Tuesday, May 08, 2018

LiDAR Technologies Compared

ArsTechnica compares different LiDAR technologies in a form of interview with Ouster CEO and co-founder Angus Pacala. Ouster develops a spinning mechanical LiDAR similar to Velodyne. Angus also co-founded Quanergy, so that he was closely involved in solid-stage LiDAR design. Few quotes:

"Pacala pointed out a couple of big advantages of the classic spinning design. The most obvious one is the 360° field of view. You can stick one lidar unit on the top of a car and get a complete view of a car's surroundings. Solid state lidars, in contrast, are fixed in place and typically have a field of view of 120° or less. It takes at least four units to achieve comparable coverage with a solid-state sensor.

Another less obvious advantage, Pacala says, is that eye safety rules allow a moving laser source to emit at a higher power level than a stationary one. With a scanning solid-state unit, putting your eye inches from the laser scanner could cause 100 percent of the laser light to flood into the eye. But with a spinning sensor, the laser is only focused in any particular direction for a fraction of its 360° rotation. A spinning lidar unit can therefore put more power into each laser pulse without creating risk of eye damage.

The tiny mirrors in MEMS systems can only reflect so much light. That makes it inherently difficult to bounce a laser beam off a distant object and detect the return flash.

The phased-array approach tends to produce beams that diverge more than other techniques, making it hard to achieve a combination of long range, high scanning resolution, and wide field of view.

With flash lidar, the light from each flash is spread over the entire field of view, which means that only a fraction of the light strikes any particular point. And each pixel in the photodetector array is necessarily quite small, limiting the amount of returned light it can capture.

Overall, my conversation with Ouster's Pacala made me less bullish about improvements in lidar costs. Prices are falling, as illustrated by Velodyne's 50 percent price cut for its 16-laser unit this year. And if you're willing to settle for a lidar with lower range and resolution, you can find units that cost a few thousand or even a few hundred dollars.

But the best lidar units—and possibly the only ones that are suitable for fully driverless cars—still seem to cost tens of thousands of dollars.

The headline originally described Ouster's lidar as "bulky," but Pacala emailed to dispute that: "The Innoviz Pro and the proposed Innoviz One are both way bigger, so is AEye's iDAR, so is Continental/ASC's flash lidar, so is Princeton Lightwave's, so is Luminar's old and new device, so are all three of Cepton's products, and so is the Quanergy's S3.

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