Design ideas of navigation software based on embedded Linux system

　　With the popularity of various vehicles such as cars, the demand for vehicle navigation equipment has become increasingly strong. As a vehicle-mounted device, it must not only have reliable performance, but also be portable, low power consumption and low price. The design of a GPS navigation terminal that uses an embedded system based on an ARM microprocessor and a GPS module can well meet this system requirement. To this end, this article introduces the hardware and software structure and design method of a terminal that uses an ARM9 development board and a GPS module to implement GPS navigation functions.

　　2 GPS navigation system structure

　　The GPS global positioning navigation system introduced in this article can be divided into five parts according to its functions: embedded main control module, GPS module, display module, expansion module and power supply module.

　　The embedded main control module is based on the S3C2440 processor and is mainly responsible for responding, processing and controlling the data of the GPS navigation module. In terms of hardware, the main control module is an embedded development board, including touch LCD interface circuit, SD card interface circuit, FLASH, SDRAM, etc. In terms of software, the main control module should run an embedded Linux system. The main function of the embedded Linux operating system is to manage program module processes and schedule processes.

　　The GPS module is mainly used to receive navigation satellite data and send it to the main control module in a specific format. The display module can use a 3.5-inch TFT LCD with a touch screen, which is mainly used to interact with the user. The expansion module mainly refers to the SD card. The power supply module mainly provides power for the normal operation of the system. Figure 1 shows the structure of the system.

　　3 GPS data extraction

　　The output statements of the GR-87 GPS module follow the NMEA-0183 standard. Statements of this standard all start with "$" and end with "CR" and "LF". After "$" is a 5-character address, the first two characters are the sender identification code (GPS is "GP"), and the last 3 characters are the statement name. The data in the positioning information is divided by "," The GPS module can generally output NMEA-0183 format statements once per second. In the navigation system, generally only time, date, latitude and longitude, and speed are needed. Since the RMC statement completely contains the above information required by the system, it is only necessary to extract the RMC statement. Figure 2 shows the specific process of extracting GPS data.

　　4 Implementation of navigation map

　　After obtaining the positioning information such as longitude and latitude, it is necessary to display them intuitively on an electronic map or other display media, so that it can really play the role of navigation. In order to accurately display them on an electronic map, it is necessary to use a certain algorithm for conversion, namely a map matching algorithm.

　　Generally speaking, the basic idea of ​​map matching is to match the vehicle's GPS trajectory with the vectorized road segment objects on the map to find the current road and project the current GPS positioning point onto the road.

　　The key to map matching is to determine the matching points. The projection method can be used to find matching points during design. The basic idea of ​​the projection method is to determine the minimum value as the projected matching point based on the distance from the point to the line, and use the nearest neighbor method to process it. Then, by setting a threshold, the wrong matching points are filtered out to obtain preliminary results, thereby completing the point-to-line matching.

　　The specific implementation method is to preprocess the road layer first, then convert the road into a polyline segment, find the current road, then project the current positioning point onto the road, and then find a line segment in the highway layer closest to the positioning point, and then calculate the point with the shortest distance from the point to the line, and finally find the roads within the error range in each layer.

　　The basic process code of the algorithm is as follows:

　　The realization of the navigation map can be realized by using the embedded graphical interface tool Qt embedded. The graphical interface is a human-computer interaction interface. Users can understand the navigation information through the screen, or directly operate the touch screen to operate the system, such as zooming in and out of the map, viewing the positioning information, etc.

　　5 Conclusion

　　Since ARM processors have the characteristics of low power consumption and high performance, they can be widely used in various portable electronic products. Based on existing electronic products, this design expands the GPS navigation function by connecting an external GPS module, which can save users money without losing too much portability. To this end, the author hopes that the method of using the ARM development board and GPS module to realize the GPS navigation function can provide a reference for expanding the GPS function of smart devices.