Disclosure of Invention
The invention provides a full-automatic map building and updating method and an online distribution method of a large-scale passable regional map based on a multiline laser radar, and aims at the unmanned application requirement. The method comprises the steps that map construction and updating are achieved through a collection vehicle equipped with a multi-line laser radar, a map construction result is uploaded to a server for maintenance, the server distributes high-precision maps of passable areas around the unmanned vehicles through responding to online requests of the unmanned vehicles, decision and planning references are provided for unmanned driving, and a sensor system of the unmanned vehicles is supplemented or even partially replaced.
The technical scheme adopted by the invention is as follows (attached to a system flow chart 11):
technical scheme one of method needing protection
A construction method of a large-scale passable area driving map is characterized by comprising the following steps:
1. on the acquisition vehicle system, scanning a road environment by using a multi-line laser radar, and realizing ground filtering and barrier segmentation by using elevation difference to obtain a real-time road boundary barrier distribution map; and performing trafficable region probability grid mapping on road boundary barrier distribution of multiple frames by combining high-precision pose information provided by a differential Global Navigation Satellite System (GNSS) and inertial navigation equipment. (this step follows the conventional technique which has been generally used)
2. On the acquisition vehicle system, in the probability grid graph building process, self-adaptive subgraph block building is carried out according to the radar frame number and the acquisition vehicle motion variation, and R-Tree is introduced to build a spatial index by taking subgraphs of different sizes as nodes. And moving the nodes far away from the acquisition vehicle out of the memory in real time according to the R-Tree and storing the nodes on the disk, and simultaneously reading back the memory of the nodes close to the acquisition vehicle existing in the disk, thereby realizing dynamic memory scheduling in the process of establishing the graph and realizing large-scale graph establishment (the step is one of innovations of the method).
3. And storing the R-Tree and all node data thereof to a disk after the map is built and suspended. The map building process can be continuously read and recovered by the acquisition vehicle map building system, so that the map building of the built map area is updated and expanded, and the acquisition vehicle system realizes the automation of map large-scale map building and updating (the step is one of innovations of the method).
Method technical scheme II needing protection
1. The unmanned application method of the large-scale passable regional driving map after being constructed is characterized in that after a collection vehicle system completes map construction, R-Tree and all sub-map data thereof are uploaded to a server, and map online distribution service is provided. The server responds to concurrent requests of a plurality of unmanned vehicle clients, utilizes the R-Tree index to quickly search subgraph nodes adjacent to the unmanned vehicle clients, fuses the subgraph nodes and sends the subgraph nodes to the unmanned vehicles in real time, so that the subgraph nodes are assisted to carry out high-precision passable area maps in a visible range, and decision and planning processes of unmanned driving are assisted (the step is innovative by the method).
The invention has the beneficial effects that:
1. the full-automatic map building and updating of the high-precision passable regional map facing to the unmanned driving requirement are realized, manual interaction is not needed, the map building process can be interrupted and recovered, and the technical usability is high;
2. the map building result is maintained through the server, map requests of a plurality of unmanned vehicle clients can be responded in a concurrent mode, high-precision passable area map fusion results are distributed quickly according to needs, and therefore the sensing cost of the unmanned vehicle system is reduced, and the cost of the unmanned vehicle sensing system can be effectively reduced;
the innovation points are as follows:
1. based on the spatial index of the integrated R-Tree, efficient subgraph search and dynamic memory scheduling are realized in map building, updating, expanding and map distribution services, so that map building of any scale and real-time map distribution and fusion can be realized under the condition of limited memory occupation;
the map of the passable area with high availability and high precision for the unmanned vehicle system is provided, the defects of the sensor of the unmanned vehicle can be overcome, the configuration cost is reduced, and the driving safety is improved.
Detailed Description
The driving path planning of the unmanned vehicle depends on the perception of the surrounding environment, and the sensor is limited by factors such as resolution, shielding and weather, so that the passable area range is difficult to robustly extract. Therefore, high-precision automatic map construction is carried out on passable areas limited by static barriers such as road edges and guardrails by the collected vehicles, and online distribution is carried out by using the server, so that high-availability passable area map information can be provided for a plurality of unmanned vehicles, the correctness of decision and path planning is ensured, the dependence of the unmanned vehicles on sensors is reduced, and the cost of the unmanned vehicles is further reduced. Based on the technical scheme of the invention, the technical scheme of the invention is described in more detail with reference to the accompanying drawings.
The steps are as follows in sequence:
example 1
Construction process of large-scale passable area driving map
1. Extraction of passable region and probability grid construction map
1.1 passable region extraction based on multiline lidar
The road environment around the vehicle is scanned by a multiline lidar (see fig. 1) arranged on an acquisition platform truck. And obtaining road boundary obstacle distribution by using a point cloud screening method based on the height difference, namely passing areas.
1.1.1 multiline lidar layout and external parameter calibration
The invention adopts a multi-line laser radar (a plurality of 16 lines, 32 lines or a single 64 lines and the like) which is arranged on the roof of a collecting vehicle. Enabling its scanning area to cover the entire road area. And calibrating the external parameters of the laser radar by an automatic or manual method. And converting the three-dimensional point cloud expressed in the radar coordinate system into a vehicle local positioning coordinate system through coordinate system transformation.
1.1.2 passable region extraction
Dividing the visible plane range of the radar into grid units with the size of 1m x 1m, and counting the minimum value z of the cloud height values of three-dimensional points in each grid unit areaminGiven a threshold value Δ1The coordinates in the point cloud data of the area satisfy z-zmin>Δ1The points of (a) are marked as obstacle points. The obstacle points are then projected onto a two-dimensional grid cell map (e.g., 0.2m x 0.2m) of the resolution required to construct the map. And traversing the grid units, counting the number of the barrier points in each grid unit, and comparing the number with the vertical passable range of the vehicle. If the obstacle point is located in the passing range of the vehicle, the grid cell is marked as an obstacle cell, and the rest are passable areas. The passable area extraction is as shown in fig. 2 before and after.
1.2 probability grid map of passable area
Because the extraction result of the passable area of a single frame may cause the robustness problem due to noise and the like, the probability grid mapping method needs to use the extraction results of multiple frames to construct the probability grid map. And establishing a Cartesian coordinate system by taking the starting point of the map as the origin of the coordinate system of the global map, wherein the positive east and the positive north are respectively the positive directions of X, Y. In the mapping process, the high-precision pose of the acquisition vehicle is acquired in real time, and the point cloud is converted from the vehicle local positioning coordinate system to the global coordinate system (see step 1.2.1). And initializing and updating the probability value of the barrier in the grid unit map by using the extraction result of the multi-frame passable area, so as to realize the construction of a probability grid map (see step 1.2.2).
1.2.1 pose data acquisition and coordinate System transformation
And the RTK GPS, inertial navigation and vehicle speed information are fused through the extended Kalman filtering, so that high-frequency and high-precision vehicle pose data are acquired in good and temporary missing areas of the RTK GPS. The coordinates of the obstacle in the passable area are then converted from the vehicle local localization coordinate system to the global coordinate system (equation 1) using coordinate conversion.
Wherein P (P)x_global,py_global) Representing the coordinates of the obstacle mesh in a global coordinate system, P (P)x_local,px_local) And representing the coordinates of the obstacle grid under the vehicle local positioning coordinate system, wherein theta is a course angle, and delta x and delta y are offsets between the origin of the vehicle local positioning coordinate system and the origin of the mapping.
1.2.2 probability grid map initialization and update
The probability grid map describes the likelihood of a certain map grid cell as an obstacle using probability values. A higher set probability value represents a higher probability that the grid cell is an obstacle. Dividing the corresponding grid cells in the probability grid map into two sets of barrier (hit) and barrier-free (miss) based on the accessible region extraction result of each frame, and distributing probability value phit0.55 or pmiss0.45. If the grid cells are initialized, the result is subsequently extracted according to the passable area of each frameProbability updating is performed on the grid cell probability values (see equation 2).
Wherein M isnewFor updated grid cell probability values, MoldFor the pre-update grid cell probability values, clamp is a function that limits the valid range of probability values.
2. Adaptive blocking and dynamic memory scheduling
The probability grid map in step 1 needs to allocate a memory space with a fixed size according to the mapping range, so that the probability grid map is difficult to be expanded to mapping application in a large-scale scene due to the limitation of the memory size. Therefore, in order to realize large-scale map building, the probability grid map needs to be subjected to self-adaptive partitioning and a subgraph is built. The invention also provides a method for constructing R-Tree space index for the subgraph and realizing the dynamic scheduling mechanism of the subgraph, which realizes the basic constancy of memory occupation and has a flow chart shown in figure 3.
The details are as follows:
2.1 map adaptive partitioning
A self-adaptive map blocking method is provided, which integrates the number of radar scanning frames and the motion variation of a collection vehicle, and automatically blocks a grid map in the map building process. First, the initial sub-graph range is a range a with the current position as the center point0*a0A square area of (a). And when the number of effective scanning frames exceeds a set threshold or the collection vehicle moves out of the range of the subgraph, finishing the construction of the current subgraph. The sub-graph is assigned an ID and a minimum outer bounding rectangle (MBR) of the sub-graph is created and inserted as a node into the R-Tree. While a sub-graph is created and initialized for receiving data, adjacent sub-graphs contain overlapping parts (about 10% of the sub-graph size).
2.2 dynamic scheduling of memory based on R-Tree
The R-Tree is a dynamic balance search Tree, and the average operation complexity of the R-Tree and various varieties thereof is logarithmic, so that the operations of inserting, updating, deleting, searching and the like of indexes of the space object represented by the MBR can be efficiently performed.
2.2.1 maintenance of R-Tree
Each node in the R-Tree includes 1 to n units consisting of a subpicture number ID and an MBR of a spatial object, i.e., (MBR, ID). Wherein n is an adjustable parameter used for clustering adjacent units so as to reduce the index data volume. When a subgraph node is newly added into the R-Tree, the inserting position is selected to add the new node according to the principle of minimizing the MBR overlapping area of the R-Tree node, the subgraph ID is used as the unique identification index of the node, and the x is calculated by the space coordinate of the subgraphmin、yminAnd xmax、xmaxAnd the range attribute determines the MBR of the subgraph. (FIG. 4 is an example of a map R-Tree structure).
2.2.2 dynamic scheduling method for internal memory
In the real-time graph building process, after the sub-graph blocks are added into the R-Tree, space query is carried out on the basis of the R-Tree (see step 4.2), n sub-graphs near the current position of the vehicle are searched, and the rest sub-graphs are written out according to the identification IDs, transferred and stored to a disk and removed from a memory. And when the vehicle moves to the established map area, searching node numbers through the R-Tree index, reading corresponding sub-map blocks by a magnetic disk, loading the sub-map blocks into a memory, and updating the grid map. Therefore, the subgraph dynamically moves out and reads back in the memory and the disk, dynamic scheduling of the memory is realized, constant memory occupation of the graph building system is ensured, and large-scale graph building is realized (the subgraph and global map result is shown in fig. 5).
3. Automatic expansion and updating of large-scale passable area map
Because the map building of a large-scale area cannot be completed once in practical use, and the map needs to be updated due to road building, route change and other reasons, the map building result is required to be easy to update and expand.
The mapping system provided by the invention can be restored to the last mapping process according to the current position coordinate by using a dynamic scheduling method: and after the map is built, outputting the generated map file of the passable area, and simultaneously storing the initial position coordinate of the map and the R-Tree spatial index of the sub-map block information to a magnetic disk.
When the map needs to be expanded or updated, the sub-graph files in the disk, the corresponding R-Tree spatial index and the initial position configuration information are read, the mapping system can be restored to the previous mapping process, the map is subjected to probability updating and new area expansion mapping from any position on the basis of the existing mapping area, incremental mapping and automatic updating are achieved, and mapping and maintenance of the large-scale map are achieved, and the process diagram is shown in
Fig. 6.
Example 2
The following step 4 is further provided on the basis of example 1 to introduce the application of the map in unmanned driving
4. Accessible regional map management and application, the flow chart is shown in fig. 7.
In order to realize the concurrent map service of the unmanned vehicle client, a server platform is constructed by a MapServer open source map engine and is used for publishing the large-scale passable area driving map finally established based on the embodiment 1. Because the whole passable area map is composed of a plurality of overlapped subgraphs, the tasks of subgraph search, fusion and online distribution are efficiently completed through R-Tree space index according to the position coordinates of the client. And for the overlapped areas of the multiple sub-images, fusing the probability grids of the overlapped areas in a weighting mode to generate a final passable area binary map.
4.1 location-based client search request
When a client side sends a map request to a server in unmanned driving, based on the position of the user, the server side utilizes the R-Tree corresponding to the sub-graph data to perform adjacent sub-graph search (the specific method is shown in the implementation step 4.2), and the sub-graph data which is inquired to meet the distance condition is used as a fusion object.
4.2R-Tree based subgraph search
After a search request with a rectangle with the peripheral range (L x W) of a vehicle body of a client side as a space target search rectangle is given, recursive traversal is carried out from a root node of the R-Tree, a node pointer contained in the R-Tree is traversed from top to bottom in a mode of average time complexity O (logN), space polygon containing query is carried out (N is the total number of index data), and N sub-graph index IDs near the current position of the vehicle are rapidly queried and obtained.
4.3 subgraph fusion
Assigning values w to n sub-graphs containing overlapping regions according to timestampsiProbability p of map grid of final passable areaiWeighted averaging is performed to obtain an obstacle probability value representation result p' (equation 3). Taking a probability threshold value theta as an obstacle classification basis, and taking p'>The grid cells of θ are marked as obstacles, and a binary map of the area where no-one vehicles can pass can be obtained, as shown in fig. 8. According to the pose of the unmanned vehicle client, a local map of the unmanned vehicle in the passable area under the current pose can be obtained, high-precision analysis reference is provided for driving decision and path planning (as shown in fig. 9), and the sensing range and the obstacle result of a vehicle sensor are supplemented.
4.4 Online distribution
The system is based on a mature map engine, can respond to map requests of multiple clients, realizes rapid map downloading and caching, and meets the real-time requirement of unmanned driving. The map management and distribution system flow is shown in fig. 10.