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Does anyone know how these LiDARs work?

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Patrick

Fri Aug 12 2011, 04:40AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

From my friends at the IARC, who are almost all using this device ->

(From the BNM-IT India team power point presentation.)

Im thinking of using the URG-04LX-UG01 simple one (1,200 USD), but the Michigan team was using the 6,500 USD one.

Do these devices use phase relationships to determine distance? or time of flight? If they use time of flight then the minimum useful range is 20mm, in 20mm the speed of light would mean very short emission, detection and a very fast clock.

I really think they use TDOA like the RF foxhunts with the non-moving electrically scanned radio antennas that amatures build.

Bjørn

Fri Aug 12 2011, 05:59AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

A common method is to modulate the laser (often at several frequencies) and record the returning signal. From the different phase shifts at different frequencies you can calculate the distance. The webpages for URG-04LX-UG01 suggests that is what they do.

I have a $100 pocket range finder that has a resolution of 1 mm with a range of 50 m that uses that method.

Patrick

Fri Aug 12 2011, 01:12PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

BjÃ¸rn wrote ...

A common method is to modulate the laser (often at several frequencies) and record the returning signal. From the different phase shifts at different frequencies you can calculate the distance. The webpages for URG-04LX-UG01 suggests that is what they do.

I have a $100 pocket range finder that has a resolution of 1 mm with a range of 50 m that uses that method.

Oooo... thats just the explanation i needed. Bjorn, which lidar do you have?

We are all having problems with the data rate on the $1200 one being about 12 hertz for the $6,500 they are getting 40 Hertz, i think the electric motor is the slowest part being mechanical, 2400 rpm, so maybe i could mod a pocket one like yours.

Carbon_Rod

Fri Aug 12 2011, 03:40PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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SLAM + URG driver:

You can find the 1cm resolution @ 5m one for under $3500, but note they are a fragile device originally intended for use as factory light curtains.

The Kinect at $100 for both video + LADAR-like scanning is unbeatable in terms of price:

Cheers,

Patrick

Fri Aug 12 2011, 04:01PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Carbon_Rod wrote ...

SLAM + URG driver:

You can find the 1cm resolution @ 5m one for under $3500, but note they are a fragile device originally intended for use as factory light curtains.

So far they've all survived really bad crashes multiple times, when the rest of the machine went to pieces. There are 6 teams using them and they've all crashed but not had a Lidar fail yet.

Carbon_Rod wrote ...

The Kinect at $100 for both video + LADAR-like scanning is unbeatable in terms of price:

Cheers,

But so far the Dubai and USC teams have the most experience with the Kinect and they say it cant see or generate useful data past 30 inches or so (for navigation, LiDAR), dont know what you all think, but thats what they said. The Dubai team was going to use both, but wanted to use the kinect only if possible.

PSCG

Fri Aug 12 2011, 06:05PM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
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If you want more information about Lidars, check Sam's Laser Faq - Laser Insruments and Applications. He has put a lot of work about them (and it seems that isn't difficult to construct something like this ether).

Patrick

Fri Aug 12 2011, 08:20PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

PSCG wrote ...

If you want more information about Lidars, check Sam's Laser Faq - Laser Insruments and Applications. He has put a lot of work about them (and it seems that isn't difficult to construct something like this ether).

TY PSCG, i really need a more optimal solution, so ill look at sams stuff.

Pinky's Brain

Fri Aug 12 2011, 08:31PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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wrote ...

A common method is to modulate the laser (often at several frequencies) and record the returning signal.

I assume you mean record the interference of the returning light with the (attenuated) original?

If you just record the returning signal you still have the problem of needing to detect minute time of flight for high resolution (~3 ps for 1 mm resolution). The modulation only helps with aliasing.

Patrick

Fri Aug 12 2011, 10:05PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Pinky's Brain wrote ...

wrote ...

A common method is to modulate the laser (often at several frequencies) and record the returning signal.

I think I wil use the one called phase difference or some such name they call it.

Bjørn

Fri Aug 12 2011, 10:24PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Yes, it is the phase difference that is recorded.

I have one of the Bosch units and it is very accurate but the refreshrate is about 3 Hz so it would be very slow for this use.

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