Parallel terrain-simulating flight method of unmanned aerial vehicles for mountain monitoring

Abstract

The invention discloses a method for parallel terrain-simulating flight of an unmanned aerial vehicle applied to mountain monitoring, which comprises the following steps: obtaining a mission route, determining a route spacing and a shooting spacing of the mission route according to an imaging size of a camera carried by the unmanned aerial vehicle; vertically mapping the mission route onto the ground of a research area to obtain a projection line; obtaining the number of observation points required on the projection line according to the length of the projection line and the shooting distance; moving the observation points by a preset distance in the positive direction of the normal of their tangent planes to obtain route track points; connecting all route track points to obtain a parallel terrain-simulating flight route, and further obtaining the longitude, latitude and elevation information of each track point; determining a corresponding horizontal plane vector and a vertical direction vector according to the coordinates of the track point, and calculating the pitch angle and translation angle of the camera at the current track point according to the two vectors; the unmanned aerial vehicle equipped with a camera performs terrain-simulating flight and image acquisition according to the longitude, latitude and elevation information and the pitch angle and translation angle of each track point on the parallel terrain-simulating flight route.

Description

Technical Field

[0001] The invention relates to the technical field of unmanned aerial vehicle (UAV) terrain-imitating flight, and in particular to a UAV parallel terrain-imitating flight method applied to mountain monitoring. Background Art

[0002] my country has a vast mountainous area, most of which are distributed in the western region. At the same time, mountain glaciers and alpine canyons are widely developed in the western region. Due to the characteristics of changeable climate and complex terrain in this region, there are huge challenges in conducting on-site monitoring of mountain glaciers and alpine canyons. At the same time, affected by foggy weather, snow accumulation, etc., optical remote sensing image observation is also difficult to meet research needs due to regional and environmental conditions. Due to the characteristics of small size, low cost, flexible operation, and high imaging resolution, drones are gradually being used in the monitoring of mountain glaciers and alpine canyons. By implementing monitoring work in the appropriate window period, it can make up for the shortcomings of traditional monitoring methods that are difficult to work in harsh environments and steep terrain areas.

[0003] The patent (application number: CN202311665431.5) applied for a mountain photovoltaic UAV terrain-like flight planning method based on a digital surface model. By constructing a digital surface model and combining it with a two-dimensional mission flight profile, the accurate planning of the UAV terrain-like flight trajectory in mountainous areas with complex geographical environments can be achieved. The patent (application number: CN202211196269.2) invented a large UAV terrain-like flight path planning method. By mapping the path point set of the UAV terrain-like flight to a two-dimensional space plane and smoothing it, the shortest path planning of the large UAV terrain-like flight can be achieved.

[0004] However, the above solutions all ignore the perspective deformation of the camera imaging plane caused by the undulating terrain. When the UAV performs terrain simulation flight in high mountain areas such as glaciers, the ground within the camera imaging range is not parallel to the camera imaging plane, that is, the shooting is not vertically aimed at the ground, which causes perspective deformation, resulting in differences in shape between the image and the actual ground shape, affecting the modeling accuracy of the digital surface model, resulting in the digital surface model showing a larger error in elevation than in flat areas, and failing to improve the photogrammetry accuracy of the UAV when performing terrain simulation flight in high mountain areas such as glaciers. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the method for parallel terrain-simulating flight of an unmanned aerial vehicle applied to mountain monitoring provided by the present invention solves the problem of perspective deformation of images taken by the existing unmanned aerial vehicle during terrain-simulating flight.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0007] A method for parallel terrain imitation flight of an unmanned aerial vehicle applied to mountain monitoring is provided, which comprises the following steps:

[0008] S1. Obtain the mission route of the UAV when collecting images in the study area, and determine the route spacing and shooting spacing of the mission route according to the imaging size of the camera carried by the UAV;

[0009] S2, vertically mapping the mission route on the two-dimensional plane to the ground of the study area to obtain the projection line of the mission route on the ground of the study area;

[0010] S3. According to the length of the projection line and the shooting distance, the number and positions of the required observation points on the projection line are obtained;

[0011] S4, moving the observation point along the positive direction of the normal line of the section by a preset distance to obtain a route trajectory point; connecting all the route trajectory points to obtain a parallel terrain-simulating flight route;

[0012] S5, obtaining the longitude, latitude and elevation information of each trajectory point according to the coordinates of the trajectory points on the parallel terrain imitation flight route;

[0013] S6. According to the coordinates of the trajectory point, determine the corresponding horizontal plane vector and vertical direction vector, and calculate the pitch angle and translation angle of the camera carried by the drone at the current trajectory point according to the two vectors;

[0014] S7. The camera-equipped drone performs terrain-simulating flight and image collection based on the latitude, longitude, elevation information, pitch angle, and translation angle of each track point on the parallel terrain-simulating flight route.

[0015] Furthermore, the route parameters of the mission route include the route length, the route angle, and the heading overlap and lateral overlap of the images taken by the camera.

[0016] Furthermore, the expressions of the route spacing and the shooting spacing are respectively:

[0017] t 旁 =H 长 ×(1-p), t 航 =H 航 ×(1-c)

[0018] Among them, t 旁 is the route spacing; t 航 H is the shooting distance; 长 , H 航 are the length and width of the shooting range in the camera imaging principle; p and c are the heading overlap and lateral overlap of the images taken by the camera, respectively.

[0019] Furthermore, the expression for obtaining the shooting range H in the camera imaging principle is:

[0020]

[0021] Where A is the viewing angle; h is the size of the camera imaging sensor; f is the focal length; D is the distance between the object and the camera lens;

[0022] When h corresponds to the length of the camera imaging sensor, the length of the shooting range is obtained; when h corresponds to the width of the camera imaging sensor, the width of the shooting range is obtained.

[0023] Furthermore, the expression for calculating the number of observation points required on the projection line is:

[0024]

[0025] Where s is the number of observation points required and dl is the length of the projection line.

[0026] Furthermore, the step S2 further comprises:

[0027] Get the surface equations of the study area ground and the equations of the mission flight path:

[0028]

[0029] Where x, y and z are the coordinate values ​​of the x, y and z axes respectively; f(x, y) is the surface equation; (x0, y0, z0) is the coordinate of any point on the mission route; a, b and c are the components of the x, y and z axis direction vectors respectively; t is the number of directed line segments starting from (x0, y0, z0) and ending at any point;

[0030] Get the projection of the mission route on the xy plane:

[0031]

[0032] Substitute the horizontal and vertical coordinates of each point on the mission route into the surface equation to obtain the z-axis coordinates of each point on the surface projection line:

[0033] z=f(x0+at,y0+bt)

[0034] Combining the projection equation of the mission route on the xy plane and the z coordinate on the surface, we get the parametric equation of the projection line:

[0035]

[0036] Furthermore, the expressions of the pitch angle α and the translation angle β are respectively:

[0037]

[0038] in, is the negative normal vector of the ground point; for Vectors in the xy plane; and are the horizontal plane vector and vertical direction vector corresponding to the trajectory point respectively.

[0039] Furthermore, the expressions of the pitch angle α and the translation angle β are respectively:

[0040]

[0041] in, is the normal vector of the ground point; for Vectors in the xy plane; and They are the horizontal plane vector and vertical direction vector corresponding to the trajectory point respectively;

[0042] When the pitch angle and the pan angle are positive, the camera lens rotates counterclockwise according to the pitch angle and the pan angle; when the pitch angle and the pan angle are negative, the camera lens rotates clockwise according to the pitch angle and the pan angle.

[0043] The beneficial effects of the present invention are as follows: based on the generated parallel terrain-simulating flight route, the present scheme controls the camera lens of the UAV to always vertically align with the tangent direction of the ground point during the shooting process to shoot. The preset distance can ensure that the distance between the camera and the shot object at each shooting point is equal, so that the image and the original object always maintain a certain proportional relationship, avoiding the perspective deformation of the UAV imaging caused by the undulating terrain during the flight operation of the UAV, effectively reducing the elevation error of the photogrammetry, and improving the modeling accuracy of the digital surface model. This method is particularly suitable for high mountain areas such as glaciers.

[0044] The high-resolution DSM model of glaciers constructed using aerial images obtained through this method can accurately reflect the topographic characteristics of the glacier surface and provide a solid foundation for glacier monitoring such as the later glacier movement speed and glacier surface elevation changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Flowchart of the UAV parallel terrain-simulating flight method applied to mountain monitoring.

[0046] Figure 2 Schematic diagram of parallel terrain-following flight on a two-dimensional plane.

[0047] Figure 3 A schematic diagram of vertically mapping the mission route on a two-dimensional plane to the ground of the study area.

[0048] Figure 4 Schematic diagram of the rotation angle of the camera mounted on the drone. DETAILED DESCRIPTION

[0049] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0050] Based on the shortcomings of existing photogrammetry, this scheme proposes parallel terrain-simulating flight, so that each shooting lens of the drone is vertically aimed at the tangent direction of the ground point during the shooting process, and the distance between each shooting point and the ground is equal. Figure 2 The figure is a two-dimensional plane diagram of parallel terrain-imitating flight. The bottom curve is the ground line. The line connecting the bottom of the bottom curve and the top of the top curve is the normal line of the tangent line of each point on the ground line. The second curve and the top curve represent two parallel terrain-imitating flight trajectories at different heights. The lengths of all the lines connecting the bottom curve and the second curve are equal, and the lengths of all the lines connecting the second curve and the top curve are also equal. Figure 2 It can be seen from the figure that when the UAV flies according to a parallel terrain-following flight trajectory and its onboard lens is facing the normal direction, the photos taken by the UAV at this time are normal photos of the ground, and the distance between the photo position and the ground is equal. This is the principle of parallel terrain-following flight in a two-dimensional plane.

[0051] refer to Figure 1 , Figure 1 The flowchart of the method for parallel terrain imitation flight of unmanned aerial vehicles applied to mountain monitoring is shown; Figure 1 As shown, the method S includes steps S1 to S7.

[0052] In step S1, the mission route of the UAV when collecting images in the study area is obtained, and the route parameters of the mission route include the route length, the route angle, and the heading overlap and lateral overlap of the images taken by the camera.

[0053] According to the imaging size of the camera carried by the drone, determine the route spacing and shooting spacing of the mission route:

[0054] t 旁 =H 长 ×(1-p), t 航 =H 航 ×(1-c)

[0055] Among them, t 旁 is the route spacing; t 航 H is the shooting distance; 长 , H航 are the length and width of the shooting range in the camera imaging principle; p and c are the heading overlap and lateral overlap of the images taken by the camera, respectively.

[0056] During implementation, this solution preferably obtains the expression of the shooting range H in the camera imaging principle as follows:

[0057]

[0058] Where A is the viewing angle; h is the size of the camera imaging sensor; f is the focal length; D is the distance between the object and the camera lens;

[0059] When h corresponds to the length of the camera imaging sensor, the length of the shooting range is obtained; when h corresponds to the width of the camera imaging sensor, the width of the shooting range is obtained.

[0060] In step S2, the mission route on the two-dimensional plane is vertically mapped to the ground of the study area to obtain the projection line of the mission route on the ground of the study area. The schematic diagram can be referred to Figure 3 , Figure 3 Here, S represents the surface in the figure, and L represents the mission route.

[0061] In one embodiment of the present invention, the step S2 further comprises:

[0062] Get the surface equations of the study area ground and the equations of the mission flight path:

[0063]

[0064] Where x, y and z are the coordinate values ​​of the x, y and z axes respectively; f(x, y) is the surface equation; (x0, y0, z0) is the coordinate of any point on the mission route; a, b and c are the components of the x, y and z axis direction vectors respectively; t is the number of directed line segments starting from (x0, y0, z0) and ending at any point;

[0065] Get the projection of the mission route on the xy plane:

[0066]

[0067] Substitute the horizontal and vertical coordinates of each point on the mission route into the surface equation to obtain the z-axis coordinates of each point on the surface projection line:

[0068] z=f(x0+at,y0+bt)

[0069] Combining the projection equation of the mission route on the xy plane and the z coordinate on the surface, we get the parametric equation of the projection line:

[0070]

[0071] In step S3, the number and positions of the required observation points on the projection line are obtained according to the length of the projection line and the shooting distance; wherein the expression for calculating the number of required observation points on the projection line is:

[0072]

[0073] Where s is the number of observation points required and dl is the length of the projection line.

[0074] The length of the projection line is calculated based on the coordinates of the two endpoints of the projection line and the parametric equation of the projection line, that is, the distance between the two endpoints.

[0075] In step S4, the observation point is moved along the positive direction of the normal of the section by a preset distance to obtain a route trajectory point; all the route trajectory points are connected to obtain a parallel terrain imitation flight route;

[0076] The calculation formula of the normal vector N of the observation point is:

[0077]

[0078] In step S5, the longitude, latitude and elevation information of each track point is obtained according to the coordinates of the track points on the parallel terrain simulation flight route;

[0079] In step S6, the horizontal plane vector and the vertical direction vector corresponding to the trajectory point are determined according to the coordinates of the trajectory point, and the pitch angle and translation angle of the camera carried by the drone at the current trajectory point are calculated according to the two vectors; the rotation angle of the camera carried by the drone can be referred to Figure 4 .

[0080] Assuming that the coordinates of the track point (a, b, c) are known, we can obtain the vector Q = (a, b, 0) on the horizontal plane and the vertical vector W = (0, 0, c). These two vectors represent the vector on the XY plane and the vector in the Z direction respectively.

[0081] During implementation, the preferred expressions of the pitch angle α and the translation angle β of this scheme are:

[0082]

[0083] in, is the negative normal vector of the ground point; for Vectors in the xy plane; and are the horizontal plane vector and vertical direction vector corresponding to the trajectory point respectively.

[0084] The pitch angle α and translation angle β of this scheme can also be calculated using the following expression:

[0085]

[0086] in, is the normal vector of the ground point; for Vectors in the xy plane; and They are the horizontal plane vector and vertical direction vector corresponding to the trajectory point respectively;

[0087] When the pitch angle and the pan angle are positive, the camera lens rotates counterclockwise according to the pitch angle and the pan angle; when the pitch angle and the pan angle are negative, the camera lens rotates clockwise according to the pitch angle and the pan angle.

[0088] In step S7, the camera-equipped drone performs terrain-simulating flight and image collection according to the latitude, longitude, and elevation information and the pitch angle and translation angle of each track point on the parallel terrain-simulating flight route.

[0089] In summary, this scheme can prevent the perspective deformation of UAV imaging caused by terrain undulations during UAV flight operations, and improve the accuracy of the high-resolution DSM model of glaciers constructed by UAV aerial survey.

Claims

1. A method for parallel terrain-simulating flight of unmanned aerial vehicles for mountain monitoring, characterized in that: Includes steps: S1. Obtain the mission route of the UAV when collecting images in the study area, and determine the route spacing and shooting spacing of the mission route according to the imaging size of the camera carried by the UAV; S2, vertically mapping the mission route on the two-dimensional plane to the ground of the study area to obtain the projection line of the mission route on the ground of the study area; S3. According to the length of the projection line and the shooting distance, the number and positions of the required observation points on the projection line are obtained; S4, moving the observation point along the positive direction of the normal line of the section by a preset distance to obtain a route trajectory point; connecting all the route trajectory points to obtain a parallel terrain-simulating flight route; S5, obtaining the longitude, latitude and elevation information of each trajectory point according to the coordinates of the trajectory points on the parallel terrain imitation flight route; S6. According to the coordinates of the trajectory point, determine the corresponding horizontal plane vector and vertical direction vector, and calculate the pitch angle and translation angle of the camera carried by the drone at the current trajectory point according to the two vectors; S7. The camera-equipped drone performs terrain-simulating flight and image collection based on the latitude, longitude, elevation information, pitch angle, and translation angle of each track point on the parallel terrain-simulating flight route.

2. The method for parallel terrain imitation flight of unmanned aerial vehicles for mountain monitoring according to claim 1 is characterized in that: The route parameters of the mission route include the route length, the route angle, and the heading overlap and lateral overlap of the images taken by the camera.

3. The method for parallel terrain imitation flight of an unmanned aerial vehicle for mountain monitoring according to claim 1 or 2, characterized in that: The expressions of the route spacing and shooting spacing are respectively: ， in, t 旁 is the route spacing; t 航 For shooting distance; H 长 , H 航 They are the length and width of the shooting range in the camera imaging principle; p and c They are respectively the heading overlap and lateral overlap of the images taken by the camera.

4. The method for parallel terrain imitation flight of unmanned aerial vehicles for mountain monitoring according to claim 3 is characterized in that: The expression for obtaining the shooting range H in the camera imaging principle is: ， in, A For perspective; h is the size of the camera imaging sensor; f is the focal length; D is the distance between the object and the camera lens; when h When it corresponds to the length of the camera imaging sensor, the length of the shooting range is obtained; when h Corresponding to the width of the camera imaging sensor, the width of the shooting range is obtained.

5. The method for parallel terrain imitation flight of unmanned aerial vehicle applied to mountain monitoring according to claim 3 is characterized in that: The expression for calculating the number of observation points required on the projection line is: in, s is the number of observation points required; dl is the length of the projection line.

6. The method for parallel terrain imitation flight of unmanned aerial vehicles for mountain monitoring according to claim 1, characterized in that: The step S2 further comprises: Get the surface equations of the study area ground and the equations of the mission flight path: ， in, x , y and z They are x , y and z The coordinate values ​​of the axis; is the surface equation; (x0, y0, z0) is the coordinate of any point on the mission route; a , b and c They are x , y and z The component of the axis direction vector; t is the number of directed line segments starting at (x0, y0, z0) and ending at any point; Get the mission route in x - y Projection on a plane: Substitute the horizontal and vertical coordinates of each point on the mission route into the surface equation to obtain the z-axis coordinates of each point on the surface projection line: Combined mission routes x - y Projection equations on planes and surfaces z Coordinates, get the parametric equation of the projection line: 。 7. The method for parallel terrain imitation flight of unmanned aerial vehicles for mountain monitoring according to claim 1, characterized in that: The expressions of the pitch angle and the translation angle are: in, is the negative normal vector of the ground point; for Vectors in the xy plane; and They are the horizontal plane vector and vertical direction vector corresponding to the trajectory point respectively; α is the pitch angle; β is the translation angle.

8. The method for parallel terrain imitation flight of unmanned aerial vehicles for mountain monitoring according to claim 1, characterized in that: The expressions of the pitch angle and the translation angle are: in, is the normal vector of the ground point; for Vectors in the xy plane; and They are the horizontal plane vector and vertical direction vector corresponding to the trajectory point respectively; α is the pitch angle; β is the translation angle; When the pitch angle and the pan angle are positive, the camera lens rotates counterclockwise according to the pitch angle and the pan angle; when the pitch angle and the pan angle are negative, the camera lens rotates clockwise according to the pitch angle and the pan angle.

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