The first zoning planning method based on gap identification

Abstract

This application discloses the first zoning planning method based on gap identification, which includes: a robot walking along a wall and identifying target gaps to complete at least one closed-loop path, and forming the first zoning by enclosing at least one ring of walls with at least one target gap, so that the robot can enter the unmapped area from the first zoning after passing through the identified target gap.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of regional planning, and in particular to a first partition planning method based on gap identification. BACKGROUND

[0002] For a sweeping robot, partition sweeping is a very important function. Although a home environment is a highly structured environment, currently, a sweeping robot basically uses laser radar or depth camera detection technology to obtain entire environment contour data before performing regional division. Therefore, the sweeping robot is relatively slow in dividing a first room region in mapping and navigation.

[0003] In a robot regional division method disclosed in Chinese Patent Application No. 202010764284.7, after the robot ends edge walking in a preset edge direction, a door at a position of a reference division boundary line is identified according to image feature information of an image collected by a camera of the robot at the position of the reference division boundary line, and the reference division boundary line is marked in a laser map. The purpose is to divide an indoor working region into different room sub-regions through the door. Since the marking in the laser map is for point cloud information processing, the division speed of the room sub-regions is reduced. Moreover, during the robot performing edge walking in the preset edge direction, the reference division boundary line is set in a pre-constructed global laser map around the same room region, and a door frame is not directly identified. Therefore, the robot cannot quickly divide a first room region that meets an actual room environment layout without constructing a global map, which is not conducive to providing a reference map region for subsequent partition. SUMMARY

[0004] The application discloses a first partition planning method based on gap identification. The specific technical solutions are as follows:

[0005] The first partition planning method based on gap identification comprises the following steps: a robot walks along a wall and identifies a target gap to complete at least one closed loop path, and encloses a wall chain searched with at least one target gap in a first partition, so that the robot enters an un-mapped region from the first partition through the identified target gap. In an actual planning room region scenario, the robot encloses a vertical corner line and a target gap to form a first room region by walking along a complete loop. The first room region is a first partition divided by the robot in a target region, and a map of the first partition is constructed correspondingly, thereby providing a reference map region for subsequent partition of the robot and accelerating the mapping process of the robot.

[0006] Further, the specific method of the first partition planning method comprises: step A1, the robot searches for a wall, then walks along the wall and identifies a target gap, while constructing a map, and walks along the target gap when the target gap is identified until the robot walks a closed loop path, obtains a wall chain with at least one target gap reserved in at least one round, and encloses the first partition with the wall chain with at least one target gap reserved in at least one round, and sets a partition map according to the first partition; then step A2 is executed; step A2, the robot enters an un-mapped area from the first partition through the target gap identified in step A1. As can be seen from the technical solutions of steps A1 and A2, the present application takes a closed loop path and a target gap, which helps to divide the first partition, i.e., the first independent space, in the environment, and determines the passable position information from the first independent space in the environment to the un-explored area based on the target gap. And the first partition is created in a region with a complex layout, which has good applicability.

[0007] Further, in step A1, the method for the robot to search for a wall comprises: the robot collects an environment image, extracts wall vertical projection lines in the environment image, and then identifies a combination of a plurality of wall vertical projection lines located in the same plane or the same curved surface as a wall to be searched. When the robot walks along a wall, a plane or a curved surface where a combination of a plurality of wall vertical projection lines located in the same plane or the same curved surface extracted in the same direction is regarded as a wall surface extending in the direction.

[0008] Further, in step A1, the method for the robot to walk a closed loop path comprises: step A101, when the robot identifies a current wall, the robot walks along the current wall in a preset clockwise direction, which can be in a clockwise direction or a counterclockwise direction, while determining whether the robot identifies the target gap, yes, then step A102 is executed, otherwise step A103 is executed; step A102, determining whether the robot walks back to a preset edge starting point, yes, then it is determined that the robot walks a closed loop path, otherwise step A103 is executed; step A103, the robot walks along the boundary formed by the position of the target gap in step A101 and keeps searching for a wall; then step A104 is executed; step A104, when the robot identifies a next wall, the robot updates the next wall as the current wall, and then step A101 is executed. The target gap between the two walls adjacent in position is identified, or the next wall is searched when the target gap is identified and walked along, until the robot walks back to the preset edge starting point used when step A101 is first executed, and the robot has walked a closed loop path.

[0009] Further, when the robot walks along a closed loop path, the robot forms a wall chain with the walls and target gaps identified in steps A101 to A104 in the preset clockwise direction, and the projections of the walls and target gaps on the ground form a continuous line segment to form a complete closed loop.

[0010] Further, in a frame of environment image collected by the robot in real time, the target gap is between two adjacent walls; the target gap is surrounded by the vertical projection lines of the walls on the opposite sides of the two adjacent walls, forming two vertical projection lines of the walls corresponding to the target gap; wherein the distance between the two endpoints of the target gap is within a preset width threshold range, and the intersection points of the extended lines of the two vertical projection lines of the walls corresponding to the target gap are within a preset projection distance threshold range from the nearest endpoints of the two vertical projection lines of the walls corresponding to the target gap. Thus, the size characteristics and positional relationship of the two vertical projection lines of the walls in a frame of environment image are used to define the target gap, providing positional and dimensional basis for the robot to identify the target gap.

[0011] Further, the method for the robot to identify the target gap comprises: the robot collects an environment image and extracts a plurality of straight line segments from the environment image; according to the length characteristics, angle characteristics and number characteristics of the line segments, two reference vertical projection lines and one reference horizontal projection line forming a cross relationship are selected from the plurality of straight line segments; according to a preset door frame size condition, two wall vertical projection lines and one door beam line used to form a door frame are selected from the two reference vertical projection lines and one reference horizontal projection line forming a cross relationship, and it is determined that the two wall vertical projection lines and one door beam line form the target gap. Thus, in the case that the reference vertical projection lines and the reference horizontal projection lines that cannot form a cross relationship are excluded from the length characteristics of a single line segment, the angle characteristics between two line segments and the number characteristics of the cumulative extracted straight line segments, the preset door frame size condition is used for further screening to reduce the number of straight line segment samples required for screening wall vertical projection lines and door beam lines, and to improve the accuracy of the robot identifying the door frame.

[0012] Further, the method of screening two reference vertical projection lines and one reference horizontal projection line forming intersection relationship from the plurality of straight line segments according to the length feature, the angle feature and the number feature comprises: step A111, screening straight line segments perpendicular to the ground from the plurality of straight line segments; then in the screened straight line segments perpendicular to the ground, selecting straight line segments with length greater than a preset wall height threshold as reference vertical projection lines; then executing step A112; step A112, judging whether the number of the reference vertical projection lines marked in step A111 is less than the value two, yes, determining that the robot cannot screen two wall vertical projection lines from the environment image, otherwise executing step A113; step A113, screening straight line segments with length in a preset width threshold range within a preset projection distance threshold range corresponding to the center of the environment image, and then marking the screened straight line segments with length in the preset width threshold range as reference horizontal projection lines; then executing step A114; step A114, judging whether the number of the reference horizontal projection lines marked in step A113 is less than the value one, yes, determining that the robot cannot screen a door beam line from the environment image, otherwise executing step A115; step A115, screening a reference horizontal projection line conforming to a door structure by enumerating the reference vertical projection lines and the reference horizontal projection lines, and then executing step A116; wherein the reference horizontal projection line conforming to the door structure is a reference horizontal projection line forming intersection relationship with the two reference vertical projection lines; step A116, judging whether the number of the reference horizontal projection lines conforming to the door structure screened in step A115 is greater than the value one, yes, executing step A117, otherwise determining that the robot cannot screen a door beam line from the environment image; step A117, obtaining a plurality of groups of two reference vertical projection lines and one reference horizontal projection line forming intersection relationship; then in each group of two reference vertical projection lines and one reference horizontal projection line forming intersection relationship, marking the two reference vertical projection lines as two wall vertical projection lines, and marking the one reference horizontal projection line as one door beam line; wherein the extension lines of the two reference vertical projection lines intersect. In summary, the robot determines two wall vertical projection lines and one door beam line as candidate door frame component line segments by executing steps A111 to A117. Then the robot determines the direction information of the door frame in which the door beam line is located relative to the current position of the robot according to the positional relationship between the center point of each door beam line and the intersection point between the extension lines of the two wall vertical projection lines, and also determines the entrance and exit position of the first partition.

[0013] Further, the method for selecting two wall vertical projection lines and one door beam line to form the door frame from the two reference vertical projection lines and one reference horizontal projection line that form an intersection relationship, based on the preset door frame size conditions, includes: step A118, marking the set of two reference vertical projection lines and one reference horizontal projection line that form an intersection relationship determined in step A117 as a set of candidate door frame lines; then executing step A119; step A119, determining whether the physical distance between the vertical corner lines corresponding to the two reference vertical projection lines in the set of candidate door frame lines is within the preset door width distance range, if yes, executing step A120, otherwise, no two wall vertical projection lines to form the door frame can be selected; wherein, the robot uses a depth sensor to detect the physical distance between the vertical corner lines corresponding to the two reference vertical projection lines; step A120, calculating one of the door beam lines in the set of candidate door frame lines. The ratio between the length of the reference horizontal projection line and the physical distance is used to calculate the length of the vertical corner line corresponding to each reference vertical projection line based on this ratio and the length of each reference vertical projection line. Then, step A121 is executed. Step A121: Determine whether the length of the vertical corner line corresponding to each reference vertical projection line in a set of candidate door frame lines is within the preset door frame height range. If yes, mark the two reference vertical projection lines in a set of candidate door frame lines as two wall vertical projection lines used to form the door frame, and mark one reference horizontal projection line in a set of candidate door frame lines as a door beam line used to form the door frame; otherwise, no two wall vertical projection lines used to form the door frame can be selected. The target gap includes the door frame. The reference vertical projection line is the projection line formed by the robot collecting the vertical corner line into the coordinate system of the environmental image. The vertical corner line is perpendicular to the ground where the robot walks. In summary, by executing steps A118 to A121, the robot converts the vertical projection lines from pixel size to physical size and, based on the physical size, determines the two vertical projection lines of the walls and one lintel line used to form the door frame. It eliminates the interference of misjudgment of door leaf and side wall lines perpendicular to the ground, constructs a simplified model of the door frame, and obtains the vertical projection lines of the walls and lintel line that conform to the simplified model of the aforementioned door frame, thus realizing the identification of a complete and accurate door frame in the first partition.

[0014] Furthermore, in step A121, the angle formed by the intersection points of the two vertical projection lines of the walls marked within a set of candidate door frame lines and the door beam line marked within the same set of candidate door frame lines in step A121 with the center of the environmental image is greater than a preset angle threshold; wherein, the length of the door beam line marked within the same set of candidate door frame lines in step A121 is greater than a preset door beam projection length. This reflects the positional relationship between the two vertical projection lines of the walls within the environmental image, simplifying the door beam model in terms of both angle and door beam line length features. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a door frame to be identified in an environmental image disclosed in an embodiment of this application. The diagram shows a vertical projection line A1B1 on the wall and a door beam line B1C1, which are captured by the robot in front of or directly below the door frame. The robot's camera is set to face the ceiling.

[0016] Figure 2 This is a flowchart of the specific steps included in step A of the sequential execution disclosed in an embodiment of this application.

[0017] Figure 3 This is a flowchart of a method for a robot to complete at least one closed-loop path in step A1 of an embodiment of this application.

[0018] Figure 4 This application discloses a flowchart of a method for selecting one reference horizontal projection line and two reference vertical projection lines that form an intersecting relationship before a robot identifies a target gap.

[0019] Figure 5 This application discloses a flowchart of a method for a robot to select two vertical projection lines of the walls and one lintel line to form a door frame, according to one embodiment of the present application. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. To further illustrate the embodiments, the present invention provides accompanying drawings. These drawings are part of the disclosure of the present invention, mainly used to illustrate the embodiments, and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments.

[0021] To address the technical challenges related to mapping the first partition, this application discloses a first partition planning method based on gap recognition. The method is executed by a robot. To ensure rapid response and improve mapping efficiency, the robot can use a monocular camera for image acquisition, identifying walls and gaps within the acquired wall images. Mapping is performed simultaneously with image acquisition and gap recognition. Alternatively, using a binocular camera or depth sensor for image acquisition and recognition can also achieve the desired recognition efficiency and partition mapping effect. The first partition planning method includes:

[0022] The robot completes at least one closed-loop path by walking along walls and identifying target gaps, forming the first zone by enclosing at least one chain of walls with at least one target gap. The prerequisite for the robot to walk along walls and identify target gaps is that it first searches for the physical elements that make up the walls. These physical elements can be images of vertical corner lines, arranged along a certain direction to form the walls, thus establishing the foundation for the robot's wall-walking. The robot's actions of identifying target gaps, walking along walls, and building the map are executed simultaneously. If the robot identifies a wall... For a target gap within the wall, a door frame is marked on the wall. The robot then walks along the marked door frame, which can be understood as continuing to walk along the door frame boundary. By walking along the door frame boundary and identifying the target gap, multiple closed-loop paths can be continuously traversed within the same room area without entering a new area through the target gap. Each closed-loop path corresponds to the collection and combination of a wall chain (not necessarily a closed wall chain, but composed of multiple links connected together; each link can be regarded as a path parallel to the robot's movement along the wall, and also as the horizontal outline of the wall). At least one target gap will be identified in the combined wall chain.

[0023] To improve mapping and region division efficiency, when the robot completes a closed-loop path for the first time, it encloses the first partition with at least one wall chain that has a target gap. After passing through the identified target gap, the robot enters the unmapped area from the first partition.

[0024] In the actual scenario of planning a room area, the robot completes a full circle to enclose the first room area by collecting the vertical corner lines and the target gap. This serves as the first partition that the robot divides within a target area, and a map of the first partition is built accordingly. This provides a reference map area for the robot to partition subsequent areas, thus accelerating the robot's mapping process.

[0025] At least one door frame is set on the boundary of the first partition, and initially there is only a relatively complete room map. Moreover, the robot can quickly complete the initial map by using a monocular camera for visual recognition.

[0026] Based on the first partition, the robot can enter the unmapped area from the first partition by passing through the identified target gap. That is, based on the accessibility of the target gap (the target gap must at least allow the robot to pass through), after the robot completes a full circle of the first partition along the wall outline, it prioritizes moving to an identified target gap and then uses that gap to enter the untraversed area (unmapped area). This can be understood as entering the untraversed area and defining another partition, and then mapping the other partition. This mapping can be achieved by overlaying the map of the first partition, realizing incremental mapping for the robot. Compared with existing technologies, this application does not require adding extra markers to the door. It only requires the gap feature formed by the door frame on the wall to appear within the robot's perception field of view to identify the target gap, thereby locating the door frame and partitioning it. This achieves door frame location and partitioning in indoor and outdoor environments using a relatively low-computing-power algorithm.

[0027] As one example, please refer to Figure 2 As shown, the specific methods of the first zoning planning method include:

[0028] Step A1: The robot searches for walls, walks along the walls, and identifies target gaps while simultaneously building a map. Specifically, it collects images of the walls and target gaps, extracts pose information of image features such as points and lines, and marks them on the map to achieve real-time mapping. When the robot identifies a target gap, it walks along the target gap. If it passes the target gap, it continues to walk along the wall to the next target gap. This process continues until the robot completes a closed-loop path, obtaining at least one wall chain with at least one target gap. The at least one wall chain with at least one target gap is then used to form the first partition, and a partition map is set based on the first partition. Then, step A2 is executed.

[0029] In step A1, when the robot completes each closed-loop path, it acquires a wall chain with at least one target gap. The robot sets the wall chain with at least one target gap as the outline of the first partition and reflects it in the map in real time, updating it to the partition map.

[0030] In step A1, the method for the robot to search for walls includes: the robot acquiring environmental images using a monocular camera, whose field of view can cover at least all sidewalls of the wall, multiple vertical line segments resembling door frames, and door lintel lines; then, the robot extracts the vertical projection lines of the walls from the environmental images, and identifies each combination of multiple vertical projection lines located in the same plane or curved surface as the wall to be searched. The combination of multiple vertical projection lines in the same plane or curved surface corresponds to parallel vertical corner lines in the robot's actual walking environment, forming a wall side-by-side. When the robot walks along the wall, each time it moves in the same direction, the plane or curved surface containing the combination of multiple vertical projection lines extracted in that direction is considered a wall extending in that direction, i.e., a wall.

[0031] In step A1, the robot can determine the boundary of the corresponding independent space area based on the combination of vertical projection lines on the wall. The target gap is set on the boundary of the independent space area. The robot crossing the target gap can be understood as the robot crossing the boundary of the independent space area. Thus, the boundaries of all independent space areas in the environment and the number of independent space areas can be obtained. The independent space area can refer to an independent room or an independent open space.

[0032] The robot maps while walking along the wall, minimizing its movement along the edges of isolated obstacles in order to increase speed. It allows the robot to collide with the wall and does not impose specific restrictions on the distance between the robot's side and the wall.

[0033] Step A2: The robot identifies the target gap in step A1. Specifically, after the robot identifies all the target gaps and sets up the partition map in the first partition, it first moves to the target gap identified in step A1, then moves out of the first partition and enters the unmapped area through the target gap.

[0034] Step A1 identifies multiple vertical projection lines of the wall located on the same plane or curved surface. By identifying the target gap, the relative positional relationship between different batches of continuously arranged vertical projection lines of the wall can be obtained. Then, step A2 uses the target gap as a boundary to effectively identify each independent space in the environment. As can be seen from the implementation method consisting of steps A1 and A2, this embodiment obtains the closed-loop path and the target gap, which helps to divide the first partition in the environment, that is, the first independent space; and determines the passable location information from the first independent space in the environment to the untraversed area based on the target gap. Moreover, it has good applicability to room layouts with complex layouts.

[0035] As one embodiment, the flowchart of the method for the robot to complete a closed-loop path in step A1 is as follows:Figure 3 As shown, it specifically includes:

[0036] Step A101: When the robot detects the current wall, it walks along the current wall in a preset clockwise direction. Specifically, it walks along the current wall from a preset edge starting point in a preset clockwise direction. Simultaneously, it determines whether the robot has detected the target gap. If yes, proceed to step A102; otherwise, proceed to step A103. For a single wall, it can be distinguished as the current wall and the next wall based on the search time and search position. The method of defining a wall using a vertical projection line of the wall surface is described in the corresponding embodiment of step A1 above and will not be repeated here. When executing step A101, after detecting the current wall, the robot first walks to the front of the current wall and maintains a certain edge distance from it, thereby determining the preset edge starting point. The preset edge starting point can be located vertically to the current wall, and the distance from the preset edge starting point to the current wall is between 0.5cm and 10cm, which can represent the distance between the robot's edge closest to the wall and the current wall.

[0037] Step A102: Determine whether the robot has walked back to the preset edge starting point used when the first step A101 was executed. If yes, it is determined that the robot has completed a closed loop path. If the preset edge starting point is located at the endpoint of a target gap that has been identified, the robot may repeatedly identify the same target gap at the preset edge starting point and be located directly below one side of the target gap. Otherwise, proceed to step A103.

[0038] Step A103: The robot walks along the boundary formed by the location of the target gap described in step A101, while maintaining the search wall; then proceed to step A104. It can be understood that the two sides of the target gap are different walls (each composed of different batches of continuously arranged vertical projection lines of the walls). The boundary formed by the location of the target gap is understood as directly below the target gap. The robot walks along the corresponding boundary without crossing the target gap, while simultaneously searching the next wall.

[0039] Step A104: When the robot detects the next wall, it updates the next wall to the current wall. When the robot completes the boundary formed by the location of the target gap described in step A101, it updates the position of the next wall detected by the robot to the preset edge starting point. Then, it executes step A101 to detect the target gap between two adjacent walls, or to search for the next wall every time it detects and walks along the target gap, until the robot walks back to the preset edge starting point used when it first executed step A101. The robot has completed a closed loop path.

[0040] In this embodiment, when the robot completes a closed-loop path, the robot forms a wall chain with at least one target gap reserved, consisting of the walls and target gaps identified in steps A101 to A104 in a predetermined clockwise direction; the projection lines of the walls and target gaps identified in steps A101 to A104 on the ground form a continuous line segment to form a complete closed loop.

[0041] In step A1, to search for walls and identify the target gap, the robot acquires images. In a frame of environmental image acquired in real time by the robot, the target gap is located between two adjacent walls; the target gap is surrounded by the vertical projection lines of the opposite side of the two adjacent walls, forming two vertical projection lines corresponding to the target gap; schematically, as shown... Figure 1 As shown, Figure 1 This is a schematic diagram of the environmental image captured by the robot in front of or directly below the door frame. The center point of the environmental image currently captured by the robot's camera is point O, which can represent the robot's current position. Line segment A1B1 is the vertical projection line of the wall to the left of the robot, and line segment D1C1 is the vertical projection line of the wall to the right of the robot. Figure 1 The extracted vertical projection lines A1B1, C1D1, and B1C1 of the wall surface are connected to form a target gap, which may be a door frame existing in the actual environment.

[0042] The pixel distance between the two endpoints of the target gap is within a preset width threshold range. In the vertical projection line A1B1 of the wall, the endpoint closest to the center of the environmental image is endpoint B1, and in the vertical projection line C1D1 of the wall, the endpoint closest to the center of the environmental image is endpoint C1. The pixel distance between the two endpoints of the target gap can be the pixel distance between endpoint B1 and endpoint C1, or the pixel distance between endpoint A1 and endpoint D1. When the pixel distance between endpoint B1 and endpoint C1 is the lower limit of the preset width threshold range, the pixel distance between endpoint A1 and endpoint D1 is the upper limit of the preset width threshold range.

[0043] Preferably, the minimum room width is typically between 60cm and 100cm, and the physical distance range calculated from the preset width threshold range is between 60cm and 100cm. The physical distance between endpoint A1 and endpoint D1 is 100cm (which will be smaller when converted to the pixel length occupied in the image), and the physical distance between endpoint B1 and endpoint C1 is 60cm (which will be smaller when converted to the pixel length occupied in the image).

[0044] The pixel distances between the intersection of the extended lines of the two vertical projection lines corresponding to the target gap and the nearest endpoints of the two vertical projection lines corresponding to the target gap are all within a preset projection distance threshold range; Figure 1 In the projection, the extension of the vertical projection line A1B1 on the wall intersects with the extension of the vertical projection line C1D1 on the wall. Preferably, the intersection point of the extension of the vertical projection line A1B1 on the wall and the extension of the vertical projection line C1D1 on the wall is point O. The pixel distance between point O and the nearest endpoint B1 of the vertical projection line A1B1 on the wall is equal to the length of line segment OB1, and the pixel distance between point O and the nearest endpoint C1 of the vertical projection line C1D1 on the wall is equal to the length of line segment OC1. Therefore, the physical distance range calculated from the preset projection distance threshold range is preferably 0 to 0.2m.

[0045] As those skilled in the field of machine vision know, converting pixel distance (the coordinate distance between two pixels) in an image to physical distance in the actual environment involves conversion factors determined by camera parameters, including focal length, field of view, and sensor size. Therefore, converting pixel distance to physical distance based on camera focal length and pixel size is a conversion method mastered by those in the field of machine vision.

[0046] Understandably, the robot, under user control or in automatic mode, divides the walking environment into its first partition, which can refer to an indoor room, an outdoor room, or a combination of indoor and outdoor rooms.

[0047] It should be noted that when the robot detects that it has walked to the location of the target gap marked on the map, and detects that the distance between the location of the target gap and the target gap is less than or equal to a preset value, the robot is controlled to walk forward in the direction of the target gap; when the robot detects that the distance between itself and the target gap is zero, the robot is controlled to continue walking forward and enter other rooms.

[0048] As one embodiment, a method for robot to identify target gaps includes:

[0049] The robot acquires environmental images and extracts multiple straight line segments from them. Preferably, the robot can identify the straight line segments in the image using various edge detection algorithms, such as vertical and horizontal corner lines. Reference vertical and horizontal projection lines that form an intersection relationship are extracted from the environmental image to represent these segments. Specifically, the extensions of two reference vertical projection lines intersect, creating an intersection relationship. In the actual environment where the robot moves, the vertical corner lines represent line segments perpendicular to the floor of indoor and outdoor room areas. The vertical and horizontal corner lines are perpendicular to each other, but the reference vertical projection lines are not necessarily perpendicular to the horizontal corner lines.

[0050] Generally, after the robot can identify straight line segments in an image using various edge detection algorithms, the robot will use Hough transform to calculate the angle of each straight line segment from the environmental image (which can be pre-binarized) (which can be obtained based on the slope of the equation in which the extracted straight line segment is located). Then, the robot selects straight line segments that can represent the post line, beam line, side wall line, etc., based on the length and angle of the straight line segments.

[0051] In this embodiment, in order to ensure that the camera's field of view fully covers the door frame, the robot's camera lens is mounted facing the ceiling. Therefore, the camera's field of view can cover the ceiling above the robot and the area below the ceiling. If the door post perpendicular to the ground and the camera are facing the same direction, then based on the perspective principle of the lens, the extensions of the two reference vertical projection lines in the environmental image will eventually intersect.

[0052] Based on the characteristics of line segment length, angle, and quantity, two reference vertical projection lines and one reference horizontal projection line that form an intersection relationship are selected from the multiple line segments. Thus, the robot can exclude reference vertical projection lines and reference horizontal projection lines that cannot form an intersection relationship from three judgment factors: the length characteristics of a single line segment, the angle characteristics between two line segments, and the cumulative extracted number of line segments, thereby reducing the number of line segment samples required to screen vertical projection lines on the wall and door beam lines.

[0053] Based on preset door frame size conditions, two vertical wall projection lines and one door lintel line are selected from the two reference vertical projection lines and one reference horizontal projection line that intersect, forming the target gap. Specifically, the two selected vertical wall projection lines and one door lintel line intersect and form a gap towards the ground. The preset door frame size conditions further refine the aforementioned line segment length characteristics, improving the accuracy of the robot in recognizing door frames.

[0054] Since the two vertical projection lines of the walls and the lintel line that form the door frame are combinations of the actual door frame's projection lines in the environmental image, the two vertical projection lines intersect. The positional relationship between the intersection of the extensions of these two vertical projection lines and the center of the lintel line represents the distribution direction, azimuth angle, and other information of the door frame (or the target gap) relative to the robot's current position. When the robot determines the center of the lintel line, the door frame is positioned.

[0055] In some implementations, the endpoints of the two vertical projection lines of the wall surface that form the door frame are set as corner points, and then the corner points are connected to form a reference door beam line. The reference door beam line can be parallel to the reference horizontal projection line (i.e., the door beam line) directly extracted from the environmental image.

[0056] As one embodiment, the method for selecting two reference vertical projection lines and one reference horizontal projection line that form an intersection relationship from the plurality of line segments based on line segment length characteristics, angle characteristics, and quantity characteristics, such as... Figure 4 As shown, it specifically includes:

[0057] Step A111: Select the line segments perpendicular to the ground from the multiple line segments. Here, "perpendicular" is defined as the line segment that is perpendicular to the ground of the robot's actual walking environment (including vertical corner lines) and is displayed / projected in the environmental image; then mark the selected line segments perpendicular to the ground as reference vertical projection lines; then proceed to step A112.

[0058] Step A112: Determine if the number of reference vertical projection lines marked in step A111 is less than two. If so, determine that the robot cannot filter out two vertical projection lines of the wall from the environmental image, and cause the robot to pause the execution of the area division method; otherwise, proceed to step A113. This eliminates invalid reference vertical projection lines.

[0059] Step A113: Within the preset projection distance threshold range corresponding to the center of the environmental image, filter out straight line segments whose length is within the preset width threshold range, and then mark the filtered straight line segments whose length is within the preset width threshold range as reference horizontal projection lines; then execute step A114; Since the door beam line is generally set above the door frame and sandwiched between two reference vertical projection lines, the door beam line will be projected into the environmental image close to the center of the environmental image. Therefore, by setting a preset projection distance threshold range at the center of the environmental image, a reference horizontal projection line that can represent the door beam line can be searched at close range.

[0060] Step A114: Determine whether the number of reference horizontal projection lines marked in step A113 is less than one. If so, determine that the robot cannot filter out the gate beam lines from the environmental image, and make the robot pause the execution of the region division method; otherwise, execute step A115; thereby eliminating invalid reference horizontal projection lines.

[0061] Step A115: Filter out reference horizontal projection lines that conform to the door structure by enumerating reference vertical projection lines and reference horizontal projection lines, and then execute step A116; wherein, the reference horizontal projection line that conforms to the door structure is a reference horizontal projection line that intersects with two reference vertical projection lines; therefore, it can be understood that there is at least one reference horizontal projection line and at least two reference vertical projection lines that conform to the door structure, and there are two reference vertical projection lines that intersect with both ends of a reference horizontal projection line respectively, and in addition, the extensions of the two reference vertical projection lines intersect.

[0062] Step A116: Determine whether the number of reference horizontal projection lines that conform to the door structure selected in step A115 is greater than the value one. If yes, proceed to step A117. Otherwise, determine that the robot cannot select door beam lines from the environmental image, and cause the robot to pause the execution of the region division method, thereby eliminating invalid reference horizontal projection lines that conform to the door structure.

[0063] Therefore, when performing step A117, there may be multiple gantry beam lines extending in the same direction. The position occupied by the gantry beam line is then determined by the connection node of the two reference vertical projection lines connected to the reference horizontal projection line.

[0064] Step A117: Obtain multiple sets of two reference vertical projection lines and one reference horizontal projection line that form an intersecting relationship; then, in each set of two reference vertical projection lines and one reference horizontal projection line that form an intersecting relationship, mark the two reference vertical projection lines as two wall vertical projection lines and mark the one reference horizontal projection line as a door lintel line; wherein, the extensions of the two reference vertical projection lines intersect, and the two reference vertical projection lines and one reference horizontal projection line that form an intersecting relationship are connected to each other to form a gap.

[0065] Step A117 is equivalent to determining that among the reference horizontal and reference vertical projection lines conforming to the door structure, there are two vertical projection lines of the wall and one door beam line that intersect. Based on step A113, within the same frame of the environment image, the pixel distance between the intersection point of the extensions of the two vertical projection lines of the wall determined in step A117 and the center of the environment image is within the range of the preset projection distance threshold.

[0066] In summary, by executing steps A111 to A117, two vertical projection lines of the walls and one door beam line are determined as candidate door frame segments. Then, based on the positional relationship between the center point of each door beam line and the intersection point of the extension lines of the two vertical projection lines of the walls, the robot determines the orientation information of the door frame containing the door beam line relative to the robot's current position. This is also equivalent to the orientation information of the door beam line relative to the robot's current position in the environmental image, and thus determines the entrance / exit location of the first partition.

[0067] In some embodiments, among the two reference vertical projection lines and one reference horizontal projection line that form an intersecting relationship, the endpoint of each reference vertical projection line that is closest to the intersection of the extensions of the two reference vertical projection lines is set as a corner point, and then the corner points of each reference vertical projection line are connected to form the reference horizontal projection line, so as to form a reference horizontal projection line that conforms to the door structure.

[0068] It should be noted that there is usually a wall above the door. To support this part of the wall, a precast wooden or reinforced concrete beam, called a door beam, is needed, which can reduce the impact of wall settlement on the door frame. In the environmental image of this embodiment, the door beam can be represented by the reference horizontal projection line through image recognition algorithm processing. On both sides below the door beam are two doorposts perpendicular to the ground. Similarly, in the environmental image of this embodiment, they can be represented by the reference vertical projection line through image recognition algorithm processing. Then, two adjacent reference vertical projection lines and one door beam line can form a door frame, forming a simplified door model.

[0069] As one embodiment, the method of selecting two vertical wall projection lines and one door lintel line to form the door frame from two reference vertical projection lines and one reference horizontal projection line that intersect, based on preset door frame size conditions, is as follows: Figure 5 As shown, it specifically includes:

[0070] Step A118: Mark the two reference vertical projection lines and one reference horizontal projection line that intersect as a set of candidate door frame lines, so that there are two wall vertical projection lines and one door beam line that intersect in a set of candidate door frame lines; then execute step A119.

[0071] Step A119: Determine whether the physical distance between the vertical corner lines corresponding to the two reference vertical projection lines within a set of candidate door frame lines is within the preset door width distance range. If yes, proceed to step A120; otherwise, no two vertical projection lines for forming the door frame can be selected, thus eliminating two reference vertical projection lines with inappropriate spacing. The robot uses a depth sensor to detect the physical distance between the vertical corner lines corresponding to the two reference vertical projection lines. The reference vertical projection lines are projection lines formed by the robot acquiring the vertical corner lines into the coordinate system of the environmental image, and the vertical corner lines are perpendicular to the ground where the robot walks.

[0072] In the robot's operating environment, the minimum room width ranges from 60cm to 100cm, and correspondingly, the preset door width distance is preferably between 60cm and 100cm. The robot's depth sensor's detection field of view also needs to cover the area between the doorpost lines on both sides of the door frame.

[0073] Step A120: Calculate the ratio between the length of a reference horizontal projection line within the set of candidate door frame lines and the physical distance. Then, based on this ratio and the length of each reference vertical projection line, calculate the length of the vertical corner line corresponding to each reference vertical projection line. This converts the reference vertical projection line from pixel size to physical size and represents it by the length of the vertical corner line. This ratio also applies to the physical size conversion operation of the reference horizontal projection line within the same frame of the environment image. Then, execute step A121. The length of the reference vertical projection line belongs to the pixel length occupied by the reference vertical projection line in the environment image. After conversion to the length of the vertical corner line, the actual height of the door frame is obtained so that the actual existing door frame can be determined in step A1.

[0074] Step A121: Determine whether the length of the vertical corner line corresponding to each reference vertical projection line within a set of candidate door frame lines is within the preset door frame height range. If so, mark the two reference vertical projection lines within the set of candidate door frame lines as the two wall vertical projection lines used to form the door frame, and mark one reference horizontal projection line within the set of candidate door frame lines as a door beam line used to form the door frame, thereby determining the door frame. The target gap includes the door frame, and of course, it also includes other channels of the same height or width. Therefore, by executing step A121, the gap channel constructed by the door frame and the straight line segment it forms (which can correspond to the projection line segment in the environmental image) can be identified in the wall. Otherwise, the two wall vertical projection lines used to form the door frame cannot be filtered out, thus eliminating wall vertical projection lines with unreasonable heights. The preset door frame height range is set to 1.6m to 2.5m, which conforms to the door frame height characteristics in the room.

[0075] In summary, this embodiment converts the vertical projection lines from pixel size to physical size by executing steps A118 to A121, and determines the two vertical projection lines of the wall and one door beam line used to form the door frame based on the physical size. It eliminates the interference of misjudgment of door leaf and side wall lines perpendicular to the ground, constructs a simplified model of the door frame, and obtains the vertical projection lines of the wall and door beam line that conform to the simplified model of the aforementioned door frame, so as to realize the identification of a complete and accurate door frame in the first partition.

[0076] It is worth noting that the vertical projection lines on the wall in this embodiment are simplified projection lines, and the wall thickness is negligible.

[0077] Of course, objects that conform to the simplified model of the aforementioned door frame, including vertical projection lines of the wall and door beams, also include square columns, side door panels, door leaves, walls between the ceiling and the door frame, thresholds, side walls, and front walls in the home environment.

[0078] In an embodiment where two vertical wall projection lines and one door lintel line can form a door frame, if two reference vertical projection lines within a set of candidate door frame lines are marked as two vertical wall projection lines for forming the door frame in step A121, and one reference horizontal projection line within a set of candidate door frame lines is marked as one door lintel line for forming the door frame in step A121, then: the intersection points formed by the two vertical wall projection lines marked in step A121 within a set of candidate door frame lines and the door lintel line marked in step A121 within the same set of candidate door frame lines are marked as follows: Two corner points are obtained by marking them as corner points; the angle formed by the two corner points and the center of the environmental image is greater than a preset angle threshold, which is preferably 20 degrees; in step A121, the length of a door beam line marked in the same group of candidate door frame lines is greater than the preset door beam projection length, which is preferably 35 pixels long; moreover, the extensions of the two reference vertical projection lines in the same group of candidate door frame lines intersect, thereby reflecting the positional relationship between the two wall vertical projection lines in the environmental image, and simplifying the door beam model in terms of angle features and door beam line length features respectively.

[0079] For illustrative purposes, see the attached document. Figure 1 It can be seen that, Figure 1This is a schematic diagram of the environmental image captured by the robot in front of the door frame. The center of the environmental image currently captured by the robot's camera is located near point O, which is the intersection of the extensions of two vertical projection lines of the wall. The pixel distance between point O and the center of the environmental image is within the preset projection distance threshold range. The preset projection distance threshold range is used to represent the error range of transforming the vertical corner lines into the pixel coordinate system. The error sources include image distortion caused by lens distortion of the camera. In some ideal cases, point O is the center of the environmental image. Then, the angle formed by corner points B1 and C1 in the diagram with the center O of the environmental image is angle B1OC1, which is greater than the preset angle threshold.

[0080] Line segment A1B1 is the vertical projection line of the wall on one side of the robot extracted by the robot, and line segment D1C1 is the vertical projection line of the wall on the other side of the robot extracted by the robot. Then, among the two endpoints of the vertical projection line A1B1, the endpoint B1 closer to point O is selected as a corner point, and among the two endpoints of the vertical projection line D1C1, the endpoint C1 closer to point O is selected as the other corner point. Then, corner point B1 and corner point C1 are connected to form line segment B1C1. Line segment B1C1 forms the door beam line, and then the robot... Figure 1 The extracted vertical projection lines A1B1, C1D1, and B1C1 of the wall surface are connected to form the target gap, which is used to represent the door frame that exists in the actual environment.

[0081] In some embodiments, the robot's current position is represented by point O, which is the center of the environmental image; then the robot sets the direction from the center of the currently acquired environmental image to the center of the door beam line as the distribution direction of the door frame relative to the robot's current position, corresponding to... Figure 1 In this context, the center of the gate beam line is the midpoint H1 of the straight line segment B1C1. The direction from point O to point H1 is the distribution direction of the gate frame where the gate beam line B1C1 is located relative to the robot's current position (specifically, its pixel coordinate position in the image). It can also be understood that the robot is located in the direction of H1O of the gate frame where the gate beam line B1C1 is located, which is regarded as the robot walking along the OH1 direction to the front of the gate frame where the gate beam line B1C1 is located.

[0082] In some embodiments, the robot sets the angle between the direction from one corner point to another and the coordinate axes of the image coordinate system, or the angle transformed into the world coordinate system, as the angle information of the door lintel line, to convert it into the orientation information of the door lintel line within the outdoor / indoor room area; the direction from one corner point to another is an extension direction of the door lintel line in the image coordinate system, schematically represented as... Figure 1Corner point B1 points in the direction of corner point C1. Specifically, the center of the portal beam line can be transformed into the world coordinate system to realize the transformation of the angle information of the portal beam line into the world coordinate system, that is, it falls into the grid map and is positioned with the help of the world coordinate system, which is suitable for use by robots in the process of walking and mapping.

[0083] Based on the foregoing embodiments, this application discloses a robot equipped with a vision sensor, typically mounted on the top of the robot's body to cover a larger field of view. The robot is used to execute the first partitioning planning method mentioned in the foregoing embodiments. Specifically, the robot executes steps A1 and A2 to divide the environment into its first partition. For step A1, the robot specifically executes steps A101 to A104 to allow it to walk along a wall to complete a closed-loop path and form a chain of walls with at least one target gap. This chain of walls with at least one target gap then forms the first partition. In step A1, the robot further determines two vertical projection lines of the walls and one lintel line as candidate door frame segments by executing steps A111 to A117. For step A1, the robot further converts the vertical projection lines from pixel size to physical size by executing steps A118 to A121, and determines the two vertical projection lines of the walls and one lintel line used to form the door frame based on the physical size. It eliminates the interference of misjudgment of door leaf and side wall lines perpendicular to the ground, and constructs a simplified model of the door frame. Based on this simplified model of the door frame, the robot divides the first room area that closely resembles the actual environment in the indoor and outdoor working areas.

[0084] In one embodiment, the visual sensor is a camera. To achieve rapid response and improve mapping efficiency, the robot can use a monocular camera for image acquisition, identifying walls and gaps within the acquired wall images. The robot's camera lens is mounted facing the ceiling of the room where the robot is located, so that the camera's field of view covers the surface of the ceiling and the space below it. A door frame is located in the space below the ceiling, serving as an entrance / exit to different room areas. In this embodiment, the camera is positioned at the front of the robot body, with its orientation set horizontally upwards. The camera's optical axis can be approximately 90 degrees to the horizontal plane, and the environmental images acquired by the camera can at least cover the area between the door frame or the lintel of the door frame and the ceiling. This embodiment can use a single camera, maintaining multi-angle imaging while performing tasks in a single room area.

[0085] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 The computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The functions specified in one or more boxes. These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes ​ The steps of the function specified in one or more boxes.

[0086] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A first partition planning method based on gap recognition, characterized in that, The application relates to a method for planning a first partition of a robot. The method comprises the following steps: The robot walks along a wall and identifies a target gap, and walks at least one closed loop path, and encloses a first partition by a wall chain with at least one target gap found by the robot, so that the robot enters an un-mapped area from the first partition through the identified target gap. The method for identifying a target gap by the robot comprises the following steps: The robot collects an environment image and extracts a plurality of straight line segments from the environment image; According to the length characteristics, angle characteristics and quantity characteristics of the line segments, two reference vertical projection lines and one reference horizontal projection line forming a crossing relationship are screened out from the plurality of straight line segments; 2. The method of claim 1, wherein: According to a preset door frame size condition, two wall surface vertical projection lines and one door beam line used for composing a door frame are screened out from the two reference vertical projection lines and the one reference horizontal projection line forming the crossing relationship, and the two wall surface vertical projection lines and the one door beam line are used for enclosing the target gap. The specific method of the first partition planning method comprises the following steps: Step A1: the robot searches for a wall, walks along the wall and identifies a target gap, simultaneously constructs a map, and walks along the target gap when the target gap is identified until the robot walks at least one closed loop path, obtains a wall chain with at least one target gap, encloses a first partition by the wall chain with at least one target gap, and sets a partition map according to the first partition; then step A2 is executed; 3. The method of claim 2, wherein: Step A2: the robot enters an un-mapped area from the first partition through the target gap identified in step A1. In the step A1, the method for searching for a wall by the robot comprises the following steps:

4. The method of claim 2, wherein: The robot collects an environment image, extracts wall surface vertical projection lines in the environment image, and identifies a wall to be searched by combining a plurality of wall surface vertical projection lines located in the same plane or the same curved surface. In the step A1, the method for walking at least one closed loop path by the robot comprises the following steps: Step A101: when the robot identifies a current wall, the robot walks along the current wall according to a preset hour hand direction, simultaneously judges whether the robot identifies the target gap, and if yes, step A102 is executed, and if not, step A103 is executed; Step A102: whether the robot walks back to a preset edge starting point is judged, and if yes, it is determined that the robot walks at least one closed loop path, and if not, step A103 is executed; Step A103: the robot walks along a boundary formed at a position of the target gap in step A101, and keeps searching for a wall; then step A104 is executed; 5. The method of claim 4, wherein: Step A104: when the robot identifies a next wall, the robot updates the next wall as the current wall; then step A101 is executed. When the robot walks at least one closed loop path, the robot forms a wall chain with at least one target gap by walls and target gaps identified in steps A101 to A104 in sequence according to the preset hour hand direction; the projections of the walls and the target gaps on the ground form continuous line segments to form a complete closed loop.

6. The method of claim 5, wherein: In a frame of environment image collected by the robot in real time, the target gap is between two adjacent walls; the target gap is surrounded by wall vertical projection lines of opposite sides of the two adjacent walls, forming two wall vertical projection lines corresponding to the target gap; Wherein, the distance between the two endpoints of the target gap is within the preset width threshold range, and the intersection points of the extension lines of the two wall vertical projection lines corresponding to the target gap are within the preset projection distance threshold range from the nearest endpoints of the two wall vertical projection lines corresponding to the target gap.

7. The method of claim 1, wherein: The method for screening two reference vertical projection lines and one reference horizontal projection line forming intersection relationship from the plurality of straight line segments according to the length feature, angle feature and number feature of the line segment includes: Step A111, screening straight line segments perpendicular to the ground from the plurality of straight line segments; then selecting straight line segments with a length greater than a preset wall height threshold from the screened straight line segments perpendicular to the ground to mark as reference vertical projection lines; and then executing step A112; Step A112, judging whether the number of the reference vertical projection lines marked in step A111 is less than two, if yes, determining that the robot cannot screen two wall vertical projection lines from the environment image, otherwise executing step A113; Step A113, screening straight line segments with a length within a preset width threshold range within a preset projection distance threshold range corresponding to the center of the environment image, and then marking the screened straight line segments with a length within the preset width threshold range as reference horizontal projection lines; and then executing step A114; Step A114, judging whether the number of the reference horizontal projection lines marked in step A113 is less than one, if yes, determining that the robot cannot screen a door beam line from the environment image, otherwise executing step A115; Step A115, screening a reference horizontal projection line conforming to a door structure by enumerating the reference vertical projection lines and the reference horizontal projection lines, and then executing step A116; wherein the reference horizontal projection line conforming to the door structure is a reference horizontal projection line forming intersection relationship with the two reference vertical projection lines; Step A116, judging whether the number of the reference horizontal projection line conforming to the door structure screened in step A115 is greater than one, if yes, executing step A117, otherwise determining that the robot cannot screen a door beam line from the environment image; Step A117, obtaining a plurality of groups of two reference vertical projection lines and one reference horizontal projection line forming intersection relationship; and then marking the two reference vertical projection lines as two wall vertical projection lines and marking the one reference horizontal projection line as one door beam line in each group of two reference vertical projection lines and one reference horizontal projection line forming intersection relationship; wherein the extension lines of the two reference vertical projection lines intersect.

8. The method of claim 7, wherein: The method for screening two wall vertical projection lines and one door beam line used for composing a door frame from the two reference vertical projection lines and the one reference horizontal projection line screened to form intersection relationship according to the preset door frame size condition includes: Step A118, marking the two reference vertical projection lines and the reference horizontal projection line determined in step A117 as a group of candidate door frame lines; then performing step A119; Step A119, judging whether the physical distance between the vertical corner lines corresponding to the two reference vertical projection lines in the group of candidate door frame lines is within a preset door width distance range, if yes, performing step A120, otherwise, failing to screen the two wall vertical projection lines for composing the door frame; wherein the robot uses the depth sensor to detect the physical distance between the vertical corner lines corresponding to the two reference vertical projection lines; Step A120, calculating the ratio between the length of the reference horizontal projection line in the group of candidate door frame lines and the physical distance, and then converting the length of the vertical corner line corresponding to each reference vertical projection line based on the ratio and the length of each reference vertical projection line, and then performing step A121; Step A121, judging whether the length of the vertical corner line corresponding to each reference vertical projection line in the group of candidate door frame lines is within a preset door frame height range, if yes, marking the two reference vertical projection lines in the group of candidate door frame lines as the two wall vertical projection lines for composing the door frame, and marking the reference horizontal projection line in the group of candidate door frame lines as a door beam line for composing the door frame; otherwise, failing to screen the two wall vertical projection lines for composing the door frame; wherein the target gap includes the door frame. The reference vertical projection line is a projection line formed by the robot collecting the vertical corner line into the coordinate system of the environment image, and the vertical corner line is perpendicular to the ground of the robot walking environment.

9. The method of claim 8, wherein: The intersection point formed by the two wall vertical projection lines marked in step A121 in the same group of candidate door frame lines and the door beam line marked in step A121 in the same group of candidate door frame lines and the center of the environment image forms an angle greater than a preset angle threshold; The length of the door beam line marked in step A121 in the same group of candidate door frame lines is greater than a preset door beam projection length.

Images