The Method And Implementation Technology Of Obtaining Geographic Information For Railway Location Based On Web Resources

With the development of aerospace remote sensing and network technology, as well as the relaxation of laws and policies, parts of satellite image data and DEM data has been open to the public, such as LANDSAT satellite series images, EO-1 satellite images, WMS (Web Map Service) images, SRTM and ASTER GDEM etc. To apply the free network satellite images and global digital elevation model to railway survey and design can reduce the field work and improve work efficiency without increasing the costs. It also provides a reference for the aerial photography. This technology and methods with obtaining image, mosaic, reprojection and correction will be discussed in this paper. The main work is as follows:1) By comprehensive comparison of Landsat series satellite images, EO-1 satellite imagery, WMS imaging and other images from the aspects of resolution, accuracy, obtaining technology etc. and considering the characteristics of the railway location, WMS images were chose as the main study object in this paper.2) Take Google Map as an example, analysis the webpage of GM and get the information of the elements on GM webpage, thereby learn the named regular of the URL of GM tiles and proposed its construction method.3) Based on CURL, the program was camouflage as a browser to access the server and realize the download of GM tiles by multithread through http protocol.4) In the case of transformation from Web Mercator coordinate system to decimal degrees raster, a method was proposed to instead the algorithm nonlinear transformation by a linear transformation and give the conditions it can be applied. The method is easy to realize and efficient and achieved good results in practical tests.5) The projection methods of commonly used coordinate systems and conversion methods between coordinate systems were summarized based on the definition and calculation method given by EPSG(The European Petroleum Survey Group).6) Mosaicing tile, matching of image and terrain,reprojection and so on were realized base on GDAL (Geospatial Data Abstraction Library). Multithread technology was applied to make full use of idle disk 10 and synchronous the writing thread by Windows critical section technology...