Visible window determination and nadir r-tree establishment method and apparatus

Abstract

The specification discloses a visible window determination and a method and device for establishing a nadir R-Tree, wherein the method for determining a visible window comprises the following steps: acquiring satellite position data in a process of flying around the earth; acquiring an R-Tree of the satellite position data; acquiring target position data; determining a space search area centered on the target according to observation parameters of a satellite-borne observation system; searching for target nadir position data in the R-Tree, wherein the target nadir position is a nadir position located in the space search area; and determining a visible window of the satellite-borne observation system for the target according to a search result. The visible window determined by the scheme has high precision, and the calculation efficiency is significantly improved compared with the prior art.

Description

Technical Field

[0001] This application relates to the field of remote sensing technology, and in particular to a method and apparatus for determining the visible window and establishing a nadir point R-Tree. Background Technology

[0002] Earth observation satellites refer to spacecraft that remotely sense the Earth's environment and resources, including meteorological satellites, land satellites, ocean satellites, and space stations. They are the primary means of acquiring Earth observation data. The Earth observation system carried on an Earth observation satellite is also called a payload. The satellite's visibility window refers to the time range within which the target can be observed by the satellite payload's field of view. Visibility window calculation is the foundation and prerequisite for practical applications such as satellite observation mission and imaging mission planning.

[0003] Currently, there are two methods for calculating the visible window.

[0004] Method 1: Utilizing a simplified motion model of the satellite and Earth, this method combines analytical and numerical approaches to calculate the visibility window. It first solves the problem based on a two-body model (i.e., a simplified motion model of the satellite and Earth), then corrects and supplements it using J2 perturbation. Visibility is determined by the relationship between the time the satellite reaches the imaging point and the time difference between the target's arrival at that point. The main steps are: 1. Based on the two-body model, obtain the equation of the circle of latitude where the target is located, calculate the coordinates of the satellite's nadir point at the imaging point, and then calculate the time when the target arrives at the satellite's imaging point due to Earth's rotation; 2. Correct the visibility time based on the J2 perturbation within the two-body model; 3. Calculate the boundary point where the target is visible when the satellite is at the imaging point using the satellite's attitude maneuvering angle; 4. Determine the target's visibility based on the time difference between the satellite and the target.

[0005] Method 2: A two-stage search approach combining coarse and fine search is used. In the coarse search stage, a large discrete time step is first set to quickly determine the approximate time interval between the start and end of the visible period. Then, a binary search is combined to calculate the precise visible time window. The main steps are: 1. Discretize the entire spacecraft orbital propulsion process into m equal parts, i.e., m+1 discrete points (taking 100s as the step size, and denoting the corresponding time series as t). i 1. (i = 1, 2, ..., m+1); 2. Calculate t for each discrete time point. i If the satellite's roll angle and pitch angle relative to a ground point are within the visible range, then the satellite is considered to be at that discrete time point t. i The target point is visible; 3, t i It can be seen that t i-1 When it is invisible, the visible window starts at time t. i-1 To t i Between; when t i-1 It can be seen that t iWhen it is invisible, the end time of the visible time window is located at t. i-1 To t i 4. If the visible window starts within the time interval (t0, t...) f Within ) , calculate the intermediate time t m The visibility of satellites to ground points. If t m Therefore, its value is assigned to t. f If t m If it is not visible, assign its value to t0; 5. Repeat the above steps until t f -t0 < error limit; 6. It can be seen that the starting time is t = (t0 + t f Similarly, the end time can be obtained by calculating () / 2.

[0006] The drawback of Method 1 is that it considers a large number of satellite orbit points and has low computational efficiency. The drawback of Method 2 is that it has the risk of missing windows and cannot guarantee that all visible windows can be obtained. Summary of the Invention

[0007] The purpose of this application is to provide a method and apparatus for determining a visible window and establishing a sub-star point R-Tree, so as to solve the problems of low accuracy or low efficiency of existing methods for determining visible windows.

[0008] To address the aforementioned technical problems, this specification provides a first aspect of a method for determining a visible window, comprising: acquiring nadir position data of a satellite during its orbit around the Earth; acquiring an R-Tree of the nadir position data of the satellite; wherein each node in the R-Tree consists of multiple index entries, an index entry of a leaf node includes at least one nadir position data and a minimum bounding box parameter, the minimum bounding box of the leaf node being the smallest three-dimensional box enclosing all nadir positions within the leaf node, and an index entry of a non-leaf node including a pointing relationship to its child nodes and a minimum bounding box parameter, the minimum bounding box of the non-leaf node being the smallest three-dimensional box enclosing the minimum bounding boxes of its leaf nodes; acquiring target position data; determining a spatial search area centered on the target based on observation parameters of an Earth observation system onboard the satellite; searching for target nadir position data in the R-Tree, wherein the target nadir position is a nadir position located within the spatial search area; and determining the visible window of the target for the spaceborne Earth observation system based on the search results.

[0009] In some embodiments, searching for target sub-satellite point location data in the R-Tree includes: starting the search from the root node of the R-Tree, and performing the following steps for each node on the search path: determining whether the minimum bounding box of the current node intersects with the spatial search area; if they intersect, if the current node is a non-leaf node, then each of the current node's child nodes is taken as the current node; if they intersect, if the current node is a leaf node, then determining whether the sub-satellite point locations in the current node are within the spatial search area; and taking the sub-satellite point location data located within the spatial search area in the current node as the target sub-satellite point.

[0010] In some embodiments, the R-Tree of the satellite's nadir position is established by the following method: predicting the volume increment of the minimum bounding box of each leaf node after adding the new nadir position; selecting the leaf node with the smallest volume increment as the target leaf node; determining whether the number of nadir position data in the target leaf node is less than M, where M is the maximum number of index entries in each node of the R-Tree, and the number of index entries in a leaf node refers to the number of nadir position data included; if the determination result is yes, inserting the new nadir position data into the target leaf node.

[0011] In some embodiments, the method further includes: if the determination result is negative, splitting the new sub-satellite point position data and the sub-satellite point position data in the target leaf node into two new leaf nodes; and adjusting the parent nodes at all levels of the target leaf node according to the splitting result.

[0012] In some embodiments, after adjusting the parent nodes of the target leaf node at each level according to the splitting result, the method further includes: if the root node of the current R-Tree splits into two nodes, then generating parent nodes for the two nodes obtained from the splitting of the root node, and using the parent nodes as the new root nodes; and incrementing the depth of the R-Tree by one.

[0013] In some embodiments, a spatial search area centered on the target is determined based on observation parameters of the Earth observation system carried on the satellite, including: a cube with a side length of 2L centered on the target location as the spatial search area, where L = 4h. s tanα,h s α represents the flight altitude of the satellite, and α is the maximum observation angle of the Earth observation system.

[0014] In some embodiments, determining the visibility window of the target for the spaceborne Earth observation system based on the search results includes: sorting the target nadir point position data in the search results according to the time sequence of their appearance during the satellite's flight; using a binary search method to find the first nadir point and the second nadir point; wherein, when the current position of the satellite corresponds to the nadir point preceding the first nadir point, the Earth observation system cannot observe the target; when the current position of the satellite corresponds to the first nadir point, the Earth observation system observes the target; when the current position of the satellite corresponds to the second nadir point, the Earth observation system observes the target; when the current position of the satellite corresponds to the nadir point following the second nadir point, the Earth observation system cannot observe the target; and using the time when the satellite's position corresponds to the first nadir point as the start time of the visibility window and the time when the satellite's position corresponds to the second nadir point as the end time of the visibility window.

[0015] The second aspect of this specification provides a method for establishing a nadir point R-Tree. Each node in the R-Tree consists of multiple index entries. An index entry for a leaf node includes at least one nadir point position data and a minimum bounding box parameter. The minimum bounding box of the leaf node is the smallest 3D box that encloses all nadir point positions within the leaf node. An index entry for a non-leaf node includes a pointer relationship to its child nodes and a minimum bounding box parameter. The minimum bounding box of the non-leaf node is the smallest 3D box that encloses the minimum bounding boxes of its child nodes. The method includes inputting data into the R-Tree using the following method... Adding new sub-satellite point position data to the R-Tree: Predict the volume increment of the minimum bounding box of each leaf node after adding the new sub-satellite point position; select the leaf node with the smallest volume increment as the target leaf node; determine whether the number of sub-satellite point position data in the target leaf node is less than M, where M is the maximum number of index entries in each node of the R-Tree, and the number of index entries in a leaf node refers to the number of sub-satellite point position data included; if the determination result is yes, insert the new sub-satellite point position data into the target leaf node.

[0016] A third aspect of this specification provides a visible window determination device, comprising: a first acquisition unit for acquiring nadir position data of a satellite during its orbit around the Earth; and a second acquisition unit for acquiring an R-Tree of the nadir position data of the satellite; wherein each node in the R-Tree consists of multiple index entries, and the index entry of a leaf node includes at least one nadir position data and a minimum bounding box parameter, wherein the minimum bounding box of the leaf node is the smallest three-dimensional box enclosing all nadir positions within the leaf node, and the index entry of a non-leaf node includes a pointing relationship to its child nodes and... The minimum bounding box parameter, wherein the minimum bounding box of the non-leaf node is the smallest three-dimensional box that surrounds the minimum bounding boxes of each of its leaf nodes; the third acquisition unit, used to acquire the target's position data; the first determination unit, used to determine the spatial search area centered on the target based on the observation parameters of the Earth observation system onboard the satellite; the search unit, used to search for the target's nadir position data in the R-Tree, wherein the target nadir position is the nadir position located within the spatial search area; the second determination unit, used to determine the visible window of the target from the satellite-borne Earth observation system based on the search results.

[0017] In some embodiments, the apparatus further includes: a prediction unit, configured to predict the volume increment of the minimum bounding box of each leaf node after adding new sub-satellite positions to each leaf node of the current R-Tree; a third determination unit, configured to select the leaf node with the smallest volume increment as the target leaf node; a judgment unit, configured to determine whether the number of sub-satellite position data in the target leaf node is less than M, where M is the maximum number of index entries in each node of the R-Tree, and the number of index entries in a leaf node refers to the number of sub-satellite position data included; and an insertion unit, configured to insert the new sub-satellite position data into the target leaf node if the judgment result is yes.

[0018] In some embodiments, the apparatus further includes: a splitting unit, configured to split the new nadir position data and the nadir position data in the target leaf node into two new leaf nodes if the determination result is negative; and an adjustment unit, configured to adjust the parent nodes at all levels of the target leaf node according to the splitting result.

[0019] In some embodiments, after adjusting the parent nodes of the target leaf node at each level according to the splitting result, the system further includes: a generation unit, configured to generate parent nodes for the two nodes obtained from the splitting of the current R-Tree if the root node of the current R-Tree splits into two nodes, and to use the parent nodes as new root nodes; and a processing unit, configured to increment the depth of the R-Tree by one.

[0020] In some embodiments, the second determining unit includes: a sorting subunit, configured to sort the target sub-satellite point position data in the search results according to the time order of their appearance during the satellite's flight; a search subunit, configured to search for the first sub-satellite point and the second sub-satellite point using a binary search method; wherein, when the current position of the satellite corresponds to the previous sub-satellite point of the first sub-satellite point, the Earth observation system cannot observe the target; when the current position of the satellite corresponds to the first sub-satellite point, the Earth observation system observes the target; when the current position of the satellite corresponds to the second sub-satellite point, the Earth observation system observes the target; and when the current position of the satellite corresponds to the next sub-satellite point of the second sub-satellite point, the Earth observation system cannot observe the target; and a determining subunit, configured to use the time when the satellite's position corresponds to the first sub-satellite point as the start time of the visible window and the time when the satellite's position corresponds to the second sub-satellite point as the end time of the visible window.

[0021] This specification provides a device for establishing a nadir point R-Tree, wherein each node in the R-Tree consists of multiple index entries. An index entry for a leaf node includes at least one nadir point position data and a minimum bounding box parameter. The minimum bounding box of the leaf node is the smallest three-dimensional box that encloses all nadir point positions within the leaf node. An index entry for a non-leaf node includes a pointer relationship to its child nodes and a minimum bounding box parameter. The minimum bounding box of the non-leaf node is the smallest three-dimensional box that encloses the minimum bounding boxes of its child nodes. The device includes adding new nadir point position data to the R-Tree using the following means. The system comprises: a prediction unit for predicting the volume increment of the minimum bounding box of each leaf node after the new sub-satellite position is added; a third determination unit for selecting the leaf node with the smallest volume increment as the target leaf node; a judgment unit for determining whether the number of sub-satellite position data in the target leaf node is less than M, where M is the maximum number of index entries in each node of the R-Tree, and the number of index entries in a leaf node refers to the number of sub-satellite position data included; and an insertion unit for inserting the new sub-satellite position data into the target leaf node if the judgment result is yes.

[0022] A fifth aspect of this specification provides an electronic device, comprising: a memory and a processor, wherein the processor and the memory are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to implement the steps of the method described in any of the first or second aspects.

[0023] A sixth aspect of this specification provides a computer storage medium storing computer program instructions that, when executed, implement the steps of the method described in any of the first or second aspects.

[0024] The visible window determination method and apparatus for establishing the R-Tree of nadir points provided in this specification have high accuracy and significantly improved computational efficiency. The visible window is determined based on the R-Tree of the nadir point trajectory. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 A schematic diagram showing the relative positions of the satellite and ground targets is provided.

[0027] Figure 2 This document shows a flowchart of the method for establishing the R-Tree of nadir position data provided in this specification;

[0028] Figure 3 A schematic diagram of the state of an R-Tree is shown;

[0029] Figure 4 It shows Figure 3 The diagram shows the positional relationships within the R-Tree.

[0030] Figure 5 A schematic diagram of node E4 after splitting is shown;

[0031] Figure 6 It shows Figure 5 The diagram shows the positional relationships within the R-Tree.

[0032] Figure 7 A schematic diagram of node E7 after splitting is shown;

[0033] Figure 8 It shows Figure 7 The diagram shows the positional relationships within the R-Tree.

[0034] Figure 9 This diagram illustrates the process after a root node splits and generates a new root node.

[0035] Figure 10 It shows Figure 9 The diagram shows the positional relationships within the R-Tree.

[0036] Figure 11 A flowchart of the visible window determination method provided in this specification is shown;

[0037] Figure 12 A schematic diagram of the SAR coverage area model is shown;

[0038] Figure 13 A schematic diagram showing the intersection of the satellite's farthest visible direction with the Earth is shown;

[0039] Figure 14 A schematic diagram is shown showing whether the satellite's farthest visible direction is tangent to or separate from the Earth;

[0040] Figure 15 A schematic diagram of the search method for R-Tree is shown;

[0041] Figure 16 A spatial diagram of the search method is shown;

[0042] Figure 17 A comparison chart showing the time required to calculate the visibility of different numbers of targets using three methods for determining the visible window is presented.

[0043] Figure 18 A schematic diagram of the electronic device provided in this specification is shown. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0045] This specification proposes a method for determining the visible window of a spaceborne Earth observation system. The method acquires the nadir position data of the satellite, establishes an R-Tree of the nadir position data, determines a spatial search area centered on the target based on the observation parameters of the Earth observation system, searches for the target nadir position data within the R-Tree that is located within the spatial search area, and determines the visible window of the spaceborne Earth observation system for the target based on the search results.

[0046] The nadir point is the intersection of a line connecting the Earth's center and a satellite on the Earth's surface. The collection of nadir points is also called the nadir trajectory. For example... Figure 1 As shown, O is the Earth's center, and SP is the sub-satellite point.

[0047] The position data of the nadir point can be calculated based on the satellite orbit. The nadir point position data is three-dimensional coordinate data.

[0048] An R-Tree is a highly balanced tree-like data structure containing two types of nodes: leaf nodes and non-leaf nodes. In this specification, each node in an R-Tree consists of multiple index entries. A leaf node's index entry includes at least one nadir position and a minimum bounding box parameter. The minimum bounding box of a leaf node is the smallest 3D box that encloses all nadir positions within that leaf node. A non-leaf node's index entry includes pointers to its child nodes and a minimum bounding box parameter. The minimum bounding box of a non-leaf node is the smallest 3D box that encloses the minimum bounding boxes of its leaf nodes. For example, if a node has three non-coplanar nadir positions A, B, and C, then the smallest cuboid that can enclose these three nadir positions is the node's minimum bounding box. The minimum bounding box can be represented using parameters such as target point position, length, width, and height, where the target point position can be the center point or a vertex. The maximum number of index entries in each node of an R-Tree can be preset to M. The number of index entries for a leaf node refers to the number of sub-satellite point position data it includes, while the number of index entries for a non-leaf node refers to the number of child nodes of that non-leaf node.

[0049] This manual provides a method for establishing a sub-satellite R-Tree, such as... Figure 2 As shown, the method includes adding new sub-satellite point position data to the R-Tree through the following steps S11 to S16.

[0050] S11: Predict the volume increment of the minimum bounding box of each leaf node after the new sub-star point position is added to each leaf node of the current R-Tree.

[0051] S12: Select the leaf node with the smallest volume increment as the target leaf node.

[0052] S13: Determine whether the number of sub-satellite point position data in the target leaf node is less than M. If the determination result is yes, execute S14; otherwise, execute S15 and S16.

[0053] S14: Insert the new sub-satellite point position data into the target leaf node.

[0054] S15: Split the new nadir position data and the nadir position data in the target leaf node into two new leaf nodes.

[0055] S16: Adjust the parent nodes of the target leaf node at all levels according to the splitting result.

[0056] Specifically, adjust the parent nodes at each level in the following two ways: 1. Adjust the minimum bounding box in the parent node of the target leaf node; 2. If the splitting result makes the number of sub-point position data in the parent node greater than M, split the parent node into two new nodes and adjust the parent node at the next higher level according to the splitting result.

[0057] In some embodiments, after adjusting the parent nodes of the target leaf node at each level according to the splitting result, if the root node of the current R-Tree splits into two nodes, then a parent node is generated for the two nodes obtained from the splitting of the root node, and the parent node is used as the new root node; the depth of the R-Tree is incremented by one.

[0058] The following two-dimensional diagram illustrates the method for constructing the R-Tree provided in this manual. Assume M = 3, and there exists an R-Tree as shown below. Figure 3 As shown, the root node contains three child nodes: E6, E7, and E8. E6 contains two leaf nodes: E1 and E2; E7 contains three leaf nodes: E3, E4, and E5; and E8 contains three leaf nodes: E9 and E10. E1 contains three sub-nodes: h, k, and m; E2 contains three sub-nodes: a, c, and d; E3 contains three sub-nodes: f, g, and j; E4 contains three sub-nodes: l, m, and s; E5 contains three sub-nodes: b, i, and e; E9 contains two sub-nodes: q and r; and E10 contains two sub-nodes: o and p. Figure 4 It shows Figure 3 The diagram shows the positional relationships within the R-Tree.

[0059] If you want to insert the nadir point t into the R-Tree, you need to traverse all leaf nodes and find the leaf node with the smallest increase in the volume of the bounding box after adding the new nadir point t coordinates. For example... Figure 4 As shown, compared with the original minimum bounding box of each leaf node, it is found that inserting t into the minimum bounding box of leaf node E4 produces the smallest increment. However, at this time, leaf node E4 already contains 3 sub-star data points. Inserting another sub-star point will cause overflow. Therefore, it is necessary to split the three sub-star points l, n, s in leaf node E4 and the four sub-star points t to be inserted into two leaf nodes.

[0060] Forming minimum bounding boxes from each of the four star-shaped points l, n, s, and t in pairs, we find that the area formed by l and s is the largest. Therefore, we first assign l and s to two leaf nodes; here, we assign l to E12 and s to E11. At this point, the minimum bounding box of E11 and E12 is considered a minimum bounding box with an area of ​​0. We then insert n and t into E11 and E12 respectively to form new minimum bounding boxes. We find that the increment of the minimum bounding box after inserting n into E12 is smaller than the increment after inserting n into E11, so we insert n into E12. Similarly, we find that the increment of the minimum bounding box after inserting t into E11 is smaller, so we insert t into E11. Figure 5 A schematic diagram of node E4 after splitting is shown. Figure 6 It shows Figure 5 The diagram shows the positional relationships within the R-Tree.

[0061] Since leaf node E4 split into two nodes, the number of child nodes in its original parent node E7 exceeds the maximum capacity of the node. At this time, node E7 contains data from four leaf nodes: E3, E5, E11, and E12. Therefore, these four nodes need to be split into two nodes. Following the principle of minimum bounding box increment, E3 and E5 are assigned to the same node, denoted as E13. The minimum bounding box of E13 is then adjusted to contain the minimum bounding boxes of E3 and E5. Similarly, E11 and E12 are assigned to the same node, denoted as E14. The minimum bounding box of node E14 is then adjusted to contain the minimum bounding boxes of E11 and E12. Figure 7 A schematic diagram of node E7 after splitting is shown. Figure 8 It shows Figure 7 The diagram shows the positional relationships within the R-Tree.

[0062] Since node E7 has now been adjusted to two nodes, E13 and E14, the capacity of its original parent node, which is also the root node, has exceeded the maximum capacity. Therefore, the data of the root node needs to be split into the two nodes, following the principle of minimum bounding box increment. A new root node needs to be generated as the parent node of the two newly generated nodes. The depth of the R-Tree is increased by one, and the entire structure of the R-Tree is adjusted. Figure 9 This diagram illustrates the process after the root node splits and generates a new root node. Figure 10 It shows Figure 9 The diagram shows the positional relationships within the R-Tree.

[0063] repeat Figures 3 to 9 The above steps are repeated until all nadir points are inserted, constructing a complete R-Tree of nadir point position data.

[0064] The satellite's nadir position data is related to the satellite's flight parameters. When the satellite's flight parameters remain unchanged, the nadir trajectory of the satellite as it orbits the Earth multiple times changes periodically.

[0065] The satellite nadir trajectory is independent of the position of the observed target. When there are multiple observed targets, the R-Tree of the nadir position data of each satellite only needs to be established once.

[0066] Based on the satellite nadir point position data R-Tree established by the above method, this specification also provides a method for determining the visible window. For example... Figure 11 As shown, the visible window determination method includes the following steps S21, S22, S23 and S24.

[0067] S21: Acquire the sub-satellite position data during the satellite's orbit around the Earth.

[0068] S22: R-Tree for acquiring the sub-satellite position data of the satellite.

[0069] S23: Obtain the target's location data.

[0070] S24: Determine the space search area centered on the target based on the observation parameters of the Earth observation system carried on the satellite.

[0071] Earth observation systems can be SAR (synthetic aperture radar) systems. SAR is an active detection technology that acquires high-resolution images through two-dimensional matched filtering. SAR utilizes Doppler information generated by the relative motion between the antenna and the target, converting the motion of a small-aperture antenna into a larger synthetic aperture, thus improving azimuth resolution. Pulse compression technology is used to improve range resolution. Compared with traditional optical sensors, SAR has advantages such as strong anti-interference capability, all-weather operation, and certain cloud and fog penetration, making it a promising wide-area, long-range sensing method.

[0072] When determining the space search area, it is necessary to determine the necessary conditions for the target to be visible based on the positional relationship between the satellite and the target.

[0073] Specifically, such as Figure 1 As shown, the relative geometric position of the satellite in orbit and the ground target changes over time, where r S and r T Let r represent the instantaneous positions of the satellite and the target center in the geocentric inertial frame, respectively. ST Let v represent the relative position of the satellite and the target, and v represent the instantaneous velocity of the satellite in the geocentric inertial frame. Satellite visibility means the ground target is within the satellite's line of sight. The satellite's visible range is typically determined by its elevation angle θ. pitchRange of variation and roll angle θ roll The variation range is related to the field of view of the load and its related parameters.

[0074] Pitch angle θ pitch The angle of counterclockwise rotation around the negative normal of the satellite's orbital plane can be calculated from the instantaneous positions and velocities of the satellite and target in the geocentric inertial frame:

[0075]

[0076] In the formula: "·" represents the dot product, and "×" represents the cross product. Roll angle θ roll The angle of counterclockwise rotation around the satellite's velocity direction is expressed by the formula:

[0077]

[0078] The range of variation for pitch and roll angles is defined by satellite parameters, namely: in These represent the lower and upper bounds of the satellite's pitch and roll angle ranges, respectively.

[0079] A simplified geometric model of the radar location and beam coverage area on the ground, as follows: Figure 12 As shown, the radar beam of a satellite equipped with a SAR sensor can be viewed as a cone, and the area covered by the beam is the cross-section formed by the cone being tangent to the ground. The radar beam has two important measurements: the angular width in the azimuth plane and the angular width in the elevation plane. Figure 12 In this context, 'e' represents the direction of the load center, and 'θ' represents the direction of the load center. hor and θ ver These represent the pitch plane angle and azimuth plane angle of the field of view, respectively, with the shaded area representing the visible range of the load.

[0080] Furthermore, the satellite's ground visibility range is also related to the order of its attitude rotation. Assuming the satellite's attitude adjustment sequence is pitch first, then roll, the rotation matrix for attitude adjustment is:

[0081]

[0082] In the formula: R(θ) roll R(θ) is the rotation matrix of the satellite in the rolling direction. pitch Let be the rotation matrix of the satellite in the pitch direction, denoted as:

[0083]

[0084] Let α be (0,0,1) T If the angle between the two points is , then the necessary condition for the target to be visible is .

[0085]

[0086] Therefore, we can conclude that the necessary condition for a target to be observed is that the angle between the satellite target vector and the satellite geocentric vector must be less than α.

[0087] Under normal circumstances, the satellite's orbital altitude does not change much, and the capabilities of the satellite's onboard sensors are also known. Therefore, the satellite's maximum visible range on the ground can be calculated using α.

[0088] If the target is visible, it must be within the satellite's maximum visible range. Correspondingly, the satellite's nadir point must also be within a certain range centered on the target. This range is defined as "a cube with a side length of 2L centered on the target".

[0089] The following is a brief explanation of why the constructed search area is this range:

[0090] First, the Earth is an irregular ellipsoid. For simplicity, we can use the Earth's semi-major axis R as the radius to obtain the circumsphere, and take a great circle passing through the center of this sphere. Let O represent the Earth's center, S represent the satellite's position, and h... s Let α be the satellite's orbital altitude and D be the satellite's nadir position. Based on the necessary conditions for target visibility, the satellite's farthest visible angle is α.

[0091] (1) As Figure 13 As shown, if If the satellite intersects the Earth along the farthest visible direction, and the intersection point is denoted as B, then twice the length of BD can be regarded as the farthest visible distance of the satellite S on Earth.

[0092] Draw a tangent to the Earth through point D below the satellite, intersecting the visible direction of the satellite at point C. Let ∠COD = β1 and ∠BOC = β2.

[0093] Since the satellite intersects the Earth along its farthest visible direction.

[0094] Therefore, β2 < β1, l BE <l ED ,∴l BD <2l ED

[0095] Since β1≤tanβ1, therefore l ED ≤l CD ,∴l BD <2l ED ≤2l CD

[0096] Also ∵l CD =h s tanα,∴l BD <2lED ≤2l CD =2h s tanα,

[0097] Let L = 4h s tanα

[0098] ∴2l BD <L

[0099] (2) Figure 14 As shown, if Pick If the satellite is tangent to the Earth along the δ direction, and the point of tangency is denoted as B, then twice the length of BD can be regarded as the farthest visible distance of the satellite S on Earth.

[0100] and Figure 13 The same applies; let ∠COD = β1, ∠BOC = β2.

[0101] Since the satellite is tangent to the Earth along the δ direction.

[0102] Therefore, β2 = β1, l BE =l ED ,∴l BD =2l ED

[0103] Since β1 < tanβ1, therefore l ED <l CD ,∴l BD =2l ED <2l CD

[0104] Also ∵l CD =h s tanδ, δ≤α

[0105] ∴l BD =2l ED <2l CD =2h s tanδ≤2h s tanα,

[0106] Let L = 4h s tanα

[0107] ∴2l BD <L

[0108] Therefore, a cube with a side length of 2L centered on the target ensures that the nadir trajectory obtained in the R-Tree search includes the corresponding nadir trajectory within the truly visible arc of the satellite relative to the target. Based on the observation parameters of the Earth observation system onboard the satellite, a spatial search area centered on the target is determined, including: a cube with a side length of 2L centered on the target location as the spatial search area, where L = 4h. s tanα,h s α represents the flight altitude of the satellite, and α is the maximum observation angle of the Earth observation system.

[0109] In this specification, “∵” represents the conditions required for the derivation process, and “∴” represents the result obtained from the derivation process.

[0110] S25: Search for target nadir position data in the R-Tree, wherein the target nadir position is the nadir position located within the spatial search area.

[0111] For example, starting the search from the root node of the R-Tree, the following steps are performed for each node on the search path:

[0112] S251: Determine whether the minimum bounding box of the current node intersects with the spatial search region. If they intersect, and the current node is a non-leaf node, proceed to S252; if they intersect, and the current node is a leaf node, proceed to S253 and S254. If they do not intersect, proceed to step S251 for the next current node.

[0113] S252: Set each child node of the current node as the current node and jump to S251 to continue execution.

[0114] S253: Determine whether the positions of each sub-satellite point in the current node are within the spatial search area.

[0115] S254: Add the sub-satellite point position data of the current node within the spatial search area to the search results.

[0116] by Figure 15 The R-Tree shown is used as an example to illustrate the search method. Databases with gray shading represent search paths. Figure 16 It shows Figure 15 The diagram shows the positional relationships in the R-Tree, where the rectangles with gray shading represent the spatial search areas.

[0117] The input when searching is Figure 16The spatial search region is defined, and the output is the positions of all sub-satellite points within that region. Starting from the root node, the node to be queried next is selected by checking if the spatial search region intersects with the minimum bounding box within the node. If it intersects with the minimum bounding boxes of multiple nodes, then all corresponding child nodes must be searched. This process continues until leaf nodes are reached, at which point the sub-satellite points within the spatial search region are filtered out.

[0118] like Figure 16 As shown, the search area intersects with nodes E15 and E16, so the search continues with the child nodes of E15 and E16. Since it intersects with E13 in E15, the search continues with the child nodes of E13. It is found that it intersects with the leaf node E3, so the sub-nodes g and j in E3 are selected as the result sub-nodes. Similarly, for the subsequent search of E16, the sub-nodes l and n in the leaf node E12 can be obtained. Therefore, g, j, l, and n are the searched sub-node data.

[0119] Therefore, organizing the nadir point position data into an R-Tree structure can efficiently search for nadir point positions within the spatial search range.

[0120] S26: Determine the visible window of the target by the spaceborne Earth observation system based on the search results.

[0121] In some embodiments, S26 includes the following steps S261, S262 and S263.

[0122] S261: Sort the target satellite sub-satellite position data in the search results according to the time sequence of their appearance during the satellite's flight.

[0123] S262: Determine the first sub-satellite point and the second sub-satellite point from the search results; wherein, when the current position of the satellite corresponds to the sub-satellite point preceding the first sub-satellite point, the Earth observation system cannot observe the target; when the current position of the satellite corresponds to the first sub-satellite point, the Earth observation system observes the target; when the current position of the satellite corresponds to the second sub-satellite point, the Earth observation system observes the target; when the current position of the satellite corresponds to the sub-satellite point following the second sub-satellite point, the Earth observation system cannot observe the target.

[0124] Specifically, S262 can use a binary search method to determine the first and second sub-points. Given a known search result, determining the first and second sub-points using a binary search method is achievable with existing technology and will not be elaborated upon here.

[0125] S263: The time when the satellite's position corresponds to the first nadir point is taken as the start time of the visible window, and the time when the satellite's position corresponds to the second nadir point is taken as the end time of the visible window.

[0126] With the increasing number of satellites and the expanding user demands, joint observation of multi-satellite networks has become a hot research topic, placing higher demands on accuracy and efficiency. Therefore, for multi-satellite, multi-target reconnaissance missions, during actual mission execution, mission information is allocated to different node servers according to service configuration. Each server processes its assigned task, and finally, the execution results of all node tasks are aggregated and output.

[0127] To ensure high utilization of node server resources and high efficiency of task planning, this paper proposes a task allocation and parallel scheme. Based on the satellite configuration information, the overall task information is first decomposed into multi-satellite sub-tasks. Combined with parallel computing, the satellite sub-tasks are further decomposed into one-to-one visibility problem solving. Finally, the results of all sub-problems are summarized into the overall task result, forming the R-Tree visibility window algorithm.

[0128] In summary, the main steps of the R-Tree visible window algorithm are as follows:

[0129] (1) Construct a configuration table for the number of satellite subtasks. The number of subtasks m for satellite i during mission execution can be directly specified. If not specified, the maximum observable ground area (area) for each satellite in the mission satellite set is calculated. i The minimum value of area is obtained. min Then the number of subtasks of satellite i This indicates rounding up to the nearest integer.

[0130] (2) Satellite Subtask Construction. Construct the satellite nadir trajectory R-Tree, and divide the satellite into subtasks according to the satellite subtask number configuration table, denoted as i. j Let represent the j-th subtask of satellite i. Each satellite subtask contains k. j There are n observation targets, where n is the number of observation targets in the total mission information.

[0131]

[0132] In addition, the sub-task also includes information such as the mission execution satellite, satellite R-Tree, onboard sensor constraints, and mission start and end times.

[0133] (3) Parallel solution of target visibility window information. For each satellite sub-task, the multi-target observation task is decomposed, and the target visibility problem is solved based on the single-satellite single-target R-Tree visibility window algorithm.

[0134] (4) Merge and output the results of satellite sub-tasks.

[0135] The accuracy and efficiency of the visible window determination method provided in this specification are compared through simulation. The comparison is between the results of the tracking propagation method and STK software (a highly accurate visible window calculation software in the industry).

[0136] The simulation start time and the corresponding time for the satellite orbit elements are both 2022-03-23 ​​16:00:00.000 (UTCG), and the simulation end time is 2022-03-24 16:00:00.000 (UTCG). The simulation duration is 1 day, the satellite orbit position estimation step is 1 second, the linear interpolation time accuracy is 1 ms, the maximum node capacity in the R-Tree is set to M=4, the development language is Java, and the running environment is an Intel(R) Xeon(R) CPU E5-2640 v4@2.40GHz computer.

[0137] The satellite root number information is set as shown in Table 1 below.

[0138] Table 1 Satellite element information

[0139] satellite Semi-long wheelbase / km Eccentricity Track inclination angle / ° Perimeter Argument / ° Ascending node right ascension / ° Horizontal near point angle / ° sat1 7009.835 0 97.814 0 204.456 44.242

[0140] The SAR sensor and satellite attitude conversion parameters are shown in Table 2 below.

[0141] Table 2. Onboard Sensors and Attitude Conversion Capabilities

[0142]

[0143] The target location information is shown in Table 3 below.

[0144] Table 3 Target Location Information

[0145] Target Longitude / ° Latitude / ° 1 115 29.9 2 -46 -6

[0146] The comparison results are shown in Table 4 below. In Table 4, the results of STK are used as the benchmark, and the accuracy is confirmed to be 1ms. The values ​​in parentheses are the deviations between the results of this algorithm and the results of STK. Positive values ​​indicate that the obtained visible start time is after the STK result, or the obtained visible window duration is longer than the STK result; conversely, negative values ​​indicate that the obtained visible start time is before the STK result, or the obtained visible window duration is shorter than the STK result.

[0147] Table 4 Comparison of single-target visibility window information from satellites equipped with sensor1

[0148]

[0149] Figure 17 A comparison chart showing the time required to calculate the visibility of different numbers of targets using three methods for determining the visibility window is presented.

[0150] From Table 4 above and Figure 17 It can be seen that the visible window determination method based on R-Tree provided in this specification has an average relative error of -8.5x10 compared to STK. -4 In terms of efficiency, it is 10,000 times faster than the tracking propagation method with a time step of 1 ms. In other words, the visible window determination method based on R-Tree provided in this specification has higher accuracy and significantly improved computational efficiency.

[0151] This specification provides a visible window determination device, which can be used to implement the above-described visible window determination method. The device includes a first acquisition unit 11, a second acquisition unit 12, a third acquisition unit 13, a first determination unit 14, a search unit 15, and a second determination unit 16.

[0152] The first acquisition unit 11 is used to acquire the sub-satellite point position data during the satellite's orbital flight.

[0153] The second acquisition unit 12 is used to acquire the R-Tree of the satellite's nadir position data; wherein, each node in the R-Tree consists of multiple index entries, and the index entry of a leaf node includes at least one nadir position data and a minimum bounding box parameter. The minimum bounding box of the leaf node is the minimum three-dimensional box that surrounds all nadir positions in the leaf node. The index entry of a non-leaf node includes the pointing relationship to its child nodes and the minimum bounding box parameter. The minimum bounding box of the non-leaf node is the minimum three-dimensional box that surrounds the minimum bounding boxes of its leaf nodes.

[0154] The third acquisition unit 13 is used to acquire the target's location data.

[0155] The first determining unit 14 is used to determine the space search area centered on the target based on the observation parameters of the Earth observation system carried on the satellite.

[0156] The search unit 15 is used to search for target sub-satellite point location data in the R-Tree, wherein the target sub-satellite point location is the sub-satellite point location located within the spatial search area.

[0157] The second determining unit 16 is used to determine the visible window of the target by the spaceborne Earth observation system based on the search results.

[0158] In some embodiments, the apparatus further includes: a prediction unit, configured to predict the volume increment of the minimum bounding box of each leaf node after the new sub-satellite position is added to each leaf node of the current R-Tree; a third determination unit, configured to select the leaf node with the smallest volume increment as the target leaf node; a judgment unit, configured to determine whether the number of sub-satellite position data in the target leaf node is less than M; and an insertion unit, configured to insert the new sub-satellite position data into the target leaf node if the judgment result is yes.

[0159] In some embodiments, the apparatus further includes: a splitting unit, configured to split the new nadir position data and the nadir position data in the target leaf node into two new leaf nodes if the determination result is negative; and an adjustment unit, configured to adjust the parent nodes at all levels of the target leaf node according to the splitting result.

[0160] In some embodiments, after adjusting the parent nodes of the target leaf node at each level according to the splitting result, the system further includes: a generation unit, configured to generate parent nodes for the two nodes obtained from the splitting of the current R-Tree if the root node of the current R-Tree splits into two nodes, and to use the parent nodes as new root nodes; and a processing unit, configured to increment the depth of the R-Tree by one.

[0161] In some embodiments, the second determining unit includes: a sorting subunit, configured to sort the target sub-satellite point position data in the search results according to the time order of their appearance during the satellite's flight; a search subunit, configured to search for the first sub-satellite point and the second sub-satellite point using a binary search method; wherein, when the current position of the satellite corresponds to the previous sub-satellite point of the first sub-satellite point, the Earth observation system cannot observe the target; when the current position of the satellite corresponds to the first sub-satellite point, the Earth observation system observes the target; when the current position of the satellite corresponds to the second sub-satellite point, the Earth observation system observes the target; and when the current position of the satellite corresponds to the next sub-satellite point of the second sub-satellite point, the Earth observation system cannot observe the target; and a determining subunit, configured to use the time when the satellite's position corresponds to the first sub-satellite point as the start time of the visible window and the time when the satellite's position corresponds to the second sub-satellite point as the end time of the visible window.

[0162] This specification also provides a device for establishing a sub-satellite R-Tree. Each node in the R-Tree consists of multiple index entries. The index entry of a leaf node includes at least one sub-satellite position data and a minimum bounding box parameter. The minimum bounding box of the leaf node is the smallest three-dimensional box that encloses all sub-satellite positions within the leaf node. The index entry of a non-leaf node includes a pointing relationship to its child nodes and a minimum bounding box parameter. The minimum bounding box of the non-leaf node is the smallest three-dimensional box that encloses the minimum bounding boxes of its child nodes. The device includes a prediction unit 21, a third determination unit 22, a judgment unit 23, and an insertion unit 24.

[0163] The prediction unit 21 is used to predict the volume increment of the minimum bounding box of each leaf node after the new sub-star point position is added to each leaf node of the current R-Tree.

[0164] The third determining unit 22 is used to select the leaf node with the smallest volume increment as the target leaf node.

[0165] The judgment unit 23 is used to determine whether the number of sub-star position data in the target leaf node is less than M, where M is the maximum number of index entries in each node of the R-Tree, and the number of index entries in the leaf node refers to the number of sub-star position data included.

[0166] The insertion unit 24 is used to insert the new sub-satellite point position data into the target leaf node if the determination result is yes.

[0167] The descriptions and functions of the above units can be understood by referring to the corresponding methods section, and will not be repeated here.

[0168] This invention also provides an electronic device, such as... Figure 18 As shown, the electronic device may include a processor 1801 and a memory 1802, wherein the processor 1801 and the memory 1802 may be connected via a bus or other means. Figure 18 Taking the example of a connection between China and Israel via a bus.

[0169] Processor 1801 can be a Central Processing Unit (CPU). Processor 1801 can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or combinations of the above types of chips.

[0170] The memory 1802, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs, non-transitory computer-executable programs, and modules, such as the program instructions / modules corresponding to the visible window determination and R-Tree establishment method in the embodiments of the present invention. The processor 1801 executes various functional applications and data processing by running the non-transitory software programs, instructions, and modules stored in the memory 1802, thereby implementing the visible window determination and R-Tree establishment method in the above method embodiments.

[0171] The memory 1802 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created by the processor 1801, etc. Furthermore, the memory 1802 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, the memory 1802 may optionally include memory remotely located relative to the processor 1801, and these remote memories may be connected to the processor 1801 via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0172] The one or more modules are stored in the memory 1802, and when executed by the processor 1801, they perform the following: Figure 1 The method for determining the visible window and establishing the R-Tree in the illustrated embodiment.

[0173] The specific details of the aforementioned electronic device can be understood by referring to the relevant descriptions and effects in the method embodiments, and will not be repeated here.

[0174] This specification also provides a computer storage medium storing computer program instructions, which, when executed, implement the steps of the above-described visible window determination and R-Tree creation method.

[0175] This specification also provides a computer program product comprising a computer program that, when executed by a processor, implements the steps of the above-described visible window determination and R-Tree creation method.

[0176] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk drive (HDD), or solid-state drive (SSD), etc.; the storage medium can also include combinations of the above types of memory.

[0177] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. The focus of each embodiment is to describe the differences from other embodiments.

[0178] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions.

[0179] Although this application has been described through embodiments, those skilled in the art will know that this application has many modifications and variations without departing from the spirit of this application, and it is intended that the appended claims cover such modifications and variations without departing from the spirit of this application.

Claims

1. A method for determining a visible window, characterized in that, include: To acquire the sub-satellite position data during the satellite's orbit around the Earth; An R-Tree is used to obtain the sub-satellite point position data of the satellite; wherein each node in the R-Tree consists of multiple index entries, the index entry of a leaf node includes at least one sub-satellite point position data and a minimum bounding box parameter, the minimum bounding box of the leaf node is the minimum three-dimensional box that surrounds all sub-satellite point positions in the leaf node, the index entry of a non-leaf node includes the pointing relationship to its child nodes and a minimum bounding box parameter, the minimum bounding box of the non-leaf node is the minimum three-dimensional box that surrounds the minimum bounding boxes of its leaf nodes. Obtain the target's location data; Based on the observation parameters of the Earth observation system carried on the satellite, a space search area centered on the target is determined; Search for target nadir position data in the R-Tree, wherein the target nadir position is the nadir position located within the spatial search area; The visible window of the target by the spaceborne Earth observation system is determined based on the search results; Based on the observation parameters of the Earth observation system onboard the satellite, a space search area centered on the target is determined, including: The spatial search area is a cube with a side length of 2L centered at the target location, where L = 4h. s tanα,h s Where α is the flight altitude of the satellite, and α is the maximum observation angle of the Earth observation system; Determining the visible window of the target from the spaceborne Earth observation system based on the search results includes: The location data of each target sub-satellite point in the search results are sorted according to the time sequence in which they appear during the satellite's flight. A binary search method is used to find the first and second sub-satellite points. Specifically, when the satellite's current position corresponds to the sub-satellite point preceding the first sub-satellite point, the Earth observation system cannot observe the target; when the satellite's current position corresponds to the first sub-satellite point, the Earth observation system observes the target; when the satellite's current position corresponds to the second sub-satellite point, the Earth observation system observes the target; and when the satellite's current position corresponds to the sub-satellite point following the second sub-satellite point, the Earth observation system cannot observe the target. The time when the satellite's position corresponds to the first nadir point is taken as the start time of the visible window, and the time when the satellite's position corresponds to the second nadir point is taken as the end time of the visible window.

2. The method according to claim 1, characterized in that, Searching for the target sub-satellite point position data in the R-Tree includes: starting the search from the root node of the R-Tree, and performing the following steps for each node on the search path: Determine whether the minimum bounding box of the current node intersects with the spatial search region; In the case of intersection, if the current node is a non-leaf node, then each of the current node's child nodes is taken as the current node. In the case of intersection, if the current node is a leaf node, it is determined whether the positions of each sub-satellite point in the current node are within the spatial search area; the sub-satellite point position data of the current node located within the spatial search area is taken as the target sub-satellite point.

3. The method according to claim 1, characterized in that, The R-Tree for the satellite's nadir position is established using the following method: Predict the volume increment of the minimum bounding box of each leaf node in the current R-Tree after adding the new sub-star point position; The leaf node with the smallest volume increment is selected as the target leaf node. Determine whether the number of sub-star position data in the target leaf node is less than M, where M is the maximum number of index entries in each node of the R-Tree, and the number of index entries in the leaf node refers to the number of sub-star position data included. If the determination result is yes, the new sub-satellite point position data is inserted into the target leaf node.

4. The method according to claim 3, characterized in that, The method further includes: If the result is negative, the new nadir position data and the nadir position data in the target leaf node are split into two new leaf nodes. Adjust the parent nodes of the target leaf node at all levels according to the splitting results.

5. The method according to claim 4, characterized in that, After adjusting the parent nodes of the target leaf node according to the splitting results, the process also includes: If the root node of the current R-Tree splits into two nodes, then a parent node is generated for the two nodes resulting from the split root node, and the parent node is used as the new root node. Increment the depth of the R-Tree by one.

6. A visible window determination device, characterized in that, include: The first acquisition unit is used to acquire the sub-satellite point position data during the satellite's orbit around the Earth. The second acquisition unit is used to acquire the R-Tree of the satellite's nadir position data; wherein, each node in the R-Tree consists of multiple index entries, the index entry of a leaf node includes at least one nadir position data and a minimum bounding box parameter, the minimum bounding box of the leaf node is the minimum three-dimensional box that surrounds all nadir positions in the leaf node, the index entry of a non-leaf node includes the pointing relationship to its child nodes and the minimum bounding box parameter, the minimum bounding box of the non-leaf node is the minimum three-dimensional box that surrounds the minimum bounding boxes of its leaf nodes. The third acquisition unit is used to acquire the target's location data; The first determining unit is configured to determine a spatial search area centered on the target based on observation parameters from the Earth observation system carried on the satellite; the first determining unit determines a cube with a side length of 2L centered on the target location as the spatial search area, where L=4h. s tanα,h s Where α is the flight altitude of the satellite, and α is the maximum observation angle of the Earth observation system; The search unit is used to search for target nadir point position data in the R-Tree, wherein the target nadir point position is the nadir point position located within the spatial search area; The second determining unit is used to determine the visible window of the target by the spaceborne Earth observation system based on the search results; The second determining unit includes: The sorting subunit is used to sort the target sub-satellite point position data in the search results according to the time order in which they appear during the satellite's flight. The search subunit is used to search for the first and second sub-satellite points using a binary search method. Specifically, when the satellite's current position corresponds to the sub-satellite point preceding the first sub-satellite point, the Earth observation system cannot observe the target; when the satellite's current position corresponds to the first sub-satellite point, the Earth observation system observes the target; when the satellite's current position corresponds to the second sub-satellite point, the Earth observation system observes the target; and when the satellite's current position corresponds to the sub-satellite point following the second sub-satellite point, the Earth observation system cannot observe the target. A sub-unit is defined to use the time when the satellite's position corresponds to the first nadir point as the start time of the visible window, and the time when the satellite's position corresponds to the second nadir point as the end time of the visible window.

7. The apparatus according to claim 6, characterized in that, The device further includes: The prediction unit is used to predict the volume increment of the minimum bounding box of each leaf node after the new sub-star point position is added to each leaf node of the current R-Tree. The third determining unit is used to select the leaf node with the smallest volume increment as the target leaf node. The judgment unit is used to determine whether the number of sub-star position data in the target leaf node is less than M, where M is the maximum number of index entries in each node of the R-Tree, and the number of index entries in the leaf node refers to the number of sub-star position data included. An insertion unit is used to insert the new sub-satellite point position data into the target leaf node if the determination result is yes.

8. The apparatus according to claim 7, characterized in that, The device further includes: A splitting unit is used to split the new nadir position data and the nadir position data in the target leaf node into two new leaf nodes if the judgment result is negative. An adjustment unit is used to adjust the parent nodes at all levels of the target leaf node according to the splitting result.

9. The apparatus according to claim 8, characterized in that, The device further includes: The generation unit is used to generate a parent node for the two nodes obtained by splitting the current R-Tree root node into two nodes, and to use the parent node as the new root node. A processing unit is used to increment the depth of the R-Tree by one.

10. An electronic device, characterized in that, include: A memory and a processor, the processor and the memory being communicatively connected to each other, the memory storing computer instructions, the processor executing the computer instructions to implement the steps of the method according to any one of claims 1 to 5.

11. A computer storage medium, characterized in that, The computer storage medium stores computer program instructions, which, when executed, implement the steps of the method according to any one of claims 1 to 5.

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