Geographical Information System Shell and Geographical Information Query Tool

 This paper discusses traditional development models of GIS and proposes another model, geographical information system shell(GISS). Following the thought of GISS, a geographic information query tool(GIQT) is developed. GIQT's main purpose and menu structure are introduced, as well as the classification and encoding. This paper especially describes the implementation of "two-direction multi-function query" and "compressed tree-like binary search" in length. The indexing mechanism and search method greatly improve the efficiency of GIQT's functions. Index Terms geographical information system shell(GISS), geographic information query tool(GIQT), two-direction multifunction query, compressed tree-like binary search I. GEOGRAPHICAL INFORMATION SYSTEM SHELL(GISS) The two kinds of development models to a certain Geographic information system(GIS) application are platform model and construction model. As GIS is getting more widely used, the two models’ weaknesses is becoming clearer. On the one hand, GIS users with different duties, technical conditions and financial conditions need GISs having different functions and prices. On the other hand , GISs are developing toward more modules, stronger functions, bigger size, more expensive hardware setup and price. Being the base of GIS’ user pyramid, general users always have only several specific requirements for a GIS software to meet. For them, adopting platform model means buying the whole platform, expensive hardware setup and financial waste is obviously inevitable. General users’ amount is very large and many of their requirements are basically similar. Employing construction model means repeated development and waste of personal and financial resources. A new development model, shell model, is needed. Under the thought of shell model, geographic information system shells (GISS) of specific functions can be built and serve the users better. This paper generally defines GISS as a self-contained, compact, GIS-building tool, which is used to collect some specific kinds of geographic information and serve specific area according to the data input by users. From GISS’ 0-7803-7033-3/01/$10.00 (C) 2001 IEEE 0-7803-7031-7/01/$10.00 (C) 2001 IEEE 1925 definition, it can be learned that its size is small, its price and hardware setup is economical. Without much knowledge about GIS, user can still input and modify data through menu interface. Hence, GISS is suited to numbers of basic users. query of spatial data and attribute data are the most ordinary daily businesses of many professions. So, it is meaningful to develop a GISS concerning query of spatial data and attribute data, which is a geographic information query tool(GIQT). In the next sections is the implementation of GIQT. II. DESIGN OF GIQT A. Main Purposes of GIQT In view of geographic information to be collected [1], GIQT attempts to realize “two direction multi-function query”, which includes: 1) While mouse walks in the screen map, system can retrieve the text data, image data and graphics data of the point selected by the mouse. 2) Having selected an object according to attribute data, system can mark the object on the screen map.3)Having selected an object according to attribute data, system can retrieve the image data and graphic data of the object.4)Having selected a kind of objects, system can mark them on the screen map. B. Structure of GIQT Fig. 1 shows the menu structure of GIQT. III. DATA ORGANIZATION OF GIQT A. Classification and Encoding About encoding entities, according to the several fundamental requirements[2], GIQT encodes entities with unsigned integer, which means GIQT can meet encoding requirements of a middle-small area. Based on characteristics of serving mid-small area, GIQT defines figure implication of code. The first three figures represent a level respectively and the last two figures represent a fourth level. When inputting data, user can define concrete imp lication of the four levels according to practical situation. B. Implementation of “Two Direction Multi-Function” Query GIQT is a dual structure system. No matter queries are based on images or attributes, their essence is trying to acquire entities’ cod es. While using “query system”, user firstly select working area from “working area” menu to open working map of the selected area. Menu items of “working area” make up a text file and the names of each areas’ working maps make up another text file. The two files’ components correspond one -to-one. User can edit the two files (which appear as a menu in “editor” module). That is, user can modify menu interfaces and concrete content which menu interfaces correspond. The working maps of queries based on images are runlength code file. So, mouse’s position on screen has only logic relationship with pixel value’s address in raster files. In GIQT, “indexing creator” can create indexing files for raster files, in which the first pixel’s address in raster file of each row is stored. The working maps of queries based on attributes are vector maps. User’s choice of working area means the first figures of all entities’ codes have been determined. User’ s choosing class equals to determining the second figures of queried objects. Similarly, after choosing a concrete entity, GIQT has gotten the code of the entity. The menu items of“ class name”, “sub-class name” and “ entity name” can also be input or modified in “editor” module with menu interface. But the Fig.1. Menu structure of GIQT system menu set and modify password