Faro Scene LT Mark Sphere tool works with bugs

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lsf
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Faro Scene LT Mark Sphere tool works with bugs

Post by lsf »

Please see this 2 minute video https://youtu.be/EEoIKOS0_tM where I struggle with this tool.

youtu.be/EEoIKOS0_tM
Besides the software error message, it is interesting that Faro Scene automatched the sphere with 68k Number Of Scan Points but Faro Scene LT Mark Sphere tool matched it with ~9k points.

Also it is interesting that Radius Deviation field is 0 and grayed out.

What are your thoughts? Is this working correctly on your end or you just force it like I do?
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Re: Faro Scene LT Mark Sphere tool works with bugs

Post by Least »

68K points on one sphere, a bit overkill!
How big is the full scan and what scanner are you using for that sort of density?
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Re: Faro Scene LT Mark Sphere tool works with bugs

Post by lsf »

That scan was 1/2 resolution @ 3x quality, scan time ~15min. The key issue is that Sphere Mark tool is not consistent.
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Tanguy Nédélec
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Re: Faro Scene LT Mark Sphere tool works with bugs

Post by Tanguy Nédélec »

I've noticed the same issues with the full version of Scene:
- "insufficient number of points" despite there being more than enough points. Happens a lot when spheres are very close to the scanner
- only a partial area of the sphere is selected for matching
- sometimes too many points are selected, including some not on the sphere, resulting in a wrong placement.

A semi-solution is to open the scan in planar view (not quick view), and make sure that the selection tool is on "new selection" and not "add selection". That way you can see which points have been selected by Scene (the yellow area). If not satisfactory, delete the sphere and try again. Also check the "scan point distance" statistic, it shouldn't be big.
If that fails, you can use the polygon or circle selection tool, take the points on the sphere, right-click the selection -> create objects -> sphere radius.

A radius deviation of 0 is normal if you specified a radius in the settings.
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Re: Faro Scene LT Mark Sphere tool works with bugs

Post by lsf »

Really good info! Your comment
Tanguy Nédélec wrote: Mon Jan 30, 2023 7:56 am A radius deviation of 0 is normal if you specified a radius in the settings.
made me wonder how to achieve some radius deviation. Would I remove all the defined radiuses from the settings and then try to automatically match spheres? Or when would the 'radius deviation' have some value other than 0?
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Re: Faro Scene LT Mark Sphere tool works with bugs

Post by Tanguy Nédélec »

lsf wrote: Mon Jan 30, 2023 2:48 pm Would I remove all the defined radiuses from the settings
Yes, and then the usual manual "mark sphere" tool will show some radius deviation. The automated match too, most probably (never tested it). I believe it's an iterative least squares algorithm, so Scene tries a given radius first and then narrows it down.

You can check Scene's manual, chapter 17.3.20 "Sphere Fit":
Global Coordinates – If checked, coordinates are displayed in the global
coordinate system; else they are displayed in the coordinate system of the
scanner.
Sphere Name – The name of the corresponding sphere.
Name – The name of the fit object.
Radius – The sphere radius determined by the fit.
Position – The position of the sphere mean point determined by the fit.
Number of scan points – The number of scan points in the selection used for
the fit.
Radius deviation – The standard deviation of the radius, which is determined
using the interim results of the fit.
Position deviation – The standard deviation of the position of the sphere mean
point, which is determined using the interim results of the fit.
Scan point distance – The standard deviation of the distance of the scan points from the calculated sphere surface.
Scan point drift – The average distance of the scan points from the calculated
sphere surface. Scan points outside the sphere can be averaged out with scan
point within the sphere.
GPS Position – see fit of point object chapter Point Fit on page 298.
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