The rational planning and use of rural land is an important step in the development of China's agricultural economy. Therefore, the land resources must first be sorted out from the measurement of land area. The GPS area measuring instrument is based on GPS technology to realize the measurement and recording of the land area of ​​the farmland, which provides help for the agricultural production and rational land planning and utilization.
Identifying the quantity, distribution, and utilization of land resources, and giving scientific assessment of their use structures, will become a very important issue in order to better and rationally develop and utilize land resources and provide scientific basis for agricultural divisions and land use planning. task.
Over the past few years, we have trained more than twenty counties and cities on the detailed investigation of the workforce, participated in the detailed inspection and acceptance of land, and encountered many problems related to area calculation theory and methods. In this paper, according to the existing conditions and technical level of each county, the essence of the Savich method and the simple calculation formula in the area calculation are discussed for reference by relevant parties.
The measurement area on the map is affected by the accuracy of the map scale, mapping, and drawing accuracy on the map: the effect of map projection deformation and cartographic integration: the effect of the deformation of the drawing: the effect of the adjustment of the boundary of the land type boundary and the accuracy of the mapping: As well as the influence of factors such as photogrammetry instruments and methods of operation. The larger the map scale, the higher the accuracy is.
The measurement of the land type area is ideal with a 1:10 000 topographic map. It is not possible to use the 1:50000 graph to enlarge the 1:l or 1:2.5 million measurements. This not only does not achieve the effect of improving accuracy, but due to the inaccurate theoretical size control when zooming in, or the deformation of the blueprint paper, etc., resulting in a decrease in the accuracy ratio of the l:50,000 graph.
The projection used in China's topographic maps is a Gaussian projection, and the maximum area of ​​the area deformation of each band is no more than 1/500. Therefore, it has little influence on the accuracy of land area measurement and can be omitted.
However, the paper deformation has a great influence on the area measurement. The deformation coefficient is in the range of 1 to 00/1/00, and the deformation distribution is not uniform. The size of the paper deformation depends on the type of drawing, the method of preservation, temperature, humidity, and other factors. As the paper folded, spliced, rubbed, hot and humid weather, etc., its deformation is even more pronounced. Therefore, the amount of map should be reduced as much as possible.
As for the selection and methods of measuring instruments, in the measurement of land area at the county level, the conditions and technical levels limit the use of the planimeter with the grid method. According to the National Land Survey “Regulationsâ€, area measurement must follow the “layered control, grading calculations, proportionate adjustment†of the taste is measured by the quadrature instrument can generally reach a relative accuracy of 1/400. When calculating the area, if the poles are placed outside the graph, the accuracies of the planimeter are not required when the area is calculated using the Shavki method.
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