Research On Key Technoliogies Of Vector Map Publishing Based On HTML5

With the great development and extensive application of Internet technology, WWW is becoming an efficient way to publish information and providing a new and effective media for delivery and publishing of geographic information. Web publishing of map has become a hot topic of researches in geographic infomation field.Because of the current restrictions on common Web standards and spatial data's characteristics (unstructured, large amount of data), map web publishing is facing a range of issues,such as efficient transmission of data and display methods of the client. Web Hypertext Application Technology Working Group (WHATWG) established the specification of HTML5 in 2004. HTML5 strictly built on the basis of HTML4. This specification provides several new API for handling multimedia data, which brought new opportunities for map web publishing.This paper analyzes the difficulties and problems of map web publishing technique. It puts forward the solution of map web publishing based on HTML5 and discusses the main problems needed to be solved. The main content and achievement of this paper are showed as follows:(1)The structure of map web publishing based on HTML5. Integrating with new HTML5 features, this paper applied HTML5 Canvas,HTML5 Web Database to map web publishing, and put forward the HTML5-based scalable and fat thin balanced map web publishing system structure.(2)The method of vector data transmission and the local store based on HTML5. On the server side, the preprocessing of vector data use Douglas-Peucker algorithm to simplify the curve, record the intermediate results of algorithm execution by scale features and organize them by BLG-Tree, and store BLG-Tree in the spatial database by scale features. In the transfer phase, firstly, transmitte the initial data, then according to the request of client, retrieve incremental data and return the data in a specific encoding format to the client. On the client side, firstly, resolved the code according to some rules, then, establishment multi-scale dara organization as server, and use HTML5 local data storage technology to store the data in the client database which has been transmitted.(3)Vector map render based on HTML5 Canvas. Firstly, comparation analysis of the current map symbol data structure was conducted. Integrating with HTML5 Canvas drawing mechanism and using the map symbol data structure based on Path, the drawing of point,line and polygon based on Canvas was designed and realized.(4)Vector map publishing prototype system based on HTML5 was developed.Vector map publishing prototype system which adopted IIS as a Web server is developed in Visual C# and Javascipt language.The model of HTML5-based map web publishing, the method of HTML5-based vector data transmission and the Canvas-based client map rendering are put forward in this paper which have great signification to the map web publishing technology.