Research And Application Of SVG In WebGIS And Mobile GIS

With the development of scientific information, the demand for location is increasingly clear, GIS (Geographic Information System) applications has become increasingly widespread, and with the rapid development of computer technology and network technology, GIS systems have long been a WebGIS through a combination of Internet technology from the original independent stand-alone mode. WebGIS has been very different with the traditional GIS in structure and application technology parts,it also has become an important trend of the GIS technology development. WebGIS represented by GoogleMap has been achieved to move all of the functions of GIS into the web applications,and it gives more quickly,friendly and real-time experience to users. In recent years,with the further development of wireless network technology,mobile hardware devices's conditions have been rapid enhanced, people's need of information and dependence of procedure are enhanced,and want to have a breakthrough of time and space constraints about information accessing,so the demand for wireless applications is also enhanced, the demand for mobile GIS included.Compared to WebGIS,because out of the fixed network and cable Internet restrictions,mobile GIS have a higher demand of information quality and data transmission for being difference in application technology and design philosophy with WebGIS.SVG technology is a language of describing the two-dimensional vector graphics based on XML launched by W3C organizations,it is a new open standard vector graphics specification.SVG graphics have the characteristics of small storage capacity, super-interactive, no-easy-distortion as well as the cable-script, and so on. SVG as an open, standards-based XML language, so it can work well for cross-platform working,solve the problem of non-uniform format map data. For these reasons, SVG should become the new favorite of WebGIS and mobile GIS, but in this stage,whether the WebGIS with relatively mature technology or the mobile GIS in the stage of rapid development,they all use the form raster image to storage and transmit GIS data.Raster graphics and vector graphics have their own advantages and disadvantages, the main difference between them are data distortion and interactive, vector graphics in these two areas have a unique advantage, but the raster data is the trend of WebGIS and mobile GIS at this stage.The main reasons of SVG vector data is not widely used in WebGIS and mobile GIS area are the following three points: first of all, browser needs corresponding plug-ins to display SVG graphics, this defect will be solved with the support of mainstream browser support for SVG; the next is the relative lack of SVG format map data;finally, the size of original SVG graphics is still too large, at this stage of network, the transmission will be definitely impacted.In this paper,for the above-mentioned problems, the main objective is to achieve the generation of SVG map format as well as the construction of the WebGIS system model and mobile GIS model based on the SVGThe main work of this paper are the following three main parts:First,design and implementation of the generation of the SVG format and Mobile SVG format map data applicated by WebGIS, as well as the implementation of SVG compressing.Second, the establishment of WebGIS architecture based on SVG technology,and introduced its working processe, design plan and specific modules implementation method,focused on the realization of SVG client.Third, the establishment of mobile GIS architecture based on Mobile SVG technology,elaborate and resolve the major issues which will be faced, focused on J2ME client's Mobile SVG graphics resolution and the realization of representation.Through the analysis of MIF/MID file opened by MapInfo Corporation for graphics data exchange as well as SVG graphic elements' expression to MIF documents,developed a conversion program from Mapinfo Map to SVG vector format map.The main solution to the following problems: conversion and expression from SVG to MIF file graphic elements,conversion from geographical coordinates to the SVG coordinate,MID attribute data storage form and storage format,proprietary map symbols and layers' SVG denotation in MIF file.Eventual, realization the conversion of the MIF/MID files and SVG format.Through the analysis the differences between Mobile SVG specification and SVG specification,propose the generation program of the Mobile SVG,and through the independent programe,design and use the SVGT editing tools provided by NetBeans to achieve the generation of Mobile SVG file in two methods.For the obviously effect through the gzip compression algorithm to generate SVGZ compressed,you can extract through a browser, and it is the official SVG compression method,this paper use gzip algorithm to compresse SVG,good practical results.Through the analysis of WebGIS main constructing methods,and combination with characteristics,select the Plug-ins construction method to construct of WebGIS architecture based on SVG, All the plug-ins are Adobe SVG Viewer of Adobe company.WebGIS architecture based on SVG technology now is more popular using of the client,service layer and data layer three-tier structure to construct,In this paper,first intruduced SVG graphics data of the data layer and storage of attribute data simply,Second, described the map engine of web service layer, Servlet component and jax components'achievement.The main method of map engine applicated to the XML:servlet components mainly include the filter for certification authority,provide front service module for external interface and deal with the business logic module of logic relationship;Ajax components mainly implement the attributes data asynchronous transmission.Because of all the WebGIS functions based on SVG are focused on the client,so this article focused on the implementing of the client functional components,mainly used for external JavaScript language analysis operation for SVG dynamic DOM tree,the realization of the map enlarging and narrowing, roaming, locating,layer controlling, as well as Eagle Eye and so on.And add plug-ins detection module on the client prompt the user to install plug-ASV.As J2ME technology's platform transplanting feature,MobileSVG-based GIS system model takes J2ME technology development to develop client.The overall framework takes client,service layer, data layer the three-layer structure as usual, in order to achieve the location services, adding a LBS layer in the service layer,The main function is to realize the user's location-based services, using the optional J2ME package JSR179 to achieve.Location information converted into SVG format in line with the norms through the resolver module and return to the client to display. Through the analysis of Generic Connection Framework,determine the client and server's communication with HTTP transmission protocol, comparing the XML parser and KXML resolver provided by JSR172,as a result of the general conditions of KXML equipment, using KXML to resolve analysising attribute data.Also in Mobile GIS based on mobile SVG system model focused on the realization of the client J2ME platform and methods. First of all, introduce the basic structure of the J2ME and life cycle of MIDlet, and then introduces the client-side SVG map showing,Mainly used the J2ME optional package JSR226 mobile 2D graphics API,according to the providing package, construct a core operation package for rendering, resolution, zooming, and dynamic interactiving features encapsulation, achieve the SVG map to performance in the client. Through the operating effect of the WebGIS system model and the mobile GIS system model based on SVG,you can see that no matter the WebGIS or the mobile GIS,they all complete the basic operations of GIS map well, with server smooth communications, non-distortion map zoom, achieved a good visual effect.