Drawn Based On Pvm Parallel Terrain Study

Recently, with the development of computer graphics, visualization in scientific computing, remote sensing technology, computer vision and related subjects, it is very popular to render the terrain with the data captured by space and aerial photogrammetry. Real-time rendering terrain is the hotspot in computer graphics, Virtual Reality, geography system and so on. At present, real-time rendering of thousands upon thousands triangles can be done by using many top grade graphic workstations, however, the terrain data is too large, it exceeds the ability of real-time rendering and memory management of the common graphics. So, parallel rendering technology became breakthrough for super large terrain data. Especially, parallel rendering technology based on PC cluster which is highly efficient and cost-effective, flexibility in use, good scalability.This dissertation proposes a parallel terrain rendering system. This system is implemented in PC cluster, adopt retain mode based sort-first architecture, and output the image with the multi-channel. PC cluster which interconnected with Ethernet use the PVMD preserving in every PC to allocating task and transiting message. And interface in PVM completes the tasks of sending and receiving data, establishing tasks and synchronizing. This dissertation makes contribution on three aspects:(1) Introduce the principle of PVM, and make the program by the method of transmitting message. The PVM completes by three parts: daemon threads, interface and monitor console. When starting PVM, PVMD run in every PC. The local PC send the task to its PVMD, then the local PVMD send the data to remote PVMD, when the remote PVMD receives the data, it hand in the tata to its PVMD. If remote computer completed the tasks, they feedback the result to the master. In the process, PVM should be installed in every PC including master node and slave node internet should keep running normally. This paper introduces the every step, and summarizes the problems in the whole process.(2) Research the algorithm for terrain rendering both at home and abroad, and summarize the characteristic of parallel rendering. The classical algorithm usually adopt the binary tree or quad-tree to store the data; and levels of detail model usually simplify the data top-down or from bottom to top; it is popular to simplify the model considering the view point; the regular square grids(RSG) is more popular than Triangulated Irregular Networks(TINs). Otherwise, the algorithm of terrain rendering has been improved on many times. Among so many methods, ROAM is well fit the characteristic of parallel rendering. The advantages: The data structure is very simple and is easy to visit the every node in the binary tree; ROAM is easy to divide into many patches; the crack can be avoided by split the node of the tree under compulsion. The disadvantages: if it split the node frequently, it always cost too much time and memory. So, two points to be improved on:(1) Divide the terrain into patches. When rendering the terrain with ROAM algorithm, the terrain data can be rendering by only one patch or by many patches.(2) Control the depth when the node is splitting by viewpoint and error of screen.This paper proposes the method of data localized to lighten the burden on internet. The data should store in every PC, only transmit the data including starting position and ending position. More over, simple synchronizing is realized, such as changing the model of rendering, and so on.