多伦多代写essay 计算机论文代写 数字地形模型的发展
ABSTRACT
With the advancement of communication technology and hardware in these recent years, Geographical Information System (GIS) applications have rapidly evolved to integrate Mobile GIS. Mobile GIS provide geographic information services from indoor work station or desktop system to field work application using mobile computing device such as hand phone and personal digital assistant (PDA). Although many applications such as navigation system and mobile tourist guide have been developed in Mobile GIS, the implementation mostly in 2 Dimensional (2D) based content. Since recent mobile devices attain the level of performance that makes them to be able to manage 3D graphics, bringing 3 Dimensional (3D) based content is highly preferable. However, the used of 3D in mobile devices still involves some troubles of performance and usability due to its limitation. Furthermore, the development of 3D terrain rendering for Mobile GIS which used Digital Terrain Model (DTM) adding more constraint. In this paper, the development processes of rendering terrain on mobile devices are explained. The development consists of several processes. First, the data need to be loaded and then normalized. Later, backface culling is executed using the normalized data to identify the visibility of polygon face. Finally, the data is rendered on mobile device. Experiments were conducted using several terrain datasets derived from aerial images to___. The results from these experiments showed that rendering DTM data of 836 triangles is between 3-4 frames per second (fps) while frame rate within 1-2 fps is the result using DTM data of size 3108 triangles. Furthermore, the appearance of the surfaces is a little unrealistic on the device than on the computer and needs to be improved. Future expansion of this implementation will consider the integration of GPS feature to add functionality for future mobile GIS applications such as navigation and land surveying.
Keywords: Mobile Device; Terrain Rendering; OpenGL ES; Mobile Rendering; Mobile GIS
INTRODUCTION
Throughout recent years, GIS applications and technological trends have improved constantly starting with mainframe computers to various other GIS from stand-alone desktop computers GIS, local networking GIS, Web GIS and to the latest, Mobile GIS. Mobile GIS is the used of geographic data and functions in the field where maps are displayed and processed on mobile devices such as Personal Digital Assistants (PDAs) and Web-accessible smart phones [ni buku Peng]. Mobile GIS is a combination of one or more technologies such as mobile devices, Global Positioning System (GPS), wireless communication and GIS software that integrated together. Mobile GIS makes possible the ability to access spatial and information at any time and place. In spite of the advantages of Mobile GIS, most of its applications are in 2D. Since 3D based application are more perceivable and attractive to viewers than 2D [advance 3d games], research towards 3D based applications for Mobile GIS are indeed important.
Since the later 1950s, Digital Terrain Model (DTM) has been used in many applications mainly in the area of simulation, visualization, games and Geographical Information System (GIS) applications. DTM is one of the major concepts in representing terrain surface. DTM as defined by Miller and Laflamme, is representations of continuous surface of the ground by a large number of points consist of x, y, z coordinates in an arbitrary coordinate field [buku ijau] and are obtainable via satellite, stereoscopic aerial images and contour data from geographical maps before it is saved as a certain file format.
Recent mobile devices are able to manage 3D graphics due to the programmability and usability that have been greatly enhanced by the continuous improvements of its hardware and software capabilities. Despite the improvement, mobile devices still have limitation in their capabilities like small screen sizes, low-bandwidth, colour resolution limited processing power, small memory, critical power consumption and its limited application capabilities [Evolution of 3D games, Jong-Woo Kim]. Moreover, rendering DTM on mobile device has its own issues and constraint. The major problems encountered are massive terrain data and the appearance of the terrain surface. Therefore, some consideration and issue need to be focuses for the development of terrain rendering for Mobile GIS.
This paper will discuss the development process for rendering DTM on Mobile GIS. Through the development process, a prototype of terrain visualization on mobile device is developed using OpenGL ES running in HTC TyTN II mobile phone. General development process of rendering terrain dataset for mobile GIS will be described followed by the explanation of the development.
