3 ms·

> They generally can't detect stationary objects, have problems with reflections, most of them are VERY low resolution, and so on. Radar can absolutely detect

> They generally can't detect stationary objects, have problems with reflections, most of them are VERY low resolution, and so on. Radar can absolutely detect a stationary object. The problem is not, "moving or not moving", it's "is the energy reflected back to the detector," as alluded to by your second qualification. So something that scatters or absorbs the transmitted energy is hard to measure with radar because the energy doesn't get back to the detector completing the measurement. This is the guiding principle behind stealth. And, as you mentioned, things with this property naturally occur. For example, trees with low hanging branches and bushes with sparse leaves can be difficult to get an accurate (say within 1 meter) distance measurement from.

potato3732842 2y ago
Imagine if you could only see in a very narrow portion of the visible light spectrum, like only green or something. That's kind of how radar "sees" (I'm grossly over-simplifying here but point is it doesn't see the way we do). It's hard to tell something sticking off the back of a truck or a motorcycle behind a vehicle without false positive triggering off of other stuff and panic braking at dumb times, something early systems (generically, not any particular OEM) were known for, which is why they were mostly limited to warnings not actual braking. And while one can make bad faith comments all day about that not technically being the fault of the system doing the braking allowing such systems to proliferate would be a big class action lawsuit, and maybe even a revision of how liability is handled, waiting to happen.
- throwaway31131 2y ago
  I guess it boils down to this. Earlier in the thread people were saying removing lidar was bad becuase multiple sensors types is good, presuming the camera stay either way, and one is not replacing camera with radar. I agree with this. It's usually trivially easy to corner case defeat one sensor type, as your example shows, regardless of sensor type. They all have one weakness or another. That's why things like military systems have many sensor types. They really don't want to miss the incoming object so they measure it many different ways. Defeating many different sensor types is just way harder and therefore more unlikely to occur naturally. And yes, control systems can absolutely reliably combine the input of many sensors. This has been true for decades. Frankly I surprised more of these systems don't take advantage of sound. It's crazy cheap and society has been adding sound alerts to driving for a long time (sirens, car horns, train horns, etc.)
- hwillis 2y ago
  > Imagine if you could only see in a very narrow portion of the visible light spectrum, like only green or something. No, that's how lidar works. Lidars have a single frequency and a very narrow bandwidth. Automotive radars have a bandwidth of 1-5 GHz. They operate around 80 GHz, which is very well reflected by water (including people) and moderately reflected by things like plastic. 80 GHz is industrially used to measure levels of plastic feedstock. Compare TSA scanner images, which are ~300 GHz: https://www.researchgate.net/figure/a-Front-and-back-millimeter-wave-whole-body-imaging-results-from-deployed-scanners-b_fig6_252176262 https://www.researchgate.net/figure/a-Front-and-back-millime... You are correct that most automotive radars like Bosch units [1] are very low detail though. Most of them don't output images or anything- they run proprietary algorithms that identify the largest detection frequencies (usually a limited number of them) and calculate the direction and distance to them. Unlike cameras and lidars they do not return raw data, so naturally when building driver assistance companies instead relied on cameras and lidar. Progress was instead driven by the manufacturers and with smaller incentives the progress is slower. [1]: https://www.bosch-mobility.com/en/solutions/sensors/front-radar-sensor/ https://www.bosch-mobility.com/en/solutions/sensors/front-ra...
  - potato3732842 2y ago
    I was talking about radar
redox99 2y ago
They can detect stationary objects, yes. But there's so much clutter from things like overpasses, road signs, and other objects that confuse the radar, that for things like adaptive cruise control, stationary objects are often intentionally filtered out or assigned much lower priority. So you detect moving objects (which stand out because of doppler shift).
- y1n0 2y ago
  Well, if we're talking about radar in a moving car, it's the other vehicles moving at the same speed that appear stationary. Non-moving vehicles are seen as approaching you at whatever speed you are moving at. Along with all the other things you mentioned. So they all have doppler shift but the "stationary" things approaching your car at your speed actually have much higher shift than the traffic around you.
  - porphyra 2y ago
    Yea, and they are designed to filter out actually stationary things by ignoring anything that's coming at you at the same speed as the current car speed (from measuring wheel rotation).

potato3732842 2y ago

Imagine if you could only see in a very narrow portion of the visible light spectrum, like only green or something. That's kind of how radar "sees" (I'm grossly over-simplifying here but point is it doesn't see the way we do). It's hard to tell something sticking off the back of a truck or a motorcycle behind a vehicle without false positive triggering off of other stuff and panic braking at dumb times, something early systems (generically, not any particular OEM) were known for, which is why they were mostly limited to warnings not actual braking. And while one can make bad faith comments all day about that not technically being the fault of the system doing the braking allowing such systems to proliferate would be a big class action lawsuit, and maybe even a revision of how liability is handled, waiting to happen.

throwaway31131 2y ago
I guess it boils down to this. Earlier in the thread people were saying removing lidar was bad becuase multiple sensors types is good, presuming the camera stay either way, and one is not replacing camera with radar. I agree with this. It's usually trivially easy to corner case defeat one sensor type, as your example shows, regardless of sensor type. They all have one weakness or another. That's why things like military systems have many sensor types. They really don't want to miss the incoming object so they measure it many different ways. Defeating many different sensor types is just way harder and therefore more unlikely to occur naturally. And yes, control systems can absolutely reliably combine the input of many sensors. This has been true for decades. Frankly I surprised more of these systems don't take advantage of sound. It's crazy cheap and society has been adding sound alerts to driving for a long time (sirens, car horns, train horns, etc.)
hwillis 2y ago
> Imagine if you could only see in a very narrow portion of the visible light spectrum, like only green or something. No, that's how lidar works. Lidars have a single frequency and a very narrow bandwidth. Automotive radars have a bandwidth of 1-5 GHz. They operate around 80 GHz, which is very well reflected by water (including people) and moderately reflected by things like plastic. 80 GHz is industrially used to measure levels of plastic feedstock. Compare TSA scanner images, which are ~300 GHz: https://www.researchgate.net/figure/a-Front-and-back-millimeter-wave-whole-body-imaging-results-from-deployed-scanners-b_fig6_252176262 https://www.researchgate.net/figure/a-Front-and-back-millime... You are correct that most automotive radars like Bosch units [1] are very low detail though. Most of them don't output images or anything- they run proprietary algorithms that identify the largest detection frequencies (usually a limited number of them) and calculate the direction and distance to them. Unlike cameras and lidars they do not return raw data, so naturally when building driver assistance companies instead relied on cameras and lidar. Progress was instead driven by the manufacturers and with smaller incentives the progress is slower. [1]: https://www.bosch-mobility.com/en/solutions/sensors/front-radar-sensor/ https://www.bosch-mobility.com/en/solutions/sensors/front-ra...
- potato3732842 2y ago
  I was talking about radar

redox99 2y ago

They can detect stationary objects, yes. But there's so much clutter from things like overpasses, road signs, and other objects that confuse the radar, that for things like adaptive cruise control, stationary objects are often intentionally filtered out or assigned much lower priority. So you detect moving objects (which stand out because of doppler shift).

y1n0 2y ago
Well, if we're talking about radar in a moving car, it's the other vehicles moving at the same speed that appear stationary. Non-moving vehicles are seen as approaching you at whatever speed you are moving at. Along with all the other things you mentioned. So they all have doppler shift but the "stationary" things approaching your car at your speed actually have much higher shift than the traffic around you.
- porphyra 2y ago
  Yea, and they are designed to filter out actually stationary things by ignoring anything that's coming at you at the same speed as the current car speed (from measuring wheel rotation).