Mastering the Datasheet: A Complete Guide to Lidar Specs

In a previous article, we unraveled the intricacies of two seemingly straightforward lidar specs – Maximum Detection Range (Max Range) and Field of View (FOV):

·??????? How is Max Range measured?

·??????? Why is Max Range coupled with Reflectivity?

·??????? What does a long Max Range mean?

·??????? What is effective FOV?

·??????? Can FOV change without hardware change?

·??????? Read full article

While Max Range and FOV are two major specs that indicate lidar performance and determine its application (long-range vs. near-range sensing, ADAS vs. autonomous vehicles, etc.), there are other key specs in a lidar’s datasheet that one would need to pay close attention to, in order to comprehensively understand a lidar’s performance and its suitability for a specific use case and environment.

Points Per Second (PPS), for example, is often used as a key indicator of a lidar’s true capability of data collection and processing.

Points Per Second (PPS)

Lidar images consist of point clouds, and PPS refers to the number of points the lidar processes each second. Every second, the lidar emits a certain number of points and receives part of them back from the object. The difference between the two would be a number of points that never return, which is meaningful in that those “lost” points map out unoccupied spaces. Theoretically, PPS can mean both the number of emitted points, or the total count of returned and lost points.

Within a given FOV, a higher PPS results in denser point clouds, which enables us to see more details of an object. That means PPS needs to be looked at together with FOV – 1 million points per second across a 120° x 15° FOV are likely to enable a denser image than the same number across a 360° x 15° FOV.

We previously talked about effective FOV. Similarly, only PPS within the effective FOV is considered effective PPS. For example, a rotational lidar might have a high PPS, but if it's mounted on a vehicle's front grille, with a significant part of its FOV obstructed by the vehicle, its effective PPS is considerably reduced.

Frame Rate

Frame Rate is the frequency the lidar repeats the processing of an entire FOV within a second. Each frame provides a snapshot of the environment, enabling the creation of dynamic point clouds that capture object motion. Frame Rate is an important specification to consider alongside PPS.

With a fixed FOV and given PPS, a higher frame rate results in fewer points per frame but more frequent updates of the scene; a lower frame rate allows for more points per frame but fewer updates. Similarly, maintaining the same point density in each frame with a higher frame rate often results in a smaller FOV.

Lidar companies adjust these parameters to find the optimal balance for their specific applications. Different OEMs may require different frame rates, with common choices being 10Hz and 20Hz, both of which are often configurable. Product marketing for lidar systems typically showcases data captured at 10Hz.

Angular Resolution

Angular Resolution refers to the average FOV allocated to each point, or lidar “pixel”. That’s why they are written as h° x v° (e.g. 0.05° x 0.05° or 0.1° x 0.3°). It's important to note that this average can vary depending on the lidar's scan pattern. When h=v, that means the points are distributed relatively evenly in both horizontal and vertical directions. For some lidars, especially those line scanning ones with fewer channels, v is significantly larger than h. As a result, their images often have large vertical gaps.

Cepton's Vista lidar and Ultra lidar employ different scan patterns, for example. While one generates mesh-like point clouds, the other produces more linear arrangements. Despite their design to both create dense and evenly distributed point clouds, their angular resolutions are both average values. The spacing between individual points may vary slightly.

Range Accuracy

Like our eyes, lidars can suffer from mild astigmatism. Range Accuracy refers to the precision with which a lidar can measure the true distance to a target. For example, a range accuracy of ±3cm means that the actual distance to a detected object could vary by up to 3cm from the measurement provided by the lidar.

Different lidar applications have varying standards for acceptable range accuracy. In automotive applications, ±2cm is usually standard. However, this tolerance may differ for other uses – the flash lidar used in an iPhone, for example, would require a much smaller Range Accuracy error to enable Face ID.

Range Accuracy depends on the lidar's detection method, the quality of its components, and its overall data processing capabilities. The choice between two major detection methods – Time of Flight (ToF) and Frequency Modulated Continuous Wave (FMCW) – may result in different range accuracies.

FMCW lidars are more susceptible to poor laser source stability, both optically and electronically. They are more reliant on the quality of laser and detector modules to perform well. As a result, they typically offer poorer Range Accuracy per dollar compared to ToF lidars. In contrast, ToF technology provides a more cost-effective solution for achieving OEM-required range accuracy.

Size

While size does not describe a lidar’s performance, it is a crucial specification.

OEMs puts significant emphasis on the size of the lidar system. A compact lidar design ensures optimized compatibility with the sleek designs of modern vehicles. In addition to an overall small package, thinner designs are preferable in many automotive applications, as roofline and windshield are common locations for lidar integration.

Achieving high performance in a small form is made possible by an efficient lidar architecture combined with a powerful System on Chip (SoC), which optimizes signal processing for superior results. Proprietary lidar SoCs, compared to off-the-shelf alternatives (i.e. FPGAs), deliver targeted performance with a much smaller footprint, lower power consumption and reduced costs. This is why Cepton has been developing its own lidar SoCs since 2019.

Power Consumption

Implementing a powerful lidar solution should not come at the cost of high power consumption. As OEMs focus on energy efficiency, minimizing power consumption in lidar systems has become crucial. This is especially true for electric vehicles where mileage between charges is key.

Low power consumption is also crucial for smooth vehicle integration, as excessive heat from high power use limits where the lidar can be placed. Overheating not only compromises sensor performance, but also causes premature wear and failure and poses safety risks. Even devices like iPhones shut down automatically to prevent overheating, not to mention automotive lidars in enclosed spaces.

Some lidar manufacturers address overheating by integrating active cooling systems, such as fans. However, these systems only dissipate heat rather than eliminating it; they also require extra power budgets and increase the overall system footprint.

At Cepton, we believe the optimal solution is to minimize the lidar’s power consumption so that only passive cooling is needed. Our Ultra lidar, for example, consumes under 13W to enable seamless integration behind the windshield and in the roofline without the need for active cooling.

Laser Wavelength

This refers to the type of infrared light used in the lidar system. Common options are 1550nm, 905nm and 850nm. While 1550nm has a higher eye-safe threshold that enables the lidar to “see” further without causing eye damage, it does not necessarily guarantee better performance, as we’ve illustrated previously.

To learn more about how 1550nm lidar compares with 905nm lidar, visit this blog post.

Eye Safety

To be deployed in vehicles and infrastructure, lidars must be Class-1 eye safe. Look for this important specification in a lidar datasheet or check for the eye safety certification from its supplier.

Proper optical design is crucial for ensuring eye safety, which depends on many factors – read more on the subject here.

Other Key Specifications

In addition to the above-mentioned specifications, a lidar datasheet often includes Operating Temperature, Storage Temperature, Environmental Protection Rating, Data Per Point, Network and Synchronization.

Talk to our Custom GPT, the Cepton Lidar Companion, to find more information.

While ongoing advancements in lidar architecture continue to enhance lidar performance through longer range and higher resolution or data rate, achieving the optimal balance between performance and size, power and cost remain crucial for lidar manufacturers. We are dedicated to delivering practical, scalable lidar solutions that meet rigorous mass-market demands by addressing implementation challenges alongside performance metrics.