(Guangzhou Marine Geological Survey Guangzhou 5 10760)
Brief introduction of the first author: Shao (1983-), male, master, main research direction: application and development of 3S technology in resource investigation, dynamic monitoring of ecological environment and digital ocean. Email: zkyscg @ yahoo.com.cn.
The traditional calculation model of mineral reserves is based on Euclidean measurement, which has the problem of poor accuracy when applied to small-scale marine mineral reserves calculation. By studying the characteristics of WGS 1984 projection, Mercator projection, lamberto projection and Albers projection, a method of slicing mineral entities and calculating the volume cumulative sum of mineral entities between slices is proposed. The accurate measurement and volume calculation of reserves under the projection of small-scale ocean map are realized, and how to realize the calculation of marine mineral reserves under the irregular ellipsoid of the earth is systematically discussed, which provides basic services for China's marine resources exploration and military strategy.
Keywords: calculation of predicted reserves of marine survey geographic information system map
1 preface
In recent years, resource exploration has covered most land areas. More and more countries are looking to the ocean. As a huge treasure house of energy and resources, the importance of the ocean in the national economy and military strategy is increasingly apparent. Countries are competing to formulate plans and strategic plans for the development of marine science and technology, giving priority to the development of new marine technologies [1]. Marine research has become a hot spot, and scientific and technological innovation is changing with each passing day.
Because the ocean is a large area, it is very different from the exploration technology of land resources, especially in the calculation of large-scale mineral reserves in the ocean. The earth is an irregular ellipsoid. When the traditional plane-based European survey method is used for small-scale marine map survey, it will be deformed due to map projection and other reasons, which will seriously affect the accuracy of reserve calculation [2]. In order to eliminate this influence, a series of projection conversion formulas have been established by domestic and foreign institutions, including the European Organization for Petroleum Exploration. Applying these projection transformations to two-dimensional projection improves the accuracy of map measurement to a certain extent. However, there is no effective method for the calculation error of three-dimensional reserves caused by earth deformation. On the basis of predecessors' research, this paper introduces the method based on projection transformation, studies the characteristics of WGS 1984 projection, Mercator projection, lamberto projection and Albers projection, puts forward the method of slicing mineral entities and calculating the volume cumulative sum between slices, realizes the accurate measurement and volume calculation of reserves under the projection of small-scale ocean map, and systematically discusses how to realize the exploration and development of marine resources in China and the calculation of marine mineral reserves under the irregular ellipsoid of the earth.
2 Overview of ocean forecasting
In the basic scale topographic maps of China's oceans, the topographic maps with the sea area less than1:500,000 are mostly projected by equiangular cylinders, also known as Mercator [1]. At present, the charts used by researchers in state-owned enterprises and institutions in China are mostly Mercator projection. However, it is necessary to eliminate the map deformation error caused by Mercator projection when calculating mineral reserves on a small scale in the ocean. In this paper, Albers projection is introduced, and the error is eliminated and the reserves are calculated by using its feature of constant area in projection transformation. In the direction of mineral depth, the distance between slices takes the difference of depth values.
3 technical route
Large-scale marine mineral entities have large span, obvious map projection deformation and irregular shape, which greatly increases the difficulty of reserves calculation. In this paper, slicing technology is introduced to cut mineral entities into solid surfaces, and the reserves of mineral entities are obtained by calculating the volume between solid surfaces and the accumulation of entities between slices. Schematic diagram (figure 1) is as follows:
Figure 1 Mineral Entity Slice 1 Mineral Reserves Slice
The marine mineral entity in figure 1 is divided into n segments, and the sum of the volumes between the segments is the volume of the whole entity. When n tends to infinity, it is closer to the actual volume. The value of n depends on the accuracy of measured data, that is, the accuracy of latitude, longitude and depth.
3. 1 data preprocessing
3. 1. 1 data source
1) Multi-wave velocity and water depth data: Multi-wave data are often used to calculate the volume of lake basins. The working principle of multi-beam bathymetry is to transmit and receive sound waves in the wide-angle direction through the array of sound wave transmitting and receiving transducers, and calculate the spatial position of each beam measuring point through various sensors (satellite positioning system, motion sensor, gyro compass, sound velocity profiler, etc.). ), so as to obtain strip high-density water depth data perpendicular to the course [6].
2) Seismic profile data: The data of marine mineral reserves mainly come from the fault data of marine seismic profile. The seismic exploration method is to lay survey lines on the ground, carry out seismic construction along each survey line, collect seismic information, and then obtain seismic profiles through computer processing. The seismic profile after geological interpretation is like a knife cut from the ground, showing the underground geological structure in two-dimensional space (length and depth) (Figure 2)[7]. In the marine seismic profile, the number of shots can be read according to the fault plane, and the coordinate data of mineral deposits can be read in combination with navigation data.
Fig. 2 Schematic Diagram of 2D Seismic Profile 1 2D Seismic Data
3. 1.2 data warehouse
Location data extracted from multi-beam or seismic profile shall be stored in the following database format:
Table 1 mineral reserves data structure table 1 mineral reserves data table
The longitude and latitude data in the table should be stored as Albers projection data after projection conversion.
3.2 Calculation of cross-sectional area
3.2. 1 Section
Search the boundary value of equal depth polygon with sql language and draw the section plane. The method is:
1) uses sql language to search for data with the same depth value in database data.
2) take a specific data (a 1, b 1) from all the data, which needs to be between all the coordinate values (ax, bx).
3) Calculate the distance value L = sqrt [(B2-b1) 2+(A2-A 1) 2] counterclockwise from the 0 degree angle of (a1). At the same time calculate the angle difference. If the angle difference is equal, take the point with larger L value.
4) Connect all the data extracted in 3) into polygons, which is the tangent plane.
Section calculation
In order to make the area calculation result unaffected by the earth ellipsoid, it is necessary to convert Mercator projection into Albers projection. The method of converting Mercator projection into Albers projection under ArcEngine is as follows [4]:
The dimension point is esriGeometry. IPoint
Set pPoint = new point.
Point p PutCoords mx, mine
Set the pPoint. SpatialReference=pSpRef2
Point p Here, Mercator projection is first realized as WGS 1984 projection.
lon=pPoint。 X
lat=pPoint。 Y
Set pPCS=pSpRFc. CreateProjectedController System (esrisprojcs _ nad1983 USA _ Albers)
Set pSpRef2=pPCS.
Point p Project pSpRef2'' realizes the conversion from WGS 1984 projection to Albers projection.
Lon = point p. X' lon is the longitude value in Albers projection.
Latitude = point p. Y' lat is the latitude value in Albers projection [4].
ArcEngine is a popular tool for secondary development of GIS processing. When Mercator projection is converted into Albers projection, every coordinate point needs to be converted. Usually, W GS 1984 projection is used as the intermediate conversion projection. Firstly, Mercator projection is converted into WGS 1984 projection, and then the converted WGS 1984 projection is converted into Albers projection.
The biggest feature of Albers projection is that the area before and after projection remains unchanged. In this paper, centroid algorithm is used to calculate the area. The concrete steps are as follows: first, find the centroid of the polygon, then draw a straight line from the centroid to the vertex of each polygon, and finally add up the area of each polygon to get the result. The calculation steps are shown in Figure 3[4].
The method is [4]:
1) First, traverse the database and read the coordinate values of data with equal elevation in the database to form a planar polygon. Find the centroid of a polygon.
2) Connect each point of the polygon with the center of mass.
3) Calculate the area of each small polygon and add them. S = s 1+s2+s3 ......................................................................................................................................................... Represents the area of a small triangle [4].
Let l be the side length, and the coordinate values at both ends of l are (a 1, b 1), (a2, b2). As shown in Figure 4:
Then: l = sqrt [(B2-b1) 2+(A2-a1) 2]
The source code for calculating the area of each small triangle is [4]:
s=(L 1+L2+L3)/2
s = sqrt[s *(s-l 1))*(s-L2)*(s-L3)]
Figure 3 Area Measurement of Polygon [4] Figure 3 Area Measurement of Polygon
Figure 4 area calculation of each small triangle Figure 4 area calculation of each triangle
Here, the value of s is the cross-sectional area. The error caused by the ellipsoid of the earth is considered in the calculation result of cross-sectional area, which is closer to the actual value.
3.3 Volume calculation between sections
The calculation of the volume V between sections after the mineral entity is divided and sliced simulates a trapezoidal calculation method. The area of the upper section is above s, the area of the lower section is below s, and h is the height difference between sections. As shown in Figure 5:
Fig. 5 Single slice entity Fig. 5 Single slice object
Then the volume between planes v = (above s+below s) h/2. In Figure 1 and Figure 5, when the number of tangent planes n tends to infinity, the smaller the area difference between tangent plane 1 and tangent plane 2, the closer the shapes of the corresponding two polygons are, and the smallest the H value. At this time, the calculation results of cross-sectional volume with small error can be obtained.
3.4 Calculation of Mineral Reserves
After the mineral entity is divided into n sections, the cumulative sum of the volumes of each section is the reserves of the whole mineral entity. The larger the number of sections n is, the more volumes are cut, and the closer the tangent value is to the actual value. The volume value v is the cumulative sum of the volumes v between each face.
South China Sea Geological Research 20 10
Where: V is the total mineral reserves. It accumulates the sum of the volumes of all entities between planes. The number of entities between planes depends on the size of n, and when n approaches infinity, it is closest to the actual value.
4 conclusion
This paper introduces the calculation method of marine small mineral reserves based on projection transformation, and gives the projection transformation method based on Ar-engine. The calculation model of mineral reserves is different from the traditional calculation model, and the key lies in considering the error caused by the deformation of the earth ellipsoid on a small scale. Therefore, the paper introduces the method of projection transformation, which reduces the error caused by the irregularity of the earth to some extent. But this method is only applicable to the calculation of reserves of solid minerals, and the calculation of reserves of oil and hydrate can only use one parameter of volume calculation.
refer to
[1] Mountain, Mao Yongqiang. Definition and transformation of coordinate system in GIS [J]. Heilongjiang Land and Resources, 2005, 1 1, 38 ~ 39
[2] European Petroleum Exploration Group. Coordinate transformation and transformation, including formula [M]. International Petroleum Technology Software Open Company, 2008
Su, Dai Qinqin, Wei and Long. Storage structure of marine geological database data [J]. Marine Geodynamics, 2003, 19 (6): 5 ~ 7
Shao, Tan Jianjun, et al. Accurate calculation method of small-scale ocean map [J]. Geography and Geographic Information Science, 2009,25 (2): 42 ~ 45
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Accurate calculation method of small-scale mineral reserves calculation
Shao, Chen, Zeng
(Guangzhou Marine Geological Survey, Guangzhou, 5 10760)
Abstract: For small-scale maps in the field of marine mineral reserves, the traditional measurement methods have low accuracy in calculating reserves. In order to improve this situation, this study provides a new method, which uses Arc Engine technology to complete the conversion between different projections and accurately measure the information such as the earth area. Then cut the mine reserve object into several blocks, so that we can calculate the volume of reserves by summing each block. Different schemes such as WGS 1984, Mercator and Albers are also discussed, which provide good services for military strategy and marine resources development.
Key words: marine survey, geographic information system, map projection, reserve calculation.