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I still don't quite understand how this works. Main components are: - Laser - Lens - TSL1401 line image sensor I was always under the impression that LIDAR

I still don't quite understand how this works. Main components are: - Laser - Lens - TSL1401 line image sensor I was always under the impression that LIDAR includes a time-of-flight measurement, which does not appear to be the case here - the TSL1401 sensor has integration times and pixel transfer times in the range of dozens of microseconds, a timespan in which light travels dozens of kilometers.

fisherjeff 9y ago
Based on the diagram, I believe they're estimating distance based on parallax rather than time of flight
- donquichotte 9y ago
  I agree. The wikipedia article on LIDAR says "Lidar [...] combine[s] laser-focused imaging with the ability to calculate distances by measuring the time for a signal to return using appropriate sensors and data acquisition electronics." So this is not LIDAR. Still impressive though, I love the simplicity!
  - rtkwe 9y ago
    That's probably an overly specific definition. Their source for the lidar definition is a NOAA webpage [0] with a broader definition that doesn't include specifics about implementation: > LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. Most lidar does use timing but I'd argue that's a type of implementation instead of a necessary part of the broader category of lidar devices. [0] https://www.webcitation.org/6H82i1Gfx?url=http://oceanservice.noaa.gov/facts/lidar.html https://www.webcitation.org/6H82i1Gfx?url=http://oceanservic...
  - adamweld 9y ago
    The LIDAR acronym doesn't specify the specific measurement technique, although Time Of Flight is by far the most common. There are other designs with interesting differences, for example Strobe[0] which varies the frequency of the transmitted light and measures the freq and phase delay of the returning light rather than straight delay. I believe this design still qualifies as LIDAR, just with significantly worse performance than a typical system. [0] https://spectrum.ieee.org/cars-that-think/transportation/self-driving/gm-cruise-snaps-up-solidstate-lidar-pioneer-strobe-inc https://spectrum.ieee.org/cars-that-think/transportation/sel...
    - dfox 9y ago
      For me paralax-based sensors (in the sense of draw a line with swept laser and look at it with some kind of imager) are the first thing I imagine when hearing "LIDAR". For a long time most industrial lidar sensors used that principle (the 25k+ ones ten years ago).
    - Kubuxu 9y ago
      As far as I know "varies the frequency of the transmitted light and measures the freq and phase delay" is the standard way of measuring ToF in case of lasers. You modulate the laser diode by a signal of a wide range of frequencies and you subtract returned signal (after cleanup). The observation is done on a spectrum. Low frequencies give you wide range but low precision and high frequencies higher precision but lower range but you can use them enhance precision of the former.
dbcurtis 9y ago
This approach based on triganometry is called "structured light"
flyingcircus3 9y ago
About 10 years ago, I worked on a project that used triangulation to measure distances with a laser. The specular reflection is falling on a pair of photodiodes. The relative amounts of light on each diode is indicative of the distance to the specular reflection. A good visual aide that helped me is to imagine a measuring stick laid horizontally across your field of vision, but at a 45 degree angle, such that the left side is closer to you, and the right side is further away. If you abstract your vision to a 2D projection of a 3D volume, you can easily see that as your eyes follow the measuring stick to the left, the distances get smaller, because they actually are closer to you. Conversely, as your eyes follow the measuring stick to the right, the measurements get larger, because they actually are further away. Your brain is just really good at trig.

fisherjeff 9y ago

Based on the diagram, I believe they're estimating distance based on parallax rather than time of flight

donquichotte 9y ago
I agree. The wikipedia article on LIDAR says "Lidar [...] combine[s] laser-focused imaging with the ability to calculate distances by measuring the time for a signal to return using appropriate sensors and data acquisition electronics." So this is not LIDAR. Still impressive though, I love the simplicity!
- rtkwe 9y ago
  That's probably an overly specific definition. Their source for the lidar definition is a NOAA webpage [0] with a broader definition that doesn't include specifics about implementation: > LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. Most lidar does use timing but I'd argue that's a type of implementation instead of a necessary part of the broader category of lidar devices. [0] https://www.webcitation.org/6H82i1Gfx?url=http://oceanservice.noaa.gov/facts/lidar.html https://www.webcitation.org/6H82i1Gfx?url=http://oceanservic...
- adamweld 9y ago
  The LIDAR acronym doesn't specify the specific measurement technique, although Time Of Flight is by far the most common. There are other designs with interesting differences, for example Strobe[0] which varies the frequency of the transmitted light and measures the freq and phase delay of the returning light rather than straight delay. I believe this design still qualifies as LIDAR, just with significantly worse performance than a typical system. [0] https://spectrum.ieee.org/cars-that-think/transportation/self-driving/gm-cruise-snaps-up-solidstate-lidar-pioneer-strobe-inc https://spectrum.ieee.org/cars-that-think/transportation/sel...
  - dfox 9y ago
    For me paralax-based sensors (in the sense of draw a line with swept laser and look at it with some kind of imager) are the first thing I imagine when hearing "LIDAR". For a long time most industrial lidar sensors used that principle (the 25k+ ones ten years ago).
  - Kubuxu 9y ago
    As far as I know "varies the frequency of the transmitted light and measures the freq and phase delay" is the standard way of measuring ToF in case of lasers. You modulate the laser diode by a signal of a wide range of frequencies and you subtract returned signal (after cleanup). The observation is done on a spectrum. Low frequencies give you wide range but low precision and high frequencies higher precision but lower range but you can use them enhance precision of the former.

dbcurtis 9y ago

This approach based on triganometry is called "structured light"

flyingcircus3 9y ago

About 10 years ago, I worked on a project that used triangulation to measure distances with a laser. The specular reflection is falling on a pair of photodiodes. The relative amounts of light on each diode is indicative of the distance to the specular reflection. A good visual aide that helped me is to imagine a measuring stick laid horizontally across your field of vision, but at a 45 degree angle, such that the left side is closer to you, and the right side is further away. If you abstract your vision to a 2D projection of a 3D volume, you can easily see that as your eyes follow the measuring stick to the left, the distances get smaller, because they actually are closer to you. Conversely, as your eyes follow the measuring stick to the right, the measurements get larger, because they actually are further away. Your brain is just really good at trig.