Design and implementation of GPS positioning and navigation system based on mobile GIS

Abstract: This paper analyzes the key technologies of GPS positioning and navigation system based on mobile GIS, designs a system development architecture based on Smart Client, and realizes GPS positioning and navigation on PDA electronic maps through GPS Intermediate Driver technology and embedded development method.

1 Introduction

With the rapid development of computer software and hardware technology, the organic combination of mobile Internet and GIS has formed a GIS application solution for portable information terminals such as mobile phones. At the same time, many new technologies such as large-capacity storage cards, wireless LAN, wireless communications, 3G networks, and GPS global positioning navigation systems have gradually been integrated into smart devices, making it possible to realize GIS functions on mobile devices. People usually call the geographic information system used by users (terminal devices) in mobile situations mobile GIS.

In recent years, mobile GIS has become a hot topic in the field of geographic information science and has attracted the attention of many scholars. In theory, foreign scholars have proposed a dynamic and customizable IMA (Intelligent Map Agent) architecture [3]; an algorithm for converting electronic maps into simple spatial formats; in China, Li Deren, Li Qingquan and others analyzed the key technologies for integrating spatial information and mobile communications and proposed the architecture of the integrated system; Liu Zhaoqin proposed an integrated data model to improve the degree of data sharing [5]. In terms of application, the Battuta project initiated by the National Center for Geographic Information and Analysis (NCGIA) of the United States is in the stage of prototype system establishment and regional trials. The project aims to study the integrated application of geographic data and related technologies in data collection systems; A. Rizzinig and K.

"Mobile Environmental Management GIS System: Design of Spatial Information Management System for Fish Habitats" written by Gardiner et al. combines wireless network and mobile GIS to realize mobile management of environmental spatial data, and provides a prototype reference for the combination of wireless network and mobile GIS; in China, Yan Changqing et al. of Nanjing University used a combination of PDA and differential GPS in "Integrated Design of Land Change Survey Data Collection System Based on GPS-PDA" to make mobile GIS data collection meet the needs of the land and resources industry; Wang Yue, Wu Yundong et al. analyzed the development trend of mobile cartography in "Spatial Information System Based on Mobile Cartography", combined with the current situation of the intersection of cartography and other disciplines, and pointed out the key factors for the development of mobile map services from the perspective of cartography.

As a major means of collecting geographic information data for mobile GIS, GPS can obtain the location information of points in real time through GPS, and realize the navigation function on this basis. GPS intermediate driver technology (referred to as GPSID) is used to design a GPS positioning and navigation system for mobile GIS. The development end and the GPS module are connected through an intermediate layer, so that developers do not need to directly contact the hardware part, thereby reducing the difficulty of developers communicating with the GPS serial port. Through embedded development, the positioning and navigation function of GPS in smart devices is realized to meet the needs of mobile GIS data collection.

2 Design of PDA electronic map

PDA electronic maps refer to visualization products of geographic information data displayed on smart mobile devices, which can provide corresponding information according to different user needs. PDA electronic maps are different from traditional paper maps or electronic media maps. Traditional paper maps are drawn on cardboard or polyester film, with single-layer display, rich content, complex production, long update cycle, and do not consider individual user needs; electronic media maps are drawn by computer, with single-layer or multi-layer superposition display, detailed content, fast update, mature production standards, and can perform complex analysis operations.

At present, due to many restrictions, the design of PDA electronic maps cannot have all the functions of the above two maps. The limitations of PDA electronic map design mainly come from the following aspects: 1) low screen resolution; 2) small display screen; 3) poor screen color; 4) low CPU processing power; 5) outdoor environmental factors: constraints of strong light, rain, snow, strong wind, etc.; 6) mobile devices do not have a mouse, and the keyboard input function is not powerful.

Therefore, the design of PDA electronic maps needs to comprehensively consider the above-mentioned restrictions and the characteristics of the device itself. Reichenbacher (2004) proposed that the design of PDA electronic maps needs to meet the following four aspects:

(1) Information content: The information carried by PDA electronic maps does not require a comprehensive and detailed description of geographic information data like traditional maps, but the loaded layer data must be able to describe the user's needs and complete the corresponding tasks. For example, if the user is a transportation department, the corresponding map design can be simplified in terms of buildings or rivers, while highlighting the display of road data. For the thematic information to be highlighted, there are also requirements for the level of detail. The data quality of the thematic information must be high, the display must be clear, and the accuracy must meet the user's needs.

(2) User interface: The interface of the PDA electronic map should be simple and neat, with as few interface elements as possible, and information should be displayed on the entire screen. Function items should be placed in the task bar below the display screen to save more screen space for displaying map information. Secondly, make full use of the keyboard and touch pen to compile system function shortcuts to achieve simplicity and practicality.

(3) Visualization: In terms of visualization, the map design should be adjusted according to different environments and different devices. Map marks and symbols should be simple and obvious. The number of marks used should not be too many. The map background color should be mainly cold colors such as gray. The contrast should be clear. The fill pattern of the feature class should not be too complicated, so as to achieve clear display content and good display effect.

(4) Technology: In terms of technology, the storage capacity, battery power, CPU processing power, display screen size, etc. of the mobile device should be fully considered. Usually, the PDA electronic map can be layered and spatial data can be simplified, and the PDA electronic map can be divided into a basic layer and a working layer. The basic layer is the background layer, which is mainly composed of images; the working layer is the layer to be operated by the mobile GIS, which is mainly composed of vector data.

The design of PDA electronic maps is the key link to realize GPS positioning navigation and mobile GIS data collection. The quality of the map is directly related to the accuracy of positioning navigation and the quality of data collection. The realization of the positioning and navigation system of mobile devices is inseparable from the GPS module. The following will introduce a new technology for developing positioning and navigation systems based on smart devices - GPS intermediate driver.

3 GPS Intermediate Driver

GPS Intermediate Driver is an intermediate layer between developers and GPS hardware devices. Developers do not need to directly access GPS hardware, but communicate with GPS indirectly by accessing the API functions provided by the intermediate driver. GPS Intermediate Driver is a concept for GPS application development based on smart devices proposed by Microsoft after Windows Mobile series 5.0 version.

The introduction of GPSID has high commercial value. For GPS hardware manufacturers, GPSID can be seamlessly integrated with applications. For application providers, it can be integrated with any GPS device that supports GPSID.

Traditional GPS development methods mostly use programming languages ​​to directly operate the GPS hardware, perform GPS data file stream work, and completely manually parse NMEA data to achieve serial communication; or use the GPS function of established mobile GIS software, such as ESRI's ArcPad and SuperMap's eSuperMap. GPS intermediate driver technology has many advantages over traditional development methods, such as:

1) Fast development speed and high efficiency; 2) Friendly API interface function; 3) Compatible with traditional GPS data file stream operations; 4) Can be simulated on the PC side; 5) Support multiple applications to access a GPS device at the same time; 6) Makes it easy to parse NMEA-0183 data.

The working process of GPS intermediate driver is shown in Figure 1:

Figure 1 GPS intermediate drive workflow.

By calling the API functions provided by GPSID through the programming language, the corresponding GPS parameter settings (port, baud rate) and port opening and closing operations are completed; the API functions modify the operating system registry information to achieve actual access to the GPS hardware, and the GPS device responds to the access signal to complete the reception and communication of GPS data. At present, the API functions provided by GPSID include the following four: 1) GPSOpenDevice: open the GPS device and establish communication with GPSID; 2) GPSCloseDevice: close the GPS device; 3) GPSGetPosition: obtain the current point information, including latitude and longitude, elevation, etc.; 4) GPSGetDeviceState: obtain GPS device status information, including the number of received satellites, positioning quality, time, etc.

Through the above four API functions, application developers can obtain positioning and navigation data and complete all operations on GPS devices.

The location data received from the GPS device cannot be directly used in actual positioning and navigation. There is also the problem of coordinate system conversion. The following will discuss the coordinate conversion problem of matching GPS data to PDA electronic maps.

4 GPS coordinate conversion

The NMEA format data received by the GPS of smart devices are geodetic coordinates in the WGS-84 coordinate system, that is, coordinates expressed in latitude, longitude and elevation (B, L, H); PDA electronic maps use rectangular coordinates in the national geodetic coordinate system or local independent coordinate system, which are plane coordinates expressed in (X, Y). Therefore, without considering the participation of elevation in the conversion, the coordinate system is unified through coordinate conversion.

The conversion process is divided into two steps. The first step is to convert the (B, L) coordinates under the WGS-84 ellipsoid into plane coordinates under the ellipsoid through Gaussian calculation; the second step is to convert the Gaussian plane coordinates into plane coordinates (X, Y) under the national geodetic coordinate system or local independent coordinate system through analytical transformation.

4.1 Gaussian arithmetic

Different Gaussian direct calculation formulas can be given according to different accuracy requirements. The following adopts an electronic calculation formula suitable for computer programming implementation. Using the 1975 international ellipsoid parameters, the plane coordinate accuracy can reach 0.001m.

4.2 Plane Coordinate Transformation

According to the actual situation and needs of the local area, the Gaussian plane coordinates are converted into plane coordinates (X, Y) in the local independent coordinate system using a four-parameter conversion model. Using this model to solve the plane coordinates is divided into three steps. The first step is to rotate the WGS-84 plane coordinate system; the second step is to unify the scale of the rotated WGS-84 plane coordinate system with the local plane coordinate system; the third step is translation.

The following is the specific form of the model:

Among them: , by collecting at least three pairs of common point data in two coordinate systems, using the least squares principle, listing the error equation, and solving four transformation parameters. With the transformation parameters, the plane coordinates of other points in the local independent coordinate system can be solved through the above formula.

5 Example Development

The hardware conditions of the example are HTC Touch HD smartphone and built-in embedded GPS module (positioning accuracy 10m); the coordinate system is Fuxin independent coordinate system; the development platform is Visual Studio.NET (2008), loading ArcGIS Mobile SDK components.

As a part of mobile GIS, the system adopts the same development architecture as mobile GIS, namely Smart Client architecture, as shown in Figure 2:

Figure 2 Smart Client system development architecture

This mode inherits and combines the advantages of C/S and B/S modes, fully utilizing client resources while supporting real-time two-way synchronization with the server. PDA electronic map data can be directly deployed in the map cache of smart devices or downloaded to the client storage card through wireless networks.

The main functions implemented by the system are shown in Figure 3, among which map management and map operation are common functions, mainly including zooming in, zooming out, and roaming; GPS settings and GPS operations mainly include port and baud rate settings, and opening and closing of GPS ports; satellite information display function mainly includes displaying latitude and longitude coordinates, number of received satellites, satellite position, and signal strength.

Figure 3 System function design diagram.

In order to verify the stability, feasibility and reliability of data transmission of the system, the system field test is to install the system on a smart phone, load the prepared Liaoning University of Engineering and Technology PDA electronic map, test the connectivity of the PDA to access the Internet through the wireless network, open the GPS port, start from the west starting point of Quanhui Road, Liaoning University of Engineering and Technology, go east to Jiedaokou, and reach the south gate of the school via Xinming Road and Ziyin Road. The route passed by the test is typical of using GPS to collect geographic data and navigation.

The GPS middleware technology sets the port number and baud rate by calling the following methods:

The location of the map data is uniquely determined by the URL (Uniform Resource Locator) and the path of the cache storage:

The following code is used to determine the coordinate reference frame, load the GPS data received by the port, and perform coordinate conversion:

From the above process of calling the main functions, it can be seen that GPS middleware technology has higher data security and stronger visual expression capabilities.

6 Conclusion

The use of GPS intermediate drive technology can develop a positioning and navigation system with stable performance and comprehensive functions in a concise, clear and efficient manner.

The system can be further expanded and customized. When the system is extended to in-vehicle navigation and the service object of the system is changed to road vehicles, map matching technology and navigation map database should be added to the system; GPS positioning and navigation accuracy can also be flexibly customized according to the needs of different industries. For example, PDA or smart phones can integrate differential GPS modules, and the positioning accuracy can reach decimeter level.