The basis of land management work is cadastral management, and cadastral mapping is an important way to obtain cadastral management information. GPS technology has the advantages of all-weather, uniform precision, and the selection of points and buried stones is more flexible than conventional methods. It does not require the conditions of mesh type and point-viewing as the conventional triangulation, and can greatly improve the cadastral measurement. The accuracy and efficiency of the first-level control network layout, so GPS technology has been widely used in cadastral control measurement. This paper studies the specific application of GSP technology in cadastral mapping.
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First, the introduction of GPS measurement methods
As one of the most advanced positioning tools, GPS is becoming a very important data acquisition tool for cadastral information. In recent years, GIS-type GPS receivers have been increasingly used to collect position data on the ground and detailed attribute information. GPS only provides geospatial location, and cadastral data should also include attribute information. For example, a road in a cadastral information system includes the spatial coordinates of a series of points of the road and the attribute information (width, grade, etc.) of the road, and GPS can only collect spatial coordinates of a series of discrete points in the field. In order for these points to be connected to the road and to know their attribute information, they must be explained and described when the field collects these discrete points. The method of description and description can be used to draw on the data dictionary technique used in the large scale machine. A data dictionary is a character set that describes the relationship between attributes and spatial data. When collecting data by GPS, the data dictionary has attributes and feature items, and the feature items reflect the characteristics of the measured points. For example, Tree represents a tree, which is an isolated point and is not connected to any other point; if Road indicates a road, the point with a Road is to be connected. When collecting data using GPS, it is generally equipped with an electronic handbook or a handheld computer. Once a location has been determined, its corresponding feature and attribute items can be entered on the electronic book. It is feasible to use GPS to collect cadastral space data, but the following problems should be paid attention to in practical applications:
(1) The GPS positioning mode and accuracy should match the cadastral information system. GPS positioning accuracy and mode are various. Before determining the GPS processing method, it must be carefully studied to achieve the accuracy required by the cadastral data. (2) Conversion of the coordinate system. Since the GPS positioning uses the WGS-84 coordinate system, the coordinates it measures are different from the general GIS (such as cadastral spatial data), and the WGS-84 coordinates must be converted. Most of the current GIS systems in China use 1954. The plane projection method of the Beijing coordinate system, therefore, the coordinate transformation and projection transformation of the WGS-84 coordinates can meet the requirements of cadastral survey.
Second, GPS cadastral surveying and mapping and related technical issues
1. Accuracy requirements for cadastral surveying and mapping
(1) Cadastral control measurement accuracy requirements
Cadastral control measurements must follow the principle of grading from the whole to the local, from high-level to low-level grading (hierarchical network, but also over-the-counter). Cadastral control measurements are divided into basic control measurements and cadastral control measurements. The basic control measurement is divided into one, two, three, four, etc., and the corresponding level of triangulation (lock), edge measurement network, wire network and GPS network can be arranged. Based on the basic control measurement, the cadastral control measurement work is divided into one or two levels, which can be set to the corresponding level of triangulation, edge measurement network, wire network and GPS network. The cadastral plane control measurement coordinate system adopts the national unified coordinate system as much as possible, and the area with no conditions can adopt the local coordinate system or any coordinate system. The accuracy index is an important quantitative indicator of GPS network technology design, and its size will directly affect the GPS network layout plan, observation plan and processing method of observation data. The accuracy of the cadastral control measurement is specified based on the accuracy of the boundary point and the accuracy of the cadastral map. According to the "Regulations on the cadastral survey t", the error of the cadastral control point relative to the starting point is not more than ± 0.05m.
(2) Measurement accuracy requirements of the cadastre
The measurement of cadastral parts, namely the boundary point and the coordinates of the object points, and the acquisition of land elements, including the boundary line, the land boundary line and boundary point of the land, the actual outline of the house and other structures, railways, highways, streets, etc. Surveying and mapping of major hydraulic facilities such as traffic lines, coasts and tidal flats. A boundary point is a turning point of a space or attribute of a boundary line or a boundary line, and a boundary point coordinate is a set of data obtained by using a measurement means in a specific coordinate system, that is, a mathematical expression of a geographical position of a boundary point. The accuracy of the coordinates of the boundary points can be selected according to the economic value of the land in the survey area and the importance of the boundary points. In China, considering the vastness of the region and the imbalance of economic development, the requirements for the accuracy of the boundary points should also have different levels.
2. Establishment of GPS cadastral control network
(1) The principle of network deployment and the formulation of observation schemes
The cadastral control measurement is to measure the cadastral basic control points and the cadastral map control points. It is a plane measurement control for the initial land registration, the establishment of basic cadastral materials, and the dynamic management of daily cadastre. According to the requirements of the “Regulations on Urban Cadastral Investigation†promulgated by the State Land Administration, the cadastral plane control network can be set up as a second, third and fourth triangular network, a trilateral network and a corner network, and a first and second small triangular network (lock). , secondary wire network and corresponding level of GPS network, and each level of cadastral plane control network, according to the size of the town can be used as the first level of control. The use of GPS technology for cadastral control requires no similar equilateralness when there is no conventional triangulation (lock) layout.
1. Benchmark design
The baseline of the GPS network includes the in-position reference, direction reference, and scale reference of the network. The determination of the basis of the network is achieved by the overall adjustment calculation of the network. The benchmark design of the GPS network generally refers to determining the location reference problem of the network. Determine the position reference of the network, select the coordinate value of a point in the network and fix it or give it the appropriate right, or the points in the network are not fixed, and determine the network through the pseudo-net pseudo-adjustment or the stable adjustment. Location benchmark. The adjustment of the GPS network with the minimum constraint method has no effect on the orientation and scale of the network. The direction and scale of the network after the adjustment and the relative accuracy of the network are the same, but the position and position accuracy of the network are not the same. Select the coordinates of thousands of points in the network and fix them, or select the coordinates of thousands of points in the net and fix them, or select the coordinate values ​​of several points in the net and give appropriate weights to determine the position of the net. At the same time, it will have an impact on the direction and scale of the GPS network, and its degree of influence is related to the number of constraints and the accuracy of the observed values.
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