The quality in FARO Focus3D 120

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macocmeliak
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The quality in FARO Focus3D 120

Post by macocmeliak »

Hi,
I am from Technical University in Zvolen (Slovakia). We are using FARO Focus3D 120 for forestry. I would like to ask you how exactly is quality working. I mean when I set up scanner the resolution 1/1, 1/2 and so on, there is also quality. The resolution is obvious. There is a explanation in scanner that it is doing something with noise. But I need to know what exactly is behind this operation. Can somebody please explain me what the scanner is doing and what is difference between different qualities.

Best regards

Martin Mokros

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Re: The quality in FARO Focus3D 120

Post by max72 »

Check the full manual. There is an interesting table. In my manual dated october 2012 is at page 51-52.

When you increase the quality you slow down the scanner. You have less points per second, but more range.
At 1x you reach 30m at 2x about 40-50, and so on...
This is true up to 4x. Above that you start doing more than a single measure, and average.
Hope it hepls
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Re: The quality in FARO Focus3D 120

Post by David Zip »

The resolution settings on the Focus3D (outdoor 20m + profile) show on the Parameters menu -

1/4 res and 4x qual scans in 9:20 min and gives 43.7 Mpts. Pt distance is 6.1mm

1/5 and 4x scans in 6:45 min and gives 28 Mpts. Pt distance is 7.7mm

1/4 and 2x scans in 3:58 min and gives 43.7 Mpts. Pt distance is 6.1mm

1/5 and 2x scans 3:19 min and gives 28 Mpts. Pt distance is 7.7mm

The difference between the settings is that the mirrors rotates noticeably faster at the 2x quality and point filtering algorithms in the Focus3D kick in.

If you are using laser scanning for forestry to determine density of growth and volumes, 2x quality is suitable.

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Re: The quality in FARO Focus3D 120

Post by MatthewByrd »

The difference between the Quality & Resolution.

The "Resolution" is increasing the number of points you're picking up, which increases the density.

What the "Quality" Setting changes....
The "Quality" feature changes how many times the laser samples each point.
The lower quality does take less time, but may have slightly more noise, due to less sampling.
If you increase quality, it will sample the point more, which may create slightly cleaner data with less noise, but will also take some more time.


I agree with the above, if this is for terrain / trees etc. 2x Quality should be suitable.

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Re: The quality in FARO Focus3D 120

Post by macocmeliak »

Thank you very much for your responses, I really appreciate it.

So if I understand it correctly when I increase the quality scanner start to remeasure the position of every point, that is beacuse the time is longer when I increase the quality? And if the quality is 2 scanner will remeasure every point 2 times if the quality is 3 scanner will remeasure every point 3 times and so on?

Thank you very much

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Re: The quality in FARO Focus3D 120

Post by max72 »

not exactly..
At 1x, 2x, 3x and 4x you do a single measure.
The difference is the number of points sampled per sedcond.
You have 976, 488, 244 and 122 kilopoints per second respectively. The main difference here is max range, the slower you measure the higher the range.
Then you have 6x, where you sample at 122kp/s and do an average of 4 samples.
With 8x you average 16 samples per point at a speed of 122kp/s.
Theory says that when you do multiple measurements and average the standard deviation decreases with the square root of the samples. We could discuss at length on what part of the error applies on a Focus, anyway simplifying with 4 samples the random error is cut in half. With 16 samples you get to 1/4, hence the data on the manual, where with quality 6x there is a 2x noise compression and with 8x the manual shows a 4x noise compression.

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Re: The quality in FARO Focus3D 120

Post by macocmeliak »

Thank you very much Massimo. Now I really understand it.

Best regards

Martin

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Re: The quality in FARO Focus3D 120

Post by SAttaya »

Here's a copy of a reply posted to basically the same question posted a while back:

''Re: What is the quantitative effect of FARO3D "quality" sett

Postby Oliver Buerkler » 21 Dec 2012 04:07

Hi,

In fact there is not too much magic behind it.
Increasing the quality setting reduces the scanning speed and thus more measurements are used to average the distance which is finally stored with the scan point.
If you see artifacts disappear it might be due to the averaging. Same for longer range - if points in a distance are confirmed by more measurements they may not be eliminated as noise.

But the main effect really is the noise reduction which can be expected to be square root of the increase of the quality setting. So changing from quality 2 to 4 means a reduction in noise by sqrt(2) ~ 1,4.

Details on the scanning speed and scan times are listed in the Focus 3D user manual.

Best regards,
Oliver Bürkler''

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Re: The quality in FARO Focus3D 120

Post by rstuckey13 »

Not sure if this paper has been mentioned in any previous post, but it will probably interest all Faro and Leica owners alike, especially in relation to quality settings. Refer in particular to pages 24 and onwards.

Paper title: "Objective Specifications of Terrestrial Laserscanners"
By: Geodetic Laboratory at the Technische Universität München

Link:
http://metrica.gr/files/downloads/Objec ... fLS-EN.pdf

I haven't yet read the paper in detail, but would be interested to see others comments.

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Re: The quality in FARO Focus3D 120

Post by Matt Young »

In section 2.1 probing error is mentioned. I believe that due to the many angles involved in a typical laser scan, that many probing errors on angled surfaces, beyond the angle of incidence, lead to problems when using algorithms to alter recorded data. The result of this can be scan information that represents a false picture of what should be a more accurate dataset. There are certain boundary's that cannot be overcome by altering data in such ways. Laser scanning is all about trade offs and I think that some algorithms push too far when trying to correct data. It's what I have seen and it's just my view - I'm not talking about particular scanners here.
SAttaya wrote:Increasing the quality setting reduces the scanning speed and thus more measurements are used to average the distance which is finally stored with the scan point.


Surely increasing quality increases scanning time, and does not reduce it?
If you don't see that there is nothing, then you are kidding yourself.

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