阅读说明：本技术 一种结合地形影响的卫星可见性判断方法 (Satellite visibility judgment method combined with terrain influence ) 是由 隋铭明 沈飞 杨易 于 2020-08-10 设计创作，主要内容包括：本发明公开了一种结合地形影响的卫星可见性判断方法,包括如下步骤：步骤1,选择观测区域,并确定测站点,利用卫星坐标和测站点的位置坐标计算卫星仰角,判断观测区域的卫星的可见性；步骤2,引入地形影响,计算地形采样点仰角,与卫星仰角对比分析,再次判断卫星可见性。采用本发明方法,考虑实验区地形遮挡后,可见卫星数量和卫星的定位精度相比于不考虑地形遮挡时有了明显下降。(The invention discloses a satellite visibility judgment method combined with terrain influence, which comprises the following steps: step 1, selecting an observation area, determining a station point, calculating a satellite elevation angle by using a satellite coordinate and a position coordinate of the station point, and judging the satellite visibility of the observation area; and 2, introducing terrain influence, calculating the elevation angle of a terrain sampling point, comparing and analyzing the elevation angle with the satellite elevation angle, and judging the satellite visibility again. By adopting the method, after the terrain occlusion of the experimental area is considered, the number of visible satellites and the positioning accuracy of the satellites are obviously reduced compared with the positioning accuracy without the terrain occlusion.)

1. A satellite visibility judgment method combined with terrain influence is characterized by comprising the following steps:

step 1, selecting an observation area, determining a station point, calculating a satellite elevation angle by using a satellite coordinate and a position coordinate of the station point, and judging the satellite visibility of the observation area;

and 2, introducing terrain influence, calculating the elevation angle of a terrain sampling point, comparing and analyzing the elevation angle with the satellite elevation angle, and judging the satellite visibility again.

2. The method of claim 1, wherein step 1 comprises:

1-1, normalizing the coordinates of a rectangular coordinate system of a satellite geocentric space to a station center coordinate system with a measuring station as an origin;

step 1-2, calculating the satellite elevation angle and azimuth angle according to the station center coordinate difference;

and 1-3, judging the visibility of the satellite in the observation area.

3. The method of claim 2, wherein step 1-1 comprises:

step 1-1-1, setting P as a station, geodetic longitude L, geodetic latitude B, Q as a satellite position, and X_Q、Y_Q、Z_QThree coordinate components of Q point in a rectangular coordinate system of geocentric space, X_P、Y_P、Z_PFor three coordinate components of point P in the geocentric space rectangular coordinate system, E, N, U is the center coordinates of satellite Q relative to station P, and the transformation relationship between the spatial rectangular coordinates and the center coordinates is as follows:

obtaining a calculation formula from the rectangular coordinates of the geocentric space to the standing-center coordinates through conversion:

wherein:

dX＝X_Q-X_P

dY＝Y_Q-Y_P

dZ＝Z_Q-Z_P

and dX, dY and dZ are the difference values of P, Q three coordinate components in a space rectangular coordinate system.

4. The method of claim 3, wherein steps 1-2 comprise:

the coordinates (E) of the satellite in the center of the station coordinate system are calculated by the formula (2)_i，N_i，U_i) Calculating the satellite elevation angle and the satellite azimuth angle by the following formula:

where Ele is the satellite elevation angle and Azi is the satellite azimuth angle.

5. The method of claim 4, wherein steps 1-3 comprise: a cutoff altitude threshold is set and satellites with satellite elevation Ele above the cutoff altitude threshold are indicated as visible and not visible otherwise.

6. The method of claim 5, wherein step 2 comprises:

step 2-1, determining a survey station, determining a visible satellite in an observation area by using the satellite coordinates and the position coordinates of the survey station, and calculating the elevation angle and the satellite azimuth angle of the visible satellite;

step 2-2, determining a required terrain sampling point on the digital elevation model according to the satellite azimuth;

step 2-3, calculating longitude and latitude coordinates corresponding to the terrain sampling points according to the row and column numbers and the like of the digital elevation model;

step 2-4, converting the longitude and latitude coordinates into geocentric space rectangular coordinates; converting the geocentric space rectangular coordinate into a station center coordinate;

step 2-5, calculating the azimuth angle of the terrain sampling point;

step 2-6, comparing the azimuth angle of the terrain sampling point with the satellite azimuth angle to find out the terrain sampling point consistent with the satellite direction;

step 2-7, calculating the elevation angles of sampling points with consistent directions;

and 2-8, comparing the elevation angles of the sampling points with the consistent directions obtained in the step 2-7 with the elevation angles of the satellites in the same direction to determine the visible satellites.

7. The method of claim 6, wherein step 2-1 comprises: calculating satellite elevation SatE according to formula (3)_iCalculating the satellite azimuth SatA according to the formula (4)_iWhere i 1, 2, and m is the number of all visible satellites in the observation area.

8. The method of claim 7, wherein step 2-2 comprises: if the azimuth angle of the satellite is integral multiple of 45 degrees, namely the satellite is positioned in the diagonal direction of the grid of the digital elevation model, directly acquiring grid point coordinates passing through the diagonal direction as terrain sampling point coordinates, and expressing the positions of the terrain sampling points by using line numbers, column numbers and elevations; if the azimuth angle of the satellite is not integral multiple of 45 degrees, grid points close to two sides of a connecting line between the survey station and the satellite are required to be acquired as terrain sampling points.

9. The method of claim 8, wherein steps 2-3 comprise: calculating the geographic coordinates of the specified grid location according to the following formula:

geoX＝geoX0+C*xPixel (5)

geoY＝geoY0+R*yPixel (6)

wherein, (geoX, geoY) represents the geographical coordinates of the designated grid position, geoX0, geoY0 are the X coordinate and the Y coordinate of the upper left corner of the grid, R is the row number of the grid, and C is the column number of the grid.

10. The method according to claim 9, wherein in step 2-4, the geocentric space rectangular coordinates of the sampling points are calculated according to the following formula;

the transformation formula of the geocentric space rectangular coordinate (X, Y, Z) is calculated by the geodetic longitude L, the latitude B and the geodetic height H of any point on the earth ellipsoid as follows:

in the formula, N represents the curvature radius of the earth-made unitary fourth of twelve earthly branches:

wherein a, e are the first eccentricity squared and major radius of the ellipsoid, respectively, where the CGCS2000 national geodetic coordinate system parameters are used;

substituting the geodetic longitude geoX, the geodetic latitude geoY and the geodetic height H of the corresponding grid point, which are obtained by the calculation in the step 2-3, into the formula to calculate the corresponding geocentric space rectangular coordinate, and calculating the station center coordinate of the topographic sampling point according to the formula (2);

in the step 2-5, the azimuth angle A of the terrain sampling point is calculated according to the formula (4)_jN is the number of all grid sampling points;

in step 2-6, the azimuth angle A from the satellite to the terrain sampling point_jAzimuth SatA to satellite from survey station_iIn contrast, if the difference between the two azimuth angles is less than 1', the directions are determined to be consistent;

in the steps 2-7, the coordinates of the terrain sampling points with the same direction are substituted into the formula (3) to calculate the elevation angle E of the terrain sampling point_u；

In step 2-8, judging the elevation angle E of the terrain sampling point_uAnd satellite elevation angle SatE_iFor a series of terrain sampling points elevation angles E of the survey station_uThe maximum value E _ Max is obtained, if the satellite elevation SatE is satisfied_k> E _ Max, and SatE_kAnd if the height angle is larger than the cut-off height angle threshold value, the satellite is judged to be visible, otherwise, the satellite is judged to be invisible.

Technical Field

The invention relates to a satellite visibility judgment method combined with terrain influence.

Background

In the GPS positioning, a plurality of satellites are required to cover a measurement area to obtain a better measurement result, but the number of visible satellites is often reduced due to influence of terrain in actual work. For example, due to the diversity of mountainous terrain and the influence of urban buildings, satellite signals are obstructed by high buildings, overpasses and natural terrains, so that the visible quantity of satellites is obviously reduced, and even the quantity of the satellites cannot reach the minimum positioning standard. Most satellite visibility analysis ignores the influence of the factors, so that the satellite visibility evaluation result is greatly different from the actual result.

Disclosure of Invention

The purpose of the invention is as follows: in order to more accurately evaluate the visibility of the GPS satellite, the invention introduces a terrain factor into satellite visibility analysis, and provides a satellite visibility judgment method combined with terrain influence, which comprises the following steps:

step 1, selecting an observation area, determining a station point, calculating a satellite elevation angle by using a satellite coordinate and a position coordinate of the station point, and judging the satellite visibility of the observation area;

and 2, introducing terrain influence, calculating the elevation angle of a terrain sampling point, comparing and analyzing the elevation angle with the satellite elevation angle, and judging the satellite visibility again.

The step 1 comprises the following steps:

1-1, normalizing the coordinates of a rectangular coordinate system of a satellite geocentric space to a station center coordinate system with a measuring station as an origin;

step 1-2, calculating the satellite elevation angle and azimuth angle according to the station center coordinate difference;

and 1-3, judging the visibility of the satellite in the observation area.

The step 1-1 comprises the following steps:

step 1-1-1, setting P as a station, geodetic longitude L, geodetic latitude B, Q as a satellite position, and X_Q、Y_Q、Z_QThree coordinate components of Q point in a rectangular coordinate system of geocentric space, X_P、Y_P、Z_PFor three coordinate components of point P in the geocentric space rectangular coordinate system, E, N, U is the center coordinates of satellite Q relative to station P, and the transformation relationship between the spatial rectangular coordinates and the center coordinates is as follows:

obtaining a calculation formula from the rectangular coordinates of the geocentric space to the standing-center coordinates through conversion:

wherein:

dX＝X_Q-X_P

dY＝Y_Q-Y_P

dZ＝Z_Q-Z_P

and dX, dY and dZ are the difference values of P, Q three coordinate components in a space rectangular coordinate system.

The step 1-2 comprises the following steps:

the coordinates (E) of the satellite in the center of the station coordinate system are calculated by the formula (2)_i，N_i，U_i) Calculating the satellite elevation angle and the satellite azimuth angle by the following formula:

where Ele is the satellite elevation angle and Azi is the satellite azimuth angle.

The steps 1-3 comprise: a cutoff altitude threshold is set and satellites with satellite elevation Ele above the cutoff altitude threshold are indicated as visible and not visible otherwise.

The step 2 comprises the following steps:

step 2-1, determining a survey station, determining a visible satellite in an observation area by using the satellite coordinates and the position coordinates of the survey station, and calculating the elevation angle and the satellite azimuth angle of the visible satellite;

step 2-2, determining a required terrain sampling point on the digital elevation model according to the satellite azimuth;

step 2-3, calculating longitude and latitude coordinates corresponding to the terrain sampling points according to the row and column numbers and the like of the digital elevation model;

step 2-4, converting the longitude and latitude coordinates into geocentric space rectangular coordinates; converting the geocentric space rectangular coordinate into a station center coordinate;

step 2-5, calculating the azimuth angle of the terrain sampling point;

step 2-6, comparing the azimuth angle of the terrain sampling point with the satellite azimuth angle to find out the terrain sampling point consistent with the satellite direction;

step 2-7, calculating the elevation angles of sampling points with consistent directions;

and 2-8, comparing the elevation angles of the sampling points with the consistent directions obtained in the step 2-7 with the elevation angles of the satellites in the same direction to determine the visible satellites.

Step 2-1 comprises: calculating satellite elevation SatE according to formula (3)_iCalculating the satellite azimuth SatA according to the formula (4)_iWherein i is 1, 2, …, m is the number of all visible satellites in the observation area;

step 2-2 comprises: if the azimuth angle of the satellite is integral multiple of 45 degrees, namely the satellite is positioned in the diagonal direction of the grid of the digital elevation model, directly acquiring grid point coordinates passing through the diagonal direction as terrain sampling point coordinates, and expressing the positions of the terrain sampling points by using line numbers, column numbers and elevations; if the azimuth angle of the satellite is not integral multiple of 45 degrees, grid points close to two sides of a connecting line between the survey station and the satellite are required to be acquired as terrain sampling points.

The step 2-3 comprises the following steps: calculating the geographic coordinates of the specified grid location according to the following formula:

geoX＝geoX0+C*xPixel (5)

geoY＝geoY0+R*yPixel (6)

wherein, (geoX, geoY) represents the geographical coordinates of the designated grid position, geoX0, geoY0 are the X coordinate and the Y coordinate of the upper left corner of the grid, R is the row number of the grid, and C is the column number of the grid.

In the step 2-4, calculating the geocentric space rectangular coordinates of the sampling points according to the following formula;

the transformation formula of the geocentric space rectangular coordinate (X, Y, Z) is calculated by the geodetic longitude L, the latitude B and the geodetic height H of any point on the earth ellipsoid as follows:

in the formula, N represents the curvature radius of the earth-made unitary fourth of twelve earthly branches:

wherein a, e are the first eccentricity squared and major radius of the ellipsoid, respectively, where the CGCS2000 national geodetic coordinate system parameters are used;

substituting geodetic longitude geoX, geodetic latitude geoY and geodetic height H of the corresponding grid points (the geodetic height is obtained by summing the elevation of the grid points and the elevation abnormity of the grid points determined by the global ultra-high order earth gravitational field model EGM 2008) calculated in the step 2-3 into the formula to calculate the corresponding geocentric space rectangular coordinates, and then calculating the station center coordinates of the terrain sampling points according to the formula (2);

in the step 2-5, the azimuth angle A of the terrain sampling point is calculated according to the formula (4)_jJ is 1, 2 and 3 … n, and n is the number of all grid sampling points;

in step 2-6, the azimuth angle A from the satellite to the terrain sampling point_jAzimuth SatA to satellite from survey station_iIn contrast, if the difference between the two azimuth angles is less than 1', the directions are determined to be consistent;

in the steps 2-7, the coordinates of the terrain sampling points with the same direction are substituted into the formula (3) to calculate the elevation angle E of the terrain sampling point_u；

In step 2-8, judging the elevation angle E of the terrain sampling point_uAnd satellite elevation angle SatE_iFor a series of terrain sampling points elevation angles E of the survey station_uThe maximum value E _ Max is obtained, if the satellite elevation SatE is satisfied_k>E _ Max, and SatE_kAnd if the height angle is larger than the cut-off height angle threshold value, the satellite is judged to be visible, otherwise, the satellite is judged to be invisible.

Has the advantages that: in satellite positioning, a plurality of satellites are required to cover a measurement area to obtain a good measurement result, but the visible number of the satellites is reduced due to the influence of terrain in actual work. For example, due to the diversity of mountainous terrain and the influence of urban buildings, satellite signals are obstructed by high buildings, overpasses and natural terrains, so that the visible quantity of satellites is obviously reduced, and even the quantity of the satellites cannot reach the minimum positioning standard. Most satellite visibility analysis ignores the influence of the factors, so that the satellite visibility evaluation result is greatly different from the actual result. According to the invention, terrain factors are introduced into satellite visibility analysis, and a method for judging satellite visibility under the condition of considering terrain is designed, so that satellite visibility can be more accurately evaluated.

Drawings

The foregoing and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of transforming geocentric space rectangular coordinates into station-centric space rectangular coordinates.

Fig. 2 is a flow chart of a satellite visibility analysis.

Figure 3 is a schematic diagram of determining a topographical sampling point from satellite azimuth angles.

Fig. 4 is a schematic diagram comparing satellite elevation and sample point elevation.

FIG. 5 is a satellite map plotted with different ENU coordinates.

Detailed Description

The invention is further explained below with reference to the drawings and the embodiments.