CN107945242B - IDL-oriented projection conversion method - Google Patents
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Abstract
The invention relates to an IDL projection conversion algorithm, which converts the arctic region data of the global temperature data projected by UTM into polar region positive axis projection. Reading the longitude and latitude (hereinafter, simply referred to as global longitude and latitude) of the global temperature data projected by the UTM, the longitude and latitude (hereinafter, simply referred to as north pole longitude and latitude) of the north pole area projected by the polar region positive axis and the global temperature data by adopting an IDL language; defining variables for storing the converted arctic air temperature data; and calculating the distance between each grid of the north pole longitude and latitude and each grid of the global longitude and latitude, endowing the air temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to the variable grid pointed by the north pole longitude and latitude index, and sequentially and circularly calculating all grids to finally obtain the air temperature data of the north pole region projected by the polar region positive axis. The method of the invention faces to the IDL projection conversion algorithm, can directly cut the polar region part from the data of global UTM projection and convert the polar region part into polar region positive axis projection, and solves the problem that the original data of a certain global parameter is difficult to convert into polar region.
Description
Technical Field
The invention relates to an IDL projection conversion-oriented algorithm. Belongs to the technical field of remote sensing data processing.
Background
The IDL programming language has powerful functions and is widely applied in the fields of aerospace, remote sensing and land letter and the like. Many researchers have encountered a problem when studying polar relevant parameters such as air temperature, sea temperature, wind, etc., which are mostly global data projected by UTM, as shown in fig. 4, which is a global air temperature map, not regional data of a polar part. Researchers cannot simply clip off data of the polar region part, and the problem brings more difficulty to the researchers because the projection of the global data is different from the projection of the special research polar region. However, there is no method for directly cropping and converting the data projected from the global UTM into polar orthographic projection. Aiming at the problems, the invention implements a specific solving algorithm, a researcher can download global longitude and latitude grid data and polar region grid data, and based on the data, the invention can cut the data projected by global UTM and convert the data into polar region positive axis projected data.
Disclosure of Invention
In view of the above problems, the present invention provides an IDL-oriented projection transformation algorithm, which can directly cut polar regions from the data of global UTM projection and transform the polar regions into polar region orthographic projection.
The technical scheme adopted by the invention for solving the technical problems is as follows: an IDL-oriented projection conversion algorithm, comprising the steps of:
reading global longitude and latitude, north pole longitude and latitude and global air temperature data projected by the UTM; the global longitude and latitude is the longitude and latitude corresponding to the global temperature data; the north pole longitude and latitude are converted into longitude and latitude corresponding to polar region positive axis projection data;
defining variables for storing the converted arctic air temperature data;
calculating the distance between each grid point of the north pole longitude and latitude and each grid point of the global longitude and latitude; and assigning the air temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to a variable grid pointed by the north pole longitude and latitude index, and finally obtaining the air temperature data of the north pole region projected by the polar region positive axis.
The definition variable type is a floating point type.
The step of assigning the air temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to the variable grid pointed by the north pole longitude and latitude index to finally obtain the air temperature data of the north pole region projected by the polar region positive axis comprises the following steps:
the numerical values of grid points AT [ x-1, y-1] of the x-th column and y-th row of the arctic air temperature grid are obtained by comparing the distances: in the distances from the north pole longitude and latitude data grid points (lon [ x-1, y-1], lat [ x-1, y-1]) to all the global longitude and latitude data grid points, the global air temperature value AT the global longitude and latitude grid point corresponding to the minimum distance is equal to the air temperature value AT the polar region air temperature grid point AT [ x, y ];
and traversing all data grid points of the north longitude and latitude to finally obtain the air temperature data of the north region projected by the polar region positive axis.
The distance is obtained by the following formula:
the distance L between grid points (LON [ X-1, Y-1], LAT [ X-1, Y-1]) of X-th column and Y-th row of north pole longitude and latitude data grid and grid points (LON [ X-1, Y-1], LAT [ X-1, Y-1]) of X-th column and Y-th row of global longitude and latitude data grid is expressed as
An IDL projection conversion algorithm is realized by an IDL program.
The invention has the following beneficial effects and advantages:
1. the method of the invention faces to the IDL projection conversion algorithm, can directly cut the polar region part from the data of global UTM projection and convert the polar region part into polar region positive axis projection, and solves the problem that the original data of a certain global parameter is difficult to convert into polar region.
2. The algorithm is simple and convenient to operate.
3. The algorithm converts between a plurality of projection data.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic diagram of a grid;
FIG. 3 is a schematic representation of air temperature grid data;
FIG. 4 is a temperature map of a global UTM projection;
FIG. 5 is an arctic temperature profile projected on the forward axis of the polar region;
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, reading the longitude and latitude of the global temperature data projected by the UTM, the longitude and latitude of the polar region projected by the polar region positive axis, and the global temperature data; defining variables for storing the converted polar region air temperature data; the method comprises the steps of calculating the distance between each grid of the polar region longitude and latitude and each grid of the global longitude and latitude, giving temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to a variable grid pointed by the north pole longitude and latitude index, sequentially and circularly calculating all grids, and finally obtaining polar region temperature data projected by a polar region positive axis. An example of the invention is to convert arctic region data of the global air temperature data of the UTM projection into polar region orthographic projection. The method comprises the following steps:
reading global longitude and latitude, north pole longitude and latitude and global air temperature data projected by the UTM; the global longitude and latitude is the longitude and latitude corresponding to the global temperature data; the north pole longitude and latitude are converted into the longitude and latitude corresponding to the polar region positive axis projection data.
Defining variables for storing the converted arctic air temperature data. Variables consistent with the size and the number of the north pole longitude and latitude grids need to be defined, and for accurately storing data in the later period, the variable type is defined as a floating point type. The north pole longitude and latitude grid of this example is 304 columns, 448 rows. The arctic air temperature variable AT is thus defined as a 304 column 448 row floating point type array for storing converted arctic air temperature data.
And calculating the distance between each grid of the north pole longitude and latitude and each grid of the global longitude and latitude. Suppose the grid values of the first column of the first row of global longitude and latitude are represented by LON [0,0] (LON [0,0], LON represents the global longitude grid, [0,0] represents the grid points of the first row of the 1 st column of the longitude grid), and the dimension is represented by LAT [0,0], i.e., (LON [0,0], LAT [0,0 ]); the grid value of the north pole longitude and latitude first row and first column is represented by lon [0,0], and the dimension is represented by lat [0,0], i.e. (lon [0,0], lat [0,0 ]). The distance L [0,0] between the grid of the first row and the first column of the north pole longitude and latitude and the grid of the first row and the first column of the global longitude and latitude is calculated according to the following formula:
distances between the grid points (lon [0,0], lat [0,0]) and all grid points of the global longitude are sequentially obtained. In the example of the invention, the global latitude and longitude grid is 192 columns, 94 rows; therefore, (lon [0,0], lat [0,0]) has 18048 distances to all grid points of the global latitude and longitude.
And assigning the air temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to the variable grid pointed by the north pole longitude and latitude index. The 18048 distance values are compared, and the index corresponding to the minimum value is selected. Since the minimum value may be plural, it is necessary to make a judgment. If the index corresponding to the minimum value is only 1, assigning the temperature data pointed by the index to a variable grid AT [0,0] pointed by a north pole longitude and latitude index [0,0 ]; if the index corresponding to the minimum value is multiple, the temperature data pointed by any index is given to the variable grid AT [0,0] pointed by the north pole longitude and latitude index, and the first index is taken as an example of the invention.
Calculating the distance between the north pole longitude and latitude grid point (lon 1,0, lat 1, 0) and all the global longitude grid points by adopting circulation, and obtaining AT 1,0 according to the calculation principle of AT 0, 0; and circularly calculating until AT [303,447] is obtained, and finally obtaining the air temperature data AT of the arctic region projected by the polar region positive axis.
An IDL projection conversion algorithm is realized by an IDL program.
Some remote sensing data are in the form of remote sensing images, researchers can extract relevant information from the remote sensing images, some remote sensing data are grid data, and data acquired by a satellite are stored in regular grids in a digital mode. Referring to fig. 2, a positive axis projection grid of a region of north pole is shown, and black squares are used as grid points, which can store data. The temperature grid data is shown in FIG. 3, for example, where 11 columns 31 of temperature data are truncated due to space constraints, and the unit is K. When such mesh data is processed by the IDL program, calculation is performed in units of each mesh. The following is a specific implementation of the algorithm.
Respectively reading the longitude and latitude of the global temperature data projected by the UTM, the longitude and latitude of the polar region projected by the polar region positive axis and the global temperature data by using an IDL reading file function; the global longitude and latitude is the longitude and latitude corresponding to the global temperature data; the north pole longitude and latitude are converted into the longitude and latitude corresponding to the polar region positive axis projection data.
And defining variables consistent with the size and the number of the north pole longitude and latitude grids, and defining the variable type as a floating point type for accurately storing data in the later period. The north pole longitude and latitude grid of this example is 304 columns, 448 rows. The arctic air temperature variable AT is thus defined as a 304 column 448 row floating point type array for storing converted arctic air temperature data.
And calculating the distance between each grid of the north pole longitude and latitude and each grid of the global longitude and latitude. Suppose the grid values of the first column of the first row of global longitude and latitude are represented by LON [0,0] (LON [0,0], LON represents the global longitude grid, [0,0] represents the grid points of the first row of the 1 st column of the longitude grid), and the dimension is represented by LAT [0,0], i.e., (LON [0,0], LAT [0,0 ]); the grid value of the north pole longitude and latitude first row and first column is represented by lon [0,0], and the dimension is represented by lat [0,0], i.e. (lon [0,0], lat [0,0 ]). The distance L [0,0] between the grid of the first row and the first column of the north pole longitude and latitude and the grid of the first row and the first column of the global longitude and latitude is calculated according to the following formula:
distances between the grid points (lon [0,0], lat [0,0]) and all grid points of the global longitude are sequentially obtained. In the example of the invention, the global latitude and longitude grid is 192 columns, 94 rows; therefore, (lon [0,0], lat [0,0]) has 18048 distances to all grid points of the global latitude and longitude.
And selecting a minimum distance value from 18048 distance values by using a size judgment function, and endowing the temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to a variable grid pointed by the north pole longitude and latitude index. Since the minimum value may be plural, it is necessary to make a judgment. If the index corresponding to the minimum value is only 1, assigning the temperature data pointed by the index to a variable grid AT [0,0] pointed by a north pole longitude and latitude index [0,0 ]; if the index corresponding to the minimum value is multiple, the temperature data pointed by any index is given to the variable grid AT [0,0] pointed by the north pole longitude and latitude index, and the first index is taken as an example of the invention.
-following the loop (448) by means of the for loop, after having calculated the first grid point in the loop array (304), performing the second grid point, i.e. calculating the distance between the north longitude and latitude grid point (lon [1,0], lat [1,0]) and all the global longitude grid points, and obtaining AT [1,0] according to the principles of claims 3 and 4; and circularly calculating until AT [303,447] is obtained, and finally obtaining the air temperature data AT of the arctic region projected by the polar region positive axis. As shown in fig. 5.
Claims (4)
1. An IDL-oriented projection conversion method is characterized by comprising the following steps:
reading global longitude and latitude, north pole longitude and latitude and global air temperature data projected by the UTM; the global longitude and latitude is the longitude and latitude corresponding to the global temperature data; the north pole longitude and latitude are converted into longitude and latitude corresponding to polar region positive axis projection data;
defining variables for storing the converted arctic air temperature data;
calculating the distance between each grid point of the north pole longitude and latitude and each grid point of the global longitude and latitude; assigning the air temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to a variable grid pointed by the north pole longitude and latitude index, and finally obtaining the air temperature data of the north pole region projected by the polar region positive axis;
the step of assigning the air temperature data pointed by the global longitude and latitude index corresponding to the minimum distance to the variable grid pointed by the north pole longitude and latitude index to finally obtain the air temperature data of the north pole region projected by the polar region positive axis comprises the following steps:
the numerical values of grid points AT [ x-1, y-1] of the x-th column and y-th row of the arctic air temperature grid are obtained by comparing the distances: in the distances from the north pole longitude and latitude data grid points (lon [ x-1, y-1], lat [ x-1, y-1]) to all the global longitude and latitude data grid points, the global air temperature value AT the global longitude and latitude grid point corresponding to the minimum distance is equal to the air temperature value AT the polar region air temperature grid point AT [ x, y ];
and traversing all data grid points of the north longitude and latitude to finally obtain the air temperature data of the north region projected by the polar region positive axis.
2. The IDL-oriented projection conversion method of claim 1, wherein said defining variable type is floating point type.
3. The method of claim 1, wherein the distance is obtained by the following formula:
the distance L between grid points (LON [ X-1, Y-1], LAT [ X-1, Y-1]) of X-th column and Y-th row of north pole longitude and latitude data grid and grid points (LON [ X-1, Y-1], LAT [ X-1, Y-1]) of X-th column and Y-th row of global longitude and latitude data grid is expressed as
Column 1, line 1 are denoted as [0,0], column x, line y are denoted as [ x-1, y-1 ].
4. The IDL-oriented projection conversion method of claim 1, wherein the IDL is implemented by IDL program.
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