5 ms·

Lidar, optical distance and time of flight sensors

71 points by mahirsaid 1y ago

Animats 1y ago
I was expecting flash LIDAR and MEMS mirror systems to dominate self-driving cars by now, but rotating machinery is still dominant in the US. The trend in China and Japan is a long-range forward-facing LIDAR coupled with three shorter-range units for side and rear coverage.[1] The long-range unit still costs around US$10,000. This should come down with volume. [1] https://www.robosense.ai/en/news-show-1908 https://www.robosense.ai/en/news-show-1908 [2] https://openelab.io/products/robosense-em4-thousand-beam-long-range-digital-lidar?srsltid=AfmBOoriES25fDnDS6UT9O5CldXf6AFM4o0QU8Kal7FB2iFmY5CiAh10 https://openelab.io/products/robosense-em4-thousand-beam-lon...
- jeffreygoesto 1y ago
  Non-scanning means your flash emits the equivalent of all the beams at the same time. Look at their flagship spec, you must master 160A next to the other electronics. Two board designs are more expensive and error prone, can't get 160 amps through a flex-cable easily. Then there is the opening angle, you need wide _and_ long, at least for front and rear facing and the optics for that are challenging. Another influence certainly is that the automated driving craze has been superseded by the AI craze and scaling won't come in the time frame that was predicted some years ago. Disclaimer: worked in AD since 2012 (too late for the urban challenge unfortunately ;)) and in a company building sensors and a full stack. P.S.: a QNX desktop is possible and actually alive again, but company politics... :/
  - Joel_Mckay 1y ago
    Solid state LADAR with 8km range and spectroscopic chemical analysis capabilities have been around for decades (mostly CO2 and Nitrate concentration along with 3D point cloud data etc.) However, the chances anyone will see that technology in a consumer product is very low. These were also never cost effective, and priced several times more than most cars. Additionally, like all optics these couldn't handle excessive dust, rain, direct sunlight, and bug guts. Most platforms included millimeter Radar for when vision and LIDAR/LADAR optics fail. QNX simply missed its largest market launch window in the 1990s, and is no longer the path forward for a lot of projects. Note "AI" might be real someday (unlikely an LLM), but every hype-cycle needs to run its course. =3
  - MezzoDelCammin 1y ago
    Also there's the simple physics view of the same problem. The advantage of scanning is that you can focus all the laser pulse energy into one narrow beam. Non scanning means covering the whole field of view at once with that same laser pulse. Then you have a choice. Either somehow deal with the exponentially weaker return pulse (since it's spread over the whole field of view), or try to increase the pulse energy (and there you're limited by laser safety regulations)
    - jlokier 1y ago
      From a physics point of view, continuous transmission and correlation detection of a temporally- and spatially-diverse optical signal over the entire field of view addresses the problem of energy being spread out, and gets you better, more robust depth information for less emitted energy than scanning or full-field flashes. But from an optical and electronics point of view, it's much harder to process the return signal that way, and probably uses a lot more energy due to the processing required (with current tech).
      - namibj 1y ago
        Actually the same rule as for RADAR also applies to LIDAR: single pulse has better energy efficiency, but requires untenable peak power at any vaguely-state-of-the-art signal quality/reception performance levels. The reason is that you can time-gate the noise out that would otherwise be hitting your correlation accumulators if you have a vague idea of the supposed delay/ToF for the pulse. However, once you add mechanical scanning, at least for systems with not that many orders of magnitude between range resolution and maximum detection range, you can use systems like mode-locked lasers that for example have around 0.1% native duty cycle, circumvent the issue of peak power through the aperture/scanning 's spatial focusing (each pixel only needs a managable amount of energy, and delivering that in a single pulse won't require unreasonable peak power levels), and still get all the energy-efficiency benefits of single-pulse ranging vs. spread-spectrum/correlation ranging. The only but major downside is the requirement of mechanical scanning.
    - tubs 1y ago
      Quadratically weaker, not exponentially.
  - mahirsaid 1y ago
    While i was reading this article i did find another article (AD) that was showcasing a product of LidAR tech in a small package. It seems unpractical to be very useful a long sim module with its own processing unit and on board electronics. The require space for the module to be installed was above the windshield and the roof. Much like other products of the same category, however this was a lot more compact. Seems to be a push for further compact innovation in this category. i was under the impression there was no need for multiple LIdar module on one vehicle, all you needed was one along with cameras to further assist the LIdar module .I do know that under normal operation the LIdar and camera system are separate and have different responsibilities.
  - Animats 1y ago
    > 160A For how long? Can't be continuous. What's average power. Yes, flash LIDAR has a power problem. How does their long-range LIDAR work? > Another influence certainly is that the automated driving craze has been superseded by the AI craze and scaling won't come in the time frame that was predicted some years ago. Huh. Good point. Want to think about that one. We might max out at most taxis being self-driving, because that works and sells, but not make it to personal vehicles. > P.S.: a QNX desktop is possible and actually alive again, but company politics... :/ I'm out of that now. The closed source/open souce/closed source/open source/closed source transitions angered too many people. There was once Netscape/Firefox for QNX.
- fooblaster 1y ago
  The em4 does not cost 10000 dollars. It is going to sell for well under 1000$. Hesai's low end ATX is supposed going to be less than 300$, and the AT128 already sells for 400-500$.
moffkalast 1y ago
The first table is already outdated, there are COTS units like the STL-27L that operate on dTOF with a 25m range, return thousands of points per sweep, and fit into a package with a footprint the size of a typical wristwatch. Bulky optics are no longer a requirement, and that's even on the very low end of the price spectrum, more expensive units can do 30+ m in a similarly sized form factor.
NewsaHackO 1y ago
Very informative. I assume this is the type of industry work PhDs in physics do
- mahirsaid 1y ago
  There is still so much to be done with LIdar. I myself am so intrigued of the output these devices present. The data and capabilities that are possible with this tech is amazing to me. Terrain scanning to autonomous vehicles the list goes on. Lasers are amazing breakthrough for mankind and breakthrough for the physics that involved, light that can be manipulated to seek alternative outcomes of data or real-world applications.
sega_sai 1y ago
I was always wondering if every car around you had a Lidar, would these systems be confused by light emitted by other cars ?
- viggity 1y ago
  In general, no. And to be clear, this is my general understanding and I don't have the time to look up the specifics, but I'm pretty sure lidar uses a "carrier wave" in much the same way old telephone modems did, or your IR remote for your TV. The carrier wave is how these sensors don't get confused. If you've ever been in traffic, and you get a stray, one off "YOURE TOO CLOSE TO SOMETHING" when you in fact aren't, it is because a carrier wave from another car happens to line up and you have a collision (pun intended). two seconds of googling: https://www.digikey.com/en/maker/tutorials/2021/understanding-the-basics-of-infrared-communications#:~:text=Typically%2C%20a%20frequency%20of%2038%2C000,940%20nm%20and%2036%20kHz. https://www.digikey.com/en/maker/tutorials/2021/understandin...
amelius 1y ago
Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s But why isn't something cheap and small like this commercially available as an integrated system?
- rowanG077 1y ago
  They are available cheaply. You can purchase a blu ray reader and hack it. The reason a ready packaged sensor is not available cheaply is simply because of economics and market size.
  - amelius 1y ago
    I'm not convinced by the market/economics argument. Cheap and small ToF sensors exist, even though the market initially was also small.
    - rowanG077 1y ago
      ToF sensors have huge applications. Initially ToF sensors also cost thousands of dollars. What huge applications do you see that should have driven the prices of over the counter integrable interferometers down? As I stated blu ray (and DVD, CD and laser disc before it) readers are tiny purpose build inferometers. And they are cheap.
      - namibj 1y ago
        Since when are CD reader optics interferometers? The linked video shows a CW homodyne LIDAR used for measuring vibration frequency and counting vibration amplitude in fringes. Last I looked CD readers used a 4-detector sensor's differential low-pass signals for closed-loop track-following so the rotation need not be optically centered. I also see no reason why optical disc readouts would need homodyne let alone heterodyne readout.
ninashamsi 1y ago
The article mentions multipath interference briefly, but it’s an interesting topic by itself, https://docs.chronoptics.com/fundamentals/multipath-interference/ https://docs.chronoptics.com/fundamentals/multipath-interfer....

71 points by mahirsaid 1y ago

I was expecting flash LIDAR and MEMS mirror systems to dominate self-driving cars by now, but rotating machinery is still dominant in the US. The trend in China and Japan is a long-range forward-facing LIDAR coupled with three shorter-range units for side and rear coverage.[1] The long-range unit still costs around US$10,000. This should come down with volume. [1] https://www.robosense.ai/en/news-show-1908 https://www.robosense.ai/en/news-show-1908 [2] https://openelab.io/products/robosense-em4-thousand-beam-long-range-digital-lidar?srsltid=AfmBOoriES25fDnDS6UT9O5CldXf6AFM4o0QU8Kal7FB2iFmY5CiAh10 https://openelab.io/products/robosense-em4-thousand-beam-lon...

jeffreygoesto 1y ago
Non-scanning means your flash emits the equivalent of all the beams at the same time. Look at their flagship spec, you must master 160A next to the other electronics. Two board designs are more expensive and error prone, can't get 160 amps through a flex-cable easily. Then there is the opening angle, you need wide _and_ long, at least for front and rear facing and the optics for that are challenging. Another influence certainly is that the automated driving craze has been superseded by the AI craze and scaling won't come in the time frame that was predicted some years ago. Disclaimer: worked in AD since 2012 (too late for the urban challenge unfortunately ;)) and in a company building sensors and a full stack. P.S.: a QNX desktop is possible and actually alive again, but company politics... :/
- Joel_Mckay 1y ago
  Solid state LADAR with 8km range and spectroscopic chemical analysis capabilities have been around for decades (mostly CO2 and Nitrate concentration along with 3D point cloud data etc.) However, the chances anyone will see that technology in a consumer product is very low. These were also never cost effective, and priced several times more than most cars. Additionally, like all optics these couldn't handle excessive dust, rain, direct sunlight, and bug guts. Most platforms included millimeter Radar for when vision and LIDAR/LADAR optics fail. QNX simply missed its largest market launch window in the 1990s, and is no longer the path forward for a lot of projects. Note "AI" might be real someday (unlikely an LLM), but every hype-cycle needs to run its course. =3
- MezzoDelCammin 1y ago
  Also there's the simple physics view of the same problem. The advantage of scanning is that you can focus all the laser pulse energy into one narrow beam. Non scanning means covering the whole field of view at once with that same laser pulse. Then you have a choice. Either somehow deal with the exponentially weaker return pulse (since it's spread over the whole field of view), or try to increase the pulse energy (and there you're limited by laser safety regulations)
  - jlokier 1y ago
    From a physics point of view, continuous transmission and correlation detection of a temporally- and spatially-diverse optical signal over the entire field of view addresses the problem of energy being spread out, and gets you better, more robust depth information for less emitted energy than scanning or full-field flashes. But from an optical and electronics point of view, it's much harder to process the return signal that way, and probably uses a lot more energy due to the processing required (with current tech).
    - namibj 1y ago
      Actually the same rule as for RADAR also applies to LIDAR: single pulse has better energy efficiency, but requires untenable peak power at any vaguely-state-of-the-art signal quality/reception performance levels. The reason is that you can time-gate the noise out that would otherwise be hitting your correlation accumulators if you have a vague idea of the supposed delay/ToF for the pulse. However, once you add mechanical scanning, at least for systems with not that many orders of magnitude between range resolution and maximum detection range, you can use systems like mode-locked lasers that for example have around 0.1% native duty cycle, circumvent the issue of peak power through the aperture/scanning 's spatial focusing (each pixel only needs a managable amount of energy, and delivering that in a single pulse won't require unreasonable peak power levels), and still get all the energy-efficiency benefits of single-pulse ranging vs. spread-spectrum/correlation ranging. The only but major downside is the requirement of mechanical scanning.
  - tubs 1y ago
    Quadratically weaker, not exponentially.
- mahirsaid 1y ago
  While i was reading this article i did find another article (AD) that was showcasing a product of LidAR tech in a small package. It seems unpractical to be very useful a long sim module with its own processing unit and on board electronics. The require space for the module to be installed was above the windshield and the roof. Much like other products of the same category, however this was a lot more compact. Seems to be a push for further compact innovation in this category. i was under the impression there was no need for multiple LIdar module on one vehicle, all you needed was one along with cameras to further assist the LIdar module .I do know that under normal operation the LIdar and camera system are separate and have different responsibilities.
- Animats 1y ago
  > 160A For how long? Can't be continuous. What's average power. Yes, flash LIDAR has a power problem. How does their long-range LIDAR work? > Another influence certainly is that the automated driving craze has been superseded by the AI craze and scaling won't come in the time frame that was predicted some years ago. Huh. Good point. Want to think about that one. We might max out at most taxis being self-driving, because that works and sells, but not make it to personal vehicles. > P.S.: a QNX desktop is possible and actually alive again, but company politics... :/ I'm out of that now. The closed source/open souce/closed source/open source/closed source transitions angered too many people. There was once Netscape/Firefox for QNX.
fooblaster 1y ago
The em4 does not cost 10000 dollars. It is going to sell for well under 1000$. Hesai's low end ATX is supposed going to be less than 300$, and the AT128 already sells for 400-500$.

moffkalast 1y ago

The first table is already outdated, there are COTS units like the STL-27L that operate on dTOF with a 25m range, return thousands of points per sweep, and fit into a package with a footprint the size of a typical wristwatch. Bulky optics are no longer a requirement, and that's even on the very low end of the price spectrum, more expensive units can do 30+ m in a similarly sized form factor.

NewsaHackO 1y ago

Very informative. I assume this is the type of industry work PhDs in physics do

mahirsaid 1y ago
There is still so much to be done with LIdar. I myself am so intrigued of the output these devices present. The data and capabilities that are possible with this tech is amazing to me. Terrain scanning to autonomous vehicles the list goes on. Lasers are amazing breakthrough for mankind and breakthrough for the physics that involved, light that can be manipulated to seek alternative outcomes of data or real-world applications.

sega_sai 1y ago

I was always wondering if every car around you had a Lidar, would these systems be confused by light emitted by other cars ?

viggity 1y ago
In general, no. And to be clear, this is my general understanding and I don't have the time to look up the specifics, but I'm pretty sure lidar uses a "carrier wave" in much the same way old telephone modems did, or your IR remote for your TV. The carrier wave is how these sensors don't get confused. If you've ever been in traffic, and you get a stray, one off "YOURE TOO CLOSE TO SOMETHING" when you in fact aren't, it is because a carrier wave from another car happens to line up and you have a collision (pun intended). two seconds of googling: https://www.digikey.com/en/maker/tutorials/2021/understanding-the-basics-of-infrared-communications#:~:text=Typically%2C%20a%20frequency%20of%2038%2C000,940%20nm%20and%2036%20kHz. https://www.digikey.com/en/maker/tutorials/2021/understandin...

amelius 1y ago

Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s https://www.youtube.com/watch?v=MUdro-6u2Zg&t=770s But why isn't something cheap and small like this commercially available as an integrated system?

rowanG077 1y ago
They are available cheaply. You can purchase a blu ray reader and hack it. The reason a ready packaged sensor is not available cheaply is simply because of economics and market size.
- amelius 1y ago
  I'm not convinced by the market/economics argument. Cheap and small ToF sensors exist, even though the market initially was also small.
  - rowanG077 1y ago
    ToF sensors have huge applications. Initially ToF sensors also cost thousands of dollars. What huge applications do you see that should have driven the prices of over the counter integrable interferometers down? As I stated blu ray (and DVD, CD and laser disc before it) readers are tiny purpose build inferometers. And they are cheap.
    - namibj 1y ago
      Since when are CD reader optics interferometers? The linked video shows a CW homodyne LIDAR used for measuring vibration frequency and counting vibration amplitude in fringes. Last I looked CD readers used a 4-detector sensor's differential low-pass signals for closed-loop track-following so the rotation need not be optically centered. I also see no reason why optical disc readouts would need homodyne let alone heterodyne readout.

ninashamsi 1y ago

The article mentions multipath interference briefly, but it’s an interesting topic by itself, https://docs.chronoptics.com/fundamentals/multipath-interference/ https://docs.chronoptics.com/fundamentals/multipath-interfer....