Table of contents
1.2 Construct a path using coordinate points
1.4 Adhesion coefficient of road surface
Carsim provides a method to quickly build road scenes. In the simulation, we can use the demo scene that comes with the software itself or make corresponding modifications on this basis. At the same time, we can also choose to build a new scene map completely by ourselves. It includes the definition of roads, the introduction of terrain elements, road surface information, etc. Ronaldinho will simply explain these contents, hoping that these contents can provide some new ideas for friends who are learning Carsim. Of course, some of the opinions in the article are only Xiao Luo's careful consideration. If there are any deficiencies, please criticize and correct them.
1. Road definition
A basic road in Carsim includes path trajectory, road vertical height, road adhesion coefficient and road width. The path trajectory is the path that our target needs to make the vehicle travel. Here you can choose different methods to build the same path trajectory, or you can use one method to build different trajectories. As for which method to use, it depends on the data in your hand or what kind of path trajectory you want to build. In Figure 1.1, we can see that we can choose different methods to build the path, including road segmentation, coordinate input or importing the path from the outside. Here I mainly explain the relatively simple method of using road sections and road coordinates to build. If you want to use the following methods If you want to learn more, you can view the help documentation or discuss in the comment area.
Figure 1.1 Construction of path trajectory
1.1 Road Segment Builder
When using the road segment method to build a road, we first need to know the length of each straight road segment, or the radius, curvature, angle, etc. of the curve. In Figure 1.1.1, we can split the road and then build it according to the geometric parameters of each part. The number of road sections can be set in the red box in the lower right corner, and the red box on the right mainly sets the geometric parameters of the road section. Enter the X and Y axis coordinates in the staring section to set the starting point of the path. If not input, the default coordinate origin is the starting point. If our road is a closed loop, it is recommended to check Treat as loop. After checking this option, the vehicle will not stop when it reaches the end during simulation, or the vehicle can drive within the loop.
Figure 1.1.1 Constructing the path track in segments
1.2 Construct a path using coordinate points
Whether building a path or placing obstacles in Carsim, we can use the simpler coordinate point method. Using this method requires us to know the coordinates of the path, and a road section is composed of many coordinate points. Therefore, the smoothness of the road section depends on the density of coordinate points. As shown in Figure 1.2.1, the number of coordinates can be set in the Set Table Size section. Enter the coordinates of the x and y axes in the large box. If our road is a closed-loop road, please check Looped path. It should be noted that when using a closed-loop , the coordinates of the start and end points should be the same.
Figure 1.2.1 Building a path using coordinates
1.3 Path height
Real roads are impossible to be completely smooth. For example, some road sections have slopes or potholes. The most common thing is that some roads have speed bumps. There are many ways to set the road height. In fact, Carsim is a relatively flexible software, mainly because the modeling method is not unique, so we choose a relatively simple and easy-to-understand method for introduction. In Figure 1.3.1, we can build different path heights according to our needs. Here I take a part of them for a brief understanding. For more in-depth understanding, please refer to the help documentation or refer to related books. Figure 1.3.2 shows the road height we set randomly. The coordinates in the figure indicate that it needs to go uphill from 0, and then it starts to go downhill at 90 meters, and the slope is mainly determined by the Y coordinate value.
Figure 1.3.1 Path height
Figure 1.3.2 Set road height
1.4 Adhesion coefficient of road surface
The road surface adhesion coefficient is related to the braking force and driving force of the vehicle. If we do not choose the appropriate road surface adhesion coefficient, it will be meaningless for our tests or parameter adjustments. Carsim provides us with various road surface adhesion coefficient options, of course, we can also modify it according to the nature of the test. At the same time, different adhesion coefficients can be defined in different positions of the same road, for example, in a normal road, one side has snow and the other side is a normal road section. The following table 1.4.1 is some commonly used road surface adhesion coefficient tables that Xiao Luo found on the Internet. Please use it with caution (in the future, if something happens, don’t ask Brother Xiao Luo, manual dog head to save your life). In Figure 1.4.1, we can choose a relatively simple one, that is, the whole road is given a value of road surface adhesion coefficient. But sometimes we need to separate different road sections for different road surface adhesion coefficients when doing special working conditions, or in the same road surface, the road surface adhesion coefficients at different positions on the left and right are not the same. As shown in Figure 1.4.2, the horizontal part of the red frame is the value of the road width, the first line under X is the distance corresponding to the road, and the values of the next few lines are the road surface adhesion coefficient. We can intuitively understand it through the map in Figure 1.4.3 The road surface adhesion coefficient information has been set.
Table 1.4.1 Adhesion coefficients of common road surfaces
Figure 1.4.1 Adhesion coefficient of road surface
Figure 1.4.2 Set road adhesion coefficient
Figure 1.4.3 3D Map of Road Surface Adhesion Coefficient
1.5 Road width
The width of the road is also an essential part of scene rendering. If we do not define the width of the road, we will not be able to see the road surface in post-processing, but we can only see the car driving along the path trajectory, but this does not affect our simulation. In Carsim, some road settings can be omitted, and animation rendering generally does not affect the simulation results, but some animation rendering conflicts will cause errors in simulation or post-processing. Going back to the road width, we have the option to set some width parameters for the road as well as parameters for the road edges. At the same time, it is also necessary to define the rendered length of this road width. Figure 1.5.1 is a brief list of the functions of each option for you. Since there are many things in this part, it is not easy to understand, and usually you only need to have parts 2, 3, and 4 in the diagram, so I won’t go into details. , if you want to know more, you can read the help documentation.
Figure 1.5.1 Road rendering
In some simulations, we need to place obstacles. Although the vehicle cannot sweep away the obstacles in the animation rendering, it just passes through the obstacles (maybe I didn’t find the right way, I hope that the friends who can solve this problem can share with you share experiences). But in some simulation conditions, we need to add some obstacles as auxiliary props. The method of adding obstacles is shown in Figure 1.5.2, where we can choose to add other elements, such as houses or trees. Here we take the pile bucket as an example. There are two methods. The first method is to use coordinate points, and the second method is based on the length of the road and the distance between obstacles and the center of the road. The left picture in Figure 1.5.3 is the method of placing obstacles using coordinate elements, where x is the longitudinal position of the road, and y is the horizontal position. Of course, if we want to modify the rendered model, we can click 3 in the figure. On the right side of Figure 1.5.3, obstacles are placed using the method of road length and lateral coordinates. The advantage of this method is that even if the road is curved, the obstacles will be on the side of the road. The final effect is shown in Figure 1.5.4.
Figure 1.5.2 Two ways to add obstacles
Figure 1.5.3 Place obstacles in different ways
Figure 1.5.4 Final rendering
2. Import of terrain
In order to make our scene closer to reality, we can import more terrain elements or elements in the scene. Although rendering generally does not affect the simulation results, the reference object of the rendering can allow us to see the state of the vehicle more intuitively, or provide the driver with a good sense of the road when using the driver-in-the-loop simulation function as we will talk about later. and driving experience. So we can simply understand the import of scene elements. Figure 2.1 shows the simple operation of importing the terrain 3D model. Since this part is not commonly used and is relatively simple, it will not be explained in detail.
Figure 2.1 Related settings for importing 3D files
3. Conclusion
Before building a road, we need to know what kind of road we want to build. We need to determine the path, road height, width, road adhesion coefficient, etc. If necessary in the test, we must consider the placement of obstacles When importing 3D models, you need to pay attention to the format of the file. The explanation of road construction in this article is relatively basic and relatively simple and easy to understand. As for some details involved, the explanation is not explained because some things need to be practiced to master. The explanation is difficult to explain clearly. It may only take one or two practical operations. The boss will be able to remember, and Xiao Luo will stop talking. If there are any omissions or deficiencies, please add them.