Faro Users - What am I looking at?

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richard_m
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Faro Users - What am I looking at?

Post by richard_m »

I have little Faro knowledge, so I'm looking for advice from those who do..

I'm repeating a reasonably sized project (+/- 1500scans) recently undertaken by a rival. Long story short - their results are, ahem, not ideal (assuming they had our spec..). Looking at their data I understand why our Client is spending the money to do the project again but what I do not have a grip on is the workflow of our rival, need some help figuring this out.

Their scans are obviously Faro, they have registered relatively low res scans together upto 50m apart and NOT used targets. What they have used is a Total Station but somehow they appear to have used it to position the scanner itself - not its targets. I think this because each scan has a huge shadow under it, not just the circle under the tripod caused by the skirt angle of the scanner but also some form of big bracket sticking out the side. In some scans I can see this bracket sits on a tripod and the scanner sits on the bracket at one end (offset from the centre of the tripod) and maybe there's a prism on a tribrach the other end of the bracket. Does anyone have any information on what this bracket thingy is and the workflow to use it?
faro eg 1.jpg
I make no assumptions or statements on how well this system works, it could be brilliant for all I know but I'd just like to know more as there's obviously a workflow in use I've never considered.

Thanks

Richard.
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Dedken
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Re: Faro Users - What am I looking at?

Post by Dedken »

richard_m wrote:they have registered relatively low res scans together upto 50m apart and NOT used targets.
:o

50m apart? Low res? My my. The point spacing is going to be huge at that distance. In some recent experiments I carried out with a Faro Focus 120 it was 5.8mm at 20m on a 1/8 setting (11million pts per scan).

What have you got there - some fls files or a LSPROJ? I'd be interested to take a look at some of that data.

With regard to the shadow it's entirely possible (if you don't have possession of the raw data) that they have cut out that part of the scan. It's possible to do this in Scene at any stage.

Also I know it's possible to change the coordinates of almost anything in Scene, so total station coordinates could be applied manually to a scan position. But I don't know of any workflow or combination of methods that would allow you to then 'fix' the station which is what I'm assuming they were intending to do. Scene doesn't have that functionality as far as I know. Perhaps they weren't using Scene at all? Many questions!

EDIT:

I thought you were referring to the circular shadow, but have just realised you weren't so ignore comment about cutting out data.
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Oliver Buerkler
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Re: Faro Users - What am I looking at?

Post by Oliver Buerkler »

Hello Richard.

Might this stem from this system? http://shop.laserscanning-europe.com/RE ... Hardware_1

Could also explain the low resolution relative to the scan distance.

Best regards,
Oliver
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Re: Faro Users - What am I looking at?

Post by jcoco3 »

Interesting...I am thinking along the same lines as Oliver, but with that system you should see at least 1 spherical target in each scan that is 100mm(Edit: you should still see three spheres in each scan, including two smaller spheres just inside the bottom of the scan). As Kenneth suggested, you might not be dealing with the complete dataset, as it is very easy to export all the scans at a much lower resolution from Scene. It is a very unusual void next to the scanner, and I have no idea what it is. I guess it could be a couple of prisms, or even a total station, but I doubt they are sitting right under the scanner as they would not be visible in the scan. If you do the math under the void angle it takes a very large object to be visible in the scan. We did a test recently and a 230mm sphere is not visible when directly under the scanner. It would take a sphere of at least 1 foot diameter to be visible. For a second there I though it was deleted data, but there are some dark scan points mixed in so I am clueless :? Maybe some sort of home rig with a scanner and total station mounted on the same tripod?

I guess it really doesn't matter what this is since you are going to re-scan it anyway, but it would be nice to satisfy our curiosity :)
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Re: Faro Users - What am I looking at?

Post by Egan_irish »

Hi Richard,

Yes I am also going with the guys investigation, definitely looks like that they used the sphere bracket thingy. With my quick investigation I have found a little bit more info on how it is done see below:
http://www.pointcab-software.com/en/sup ... sampledata

See the Terrain survey (incl. reference points for Register) example..

Is this the same project you are working on!?... 8-) The grass looks the same green :o

Enda
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Re: Faro Users - What am I looking at?

Post by richard_m »

Uurgh, the mystery deepens. I felt sure this would be an easily recognizable system.

Thanks for the replies.

@Kenneth, I've a disk full of registered .fls files with their parameters written back to them. I can simply import them into Cyclone. Might be useful if you can look at a few scans if you have time, I'll PM.

@Oliver, no sorry its totally different.

@Jonathan, yep no targets/spheres to be seen. I'm starting to think you're right about the home made rig..

@Enda, oh the grass is definitely greener on our side :lol: I guess you don't see so much green grass...

In the pic below you can see some data on the "bracket", close to the scanner is a circular fixture that is actually the centre of the tripod, there must be an important reason for mounting the scanner offset in this way(?) At the far end of the bracket is a mount not unlike a tribrach only a bit more complex. Don't see how you could put a TS on it but if you used a TS to measure the position of the scanner position AND this tribrach thingy then you've two positions that could be used for position and orientation. I can hear the trained surveyors on here muttering "short baseline! working the part to the whole! ;) )
faro bracket 2.jpg
The second pic shows the full weirdness, I found the scanner shadow which shows there's a sphere mounted under the scanner. Go figure. They've definitely only used one scanner otherwise I would see the other scanner. Their TS is on its own tripod as I've seen it many times in scans.
faro bracket 3.jpg
Thoughts?

Cheers

Richard
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Re: Faro Users - What am I looking at?

Post by jcoco3 »

Hmm...interesting. That tribrach looking thing in the first image looks like a gitzo pano-head quick release which was standard issue with the earlier 120 Focus Scanners like mine.

I have no ideas what sphere looking object under the scanner is and I am having a hard time understanding how it used. The mystery continues.

Richard if you want another set of curious eyes on the .fls scans I volunteer!
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Re: Faro Users - What am I looking at?

Post by Jamesrye »

If the scans were 50m apart, then I guess they weren't joining them with common targets - because the spheres would be too far away from the next scan position to 'see them'.

I see two possibilities...

1. They've set up over a known point with the scanner and a contraption that holds the sphere out there. Then from the previous scan position, they have a total station setup that observes the sphere. So it's like a traverse.

2. Or maybe the sphere is held out on a known distance and bearing from the optical center of the scanner. Thus, this would allow you to orient the scan on two points.

Method 2 would be especially dodgy as the baseline would be tiny.
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Re: Faro Users - What am I looking at?

Post by jcoco3 »

From my experimentation with the 120 I would also think method two to be dodgy, since the mechanical start and end points of a Faro scan are elusive and somewhat erratic. They never seem to end up in the same place twice.

Looking at that bracket more it appears to be a heavy duty dual camera head, and you can almost make out the faint outline of a label on the right side of the center.
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Re: Faro Users - What am I looking at?

Post by richard_m »

Thanks for the further input

@ Jonathan, I'd appreciate any ideas you might have as to how they've reg'd these scans, if you can drop me a mail to r.merrin[at]fugro.nl I'll use our secure file transfer system to send a few scans over based upon that address (but not sending scans directly to that address..). Now you mention it the tribrach thingy could easy be a camera mount, the scans are color, maybe rotating the whole bracket 180deg around its centre point puts the camera on the nodal point of the scanner?

@James, definitely no known points under the scanner (apart from the target / sphere seen in shadow - hmmm), but under the TS yes. And yeah, I'm concerned your second point might be close to the mark. When I import a pair of adjacent scans that are typically 50m apart I can often find common objects such as roadsigns in the overlap that miss by 5-10cm, so much so that it is difficult to C-C into these existing scans.

Cheers

Richard
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