Dual LiDAR or Single LiDAR for Cars?

Jidu SIMUCar dual LiDAR solution sparks heated conversations

According to Jidu at the media communication meeting, they announced a LiDAR solution is to install dual LiDARs symmetrically on the front hood of the car, and they can be raised and lowered, and can be retracted when not in use. Once the dual LiDAR solution of Jidu SIMUCar was announced, it caused a heated discussion. The most heated topics are: Whether it is better to use dual LiDAR on the hoods of the car or one LiDAR on the roof? Where exactly should the LiDAR be installed? How does the LiDAR location affect LiDAR performance? Before Jidu dual LiDAR solution, most automotive LiDARs were installed on the roof or front bumper. The installation of two retractable LiDARs on the hood is deemed a groundbreaking solution. Considering the practicality, how does this plan work?

First, the point cloud field of view of the Jidu dual LiDAR is wider which can ensure safer driving. Compared with the 120-degree horizontal FOV of the single-LiDAR design, the dual LiDAR installed at the front hood of the vehicle can achieve a 180-degree horizontal FOV coverage. The 120-degree FOV and the 180-degree FOV are still different, and the corner cases solved are different, so there are still differences in product capabilities, experience, and safety.

In driving scenes such as when there are obstructions on the left side and right side, the dual LiDAR is better at recognizing pedestrians or obstacles crossing left and right.

Secondly, dual LiDAR is more accurate at identifying key areas of the vehicle. In the area of 60 degrees FOV directly in front of the vehicle, dual LiDAR can double overlap, and the point cloud data on the target is more and denser, and the recognition accuracy is higher.

Third, in terms of redundant safety of high-level autonomous driving, dual LiDAR solution can be mutually redundant, which is more reliable than the single LiDAR solution.

Impact of different installation locations on coverage

Roof LiDAR solution is applied on Li Auto L9. Li Xiang expressed his opinion on Jidu’s dual LiDAR solution: “there is no difference in the performance of one LiDAR on the roof or of dual LiDAR on the hood or bumper, and even single LiDAR solution on the car roof will perform better. However, the single LiDAR solution on the car roof is optimal for pedestrian collisions, maintenance costs, and vibration control (linked to the main body). The only problem is that the shape of the roof LiDAR will need to adapt.”

Whether it is better to use dual LiDAR on the hoods of the car or one LiDAR on the roof? Let’s discuss both options to compare their advantages and disadvantages.

The difference in LiDAR installation height is different for target detection. The higher the ground line, the larger the blind area. But at the same time, its field of view will also be better. For example, the LiDAR installed higher can detect two cars in front of it. The installation of the roof needs to take into account the position of the lower edge of the field of view (FOV) and the roof cover, so there are usually a few degrees of declination adjustment depending on different automotive models. If it is installed on the hood, the hood is generally flat, so the LiDAR needs to be tilted upwards, cutting part of the FOV of the LiDAR. The main influence here is the vertical FOV of the LiDAR. Generally, the vertical FOV is smaller. Taking Neuvition Titan M1-Pro as an example, its horizontal FOV and vertical FOV are 120 degrees and 25 degrees respectively.

In the vertical field of view, the higher the installation position of the LiDAR, the farther its field of view is, but the near blind spot will be relatively large. Therefore, in terms of coverage, if a forward-facing LiDAR is installed on the roof, it is safer to add 2-4 medium and short-range LiDARs at four corners of the car. This is also generally considered a more reasonable configuration.

Of course, the installation of LiDAR depends on the needs of auto companies. Considering the cost performance, if more attention is paid to the identification of nearby obstacles, installing the LiDAR in a lower position can minimize the near blind spot. For example, Mercedes-Benz EQS with L3-level autonomous driving assistance functions. Since the L3-level autonomous driving capability functions during autonomous driving at high-speed congestion and the vehicle speed is less than 60km/h, the Valeo second-generation SCALA LiDAR installed in the middle of the front bumper can well achieve its purpose. However, when the installation position is low, the problem of being easily blocked by the front should also be considered, so the cooperation of other sensors is also required.

Jidu’s dual LiDAR solution is installing the LiDAR at the center on the front cover of the car. AT128 LiDAR used by Jidu SIMUCar has a detection range of 200 meters under 10% reflectivity, to obtain a moderate field of view. In the case of a high-speed scene, there are generally fewer nearby obstacles, and the roof LiDAR can have a better vision in the distance. The NIO ET7 and Li Auto L9 have adopted this solution. Of course, omnidirectional coverage of vehicle LiDAR is naturally the best and safest.

The advantage of the Jidu dual LiDAR solution mainly focuses on the horizontal FOV.

First of all, since the LiDARs on mass-produced vehicles are semi-solid-state LiDARs, which cannot achieve the mechanical 360-degree horizontal FOV. Why not use a mechanical LiDAR? on the one hand, it is expensive, on the other hand, it is damageable and difficult to maintain.

The LiDAR used by Li Auto L9 and Jidu has a horizontal FOV of 120 degrees. At this point, the advantage of using dual LiDARs becomes apparent. On a horizontal FOV, a single LiDAR can only achieve 120-degree coverage, while using dual LiDARs can achieve 180-degree coverage. And in the overlapping area of 60 degrees in front, due to the high density of point clouds, the identification ability is also stronger and the accuracy is higher.

Of course, what is discussed here is simply taking into account the effect of LiDAR installation on the FOV based on all other variables being equal. In terms of actual effect, it is naturally also affected by the performance of the LiDAR itself.

Consideration of appearance and engineering

This involves other considerations when choosing an installation location, such as appearance. No matter how it is designed, installing a LiDAR on the roof will inevitably lead to an extra bulge. This not only affects the appearance but also affects the car’s aerodynamic performance. Therefore, Xpeng chose to install LiDAR at the headlights of the cars on both sides for concealment.

Like the Audi A8 and Mercedes-Benz EQS, which were the first to be equipped with LiDAR, the LiDAR hardware is also integrated on the bumper, which has little effect on the appearance.

In addition, there are many details to consider when choosing an installation location for LiDAR, such as engineering issues. The LiDAR installed on the roof is relatively less affected by the impact of mud and gravel. But it is difficult to control the use of cleaning devices. In addition, the roof of the car may be too hot due to sunlight exposure in summer, which might also increase the speed of product aging.

While the main challenge of the retractable LiDAR installation is the reliability of engineering. For example, due to mechanical aging, vibration, and other reasons during use, the installation angle is shifted, and the requirements for online misalignment detection and correction are higher.

Installing LiDAR on the front hood of the car has hidden dangers in pedestrian protection and may not pass the latest pedestrian collision regulations in China. The current car front hoods on the market are generally designed to be softer and more elastic, to reduce damage as much as possible when colliding with pedestrians. However, it is unable to meet this requirement if installed with LiDAR. At the same time, the position of the front hood is also easily deformed due to daily small collisions, resulting in damages to the LiDAR, which in turn pushes up the maintenance cost of minor accidents.

In general, where the LiDAR is placed is not a single-line question, but a balance and trade-off after comprehensive consideration of various factors such as perception performance, safety, cost, appearance, and engineering.