Time-of-flight vs. Phase difference vs. Triangulation

Please post any tips or advice you have in general relating to laser scanning either whilst onsite or office based.
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rnordentoft
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Time-of-flight vs. Phase difference vs. Triangulation

Post by rnordentoft »

I am in a phase of teaching myself anything I can about laser scanning, and I was wondering what one could say about the differences are between TOF, Phase difference and Triangulation. I am still in the phase where I look at a data sheet and think to myself "would the beam of this laser simply scan, would it remove my tatoo or would it cut metal?"; I assume it is much down to power.

My statements below should be considered questions to the forum as well as trying to nail down some facts. So, please do correct me where correction is needed.

The laser itself:
- I understand that laser scanning is always done with solid state lasers, and mostly using diodes (these days).
- TOF uses a diode pumped laser. It calculates the distance based on the return flight time of each laser beam.
- Phase difference uses a continuous wave with a continuous phase change. It calculates the distance based on the phase of a pulse coming (based on the phase difference we would know how long it took the pulse to make its return trip).
- Triangulation uses a continuous wave diode. It "records" the 3D image of the laser light reflection in the object it is scanning.

Sweeping in the 2D direction (X & Y):
- TOF and Phase difference use a thin directed pulse that sweeps back and forth to create the point cloud.
- Triangulation uses a lens to obtain a wide line which is then viewed by a CCD. In triangulation there is no 2D sweeping.

Note! The Z-direction (the third dimension) is obtained in various ways; this depends on your setup.

Range, speed & SNR:
- TOF has a longer range, but is slower. In the shorter range the SNR is generally higher.
- Phase difference has a medium range, and is ultra fast. It generally has a lower SNR in the short range.
- Triangulation has a very short range (?), and is also fast (depending on the frame rate of the CCD?). The SNR is higher than Phase difference (?).

That is all I can say with a limited level of accuracy at this time. I hope the experts can correct me, and maybe have more to add, and perhaps one or two people actually learned something (I hope).
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Matt Young
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Re: Time-of-flight vs. Phase difference vs. Triangulation

Post by Matt Young »

Very good description, nothing for me to add.
If you don't see that there is nothing, then you are kidding yourself.
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