Scanning polished or chrome pipes

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Oliver Buerkler
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Re: Scanning polished or chrome pipes

Post by Oliver Buerkler »

Hi Steven.

Thank you very much for your prompt reaction!

I really wrote the Ad part before by purpose to show how senseless this forum would look like if this becomes the standard behaviour.

I trust the majority here goes in line with you and me.
So, if you find anything again from myself outside the "Advertisment" or "Press release" section which looks like stupid sales pitch - please feel free to delete it! And be asured I will be the last one to blame you for it ;)

Hoping this discussion was needed only once, yours,
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Re: Scanning polished or chrome pipes

Post by Phil Marsh »

I have to echo the thoughts of both Oliver and Steven on this issue.

I see no point in anyone mentioning their product without a detailed explanation as to why that particular product is best suited to the task that is been discussed.

This is the main reason why the 'press realease' section was added, so all the manufactors could promote thier devices to their hearts content.
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Re: Scanning polished or chrome pipes

Post by GrahamKing »

Hi all,

I would be very grateful if someone could provide some insight into which type of laser scanner deals best with a highly reflective surface? (such as a crome pipe or the like)

Would it be the time of flight laser scanner or the phase measurement?


This is not for a project at the moment but a dissertation idea which I am keen to investigate so any information would be gratefully recieved.

Kind regards,

Graham King
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Re: Scanning polished or chrome pipes

Post by Matt Young »

Graham,

The problem is not so much which scanner will scan a shiny surface, but rather what you coat the surface with to make it a matt surface.

You can not scan shiny surfaces.
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Re: Scanning polished or chrome pipes

Post by GrahamKing »

Hi Matt,

Thanks for your response.

I understand the difficulties with scanning shiney objects and the need to coat them to obtain a good return signal however how would you deal with a project where the shiney surface to be scanned could not be coated, what measures would you take to try and get the best data possible?

I have been browsing this forum and am finding it very intresting and useful and have just come across one of your older posts in concerns with shiney objects,
This also depends on the type of scanner phase comparison or time of flight, scanning in the dark works better with time of flight in my experience. Even in the dark you will still have issues with a reflective/shiny surface, the point is to minimize the effect.
Could yo elaborate on why time of flight works best in the dark?
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Re: Scanning polished or chrome pipes

Post by Matt Young »

The reason that TOF works better at night is to do with the amount of light that is returned to the scanner.

Lets say that for example that during the day you send a single laser pulse to an object and that there are approximately 3 trillion light photons in the pulse - The light photons hit the object and only about 500,000 of those photons return to the scanner. A percentage of the photons returning will be ambient light, lets say 300,000 of them, so only 200,000 photons from the origional 3 trillion get back to the scanner. (all approximate because I dont have anything to measure photons).

Do the same thing at night and the number of ambient light photons that return to the scanner is much less and the number of origionally sent photons is more, there for hopefully giving a better degree of accuracy per pulse.

imagine that you shine a laser beam on a white wall at night, you can see it. try doing it on a white wall during the day, you cant see it.

You can not do much about the refraction that you get when you send light to a curved shiny surface, but by minimizing other ambient noise you get a better chance.

This is mostly theory on my part and a lot of reading about photons and their behaviour.

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Re: Scanning polished or chrome pipes

Post by GrahamKing »

Thanks again Matt,

Your posts have been very helpful and have given me some areas to research.

Would you expect one type of scanner to provide better data than the other in regards to time of flight vs phased based? For example on a object which is proving difficult to scan due to its reflectivity at a distance of 3m? or would you expect both types of scanner to produce very similar results?

Im sorry for the barrage of questions but im finding it difficult to find alot of literture on the subject as its still such a young technology and the research papers and the like, although helpful, the information is somewhat fragmented.

Graham
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Re: Scanning polished or chrome pipes

Post by Matt Young »

Graham,

My experience is mainly with Leica scanners, but I would expext the results to be similar with all scanners as the science is the same.

Good luck as you continue your research.

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Re: Scanning polished or chrome pipes

Post by Oliver Buerkler »

One point which just came to my mind and has not been mentioned here before:

Apart from getting no / too little light back from shiny objects you sometimes get measurements back which are pretty wrong. Reason for this is that the light is deflected away by the shiny surface and may then hit another surface. There it gets reflected and travels all the way back over the shiny surface to the scanner. Result will be a point with correct angular values but with a wrong distance from the scanner (can easily be seen in 3D).

As all things mentioned in this thread are simply physical facts, there should be no major difference between scanner vendors nor technologies. Some may cope better with very little reflected light than others. But the principles have been defined several million years before there was a funny species popping up on earth trying to build laser devices ;-)

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