CN114579684A - Foresight terrain early warning method - Google Patents

Abstract

The invention discloses a foresight terrain early warning method based on a synthetic view, which comprises the following steps: s1, storing terrain data of all tiles under different resolution levels, wherein the tile is the minimum unit of the terrain data of the earth; s2, determining a query area of the airplane at the current position, and dividing the query area into a near set area and a far set area; s3, loading terrain data with the highest level resolution ratio on the tiles in the near concentration area, and loading the terrain data with the corresponding level resolution ratio on the basis of the distance between the tiles in the far concentration area and the current position of the airplane, and the included angle between the connecting line between the tiles and the current position of the airplane and the heading of the airplane; s4, planning the forward looking predicted path of the current FLTA based on the altitude data of the tiles in the query area. The predicted route provides more direct early warning information of the forward-looking terrain, and the pilot can further improve the safety of flight by flying from one side of the predicted route to the other side. Therefore, the utility model has strong practicability.

Description

Foresight terrain early warning method

Technical Field

The invention belongs to the technical field of route optimization, and particularly relates to a forward-looking terrain early warning method.

Background

In recent aviation flight accidents, controlled flight ground impact (CFIT) has been a significant factor in accidents. In order to avoid CFIT accidents, the first proposed ground proximity warning system (EGPWS) in the united states plays an important role in practical applications. An enhanced near-earth early warning system (EGPWS) introduced by Honeywell company adds two functions of terrain display and forward-looking terrain early warning in the original near-earth early warning system, so that CFIT accidents in the air of civil aviation are effectively solved.

In general aviation, the aircraft has a lower flight height than in civil aviation, which makes it easier to reach terrain or obstacles with a relatively high altitude during navigation. Therefore, the existing EGPWS method cannot well meet the performance requirements of increasingly general aviation, and in addition, an enhanced ground proximity early warning system (EGPWS) is expensive, so that the application in the field of general aviation is further limited.

Disclosure of Invention

The invention provides a forward-looking terrain early warning method, aiming at improving the problems.

The invention is realized in such a way that a forward-looking terrain early warning method specifically comprises the following steps:

s1, storing terrain data of all tiles under different resolution levels, wherein the tile is the minimum unit of the terrain data of the earth;

s2, determining a query area of the airplane at the current position, and dividing the query area into a near set area and a far set area;

s3, loading terrain data with the highest level resolution ratio on the tiles in the near concentration area, and loading the terrain data with the corresponding level resolution ratio on the basis of the distance between the tiles in the far concentration area and the current position of the airplane and the included angle between the connecting line between the tiles and the current position of the airplane and the heading of the airplane;

s4, planning the forward looking predicted path of the current FLTA based on the altitude data of the tiles in the query area.

Further, after step S2, the method further includes:

and obtaining a Gaussian weight matrix A based on a two-dimensional Gaussian filter, and convolving the Gaussian weight matrix A with an altitude matrix B of the corresponding pixel point of the tile to obtain a new terrain altitude value of the corresponding pixel point of the tile.

Further, the method for forming the near-concentration region specifically includes:

the near-concentration region is a circular region with the current position as the origin and a radius r.

Further, the remote collection area is a sector, and the radius R of the sector area is determined based on formula (1) with the current position of the airplane as the origin of the sector:

R＝D/cos(FOV/2)+Len (1)

d is the distance from the current position of the airplane to the visual field end of the composite visual scene, FOV is the set visual field angle of the composite visual scene, and Len is the width of one tile;

and respectively rotating the FOV/2+70 degrees clockwise and anticlockwise by taking the aircraft heading gamma as a reference, namely forming two boundaries of the fan shape.

Further, the method for determining the resolution level of the tile in the remote collection area specifically comprises the following steps:

index＝(6–Tau)*indexFactor

tau is the error of the tile data, indexFactor is the resolution parameter, index is the resolution index,

representing the tile resolution level corresponding to the index;

the error Tau of the tile data is calculated as follows:

Tau＝BaseTau*DecayFactor*AdaptiveFactor

wherein, BaseTau is a Tau base number, the Tau base number at the connection of a near set and a far set is 4.0, and linearly increases along with the distance between a tile and the current position of the airplane, the value at 50NM is 6.0, adaptive factor is an adaptive parameter, and Decayfactor is an attenuation parameter;

the attenuation parameter DecayFactor is calculated according to the following formula:

DecayFactor＝1/cos(a*cos(1.0/1.2)/(FOV/2))

wherein a is an included angle between a connecting line between the tile and the airplane and the course, and the FOV is a set view field angle of the synthetic view.

Further, the forming method of the forward-looking predicted path of FLTA is specifically as follows:

sampling is carried out on each predicted route, the distance between every two sampling points is i, n sampling points are formed, and the following operations are carried out on each sampling point:

and acquiring two sampling points at plus and minus 30 degrees in the heading direction of the current sampling point, and outputting the maximum altitude value of the three sampling points, namely the forward looking predicted path of the FLTA.

The predicted route provides more direct early warning information of the forward-looking terrain, and the pilot can further improve the safety of flight by flying from one side of the predicted route to the other side. Therefore, the utility model has strong practicability.

Drawings

Fig. 1 is a flowchart of a forward-looking terrain early warning method according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a smoothing process for data in a tile according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a query region according to an embodiment of the present invention;

fig. 4 is a schematic diagram illustrating the formation of a forward looking predicted path of the FLTA according to an embodiment of the present invention, where (a) is the forward looking predicted path of the FLTA formed based on the sampling points, and (b) the sampling points are plus or minus 30 degrees in the flight direction.

Detailed Description

The following detailed description of the embodiments of the present invention will be given in order to provide those skilled in the art with a more complete, accurate and thorough understanding of the inventive concept and technical solutions of the present invention.

Fig. 1 is a flowchart of a forward-looking terrain early warning method according to an embodiment of the present invention, where the method specifically includes the following steps:

s1, storing terrain data of all tiles under different resolution levels, wherein the tile is the minimum unit of the terrain data of the earth;

dividing the topographic data of the earth into rectangular array files according to longitude and latitude, wherein each rectangular array file comprises a square array of data blocks, each data block comprises a square array of tiles, and acquiring data of each tile under the same level resolution; the tile resolution is represented by 'Stage', Stage 0 is the lowest level of resolution, only four vertexes of the terrain data corresponding to the tile are stored, Stage 1 stores 3 × 3 grids of terrain data, namely 3 × 3 terrain data, Stage 2 stores 5 × 5 grids of terrain data, namely 5 × 5 grids of terrain data, Stage 5 stores 32 × 32 grids of terrain data, and Stage 5 is the highest level of resolution of terrain data;

for terrain elevation data within a distance range of 2 tiles from the aircraft, the invention employs full resolution, i.e., Stage 5-level tile data, with 32 x 32 elevation data collected for each tile, and each grid taking the elevation value of one highest elevation within the grid. Causing a large discontinuity in the data in a tile. In order to smooth the data in the tiles, the invention adopts a gaussian filtering method to increase the terrain data in the tiles for smoothing, as shown in fig. 2, the tiles are taken as pictures with the resolution of 32 × 32, discretization is carried out according to a two-dimensional gaussian filter, an obtained gaussian weight matrix a is convolved with an altitude matrix B of corresponding pixel points of the tiles, and the terrain altitude data at the corresponding pixel points of the new tile data is obtained, as shown in the right side of fig. 3, a 3 × 3 weight matrix a output by the two-dimensional gaussian filter is convolved with an altitude matrix B of corresponding pixel points of the tiles, and the terrain altitude data at the corresponding pixel points of the new tile data is obtained:

h＝B·A

and h is the altitude value of a pixel point corresponding to the tile data after Gaussian filtering, and smooth tile terrain data can be finally obtained.

S2, determining a query area of the airplane at the current position, and dividing the query area into a near set area and a far set area;

based on a global positioning system GPS or an inertial navigation system IRS, current longitude and latitude data of an aircraft, that is, a current position of the aircraft, a remote set region in the embodiment of the present invention is a sector, which is called a sector region, and the current position of the aircraft is an origin of the sector region, and a radius and two boundary lines of a sector query region need to be determined, as shown in fig. 3, a determination method thereof is specifically as follows:

determining the radius R of the sector area, wherein the calculation formula is as follows:

R＝D/cos(FOV/2)+Len

wherein, D is the distance from the current position of the airplane to the end of the visual field of the composite visual scene, the value range is 50 NM-100 NM, the FOV is the set visual field angle of the composite visual scene, the value range is as follows: 30-60 degrees, Len is the width of one tile;

and determining the boundaries of the sector area, and respectively rotating the FOV/2+70 degrees clockwise and anticlockwise by taking the aircraft heading gamma as a reference, namely forming two boundaries of the sector area.

The near-concentration area is a circular area with the current position as an origin and the radius r as an empirical parameter value.

S3, loading the terrain data with the highest level resolution ratio on the data tiles in the near concentration area, and loading the terrain data with the corresponding level resolution ratio on the tiles in the far concentration area based on the distance between the tiles and the current position of the airplane and the included angle between the connection line between the tiles and the current position of the airplane and the heading of the airplane;

for the tiles in the near set area, reading high-level resolution terrain data, namely the tiles located in the near set area, and reading Stage 5 terrain data;

for tiles in a far-concentration area, reading terrain data of corresponding grade resolution based on the distance between the tiles and the current position, wherein the farther the distance is, the lower the resolution grade of the terrain data is, and the closer the distance is, the higher the resolution grade of the terrain data is, and the tiles in the far-concentration area can access the terrain data with lower resolution grade Stage, so that unnecessary terrain accuracy of the far distance of an airplane can be reduced, and the data processing speed is increased.

The allowable error of tile data at the pixel level is referred to as 'Tau'. The Tau can be adjusted to ensure that a higher tile accuracy is achieved for the aircraft position and 10NM range. For tiles in the far set, Tau for tile data is calculated as follows:

Tau＝BaseTau*DecayFactor*AdaptiveFactor

wherein, BaseTau is a Tau base number, the Tau base number at the connection of a near set and a far set is 4.0, and linearly increases along with the tile distance, the value at 50NM (nautical miles) is 6.0, adaptive factor is an adaptive parameter, the default value is 1, Decayfactor is an attenuation parameter, and the calculation is carried out according to the following formula:

DecayFactor＝1/cos(a*cos(1.0/1.2)/(FOV/2))

wherein a is an included angle between a connecting line between the tile and the airplane and the course, and the FOV is a set view field angle of the synthetic view.

According to the above formula, it is assumed that FOV is 60 °, and a is assigned two cases, and when a is 10 °, DecayFactor is 1.000017; when a is 120 °, DecayFactor 1.002443. It can be seen that as a is larger, the attenuation exponent is larger, and Tau is also larger.

In flight, in order to take account of real-time performance and accuracy of terrain data, it is only required to ensure that the resolution level of tile data at a far set is higher than Tau, namely, the resolution of a selected tile is

Since the resolution index is not necessarily an integer, a rounding-up operation is required, wherein the resolution index is calculated according to the following formula:

index＝(6–Tau)*indexFactor

wherein Tau is the error of tile data, indexFactor is the resolution parameter, and the value range is 0.85-1.15 according to engineering experience.

According to the formula, assuming that indexFactor is 1.0, when Tau is 6, index is 0, that is, the resolution of the selected tile is Stage (0); when Tau is 1, index is 5, i.e. the selected tile resolution is Stage (5). In summary, as the angle increases and the distance increases, the tiles selected in far concentration decrease in accuracy. S4, planning the forward looking predicted path of the current FLTA based on the altitude data of the tiles in the query area.

The invention takes the aircraft course as an angular bisector to judge the warning and warning areas in a sector range of 60 degrees, and the warning and warning distances are 1.5NM and 3.0NM respectively. Namely, when the clearance value is insufficient in the range of plus or minus 30 degrees of the aircraft heading angle and in the places less than 1.5 nautical miles and less than 3 nautical miles away from the aircraft, the FLTA warning and the warning level warning of the aircraft can be started respectively. On the basis, a forward-looking terrain predicted path is added to fuse the forward-looking global and local sector areas, so that more display information is provided for the pilot.

The predicted course consists of terrain heights from the current position to 30 equal distances between the maximum FLTA warning distance in the predicted track direction, represented in fig. 4(a) as a straight line x 0. Sampling is carried out on each predicted route, the distance between every two sampling points is i, 30 sampling points are formed, and for each sampling point, the following operations are carried out: acquiring two sampling points at plus and minus 30 degrees in the heading direction of a current sampling point, outputting the maximum altitude value of the three sampling points, namely a forward-looking predicted path of the FLTA, as shown by a black path in the figure, wherein the forward-looking predicted path is a planned early warning line, the sampling points acquired at plus 30 degrees in the heading direction of 30 sampling points form a straight line x1, and the sampling points acquired at minus 30 degrees in the heading direction of 30 sampling points form a straight line x 2;

at the maximum flta (forward Looking Terrain avaidance) distance (i.e. the farthest sampling point), the distance linearly increases to double the predicted sampling distance, so the offset paths x1 on both sides, the angle between x2 and x0 is:

wherein i is the sampling interval of the sampling points, i' is the distance between the initial sampling point and the vertical sampling points at two sides, and for the forward-looking predicted path sampling of each FLTA, the height value should be replaced by the positive and negative barrier heights of the route between the previous sampling point and the current sampling point.

As shown on the right side of fig. 4, assuming that the maximum FLTA guard distance is 9000m, the distance of the a-point sample 5 is:

the distance of the sample 6 at point b is likewise 1500 meters. The height of point b is the maximum terrain height in the sector between sample 5 and sample 6. Wherein the size of theta is 30 degrees, the predicted route provides more direct early warning information of the forward-looking terrain, and the pilot can further improve the safety of flight by flying from one side of the predicted route to the other side. Therefore, the utility model has strong practicability.

The invention has been described by way of example, and it is to be understood that its specific implementation is not limited to the details of construction and arrangement shown, but is within the scope of the invention.

Claims (6)

1. A forward-looking terrain early warning method is characterized by specifically comprising the following steps:

s1, storing terrain data of all tiles under different resolution levels, wherein the tile is the minimum unit of the terrain data of the earth;

s2, determining a query area of the airplane at the current position, and dividing the query area into a near set area and a far set area;

s3, loading the terrain data with the highest grade resolution ratio on the tiles in the near concentration area, and loading the terrain data with the corresponding grade resolution ratio on the basis of the distance between the tiles in the far concentration area and the current position of the airplane and the included angle between the connection line between the tiles and the current position of the airplane and the heading of the airplane;

s4, planning the current FLTA look-ahead predicted path based on the altitude data of the tiles in the query area.

2. A forward-looking terrain pre-warning method as set forth in claim 1, further comprising, after step S2:

and obtaining a Gaussian weight matrix A based on a two-dimensional Gaussian filter, and convolving the Gaussian weight matrix A with an altitude matrix B of the corresponding pixel point of the tile to obtain a new terrain altitude value of the corresponding pixel point of the tile.

3. A forward-looking terrain pre-warning method as claimed in claim 1, wherein the near-gather region is formed by a method specifically comprising:

the near-concentration region is a circular region with the current position as the origin and a radius r.

4. The forward-looking terrain early warning method of claim 1, wherein the far-set region is a sector, and with the current position of the aircraft as an origin of the sector, a radius R of the sector region is determined based on formula (1):

R＝D/cos(FOV/2)+Len (1)

d is the distance from the current position of the airplane to the end of the view of the composite view, FOV is the set view angle of the composite view, and Len is the width of one tile;

and respectively rotating the FOV/2+70 degrees clockwise and anticlockwise by taking the aircraft heading gamma as a reference, namely forming two boundaries of the fan shape.

5. A forward-looking terrain pre-warning method as claimed in claim 4, wherein the resolution level determination method for tiles in a remote area is as follows:

index＝(6–Tau)*indexFactor

tau is the error of the tile data, indexFactor is the resolution parameter, index is the resolution index,

representing the tile resolution level corresponding to the index;

the error Tau of the tile data is calculated as follows:

Tau＝BaseTau*DecayFactor*AdaptiveFactor

wherein, BaseTau is a Tau base number, the Tau base number at the connection of a near set and a far set is 4.0, and linearly increases along with the distance between a tile and the current position of the airplane, the value at 50NM is 6.0, adaptive factor is an adaptive parameter, and Decayfactor is an attenuation parameter;

the attenuation parameter DecayFactor is calculated according to the following formula:

DecayFactor＝1/cos(a*cos(1.0/1.2)/(FOV/2))

wherein a is an included angle between a connecting line between the tile and the airplane and the course, and the FOV is a set view field angle of the synthetic view.

6. A forward-looking terrain pre-warning method as claimed in claim 1, wherein the forward-looking predicted path of FLTA is formed by the following method:

sampling is carried out on each predicted route, the distance between every two sampling points is i, n sampling points are formed, and the following operations are carried out on each sampling point:

and acquiring two sampling points at plus and minus 30 degrees in the heading direction of the current sampling point, and outputting the maximum altitude value of the three sampling points, namely the forward looking predicted path of the FLTA.

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