1. Definition of database structure of geological map of Central Asia
(1) Definition of each element class in the database.
The following elements are used to describe and define the feature class, object class and comprehensive feature class of geological map spatial database:
Entity name: Chinese name of entity data; Feature class name: the Chinese name of the feature class;
Object Class Name: the Chinese name of the object class;
Name of comprehensive element class: Chinese name of comprehensive element class;
Coding of element objects and comprehensive element classes: standardized coding of data item names;
Spatial data type: pointing line and surface type;
Data type: refers to the type of data storage, generally including character type (C), single-precision numerical value (S), double-precision numerical value (D), long integer (L), plastic and so on. (1). Need to specify the data type of special system;
Relationship with other entities: indicates the relationship between the entity and other entities, such as topological relationship or dependency relationship;
Data storage length: the number of bytes stored in a specific system platform, which is the system default value;
Data display length: the length of data used for information expression, character data representing the number of characters, numerical data representing the number of digits before and after the decimal point, such as F8.2, and data items with uncertain length should be stated;
Constraints: to determine whether to fill in data items, you can choose (O), required (M) and conditional required (C) according to the following three types of regulations; If it is a required item (M), you can fill in whether it is not empty;
Default value/initial value: determine the value of the data item in the initial state;
Scope: clearly give the scope of data items;
Data item description: describes the data item that needs further explanation. For data items with special expression formats, it is also necessary to explain here, such as the delimiter of multivalued expressions and the description of special symbols.
Primary key name: the name of the data item that identifies the uniqueness of the record and is associated with other entities;
Sub-keyword name: the name of the data item used together with the main keyword to identify the uniqueness of the record and to be associated with other entities;
Index key name: used to sort data items according to certain rules;
Annotation feature class coding: standardized coding of data item names of annotation feature classes.
1) The feature data sets that constitute the geological map spatial database include basic feature data sets, comprehensive feature data sets and object data sets. See Table 7-2 for the classification, description, content and relationship description of elements and objects in the geological map spatial database.
Table 7-2 Classification of Elements and Objects in Geological Map Spatial Database and Description List of Their Relationships
sequential
2) Geological map class map based on geographic database model. Figure 7- 17 is a geological map class diagram based on geodatabase model, which reflects the relationship between geological map element class and object class.
(2) field definition of each element class in geological map database
According to the technical standard of geological survey of China Geological Survey (DD 2006-06), which is the database building standard of digital geological map spatial database, under ArcGIS 9.2 Catalog, various element classes are established according to the data format of each element data specified in the standard. The data format of "sedimentary (volcanic) lithostratigraphic unit" is now used to explain, and other data elements are established one by one according to the standard DD2006-06, which is not repeated here (Table 7-3).
Table 7-3 Sedimentary (Volcanic Rock) Stratigraphic Units (_ Strata)
2. Technical process of database construction
After scanning the vector of geological map according to the unified classification standard, it is classified according to each element on the geological map, and the attributes are entered one by one with reference to each geological map specification. In this paper, the technical process of establishing geological map spatial database based on digital mapping technology is shown in Figure 7- 18: The database establishment process adopted in this paper is based on the national digital geological map database establishment standard, combined with the actual situation of Tu Tu elements of geological map in Central Asia and the actual operation process of establishing database on ArcGIS 9.2 platform. In the process of vectorization, the vector of linear geological elements (faults, geological boundaries, lithologic boundaries, etc.). ) as a starting point. Focusing on line tracing and line copying, the geological layers of various polygons are generated by the method of transforming elements into polygons, and then the temporary polygon files are classified according to various geological elements, imported into the standard geological database of each map sheet, and then the attribute data are entered.
Figure 7- 17 Geological Map Category Map of Geodatabase Model
In the process of establishing the database, the first step is to make geometric correction on the scanned geological map. With the support of ERDAS IMAGINE 9.2 software, this paper adopts polynomial geometric correction method, selects the intersection of grid lines of drawings as control points according to the first order, and selects at least 20 control points for geometric correction of each map to ensure the accuracy within 0.5 pixel, that is, 10 meter, and completes the geometric correction of scanned geological maps in Central Asia.
The second step is to create a database table structure based on the geological element data set and geological element fields discussed above on ArcGIS Catloge platform. Under the unified standard of database construction, a complete geological map database of Central Asia 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.
Fig. 7- 18 technical process of geological map spatial database construction based on GIS digital mapping technology
After completing the vector of each lithologic boundary, if there is no omission, use the "Feature to Polygon" tool of ArcGIS spatial analysis module to convert the temporary line file into a temporary polygon file, and set the closure difference to10m. After the conversion is completed, bins are classified into sedimentary rocks, intrusive rocks, metamorphic rocks and water areas, and imported into their own independent layers one by one. For dike (surface) elements, occurrence (line) elements, craters 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 a scanned geological map 1 1 geological elements is basically completed. Next, mainly refer to legend, histogram and geological map specification to input attributes. As shown in the flow chart 7- 16. Finally, after checking that the attribute data input is complete and correct, the vectorization of the next map sheet can be carried out.
The purpose of establishing digital geological map database is to save and exchange data most effectively and digitize scanned geological map according to specifications; The database of Central Asia digital geological map is designed and established, which realizes the objective description, digitization, unified classification and integrated storage management of the original geological map data, and lays a unified foundation and a complete data platform for the spatial analysis of gold and copper deposits in Central Asia based on GIS. The establishment of digital geological map database also provides data platform support for future 3D digital deposit research, 3D quantitative prediction of ore bodies, evaluation of geological and mineral resources and exploration data management.