Coordinate system: Beijing coordinate system 1954, Gauss-Kruger projection, band number of 6 degrees 15, central meridian 85 30', unit m. ..
Elevation datum: 1956 Yellow Sea height system is adopted.
2. Working procedures of database construction
In the actual operation process, the database construction process adopted refers to the national digital geological map database construction standard, and combined with the actual situation of Tu Tu elements of1:250,000 geological map in western Tianshan area, a GeoDatabase database is created, and various element sets and classes are constructed. The database structure is shown in Figure 4-3. In the process of vectorization, the vector of linear geological elements (faults, geological boundaries, lithologic boundaries, etc.). ) as the starting point, with line tracing and line copying as the center, and finally using the method of transforming features into polygons to generate various polygonal geological layers. Then the temporary polygon file is classified according to each geological element, imported into the standard geological database of each map sheet, and then the attribute data is input.
In the process of establishing the database, the first step is to make geometric correction on the scanned geological map. The second step is to create a database table structure according to the geological element dataset and fields discussed above on the ArcGIS Catalog platform. Under the unified database building standard, a complete geological map data structure of the western Tianshan area is established. Each geological map forms an independent geological database, each database contains the same data structure and field type, and each attribute table forms a layer to store the corresponding geological geometric features; After the first step of linear vectorization, temporary line files and temporary surface files are added to their respective databases to save unclassified graphic data.
In the process of vectorization, we first vectorize fault elements, because faults are linear and smooth, and most faults are the common boundary of stratum lithology. After the completion of fault vector, vector all lithologic boundaries, including sedimentary strata, intrusive strata and metamorphic strata. Lithologic boundary data is stored in a temporary line file, which is a separate line element layer. When vectorizing, if the fault happens to be a lithologic boundary or the boundary of a common * * * edge, at this time, in order to ensure the topological consistency of geometric figures, we use the method of "line tracing" or "line copying" to make the common * * * boundary. We use the same method to vector all public boundary lines, such as the common boundary between the Geological Boundary layer and other polygon features.
After the completion of each lithologic boundary vector, if there are no omissions, the temporary line file is converted into a temporary polygon file by using the "Feature to Polygon" tool of ArcGIS spatial analysis module, and the closure difference is set to 10m. After the conversion, the bin is classified according to sedimentary rocks (volcanic rocks), intrusive rocks and rock walls, and introduced into their independent layers one by one. For dike (surface) elements, volcanic mechanism and occurrence (point) elements, there are few boundaries with other layers. So these elements can be directly vectorized separately. Finally, the graphic quality inspection is carried out, including lithology classification inspection and geometric topology inspection. Import the standard library after checking that there are no errors or omissions. In this way, the graphic vector work of various geological elements of a scanned geological map is basically completed. Next, mainly refer to legend, histogram and geological map specification to input attributes, as shown in the flow chart 4-3. Finally, after checking that the attribute data input is complete and correct, the vectorization of the next map sheet can be carried out.
There are many methods to process geochemical and aeromagnetic data. This study mainly uses Kriging interpolation and principal component analysis to process geochemical and aeromagnetic data, and combines the related contents of geological and mineral maps to store the information related to mineralization in the spatial database. The production of the above data is completed on the ArcGIS platform.
3. Spatial database content
The spatial database of this resource potential assessment contains five feature data sets, 15 feature classes and at least six raster data.
Geographic element data set: National Basic Geographic Information Center1:250,000 topographic database adopts four element classes: water system, administrative area, residential area and traffic element class.
Data set of basic geological elements: including 7 elements:1:250,000 regional strata, intrusive rocks, volcanic rocks, metamorphic rocks, structural divisions, faults and minerals. Among them, the base map data of resource potential evaluation and prediction are directly generated by data fusion of structural facies unit attributes defined by strata and intrusions, and the attribute content and corresponding data types contained in each element class should be consistent with the elements needed for regional metallogenic model and resource evaluation, so as to realize the symmetry of model requirements and information. For the coding of each attribute, please refer to the data item sub-word designated volume of National Mineral Resources Potential Evaluation Data Model.
Data set of geophysical and geochemical exploration elements: it includes four elements:1:50,000 aeromagnetic elements,1:50,000 surface magnetic elements,1:200,000 regional geochemical elements and1:50,000 regional geochemical elements.
Geophysical and geochemical raster dataset: mainly stores the raster data converted by kriging interpolation of geophysical and geochemical feature classes and the raster data generated during spatial analysis.
Remote sensing raster data set: it is mainly used to store ETM ++ satellite data in the study area, and it is the mainstream remote sensing data source for geological and mineral applications in recent years, especially for cartography and alteration information extraction.
4. Database quality control
Spatial database is required to meet the requirements of relevant technical regulations and standards formulated by China Geological Survey in terms of data integrity, logical consistency, location accuracy, attribute accuracy and joint accuracy.