First, the land area measurement method The basic principle of land area measurement is the use of geometric principles and the principle of calculus to calculate the area. Due to the different basic information provided, the applicable area calculation method is also different and can be roughly classified into two categories:
One class is the direct calculation area method, which includes the geometric element analysis method and the coordinate analysis method. It is based on the data obtained from field measurements and directly uses the analytical method to calculate the area of ​​the graph. The other category is the measurement area method on the map, including graphical calculation method, planimeter method, photoelectric measurement instrument method, computer digitization method, etc. It is on the drawing work drawing base map, in accordance with the required accuracy, use Somehow measure the area of ​​the graph.
Second, there are problems in the calculation of land area There are still some problems in the calculation method of land area currently used. If the measured area is not equal to the actual area, there are many reasons for the area distortion. The main ones are:
Measurement error in the field measurement. In the field measurement, system errors and accidental errors due to the influence of observation conditions such as people, instruments, and objective environments will directly lead to unequal measurement areas and solid areas.
The distortion produced by the map projection during the graphical calculation. The area calculated graphically from the map is the area of ​​the Gauss-Kruger projection plane, not the real area of ​​the earth ellipsoid.
Although the Gaussian projection uses a subband projection to partially control the distortion, the deformation is still large at the edge of each band, and the greater the bandwidth, the greater the distortion.
Tilt the surface to project the deformation produced on the plan. For a large-scale topographic map, the corresponding solid area on the map has a smaller range, so it can be calculated by taking the earth ellipsoid approximately as a plane. However, when the area is large, the plane error is regarded as large. The actual surface is an uneven surface with a convex surface and a concave surface. When it is projected onto the plane, it will inevitably be deformed, and the size of the area deformation will increase as the inclination angle of the ground increases.
There is an unreasonable phenomenon when the area of ​​multiple parcels is adjusted. In the urban and rural cadastres, when the land area is estimated by the analytical method, the adjustment of the area of ​​a plurality of lands with control conditions is generally based on the method of proportionate distribution according to the area size. This adjustment method is more intuitive and the calculation is convenient. use. However, this adjustment method is also flawed. When adjustment is made, only the size of the plot area is taken into account, and the real estate price of the plot is not considered.
III. Solution to Problems in Land Area Measurement 1. Improve on-site measurement accuracy to avoid measurement errors When measuring land, the system should firstly avoid system error, human error, and error factors. In addition, high-precision control data should be used. Various professional procedures, taking into account external influences, improve the measurement accuracy, so as to ensure the accuracy of land area measurement.
2. The following three methods are used to solve the distortion caused by the map projection: (1) Using the Earth's radius and the distance from the central meridian to establish a mathematical model, plus the projection area correction;
(2) Select the appropriate projection bandwidth. The distortion produced in the map projection varies with the bandwidth. Therefore, when calculating the area, first calculate the maximum length deformation value based on the known area accuracy, and then determine the projection bandwidth from this length deformation value, so as to select the banding;
(3) Use equal-area projection method instead. The distortion produced in the map projection is due to the isometric projection of the Gauss-Krueger projection. When calculating the area, to ensure that the area does not change, consider using the equal-area projection method to calculate, that is, calculate the starting latitude and longitude and the area of ​​the ending latitude and longitude. Since the enclosed area is a trapezoid after Gaussian projection, it is also called a spherical trapezoidal area. Calculations.
3. Oblique surface projection onto a plan view In the area correction for deformation, it is necessary to properly consider the deformation caused by tilting the surface projection onto the plane. The tilted surface projection area is related to the inclination of the ground and should be corrected when calculating the actual area of ​​the ground.
4. Two methods to eliminate unreasonable adjustment of area of ​​multiple lands (1) The method of weighted adjustment. According to the measurement error theory, when the area is the same, the weight of the parcel with large area error is small; when the area error is the same, the parcel of land with large area is also large. After the land rights have been determined, we can use the area closing difference between the sum of the total area and the total area measured and controlled values ​​to calculate the second estimated value of the area's weighted level difference and area error, so that multiple area area adjustments can be made. It is more reasonable.
(2) Press precision adjustment method. In the cadastral mapping and area measurement, in order to get rid of the impact of control error propagation and projected deformation on the measured area accuracy, in order to take into account both the size of the plot area and the real estate price of the plot in the area adjustment, it can be ensured. Adjustment method for area accuracy requirements. For example, in the urban areas, the measurement accuracy of the area of ​​the ownership units is relatively high, and the calculation accuracy of the public-owned land areas belonging to the cities, towns, roadways, etc. in cities and towns is relatively wide. Therefore, we can guarantee the area accuracy of the parcels and neighborhoods, allocate the closure of the control area to the public land area such as roads and roadways, and maintain the area of ​​each ownership unit unchanged, thereby improving the parcels and streets. Square area of ​​the measurement accuracy. This method not only does not affect the quality of cadastral mapping, but also improves the accuracy of the main content of cadastral maps.
With the increasing development of surveying and mapping technology and land and resources information, these methods need to be practiced and further improved in practice.
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