Research Of Several Key Technologies Of Change-only Information Collection System On Field Based On PDA

The update of spatial data is a hot issue in GIS. The incremental update will be a major trend to spatial database update because it is flexible and easier to ensure the verisimilitude of the spatial database. Change-only information collection is the primary part of spatial database update, and thus the Change-only information collection system becomes an essential tool. With the improving and promoting of handled devices such as PDA, collecting Change-only information in the field through PDA will become a feasible mode. Therefore, this paper focused on several key technologies of PDA's Change-only information collection system, including:(1) The existing incremental information file format was optimized and improved and a new file format based on XML was designed.The new file format is more better to describe and analysis the Change-only information and also is more convenient to transmit in the internet.(2) Considerating the special features of collecting Change-only information and the demand of digital mapping and Mobile GIS, a data model and structure that suitable for PDA was designed, and also a PDA based index structure was designed too.The fast reading and drawing of massive spatial vector data and raster data in PDA was implemented.(3) The problem of the PDA's communication with field data gathering equipment such as Total Station, GPS was researched and the serial (or Bluetooth serial) was employed to implement the data communication and processing.(4) An object-oriented map symbol library based on PDA was designed. For the features of incremental information collection and the platform, the auto drawing of point symbol was implemented and the drawing of line and polygon was simplified.Finally, a PDA based change-only data collection system was designed and developed in Windows Mobile by Visual C++ developing language. The system has the basic function of map surveying and GIS. It draws vector map from the coordinates obtained by the Total Station and GPS. It displays the map with multible and standard map symbol. The change-only information file which is collected and generated in the field was stored in the native device or sent to the remote server through wireless net. The change-only information file was successfully applied to the incremental information update system, and obtained a good experimental result.