SITEMAPPED WEB DIRECTORY » Article Details
ARCGIS Data Format |
|
| Date Added: May 28, 2018 04:31:14 PM | |
| Author: Wilhelmina Pelloe | |
| Category: Computers: Software | |
| When I first came into contact with the GIS, the teacher said such a sentence: 'If we do this line, the data is life, there is no data, and nothing can be done.' Now we need to do a little webgis project and realize the essence of this statement. The GIS industry relies heavily on data and its format is diversified. In order to understand the real time data synchronization software format in detail, relevant data are reviewed and summarized as follows. This article mainly summarizes the following data formats: (1)shp (2) Coverage (3) Raster (4) Geodatabase Reference address: [http://www.cppblog.com/alantop/archive/2008/08/14/58880.html] The Shapefile is a GIS file system format file developed by the U.S. Department of the Environment, and is an industry-standard vector data file. The shapefile stores the non-topological geometry objects and attribute information in the spatial feature table in the dataset. The geometry object in the feature table is saved as a graphic file represented by a set of coordinate points – the SHP file. The Shapefile does not contain Topological data structures. A Shape file consists of three files: a master file (.shp), an index file (.shx), and a dBASE(*.dbf) table. The main file is a direct-access, variable-length recorded file. Each record describes all the vertices coordinates of a feature. In the index file, each record contains the offset of the corresponding main file record from the beginning of the main file header. The dBASE table contains the feature attributes of each Feature in the SHP file. The correspondence between the geometry records and attribute data in the table is the ID based on the number of records. The attribute records in the dBASE file are in the same order as the records in the master file. The coordinate file (.shp) in the Shapefile consists of a fixed-length file header followed by variable-length spatial data records. The file header consists of 100 bytes of descriptive information. It mainly describes the length of the file, the Shape type, the scope of the entire Shape layer, and so on. This information constitutes the metadata of the spatial data. When importing spatial data, first read the file header to obtain the basic information of the Shape file, and build a corresponding metadata table based on this information. Variable-length spatial data records consist of fixed-length heads and variable-length records. Its record structure is basically similar. Each record consists of a record header and record content. The contents of the record header include the record number and the length of the coordinate record. The record numbers in the Shapefile are all from 1 and the coordinate record length is measured in 16-bit bytes. The record content includes the target's geometry type (ShapeType) and the specific coordinate record (X, Y). The content of the record varies according to the geometry type of the element, and its specific content and format are different. The property file (.dbf) is used to record property information. It is a standard DBF file. It is also composed of two parts: header file and entity information. The length of the header part of the file is variable. It gives a general description of the DBF file, the most important of which is the detailed description of the information of the DBF file record. For example, the name, data type, length and other information of each record item have specific instructions. The entity information part of the property file is an attribute record. Each record consists of a number of record items, so only one cycle of each record is required. The index file (.shx) mainly contains the index information of the coordinate file. Each record in the file contains the offset of the file header of the corresponding coordinate file record record coordinate file. Through the index file can be easily located in the coordinate file to the specified target geographic coordinate information. The header part of the file is a fixed-length (100 bytes) record segment whose content is basically the same as the file header of the coordinate file. Its entity information is recorded as a basic unit, and each record includes two record items: Offset and Content Length. note: 1. The shp file can only store one type of point, line, or face, or all points, or all lines, otherwise it is all. 2. shp can set a lot of field properties 3. shp can set different projection information. It is possible that there are no errors in the two data formats, but they cannot be superimposed because of different coordinate systems. Reference: [https://blog.csdn.net/zhongjiekangping/article/details/6112308] Coverage is a topology data structure with complex data structures and attributes stored in Info tables. | |
|
|
|