Every
American visitor to Germany wants to get out on the unlimited
autobahn. Those gloriously smooth kilometers of tarmac make for
blissful high-speed cruising, unlike our own pockmarked highways. But
how do they keep them in such good shape?
One
answer comes in the form of a laser scanning system that maps the 3D
shape of the surface. Now if I were putting together such a system
I’d be thinking triangulation, but according to “Laser
surveys Germany’s roads - at 100 km/h”,
(Optics.org, April 3rd,
2013,) the folks at the Fraunhofer Institute went with a laser
time-of-flight (ToF) system.
Now
the article doesn’t explicitly say it’s ToF, but that’s how I
interpret “The distance between the scanner and the surface of the
road can be inferred from how long it takes the laser light to travel
back,”. If I’m wrong, please let me know. And assuming I’m
right, it’s a darned clever way to do it.
Posts
2 comments:
Why do you think it's not a "regular" laser scanner? These are used in loads of devices to measure distances and can get up to KHz data rates.
It's TOF. I'm amazed that such resolutions are possible with TOF. As I understand it, light travels 1mm in 3ps. Thus, to resolve this, you should be resolving an electrical signal at 6 ps tops. No easy task at all.
I thought of triangulation at first, too, but laser safety was prime. Thus they used a low frequency laser that is considered safe even for accidental long exposures.
See this article from Fraunhofer Institute for Details:
http://www.ipm.fraunhofer.de/content/dam/ipm/de/PDFs/produktblaetter/OFM_Optische_Fertigungsmesstechnik/BMT_Bahnmesstechnik/PPS_en_web.pdf
Or navigate to Fraunhofer IPM -> Transport & Logistics -> 3D Road surfaces.
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