Quality Checking System For 1:50000 DLG And Its Key Issues

The quality of digital products has been a hot research issue of GIS both at home and abroad. As a most important part of digital products, people have taken deep concern to the quality of DLG.The traditional quality checking method for DLG is mainly to check by hand, which has a great deal of drawbacks in the respects, such as the checking fashion, checking contents, checking expenses, and checking efficiency, etc. The checking result of this method is substandard and with many mistakes and omissions, and the checking efficiency is very low. Today, the digital products increase sharply, this method will be washed out from the mainstream checking method camp gradually.People have developed some quality checking softwares for DLG in succession at present, but there are many weak points in these softwares, for example, the checking function is not complete, automatic degree is low and visualization effect is low, etc. With the rapid increase of the digital products, a new complete-content, automatic, dependable, visualization quality checking software is urgently needed. The subject for research of this text is just launched because of this background, and the main contents are as follows:1. The research meaning, research situation, research purpose, research contents, and research approach of the Quality Checking system for 1:50 000 DLG is introduced.2. Some basal concepts of the quality checking for 1:50 000 DLG are introduced, the error source and the error type of the quality checking for 1:50 000 DLG are analyzed, the checking contents of the quality checking for 1:50 000 DLG are expounded, and the checking approaches and existent problems of the quality checking for 1:50 000 DLG are discussed.3. Some key issues in the system are discussed in detail, such as the batch processing technique, the checking technique of elevation contradictions among contours, the checking technique of elevation contradictions between elevation points and the contours, the checking technique of self-intersection, the checking technique of edge matching, and the visualization technique of the checking results. And a new algorithm which name directional scanning approach to check the elevation contradictions among contours is put forward.4. The total designing of the system is done by the Object Oriented system analyzing and designing approach. And the detailed designing explanation book of the system is achieved.5. The composing and flow of the system is intrpduced, and some result pictures that several functions systems realized are showed. It also introduced the checking and accepting cirs, the applied circs of the system, and compares the system to certain software which had been used by the National Quality Supervising and Testing Center for Surveying and Mapping Products.6. The main conclusions of this subject research are summarized, the deficiency exists in the system and the research work needing carrying on further is explained.Comparison to the similar other software, this system has the following merits:1. The checking contents are very complete.The checking content of the Quality Checking system for 1:50 000 DLG is very complete, it almost includes all the aspects of the quality checking for 1:50 000 DLG. The content of the system not only includes the fundamental demand of the data, the mathematic precision, the attribute precision, the logical consistency, etc, but also includes the metadata quality checking.2. High extent of automatic.The Quality Checking system for 1:50 000 DLG has a high extent of automatic, the most part of the content in the quality checking regulation can be checked by program batch processing. If the checking mission has been set up, you just need a single hit on the mouse, and then it can accomplish the batch processing of several maps. 3. Checking result visualization.The checking result will be showed in the checking result region. Hit any row in the result table, the system will add all the layers which involved in the checking result to the platform, and automatically zooms to the error feature, and marks the error point with red marks.