Method for enhancing point cloud density of laser radar in steep slope forest region

Abstract

The invention discloses an abrupt slope forest region laser radar point cloud density enhancement method, belongs to the technical field of geographic data acquisition, and can solve the problem of low density of point cloud data acquired in the prior art. The method comprises the following steps: S1, determining a first route of an airborne laser radar according to terrain information of the abrupt slope forest region, and collecting first point cloud data of the abrupt slope forest region by using the airborne laser radar according to the first route; s2, constructing a digital elevation model of the abrupt slope forest region according to the first point cloud data, and determining contour line distribution information on the digital elevation model; s3, extracting a plurality of topographic feature points at different elevations of the digital elevation model according to the contour line distribution information, and determining a second route of the airborne laser radar according to all the topographic feature points; and S4, acquiring second point cloud data of the abrupt slope forest region according to the second route by using the airborne laser radar, and determining densified point cloud data of the abrupt slope forest region according to the second point cloud data and the first point cloud data. The method is used for enhancing the point cloud data density.

Description

Technical Field

[0001] The invention relates to a method for enhancing the density of laser radar point clouds in steep slope forest areas, and belongs to the technical field of geographic data collection. Background Art

[0002] Aircraft equipped with a lidar system (referred to as "airborne lidar") can conduct ground remote sensing according to a predetermined route. With its active detection characteristics and "penetrating" detection capabilities, it is widely used in geographic surveying and mapping, geological disaster identification, forest ecological surveys and other fields.

[0003] Currently, airborne lidar typically uses horizontal flight at a fixed altitude to detect and collect data. This produces high-quality point cloud data in plains or areas with gently undulating terrain. However, in steep forested areas, due to the steep terrain gradient, the horizontal projection range of geological hazards such as landslides and dangerous rock masses is small. Using a fixed-altitude horizontal flight to collect data results in a low point cloud data density in these geological hazard areas, making it difficult to clearly visualize the terrain details in these geological hazard areas on large-scale topographic maps.

[0004] At the same time, affected by the vertical changes in climate, the distribution of trees in steep slope forest areas presents the significant characteristics of "extremely dense horizontal density and sparse vertical density". When collecting data using a fixed-altitude horizontal flight method, the stacked and connected multi-layer canopy structure will produce multiple shielding effects on the laser pulses emitted by the lidar system, resulting in a high rate of missing ground point cloud data in areas blocked by the canopy, further reducing the density of the point cloud data.

[0005] Therefore, the point cloud data collected by airborne lidar using the existing fixed-altitude horizontal flight method has the defects of low point cloud density and high point cloud data missing rate, resulting in poor quality of point cloud data, which seriously affects the accuracy of subsequent terrain modeling. Summary of the Invention

[0006] The present invention provides a method for enhancing the density of laser radar point clouds in steep slope forest areas, which can solve the problems of low point cloud density and high point cloud data missing rate of point cloud data collected by the prior art.

[0007] The present invention provides a method for enhancing the density of laser radar point clouds in steep slope forest areas, the method comprising: S1. Determine a first route of an airborne laser radar based on terrain information of a steep slope forest area, and use the airborne laser radar to collect first point cloud data of the steep slope forest area according to the first route; S2. constructing a digital elevation model of the steep slope forest area based on the first point cloud data and determining contour line distribution information on the digital elevation model; S3. Extracting a plurality of terrain feature points at different elevations of the digital elevation model according to the contour line distribution information, and determining a second route of the airborne laser radar according to all the terrain feature points; S4. Use the airborne laser radar to collect second point cloud data of the steep slope forest area according to the second route, and determine the densified point cloud data of the steep slope forest area based on the second point cloud data and the first point cloud data.

[0008] Optionally, determining the first route of the airborne laser radar according to the terrain information of the steep slope forest area in S1 specifically includes: According to the terrain information of the steep slope forest area, the steep slope forest area is horizontally divided into a plurality of grids of equal size, and a plurality of ground protrusion points and a plurality of ground depression points are selected from each grid; the number of the ground protrusion points and the number of the ground depression points are equal; A flight reference plane of the airborne laser radar is determined based on a plurality of ground protrusion points and a plurality of ground depression points, and a first route of the airborne laser radar is determined based on the flight reference plane.

[0009] Optionally, the contour line distribution information includes contour line density in different elevation intervals on the digital elevation model.

[0010] Optionally, in S3, extracting a plurality of terrain feature points at different elevations of the digital elevation model according to the contour line distribution information specifically includes: A plurality of horizontal cross sections at different elevations are arranged upward in sequence from the lowest point of the digital elevation model; an upper horizontal cross section of two adjacent horizontal cross sections on the digital elevation model is higher than a ground cover on a lower horizontal cross section, and an average spacing between the plurality of horizontal cross sections in a first elevation interval is greater than an average spacing between the plurality of horizontal cross sections in a second elevation interval; the first elevation interval is an elevation interval in which a contour line density is greater than a preset density, and the second elevation interval is an elevation interval in which a contour line density is less than the preset density; A plurality of terrain feature points are extracted on a ground contour line formed by the intersection of the digital elevation model and each horizontal cross section.

[0011] Optionally, determining the second route of the airborne laser radar according to all terrain feature points in S3 specifically includes: constructing a digital surface model of the steep slope forest area based on the first point cloud data, and determining a cover boundary line formed by the intersection of the digital surface model and each horizontal cross section; A second route of the airborne laser radar is determined according to the covered object boundary line, the ground contour line, the contour line density, the height of the ground covered object and all terrain feature points.

[0012] Optionally, determining the second route of the airborne laser radar according to the covered object boundary line, the ground contour line, the contour line density, the height of the ground covered object, and all terrain feature points specifically includes: Obtaining a plurality of track points corresponding to each horizontal cross section according to the covered object boundary line, the ground contour line, the contour line density, the height of the ground covered object, and all terrain feature points; Determine a second route of the airborne laser radar based on all track points.

[0013] Optionally, obtaining a plurality of track points corresponding to each horizontal cross section according to the covered object boundary line, the ground contour line, the contour line density, the height of the ground covered object, and all terrain feature points specifically includes: According to the maximum distance between the boundary line of the cover and the ground contour line on each horizontal cross section, multiple terrain feature points on the corresponding horizontal cross section are horizontally translated in a direction away from the steep slope forest area to obtain multiple translated feature points; The positions of the multiple translation feature points are adjusted according to the contour line density, the height of the ground cover and the constraint conditions to obtain multiple track points corresponding to each horizontal cross section; the constraint conditions include the divergence angle constraint, scanning range constraint, flight safety constraint and scanning overlap constraint of the laser radar system.

[0014] Optionally, adjusting the positions of multiple translation feature points according to the contour line density, the height of the ground cover, and the constraint conditions to obtain multiple track points corresponding to each horizontal cross section specifically includes: According to the contour line density of the elevation interval of each horizontal cross section and the height of the ground cover on the corresponding horizontal cross section, multiple translation feature points on the corresponding horizontal cross section are vertically moved upward to obtain multiple vertically moved feature points; The positions of the plurality of vertical displacement feature points are adjusted according to the constraint conditions to obtain a plurality of track points corresponding to each horizontal cross section.

[0015] Optionally, determining the second route of the airborne laser radar according to all track points specifically includes: Connect multiple track points corresponding to the same horizontal cross section in sequence to form a track line; Multiple track lines corresponding to different horizontal cross-sections are connected in a "bow" shape from bottom to top or from top to bottom to form a second route of the airborne laser radar.

[0016] Optionally, determining the densified point cloud data of the steep slope forest area according to the second point cloud data and the first point cloud data in S4 specifically includes: The second point cloud data and the first point cloud data are point cloud fused to obtain the densified point cloud data of the steep slope forest area.

[0017] The beneficial effects that the present invention can produce include: The present invention constructs a digital elevation model based on first point cloud data from a steep-slope forest area, extracts terrain feature points from different elevations in the digital elevation model based on the contour distribution information of the digital elevation model, and then determines a second flight path based on these terrain feature points. This second flight path is able to adapt to the topographic variations of the steep-slope forest area, fluctuating with the terrain. This effectively avoids data holes in the second point cloud data collected based on the second flight path in areas with complex terrain, resulting in a more uniform spatial distribution and a higher point cloud density. The density of the point cloud data is then enhanced by fusing the first and second point cloud data, thereby improving the quality of the point cloud data.

[0018] The present invention extracts terrain feature points by sequentially arranging multiple horizontal cross sections at different elevations upward from the lowest point of a digital elevation model. When arranging multiple horizontal cross sections, by making the upper horizontal cross section of two adjacent horizontal cross sections higher than the ground cover on the lower horizontal cross section, the layout positions of the horizontal cross sections can be matched with the interlayer gaps of the vertical band spectrum of the steep slope forest area, that is, the horizontal cross sections are arranged in the interlayer gaps of vertically distributed vegetation and other ground covers. In this way, the wave transmission characteristics of the interlayer gaps can be fully utilized to collect data, and the ground cover can be prevented from shielding the laser pulse and causing the loss of ground point cloud data, thereby reducing the loss rate of ground point cloud data.

[0019] The present invention can adapt the layout density of horizontal cross-sections to the slope of steep forest areas by making the average spacing of multiple horizontal cross-sections in the first elevation interval where the contour line density is greater than the preset density greater than the average spacing of multiple horizontal cross-sections in the second elevation interval where the contour line density is less than the preset density. That is, more horizontal cross-sections are laid out in areas with greater slopes. In this way, more terrain feature points can be extracted in areas with larger slopes, and the collection route of the second route obtained based on the terrain feature points in areas with larger slopes can be denser, thereby increasing the point cloud density of the second point cloud data in areas with larger slopes, and further improving the data quality of the densified point cloud data.

[0020] The present invention extracts ground contours and terrain feature points based on a digital elevation model, and extracts ground cover boundary lines based on a digital surface model. The position of the terrain feature points is then adjusted based on the ground contours, boundary lines, and height of the ground cover to obtain a second flight path. This ensures that the second flight path closely matches the terrain variations in the steep-slope forest area while effectively preventing interference and collision with the ground cover. This balances data collection quality and flight safety, and allows the method to be applied to steep-slope forest areas of varying terrain, broadening its applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a method for enhancing the density of lidar point clouds in steep slope forest areas provided by an embodiment of the present invention; Figure 2 Schematic diagrams of the layout of horizontal cross-sections on four slope shapes provided by embodiments of the present invention, wherein (a) is a schematic diagram of the layout of horizontal cross-sections on a straight slope, (b) is a schematic diagram of the layout of horizontal cross-sections on a convex slope, (c) is a schematic diagram of the layout of horizontal cross-sections on a concave slope, and (d) is a schematic diagram of the layout of horizontal cross-sections on a stepped slope; Figure 3 A schematic diagram of extracting terrain feature points provided by an embodiment of the present invention; Figure 4 A schematic diagram of the movement of terrain feature points provided by an embodiment of the present invention; Figure 5 A schematic diagram of a scanning overlap area provided by an embodiment of the present invention; Figure 6 A schematic diagram of the layout of a second route on a straight slope provided by an embodiment of the present invention; Figure 7 A schematic diagram of the layout of the second route on a convex slope provided by an embodiment of the present invention; Figure 8 A schematic diagram of the layout of the second route on a concave slope provided by an embodiment of the present invention; Figure 9 A schematic diagram of the layout of the second route on a stepped slope provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0023] The embodiment of the present invention provides a method for enhancing the density of laser radar point clouds in steep slope forest areas. Figure 1 As shown, the method includes: S1. Determine a first route of the airborne laser radar based on the terrain information of the steep slope forest area, and use the airborne laser radar to collect first point cloud data of the steep slope forest area according to the first route.

[0024] Airborne lidar refers to an aircraft equipped with a lidar system. The aircraft can be a drone, helicopter or other flying equipment that can carry a lidar system and perform data collection tasks.

[0025] In S1, the first flight path of the airborne laser radar is determined based on the terrain information of the steep slope forest area, including: Based on the terrain information of the steep-slope forest area, the area was horizontally divided into multiple grids of equal size. Multiple ground convex points and concave points were selected from each grid; the number of ground convex points and concave points was equal. The flight reference plane for the airborne laser radar was determined based on the multiple ground convex points and concave points, and the first flight path of the airborne laser radar was determined based on the flight reference plane.

[0026] Among them, the terrain information of the steep slope forest area can be obtained based on the existing remote sensing images or topographic maps of the steep slope forest area.

[0027] This embodiment does not limit the number of grids or the number of ground protrusions and ground depressions selected in each grid. However, it is understood that the greater the number of grids or the number of ground protrusions and ground depressions selected in each grid, the more evenly the multiple ground protrusions and ground depressions are distributed within the steep slope forest area, and the more reasonable the calculated flight reference plane.

[0028] This embodiment is described using an example in which the number of grids is no less than five, and the number of ground convex points and ground concave points selected from each grid is two. The two ground convex points selected from each grid are the highest ground convex point and the second highest ground convex point in the grid, and the two ground concave points selected from each grid are the lowest ground concave point and the second lowest ground concave point in the grid.

[0029] In this embodiment, the elevation of the flight reference plane of the airborne laser radar is determined by calculating the arithmetic mean of the elevations of multiple ground convex points and multiple ground concave points. The calculation formula is: (1) In formula (1), is the elevation of the flight datum of the airborne lidar, For the The elevation of a ground protrusion point, For the The elevation of a ground protrusion point, is the number of ground protrusions or ground depressions and .

[0030] After determining the flight reference plane, a high-level flight path can be planned using existing technology to obtain a first flight path for the airborne lidar. This first flight path is located on a horizontal plane at a fixed elevation. Then, in this embodiment, the airborne lidar is used to fly horizontally along the first flight path and collect first point cloud data for the steep forest area.

[0031] S2. Construct a digital elevation model (DEM) of the steep slope forest area based on the first point cloud data, and determine contour line distribution information on the DEM.

[0032] Specifically, the contour distribution information includes the contour density of different elevation intervals on the DEM.

[0033] S3. Extract multiple terrain feature points at different elevations of the DEM according to the contour line distribution information, and determine the second route of the airborne laser radar based on all the terrain feature points.

[0034] In S3, multiple terrain feature points are extracted at different elevations of the DEM based on the contour distribution information, including: Multiple horizontal cross sections at different elevations are laid out from the lowest point of the DEM upwards, and multiple terrain feature points are extracted on the ground contour line formed by the intersection of the DEM and each horizontal cross section.

[0035] Specifically, the layout of multiple horizontal cross sections must meet the following two pre-conditions: 1) Ensure that the upper horizontal cross section of two adjacent horizontal cross sections on the DEM is higher than the ground cover on the lower horizontal cross section.

[0036] As mountain vegetation increases in altitude, it develops a zonal distribution pattern, known as a vertical zonation spectrum. A typical characteristic of a vertical zonation spectrum is a gradient of vegetation types, with regularly spaced vertical gaps forming between different vegetation types and between different layers of the same vegetation type. For example, at an altitude of 2000-3000 m, vertical niche gaps of 1-3 m are common between the 20-30 m tall tree layer, the 5-8 m tall shrub layer, and the 0.5-1 m tall herb layer.

[0037] In this embodiment, by making the upper horizontal cross-section of two adjacent horizontal cross-sections higher than the ground cover on the lower horizontal cross-section, the layout position of the horizontal cross-sections can be matched with the inter-layer gaps of the vertical band spectrum of the steep slope forest area. That is, the horizontal cross-sections are arranged in the inter-layer gaps of vertically distributed vegetation and other ground covers, so that the terrain feature points at the inter-layer gaps can be extracted.

[0038] Since the subsequent steps will lay out the second route and collect the second point cloud data based on these terrain feature points, extracting the terrain feature points at the interlayer gaps can make full use of the wave transmission characteristics of the interlayer gaps to collect the second point cloud data, avoiding the ground cover from shielding the laser pulse and causing the loss of ground point cloud data.

[0039] 2) Ensure that the average spacing of multiple horizontal cross sections in the first elevation interval where the contour line density is greater than the preset density is greater than the average spacing of multiple horizontal cross sections in the second elevation interval where the contour line density is less than the preset density.

[0040] Since contour line density is positively correlated with slope, the greater the contour line density, the greater the slope. This embodiment adapts the density of horizontal cross sections to the slope of the steep forest area by making the average spacing of multiple horizontal cross sections within the first elevation interval greater than the average spacing of multiple horizontal cross sections within the second elevation interval. That is, more horizontal cross sections are laid out in areas with greater slopes, allowing more terrain feature points to be extracted in areas with greater slopes.

[0041] Since the subsequent steps will lay out the second route and collect the second point cloud data based on these terrain feature points, extracting more terrain feature points in the area with a larger slope can make the collection route of the second route in the area with a larger slope more dense, thereby increasing the point cloud density in the area with a larger slope.

[0042] It is understandable that because contour density is positively correlated with slope, that is, with the slope of the slope's longitudinal profile, the slope shape of steep forest areas can be divided into straight slopes, convex slopes, concave slopes, and stepped slopes based on the contour density of different elevation intervals on the DEM. The criteria for determining slope shape are shown in Table 1.

[0043] Table 1 Criteria for judging slope shape

[0044] According to the above two preset conditions, multiple horizontal cross sections are arranged on the four slope shapes, and the vertical distribution characteristics of multiple horizontal cross sections on the four slope shapes can be obtained: the vertical distribution of multiple horizontal cross sections on the straight slope is generally uniform, such as Figure 2 As shown in (a) in the figure, the vertical distribution of multiple horizontal cross sections on the convex slope is generally sparse at the top and dense at the bottom, as shown in Figure 2 As shown in (b) in the figure, the vertical distribution of multiple horizontal cross sections on the concave slope is generally dense at the top and sparse at the bottom, as shown in Figure 2 As shown in (c) in the figure, the vertical distribution of multiple horizontal cross sections on the stepped slope is generally sparse and dense, as shown in the figure. Figure 2 It is worth noting that in order to accurately reflect the terrain characteristics of alternating steep slopes (risers) and platforms (treads) on the stepped slope, at least one horizontal cross section must be arranged on each steep slope and each platform of the stepped slope.

[0045] Furthermore, after the horizontal cross sections are laid out according to the above steps, this embodiment can also combine the actual distribution of vegetation in the vertical direction of the steep slope forest area, add horizontal cross sections in local areas with sparse forest stands, and encrypt the horizontal cross sections of these local areas to further improve the density of subsequent data collection.

[0046] Then, multiple terrain feature points are extracted on the ground contour line formed by the intersection of DEM and each horizontal cross section, such as Figure 3 As shown, multiple terrain feature points include ridge turning points, valley turning points, inflection points, etc. The lines connecting adjacent feature key points can truly reflect the curvature changes of the terrain.

[0047] In S3, the second route of the airborne laser radar is determined based on all terrain feature points, including: 1) Construct a digital surface model (DSM) of the steep slope forest area based on the first point cloud data, and determine the cover boundary formed by the intersection of the DSM and each horizontal cross section.

[0048] It's worth noting that the DSM includes elevation information for surface buildings, bridges, vegetation, and other ground cover, while the DEM only includes elevation information for the ground, not for ground cover. That is, the DSM includes elevation information for all other surface areas besides the ground, based on the DEM. In this embodiment, each horizontal cross section is intersected with the DSM and DEM to obtain ground contours and ground cover boundaries. Therefore, each horizontal cross section has a ground contour and a ground cover boundary.

[0049] 2) Based on the maximum distance between the boundary line of the cover and the ground contour line on each horizontal cross section, multiple terrain feature points on the corresponding horizontal cross section are horizontally translated in the direction away from the steep slope forest area to obtain multiple translated feature points.

[0050] For example, if the terrain feature points on a horizontal cross section are as follows Figure 4 As shown, and the maximum distance between the boundary line of the cover and the ground contour line on the horizontal cross section is D, multiple terrain feature points can be horizontally translated away from the slope by a distance D, and the following can be obtained: Figure 4 Multiple translation feature points are shown.

[0051] 3) According to the contour line density of the elevation interval of each horizontal cross section and the height of the ground cover on the corresponding horizontal cross section, multiple translation feature points on the corresponding horizontal cross section are vertically moved upward to obtain multiple vertically moved feature points.

[0052] For example, let the maximum height of the ground cover on a horizontal cross section be , the vertical upward movement distance of the translation feature point on the horizontal cross section is If the contour line density of the elevation interval where the horizontal cross section is located is less than the preset density, then If the contour density of the elevation interval where the horizontal cross section is located is greater than the preset density, then This will make the vertical feature points in the steep slope area with high contour line density closer to the slope surface, improving the quality of subsequent data collection. The multiple vertical displacement feature points obtained are as follows Figure 4 shown.

[0053] Furthermore, if Figure 2 As shown in (a) to (d) in FIG, this embodiment can also describe the spatial position of the vertical displacement feature point according to the relative position relationship between the vertical displacement feature point and the terrain feature point as follows: (2) In formula (2), is the distance between the vertical displacement feature point and the terrain feature point; It is the maximum distance between the boundary line of the cover and the ground contour line, that is, the distance between the horizontal feature point and the terrain feature point; is the distance between the vertical feature point and the horizontal feature point.

[0054] (3) In formula (2), The angle between the line connecting the vertical feature point and the terrain feature point and the corresponding horizontal cross section is, is the distance between the vertical feature point and the horizontal feature point, is the distance between the horizontal feature point and the terrain feature point.

[0055] According to the spatial position relationship of the vertical displacement feature point, it can be seen that the horizontal distance between the vertical displacement feature point and the slope surface is , and the distance between horizontal feature points and terrain feature points The relationship between them satisfies: (4) In formula (2), is the horizontal distance between the vertical displacement feature point and the slope surface, is the distance between the horizontal feature point and the terrain feature point.

[0056] 4) Adjust the positions of multiple vertical feature points based on constraints to obtain multiple track points corresponding to each horizontal cross section. Constraints include the laser radar system's divergence angle constraint, scanning range constraint, flight safety constraint, and scanning overlap constraint.

[0057] This embodiment superimposes and analyzes multiple vertical feature points and the DSM, and locally optimizes and adjusts the positions of the multiple vertical feature points through collision detection and constraint conditions. Specifically, when a vertical feature point has a collision risk, the vertical feature point is translated away from the slope to a safe position. When a vertical feature point does not meet the constraint conditions, the vertical feature point can be moved in a direction that meets the constraint conditions.

[0058] 5) Connect multiple track points corresponding to the same horizontal cross section in sequence to form a track line.

[0059] It should be noted that the scanning overlap constraint in the constraint condition can be pre-set according to relevant standards and data acquisition requirements. Figure 5 As shown in the figure, the scanning areas of the two track lines corresponding to adjacent horizontal cross sections on the slope surface should ensure a certain amount of scanning overlap to meet the vertical scanning overlap constraint. In addition, when the track lines in the platform area of ​​the stepped slope cannot effectively cover the platform area, one or more track lines can be added horizontally on one or both sides of the existing track lines to meet the horizontal scanning overlap constraint.

[0060] 6) Connect multiple track lines corresponding to different horizontal cross sections in a “bow” shape from bottom to top or from top to bottom to form the second route of the airborne laser radar. Specifically, the schematic diagrams of the second route on the four slope shapes are as follows: Figures 6 to 9 shown.

[0061] S4. Use the airborne laser radar to collect second point cloud data of the steep slope forest area according to the second route, and determine the densified point cloud data of the steep slope forest area based on the second point cloud data and the first point cloud data.

[0062] In S4, the densified point cloud data of the steep slope forest area is determined based on the second point cloud data and the first point cloud data, specifically including: The second point cloud data is fused with the first point cloud data to obtain the densified point cloud data of the steep slope forest area.

[0063] The present invention constructs a digital elevation model based on first point cloud data from a steep-slope forest area, extracts terrain feature points from different elevations in the digital elevation model based on the contour distribution information of the digital elevation model, and then determines a second flight path based on these terrain feature points. This second flight path is able to closely follow the topographic variations of the steep-slope forest area, fluctuating with the terrain. This effectively avoids data holes in complex terrain areas when collecting the second point cloud data, resulting in a more uniform spatial distribution of the second point cloud data and a higher point cloud density. The density of the point cloud data is then enhanced by fusing the first and second point cloud data, thereby improving the quality of the point cloud data.

[0064] The present invention extracts terrain feature points by sequentially arranging multiple horizontal cross sections at different elevations upward from the lowest point of a digital elevation model. When arranging multiple horizontal cross sections, by making the upper horizontal cross section of two adjacent horizontal cross sections higher than the ground cover on the lower horizontal cross section, the layout positions of the horizontal cross sections can be matched with the interlayer gaps of the vertical band spectrum of the steep slope forest area, that is, the horizontal cross sections are arranged in the interlayer gaps of vertically distributed vegetation and other ground covers. In this way, the wave transmission characteristics of the interlayer gaps can be fully utilized to collect data, and the ground cover can be prevented from shielding the laser pulse and causing the loss of ground point cloud data, thereby reducing the loss rate of ground point cloud data.

[0065] The present invention can adapt the layout density of horizontal cross-sections to the slope of steep forest areas by making the average spacing of multiple horizontal cross-sections in the first elevation interval where the contour line density is greater than the preset density greater than the average spacing of multiple horizontal cross-sections in the second elevation interval where the contour line density is less than the preset density. That is, more horizontal cross-sections are laid out in areas with greater slopes. In this way, more terrain feature points can be extracted in areas with larger slopes, and the collection route of the second route obtained based on the terrain feature points in areas with larger slopes can be denser, thereby increasing the point cloud density of the second point cloud data in areas with larger slopes, and further improving the data quality of the densified point cloud data.

[0066] The present invention extracts ground contours and terrain feature points based on a digital elevation model, and extracts ground cover boundary lines based on a digital surface model. The position of the terrain feature points is then adjusted based on the ground contours, boundary lines, and height of the ground cover to obtain a second flight path. This ensures that the second flight path closely matches the terrain variations in the steep-slope forest area while effectively preventing interference and collision with the ground cover. This balances data collection quality and flight safety, and allows the method to be applied to steep-slope forest areas of varying terrain, broadening its applicability.

[0067] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for enhancing the density of laser radar point clouds in steep slope forest areas, characterized in that: The method comprises: S1. Determine a first route of an airborne laser radar based on terrain information of a steep slope forest area, and use the airborne laser radar to collect first point cloud data of the steep slope forest area according to the first route; S2. constructing a digital elevation model of the steep slope forest area based on the first point cloud data and determining contour line distribution information on the digital elevation model; S3. Extracting a plurality of terrain feature points at different elevations of the digital elevation model according to the contour line distribution information, and determining a second route of the airborne laser radar according to all the terrain feature points; S4. Use the airborne laser radar to collect second point cloud data of the steep slope forest area according to the second route, and determine the densified point cloud data of the steep slope forest area based on the second point cloud data and the first point cloud data.

2. The method according to claim 1, characterized in that In S1, the first flight path of the airborne laser radar is determined based on the terrain information of the steep slope forest area, including: According to the terrain information of the steep slope forest area, the steep slope forest area is horizontally divided into a plurality of grids of equal size, and a plurality of ground protrusion points and a plurality of ground depression points are selected from each grid; the number of the ground protrusion points and the number of the ground depression points are equal; A flight reference plane of the airborne laser radar is determined based on a plurality of ground protrusion points and a plurality of ground depression points, and a first route of the airborne laser radar is determined based on the flight reference plane.

3. The method according to claim 1, characterized in that The contour line distribution information includes the contour line density of different elevation intervals on the digital elevation model.

4. The method according to claim 3, characterized in that In S3, a plurality of terrain feature points are extracted at different elevations of the digital elevation model according to the contour line distribution information, specifically including: A plurality of horizontal cross sections at different elevations are arranged upward in sequence from the lowest point of the digital elevation model; an upper horizontal cross section of two adjacent horizontal cross sections on the digital elevation model is higher than a ground cover on a lower horizontal cross section, and an average spacing between the plurality of horizontal cross sections in a first elevation interval is greater than an average spacing between the plurality of horizontal cross sections in a second elevation interval; the first elevation interval is an elevation interval in which a contour line density is greater than a preset density, and the second elevation interval is an elevation interval in which a contour line density is less than the preset density; A plurality of terrain feature points are extracted on a ground contour line formed by the intersection of the digital elevation model and each horizontal cross section.

5. The method according to claim 4, characterized in that S3 determines the second route of the airborne laser radar according to all terrain feature points, specifically including: constructing a digital surface model of the steep slope forest area based on the first point cloud data, and determining a cover boundary line formed by the intersection of the digital surface model and each horizontal cross section; A second route of the airborne laser radar is determined according to the covered object boundary line, the ground contour line, the contour line density, the height of the ground covered object and all terrain feature points.

6. The method according to claim 5, characterized in that Determining a second route of the airborne laser radar according to the covered object boundary line, the ground contour line, the contour line density, the height of the ground covered object, and all terrain feature points specifically includes: Obtaining a plurality of track points corresponding to each horizontal cross section according to the covered object boundary line, the ground contour line, the contour line density, the height of the ground covered object, and all terrain feature points; Determine a second route of the airborne laser radar based on all track points.

7. The method according to claim 6, characterized in that According to the boundary line of the covering object, the ground contour line, the density of the contour line, the height of the ground covering object and all terrain feature points, a plurality of track points corresponding to each horizontal cross section are obtained, specifically including: According to the maximum distance between the boundary line of the cover and the ground contour line on each horizontal cross section, multiple terrain feature points on the corresponding horizontal cross section are horizontally translated in a direction away from the steep slope forest area to obtain multiple translated feature points; The positions of the multiple translation feature points are adjusted according to the contour line density, the height of the ground cover and the constraint conditions to obtain multiple track points corresponding to each horizontal cross section; the constraint conditions include the divergence angle constraint, scanning range constraint, flight safety constraint and scanning overlap constraint of the laser radar system.

8. The method according to claim 7, characterized in that Adjusting the positions of the plurality of translation feature points according to the density of the contour lines, the height of the ground cover, and the constraint conditions to obtain a plurality of track points corresponding to each horizontal cross section specifically includes: According to the contour line density of the elevation interval of each horizontal cross section and the height of the ground cover on the corresponding horizontal cross section, multiple translation feature points on the corresponding horizontal cross section are vertically moved upward to obtain multiple vertically moved feature points; The positions of the plurality of vertical displacement feature points are adjusted according to the constraint conditions to obtain a plurality of track points corresponding to each horizontal cross section.

9. The method according to claim 6, characterized in that Determining a second route of the airborne laser radar according to all the track points specifically includes: Connect multiple track points corresponding to the same horizontal cross section in sequence to form a track line; The multiple track lines corresponding to different horizontal cross sections are connected in a "bow" shape from bottom to top or from top to bottom to form the second route of the airborne laser radar.

10. The method according to claim 1, characterized in that Determining the densified point cloud data of the steep slope forest area according to the second point cloud data and the first point cloud data in S4 specifically includes: The second point cloud data and the first point cloud data are point cloud fused to obtain the densified point cloud data of the steep slope forest area.

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