Line drawing robot and path planning method

Abstract

The application discloses a line drawing robot and a path planning method, and belongs to the technical field of robot path finding. The method comprises the following steps: reading point line coordinates of a to-be-drawn line pattern, dividing the to-be-drawn line pattern into a plurality of blocks, and the blocks are composed of a plurality of mutually connected line segments; finding a starting point closest to a starting position of the robot, and the starting point belongs to an un-drawn line block; when the robot drives to the starting point, drawing a line according to a path planned in advance based on the block; when all the line segments on the block are traversed and the line drawing is completed, finding a next starting point closest to a current position of the robot, and the starting point belongs to a next un-drawn line block; the robot drives to the starting point to draw a line for the next block; and the step is repeated until all the blocks are completed. According to the application, the line drawing robot can take a short return path when drawing a line, and the efficiency of the robot in drawing a line is improved.

Description

[0001] Priority application

[0002] This application will serve as the basis for priority claims in subsequent patent applications (including, but not limited to, Chinese invention patent applications, Chinese utility model applications, PCT applications, and foreign applications based on the Paris Convention). Technical Field

[0003] This invention belongs to the field of robot pathfinding technology, and particularly relates to a path planning method for a line-drawing robot and a line-drawing robot using the path planning method. Background Technology

[0004] During construction, workers first need to build load-bearing walls and columns on the foundation. To ensure that the positions are not off-center, the locations of the load-bearing walls and columns need to be drawn on the ground according to the drawings, which will facilitate the workers' construction.

[0005] In current construction practices, line drawing is generally done manually. Manual line drawing is labor-intensive for workers, and the precision of manually drawn patterns is insufficient. Therefore, to address this issue, a line-drawing robot has emerged on the market. This robot can automatically identify the lines to be drawn by reading the basic drawings provided by the upstream supplier. However, unlike other types of robots, existing path planning methods for line drawing are not very efficient. Therefore, how to efficiently complete line drawing has become a pressing problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a line-drawing robot and a path planning method, which can solve or alleviate the above problems to a certain extent, plan the optimal path for the robot to travel, and minimize the number of repeated routes the robot takes when drawing lines.

[0007] To address the aforementioned technical problems, the present invention specifically employs a path planning method for a line-drawing robot, comprising:

[0008] Read the point and line coordinates of the graphic to be drawn, and divide the graphic into several blocks, each block consisting of several interconnected line segments;

[0009] Find the starting point closest to the robot's starting position, where the starting point belongs to the unlined tile;

[0010] The robot travels to the starting point and draws a line according to the path pre-planned based on the frame.

[0011] After traversing all line segments on the tile and completing the drawing, find the next starting point closest to the robot's current location. The starting point belongs to the next undrawn tile. The robot travels to the starting point and begins drawing lines for the next undrawn tile. Repeat this step until all tiles have been drawn.

[0012] As an improvement, the steps for planning paths based on the aforementioned tiles specifically include:

[0013] The robot starts from the starting point within the block, travels along the undrawn line segment connected to the starting point to the endpoint with the shortest distance from the starting point, and then travels along the undrawn line segment connected to the endpoint to the next endpoint with the shortest distance from the endpoint, until all line segments in the block have been drawn.

[0014] As an improvement, during the line drawing process, the robot records each inflection point it passes through. The inflection point is an endpoint in the map where three or more line segments connect. Correspondingly, the step of planning the path based on the map further includes:

[0015] Determine whether the endpoint to which the robot is currently traveling is still connected to an undrawn line segment; if no undrawn line segment is connected, the robot regresses to the inflection point that it has already traveled and is connected to an undrawn line segment.

[0016] As an improvement, the step of the robot retracing its path to the inflection point connected by an unlined line segment specifically includes the following steps:

[0017] The robot retraces its path to the nearest inflection point and determines whether the inflection point to which it is retracing is connected to an undrawn line segment.

[0018] If there are undrawn line segments, start from the inflection point and draw a line along the undrawn line segment connected to the inflection point towards the endpoint with the shortest continuous distance from the inflection point.

[0019] If no undrawn line segment is connected, continue back to the previous inflection point and check if it is connected to an undrawn line segment, until an inflection point with an undrawn line segment is found.

[0020] As an improvement, the step of the robot retracing to the inflection point that has been traveled and is connected to an undrawn line segment further includes the step of: if it is determined that none of the inflection points traveled contain an undrawn line segment, then the robot retraces to the starting point within the block.

[0021] As an improvement, drawn line segments can be deleted or marked from the tile.

[0022] As an improvement, when retracing back to the inflection point or the starting point connected by an undrawn line segment, the retracing path of the robot is based on the line connecting the two points.

[0023] As an improvement, when there are two or more endpoints in the block that are the shortest distance from the starting point or the shortest distance from the inflection point, the robot selects the endpoint that is read first to drive and draw the line according to the reading order.

[0024] As an improvement, the method for finding the starting point closest to the robot's starting position includes:

[0025] Obtain the coordinates of the robot's starting position;

[0026] Iterate through the coordinates of all points in the unlined map block;

[0027] The distance from the robot's starting position to all points in the unlined block is calculated using the coordinates of the starting position and the coordinates of all points in the unlined block.

[0028] Choose the point with the shortest distance as the starting point.

[0029] As an improvement, when traversing the coordinates of all points in the unlined blocks, it is preferable to select the block closest to the starting position, then traverse the coordinates of all points within it, and find the point within the block that is closest to the starting position.

[0030] As an improvement, when reading the coordinates of the points and lines of the graphic to be drawn, the length of each line segment is calculated.

[0031] The present invention also provides a line-drawing robot, wherein the line-drawing robot uses the above-mentioned path planning method for path planning when drawing lines.

[0032] The advantages of this invention are:

[0033] This invention first treats each connected line segment in the graphic to be drawn as a block, then performs optimal path planning for each block, and then optimizes the path between blocks. Through efficient path planning, the line drawing robot can take the shortest possible backtracking when drawing lines, thus improving the efficiency of the robot's line drawing.

[0034] The robot will delete or mark the drawn line segments from the tiles, which can prevent the drawing robot from drawing lines repeatedly.

[0035] When it is necessary to retreat to the previous inflection point or starting point connected by an undrawn line segment, the retreat path is based on the line (or straight-line distance) between the two points, rather than returning along the original path. This adopts the principle that the shortest distance between two points is a straight line, which greatly reduces the distance traveled by the robot.

[0036] When there are two or more endpoints in the map that have the shortest distance to the robot's starting point or turning point, the robot selects the endpoint read first according to the reading order to draw a line. This simple choice method solves the problem of multiple selections, thus eliminating the need to design more complex and precise algorithms for endpoint selection, thereby eliminating the need to consume the robot's computing power and significantly improving the robot's computing performance, which to some extent reduces the cost of building the robot. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. The elements or parts in the drawings are not necessarily drawn to scale. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0038] Figure 1 A flowchart illustrating a path planning method of an exemplary embodiment of the present invention;

[0039] Figure 2 This is a flowchart of the path planning process within a block in a path planning method of an exemplary embodiment of the present invention;

[0040] Figure 3 A flowchart of path planning within a block in a path planning method that is another exemplary embodiment of the present invention;

[0041] Figure 4 This is a route map of a line-drawing robot in an exemplary embodiment of the present invention (solid lines in the figure represent line segments that need to be drawn by the robot). Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0043] In this document, suffixes such as "module," "part," or "unit" used to denote elements are used only for the purpose of illustrative purposes and have no specific meaning in themselves. Therefore, "module," "part," or "unit" may be used interchangeably.

[0044] In this document, the terms "upper," "lower," "inner," "outer," "front," "rear," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] In this document, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] In this document, "and / or" includes any and all combinations of one or more of the listed related items.

[0047] In this article, "multiple" means two or more, that is, it includes two, three, four, five, etc.

[0048] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0049] "Graphics to be drawn": In this article, "graphics to be drawn" refers to the graphics in the basic drawings sent from upstream that need to be drawn by the drawing robot. For example, if an upstream sends a plan of a construction site, the graphic formed by the lines representing the load-bearing walls is the graphic to be drawn by the drawing robot on the construction site based on this plan.

[0050] "Block": Typically, a basic drawing (or a drawing to be drawn) contains many line segments that need to be drawn by the drawing robot. Some line segments are connected (e.g., the line segments that form the same load-bearing wall), while some line segments are not connected to the aforementioned line segments (e.g., the line segments that form another load-bearing wall are not connected to the aforementioned load-bearing wall). Therefore, in this paper, the connected line segments in the drawing to be drawn are regarded as a whole and called "block", so that subsequent path planning can be performed using blocks as units.

[0051] "Starting point": In this article, "starting point" refers to the first point in the current tile from the starting position or the previous tile. This point can be the endpoints of a line segment in the tile, or any point between the two endpoints, as long as it satisfies the requirement that the line or distance between it and the current position of the line drawing robot (in this article, the line or distance refers to the straight-line distance between two points) is the shortest.

[0052] Existing robot path planning focuses on obstacle avoidance, following, or finding the shortest distance from point A to point B. Due to the unique characteristics of line-drawing robots, they need to traverse every line segment in the graphic to be drawn. However, the number of line segments in the graphic is not only large but also complex. Therefore, there is an urgent need for a most economical path planning method that can traverse all line segments. Clearly, existing path planning methods are not suitable for line-drawing robots.

[0053] To solve the above technical problems, such as Figure 1 As shown, this invention provides a path planning method for a line-drawing robot, specifically including the following steps:

[0054] S1 reads the point and line coordinates of the graphic to be drawn, and divides the graphic into several blocks, each block consisting of several interconnected line segments.

[0055] In this invention, 2D or 3D drawing software such as CAD is used to draw drawings according to the actual situation, such as on-site construction drawings. Therefore, as long as the origin point on the actual site is located, lines can be drawn according to the drawings.

[0056] When the robot reads the coordinates of the points and lines of the graphic to be drawn, it calculates the length of each line segment to facilitate subsequent path planning.

[0057] The block of this invention refers to a pattern composed of several interconnected line segments, that is, all line segments in the block are directly or indirectly connected. In other words, when dividing the graphic to be drawn, it is done on a block-by-block basis. Accordingly, path planning includes path planning within a block and path planning between blocks.

[0058] S2 finds the starting point closest to the robot's starting position, which is an unlined tile; and when the robot travels to the starting point, it draws a line on the tile according to the path planned in advance based on the tile where the starting point is located.

[0059] The robot's starting position is usually not on the graphic where lines need to be drawn, so it is necessary to plan the robot's path into the graphic to draw lines. In this invention, the point in the graphic closest to the robot's starting position is selected as the starting point for drawing lines.

[0060] The method for finding the point closest to the robot's starting position is as follows:

[0061] S21 obtains the coordinates of the robot's starting position in the world coordinate system;

[0062] S22 iterates through the coordinates of all points in all unlined tiles;

[0063] S23 uses the coordinates of the starting position point and the coordinates of all points in the unlined block to calculate the distance from the robot's starting position to all points in the unlined block;

[0064] S24 selects the point with the shortest distance as the starting point for the robot to draw the line.

[0065] S3 After traversing all line segments on the tile where the starting point is located and completing the drawing, find the next starting point that is closest to the current position of the drawing robot. This starting point belongs to the next undrawn tile. The robot travels to this starting point and starts drawing lines for the next tile. Repeat this step until all tiles have been drawn.

[0066] In this invention, the principle of the robot's line drawing is to draw one block at a time, continuing until all blocks are drawn. After drawing a block, the robot stays in place and then iterates through all undrawn blocks, finding the point closest to its current position as the starting point for the next block to be drawn. That is, the path planning between blocks uses the robot's current position after drawing all line segments in the current block as its starting position for entering the next block, and then finds the nearest starting point in the next block. For example, see... Figure 3 When all the line segments in tile I are drawn, the robot's position is point C. Therefore, we find the point closest to point C in other tiles, which gives us point D in tile II. Tile II is the tile the robot will draw next, and point D is the starting point for the robot to draw lines in tile II. The method for finding this point is similar to the method for finding the nearest point in step 2, and will not be repeated in this step.

[0067] In addition, such as Figure 2 As shown, the path planning method for a robot within a map in this invention includes the following steps:

[0068] The S31 robot starts from the starting point within the block and travels along the undrawn line segment connected to that starting point to draw a line towards the endpoint with the shortest distance from that starting point.

[0069] S32 starts from the endpoint and moves along the undrawn line segment connected to the endpoint to draw a line to the next endpoint with the shortest line distance to the endpoint, until all line segments in the block are drawn.

[0070] The robot's starting point within the tile may or may not be at an endpoint (e.g., Figure 3 (Point D in block II of the middle map). The robot's first task is to find the endpoint with the shortest distance to its current position and draw a line towards that endpoint. The shortest distance means that the undrawn line segment connecting the two endpoints is the shortest.

[0071] Upon reaching the endpoint, draw a line along the undrawn line segment connected to that endpoint to the next endpoint with the shortest distance from that endpoint, and so on until all line segments have been traversed.

[0072] Of course, each endpoint on the robot's path may not necessarily have a direction of travel, and it may reach a dead end (a dead end is defined as an endpoint that is not connected to any line segments or whose connecting line segments have already been drawn; in this invention, all drawn line segments are deleted or marked in the drawing to avoid redrawing lines). The handling method after reaching a dead end will be introduced later.

[0073] During the S33 line drawing process, the robot will record every turning point it passes through.

[0074] In some embodiments of the present invention, the inflection point is an endpoint connected by three or more line segments. Recording the inflection point serves to prepare for a backtracking approach when encountering a dead end.

[0075] S34 determines whether the endpoint currently reached by the robot is connected to an undrawn line segment. If the endpoint currently reached by the robot is not connected to an undrawn line segment (i.e., the dead end mentioned above), the robot will retreat to the inflection point that it has already traveled and is connected to an undrawn line segment. If none of the inflection points traveled are connected to an inflection point that is connected to an undrawn line segment, the robot will retreat to the starting point of the robot in the block.

[0076] When the robot moves and draws lines in the map, it records the starting point and all the turning points it passes through. If it encounters a dead end, it will find the last turning point it passed along the path and determine whether it is connected to any undrawn line segments. If it is connected to any undrawn line segments, it will start from that turning point and move along the undrawn line segments connected to the turning point to the endpoint with the shortest continuous distance from the turning point to draw a line. If it is not connected to any undrawn line segments, it will continue to return to the previous turning point and determine whether it is connected to any undrawn line segments. This process is repeated until a turning point connected to an undrawn line segment is found.

[0077] Of course, there might be situations where all inflection points are not connected and there are undrawn line segments. In this case, we should backtrack to the starting point of the tile. This ensures that all line segments can be drawn when the starting point is not at an endpoint.

[0078] Furthermore, in this invention, to shorten the robot's travel distance, when retracing back to the previous inflection point or starting point connected by an undrawn line segment, the retracing path is the line connecting the two points (or a straight path, but this connection does not need to be drawn as a line segment), instead of returning along the original path. For example, if the robot travels from point A to point B and then to point C, and finds that point C is a dead end, it can directly travel from point C to point A to return to the starting position A without having to go from point C to point B and then to point A.

[0079] It's also possible that when the robot reaches a starting point or an inflection point within a map, there are several endpoints connected to the starting point or inflection point. Several of these endpoints may have the same shortest connection distance, requiring line segment selection. In this invention, the selection rule is to choose the endpoint read first according to the order of map reading to draw the line.

[0080] As described in step S1, the robot first reads the drawing. The reading order is specific, so when encountering the same shortest connection distance, the endpoint to be read first can be selected. There is no need to do complex route prediction or other work, because in actual work, the difference between slightly far and slightly near will not have a significant impact, but it is not economical to spend too much computing power to solve the problem of choosing the same path.

[0081] The path planning method of the present invention will be illustrated by an example below.

[0082] like Figure 3As shown, there are three areas in the graphic to be drawn that require lines, each requiring multiple line segments. However, these three areas are not connected to each other. Therefore, the graphic is divided into three blocks: Block I (including connected line segments AB and AC), Block II (including connected line segments KG, KH, KF; GI; IH; HG; GF), and Block III (including connected line segments LM, MN, MQ; QP; PS; SR; RO; OP, ON; NM). The robot is indicated by arrows and is located outside the blocks.

[0083] First, calculate the distance between all points in each tile and the robot's initial position. Point A is the closest. The robot then travels to point A (the dashed line represents the robot's path outside the tile), and point A is designated as the robot's starting point within tile I.

[0084] The endpoints connected to point A include B and C. The line connecting point B to the starting point A is shorter, so the robot moves towards point B to draw a line, obtaining line segment AB. Upon reaching point B, there are no more undrawn line segments connecting to it, making it a dead end. Therefore, the robot retreats to point A (the starting point), then moves to point C and draws a line, obtaining line segment AC. At this point, line drawing for block I is complete.

[0085] The robot calculates the distances to all points in the other unlined tiles at point C (its current position). Point D in tile II is the closest. Therefore, point D is chosen as the robot's starting point in tile II, and the robot travels from point C to point D.

[0086] Among the undrawn line segments connected to point D, the shortest distance is to point F (i.e., among all endpoints K, F, G, H, I, and E in block II, endpoint F is closest to point D). Therefore, the robot travels from point D to point F, then passes through points E and H. Since there are two undrawn paths HK and HI at point H, meaning there are two paths to choose from when at point H, the robot chooses point I, which has the shortest distance to point I, as its next destination. Thus, the robot selects to draw a line at point I and passes through points G and K.

[0087] After reaching point K, the distance between the lines connecting points H and D, which are connected to point K, is equal, but point D was read first, so the robot moves towards point D.

[0088] After reaching point D, since point D is a dead end, the robot retreats to point K, the previous inflection point connected to the undrawn line segment, and then travels from point K to point H to complete the drawing work of block II.

[0089] The robot calculates the distance between its current position (i.e., point H) and all points in the remaining unlined tiles at point H, with point L of tile III being the closest point.

[0090] The robot travels to point L and starts drawing a line. When it passes point M, the line connecting point N is the shortest. So the robot travels from point M to point N and then to point O.

[0091] After reaching point O, the distance connecting point P is shorter, and the distance from point P to point Q and then to point M is shorter.

[0092] At this point, since line segments LM, MN, and MQ connected to point M have been drawn, point M is a dead end. The robot then retreats to the previous inflection point P. Since only line segment PS is connected to inflection point P and has not yet been drawn, the robot proceeds from point P through point S, point R, and then to point O to complete the drawing of block III.

[0093] In this diagram, the actual distance to backtrack to inflection point O would be shorter. However, considering that in most cases, returning to the previous inflection point with an undrawn line segment is actually more economical and requires no additional algorithm.

[0094] In addition, the present invention also provides a line-drawing robot, which uses the above-mentioned path planning method for path planning when drawing lines.

[0095] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0096] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A path planning method for a line-drawing robot, characterized in that... include: Read the point and line coordinates of the graphic to be drawn, and divide the graphic into several blocks, each block consisting of several interconnected line segments; Find the starting point closest to the robot's starting position, where the starting point belongs to the unlined tile; When the robot reaches the starting point, it draws a line according to the path pre-planned based on the tiles; After traversing all line segments on the tile where the starting point is located and completing the drawing, the robot finds the next starting point that is closest to its current location. This starting point belongs to the next undrawn tile. The robot then travels to the starting point and begins drawing lines for the next undrawn tile. Repeat this step until all blocks have been drawn with lines; The steps for planning paths based on the aforementioned tiles specifically include: The robot starts from the starting point and travels along the undrawn line segment connected to the starting point to the endpoint with the shortest distance from the starting point. Then, starting from the endpoint, it travels along the undrawn line segment connected to the endpoint to the next endpoint with the shortest distance from the endpoint, until all line segments in the block are drawn. During the line drawing process, the robot records each inflection point it passes through. An inflection point is an endpoint in the map segment connected by three or more line segments. Correspondingly, the step of planning the path based on the map segment further includes: Determine whether the endpoint currently reached by the robot is connected to an undrawn line segment; if not, the robot regresses to the last inflection point that is connected to an undrawn line segment.

2. The path planning method for a line-drawing robot according to claim 1, characterized in that: The step of the robot retracing its steps to the last inflection point it passed through that is connected by an unlined line segment specifically includes the following steps: The robot retraces its path to the last inflection point it passed and determines whether the inflection point it is retracing to is connected to an undrawn line segment. If there are undrawn line segments, start from the inflection point and draw a line along the undrawn line segment connected to the inflection point towards the endpoint with the shortest continuous distance from the inflection point. If no undrawn line segment is connected, continue back to the previous inflection point and check if it is connected to an undrawn line segment, until an inflection point with an undrawn line segment is found.

3. The path planning method for a line-drawing robot according to claim 2, characterized in that: The step of the robot retracing its path to the inflection point that it has already traversed and that is connected by an unlined line segment further includes the following steps: If it is determined that none of the turning points already traveled are connected to any undrawn line segments, then the robot reverts to its starting point within the block.

4. The path planning method for a line-drawing robot according to claim 3, characterized in that: Delete or mark the drawn line segments from the block.

5. The path planning method for a line-drawing robot according to claim 3, characterized in that: When retracing back to the inflection point or the starting point connected by an undrawn line segment, the retracing path of the robot is the line connecting the two points.

6. The path planning method for a line-drawing robot according to claim 4, characterized in that: When there are two or more endpoints in the map that are the shortest distance from the starting point, or the endpoints that are the shortest distance from the turning point, the robot selects the endpoint that is read first to drive and draw a line according to the reading order.

7. The path planning method for a line-drawing robot according to claim 1, characterized in that, The step of finding the starting point closest to the robot's starting position specifically includes: Obtain the coordinates of the robot's starting position; Iterate through the coordinates of all points in the unlined tile; The distance from the robot's starting position to all points in the map is calculated using the coordinates of the starting position and the coordinates of all points in the map. Choose the point with the shortest distance as the starting point.

8. The path planning method for a line-drawing robot according to claim 1, characterized in that: When reading the point and line coordinates of the graphic to be drawn, the length of each line segment is calculated.

9. A line-drawing robot, characterized in that, The line-drawing robot uses any one of the path planning methods in claims 1 to 8 for path planning when drawing lines.

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