,we have realized multi-level visualization of ocean currents.(4)This thesis designs and develops the ocean 3D visualization verification system with the Qt Creator development framework,C++ development language and OpenGL rendering engine,to verify the accuracy and applicability of the visualization methods in this thesis.