Research On Spatial Data Quality Control And Evaluation Technique System

With the development of the information technique, the use of Geographical Information System(GIS) becomes broader and broader. At the GIS development beginning stage in China, Prof. Deren Li (1991 ) pointed that the following problems must be solved: how to build quality model of GIS, which index is used to measure accurate data and uncertainty data, quantitative data and qualitative data in GIS.GIS data uncertainty and GIS data quality control technique becomes a research issue.Recent years, positional accuracy of the spatial data is a research issue, and some research result is gained. Point uncertainty is measured by error intervals, line positional uncertainty is measured by error belt, area positional uncertainty is described by uncertainty of lines which form the boundary of the area. The former research emphases on the foundation of positional uncertainty and measurement index, remote sensing classification data uncertainty etc. Fewer discussion is made on how to control data quality in the process of data collection to insure data production quality to meet the quality requirements, which deserves deep research.At first, spatial data quality problem is analyzed and possible quality problem is summed up. Map scanning digitization is used an example to discuss the error source of spatial data. After that, an uniform spatial data quality model is built. Then starting from the GIS data collection process, how to control data quality in the process of data collection to insure data product quality is researched. Next, spatial data quality control and evaluation method is discussed, and the program check arithmetic is emphasized. Finally, the correspond soft of the spatial data quality control and evaluation is developed to control and evaluate spatial data quality. So a complete spatial data quality control and evaluation technique system is founded. The main research result is shown as the following:l.Spatila data quality is analyzed.Spatial data quality problem is analyzed, and is divided into error and mistake. Aiming at GIS data can be collected by much methods and working procedure is complicated, map scanning digitization is used as an example to analyze the error source of spatial data. The error source of map scanning digitization is detailedly analyzed. Possibly imported error, error representation form and its impact on the accuracy of data product is probed. Error distribution of map scanning digitization is analyzed by the way of error distribution test to give the basis of map scanning digitization data quality control.2.An uniform spatial data quality model is founded.Aiming at much GIS data format and data type, and there is not an uniform spatial data quality model, on the basis of GIS data content, quality elements Accuracy, Consistency and Completeness & correctness are suggested to measure spatial data quality by the way of induction and subdivision. And data quality elements and their quality subelements is given in detail. As a result, an uniform spatial data quality model is advanced, which is used as the basis of GIS data quality control and evaluation. Using this data quality model, data quality evaluation models of DLG,DOM and DEM are founded, which are used as a standard of product quality testing and evaluation.3.Spatial data quality control method is advanced.Using map scanning digitization as an example, general spatial data quality control method is advanced. To insure the data product to meet quality requirements, the following method were discussed as process quality control: select data source, map scan, geometrical rectify, map orientation, screen digitization, data edit, positional accuracy limitation defining of data product, testing point number of positional accuracy test, etc. By this way, DLG data with high quality can be gotten, and DEM data with high quality can also be gotten using correlative DEM making software.4.Spatial data quality control and evaluation method is suggested.At first, data quality test index is researched according to GIS data quality model. And test method of the different quality index is discussed. Next, quality index which can be tested by program is distinguished. Finally, quality test and quality evaluation method is researched. The main research results is introduced here.? Using template match technique to check attribute data and metadata.? Using special topological relation test to check the topological consistency.? As for data cartography rule, element relative relation among different data layer, edgematch of different data file, etc., rule base is founded to check data consistency of different data by the way of rule defining by user.? Using mathematical method to check positional accuracy.? Vision model of man eye is established using experiences, the statistics value of the testing image is computed. They are compared to check image quality.? To check completeness and correctness automatically using the specific demands of the specification and technique design.? To represent error information in different ways, especially by means of graphic to become convenient for error affirming and editing.? To evaluate data quality automatically with the comparison of quality standard database and data quality testing result database.5.Spatial data quality control and evaluation software is developed.New spatial data quality test and evaluation idea is advanced. The complicated spatial data quality characteristics is abstracted as rule and model, which is used as the theoretic basis to check and evaluate the different data quality by means of program.Based on above research results, two universal software is developed, which is named as Vector Data Quality Control and Evaluation System(DLG-Checker) and Image Data Quality Check and Evaluation system(DOM-Checker) respectively. They have the following merits:? The graphic and image operation environment are developed by advanced language and database, which has independent knowledge property right.? They can be used to control procedure data quality and data product quality , check the quality data which will be imported database.? Spatial data quality control rule base is founded according to the knowledge, such as quality control experience, data quality standard cartography rule, etc. On the basis of rule and model, the test scheme is made flexibly, so test content and evaluation standard for different scale and different quality demand can be adjusted conveniently to meet the requirements of different project data quality control and evaluation. Besides this, these soft can check data quality in different type of format. In short, they can be used universally.? Using database technique to manage and update spatial data standard, the result of data quality check and evaluation.? Provide data edit function to adjust the error during data quality control process.? Facing digital surveying and mapping production, these soft can be used to check and evaluate the quality of different data by means of adjusting test scheme.Single function test and comparative test of these soft shows that these soft can be used universally, testing and evaluating result is reliable, quality control productivity is improved greatly.