UTM-Scaling in Target Statistics using Faro Scene

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marius
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UTM-Scaling in Target Statistics using Faro Scene

Post by marius »

Hey Everyone,

im currently writing my thesis in the Field of Geodesy using Faro Scene to Process and Georeference Scans done with a Faro S70.
While Georeferencing i came across the Question if Faro Scene somehow processes the scaling that comes with UTM Coordinates.
Since the Scale of the Scan itself is 1:1, UTM is approx. 1:0.9996, this scaling difference should be considered in the Registration Report's Target Statistics, cause it would otherwise manipulate the stated errors of the UTM reference points (i guess?).
Therefore Scene would have to recognize the used Coordinate System of the imported References - but i found no settings for the Input of a coordinate system.
My only workaround would be to use local coordinates for my references at first and then later, after knowing the true errors of the registration, use the Global reference points which should then worsen the test statistics depending on the size of the project. Faro Scene Manual sadly hasnt been of any help.

I'd be happy if someone has any input on that matter.
Best regards.
Marius
Last edited by marius on Tue Nov 29, 2022 11:29 pm, edited 1 time in total.
Emanuele
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Re: UTM-Scaling in Target Statistics using Faro Scene

Post by Emanuele »

Scene does not apply any scaling; the registration takes place by rigid rototranslation.
It is convenient to register in a local system and use the UTM coordinates of the targets for georeferencing only in order to adapt the whole project
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Re: UTM-Scaling in Target Statistics using Faro Scene

Post by VXGrid »

marius wrote: Sat Nov 26, 2022 10:20 am Hey Everyone,

im currently writing my bachelor's thesis in the Field of Geodesy using Faro Scene to Process and Georeference Scans done with a Faro S70.
While Georeferencing i came across the Question if Faro Scene somehow processes the scaling that comes with UTM Coordinates.
Since the Scale of the Scan itself is 1:1, UTM is approx. 1:0.9996, this scaling difference should be considered in the Registration Report's Target Statistics, cause it would otherwise manipulate the stated errors of the UTM reference points (i guess?).
Therefore Scene would have to recognize the used Coordinate System of the imported References - but i found no settings for the Input of a coordinate system.
My only workaround would be to use local coordinates for my references at first and then later, after knowing the true errors of the registration, use the Global reference points which should then worsen the test statistics depending on the size of the project. Faro Scene Manual sadly hasnt been of any help.

I'd be happy if someone has any input on that matter.
Best regards.
Marius
Just asking a couple of questions:
  1. Your local coordinate system doesn't have any distortion, why do you need it in a system which has, which you don't consider?
  2. Do you want to apply the 0.9996 scale onto Z as well (since UTM is a map projection, the height is not defined)?
  3. When you transform a FARO focus project, you need to apply the scale to the scanning position (since this is not correct either) + on any of the points in the scanner coordinate systems, quite a hassle isn't it?
  4. Whereever you are importing and using the point cloud, does it understand that the point cloud is not metric anymore? Otherwise you'll get the scale factor into your project (no worries only 4 cm / 100 meter)?
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Daniel Wujanz
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Re: UTM-Scaling in Target Statistics using Faro Scene

Post by Daniel Wujanz »

Dear Marius,

if you want to consider a superior coordinate system's scale you can suffer in three ways:

1. Re-compensate for the effect of the earth's curvature. What you need to do, is to "bend" the control points upwards, so that they fit to the "planar" laser scans.
2. Scale the point clouds by using the scaling factor.
3. "Scale" your registration parameters.

My personal preference is the first option which can be done in a couple of minutes.

Since you're German, have a look at the book with one of the the greatest titles I've ever encountered: Die Kugel (the sphere) by Eberhard Mittermeier.

All the best

Daniel

P.S. Crap Martin (VXGrid) still types a lot quicker than I do : )
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Re: UTM-Scaling in Target Statistics using Faro Scene

Post by smacl »

Daniel Wujanz wrote: Mon Nov 28, 2022 8:32 amSince you're German, have a look at the book with one of the the greatest titles I've ever encountered: Die Kugel (the sphere) by Eberhard Mittermeier.
Two other titles worthy of a look are Map Projections: A Reference Manual Paperback – 28 Jun. 1995 and Iliffe, J: Datums and Map Projections: For Remote Sensing, Gis and Surveying. (Jon Iliffe is the creator of SnakeGrid which is a wonderful tool for us mere mortals to avoid geodesy). For other tools to play around with geodetic transforms, https://proj.org/ is well worth taking time to get to grips with and is the underlying technology used in many applications, e.g. lastools.
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Re: UTM-Scaling in Target Statistics using Faro Scene

Post by marius »

Thank you guys for that input. Made me think again.

Becasue i dont want any distortion in my final result i mainly just wanted to know how scene handles targets that are in a distorted system, i.e. UTM, cause there's a possibility (see screenshot) for the input of UTM coordinates for reference points or checkerboards. My main question was, just to clarify, if this then would or would not falsify the target statistics report.
a88b80c8-9ed6-4e19-a227-1a06882189c4.png

Now to you guy's input that kind of complicated it for me.
1. Your local coordinate system doesn't have any distortion, why do you need it in a system which has, which you don't consider?
2.Do you want to apply the 0.9996 scale onto Z as well (since UTM is a map projection, the height is not defined)?
3.When you transform a FARO focus project, you need to apply the scale to the scanning position (since this is not correct either) + on any of the points in the scanner coordinate systems, quite a hassle isn't it?
4.Whereever you are importing and using the point cloud, does it understand that the point cloud is not metric anymore? Otherwise you'll get the scale factor into your project (no worries only 4 cm / 100 meter)?
1/4. It is an archeological survey where georeferencing makes sense, at least as a final result (its necessary). best would be not to have any scale factor then. Scaling it would, as you pointed out, make it impossible unterstand for anyone who uses this data in the future.
2. I will use JAG3D with a 3D adjustment, 1st with a "free" net adjustment for local coordinates, afterwards use my measured UTM points for a "connected" net. (sorry i dont know the right terms). Z would be a applied in this scenario, maybe i'll do 2D/1D seperately for the global points. Im not entirely sure how i'll deal with this yet, but height scaling with the same factor as planar is definetly not what i want.Thanks!.
3. I dont want to scale every scan itself, a 1:1 projection in slightly "false" global coordinates is what would serve my purpose and what i'm aiming for. Maybe with real UTM in the center of the object and gradual radial falsification of the UTM coordinates (no idea how thb and probably nonsense). But if ill just transform the whole thing at the end with maybe 3 or 4 identical points i get the scaling factor. maybe i just dont see the simplest solution anymore? :) Do you guys have a simple solution?



1. Re-compensate for the effect of the earth's curvature. What you need to do, is to "bend" the control points upwards, so that they fit to the "planar" laser scans.
2. Scale the point clouds by using the scaling factor.
3. "Scale" your registration parameters.
1 - i think the bending of the points in height should be insufficient in a small scale project (<1mm for 100m; 2cm for 500m) compared to UTM scaling, isnt it? (were talking maybe 100m*50m*50m pointcloud). Or are you talking local coordinates? I think i heard about this issue in BIM - great point.
2 - Seems like the simplest approach in my eyes, but isnt this adressing a different issue then what is compensated in 1?
3 - Dont really get this one, sorry..

I really appreciate the input you gave me. Thank you!
Marius
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Re: UTM-Scaling in Target Statistics using Faro Scene

Post by Daniel Wujanz »

Dear Marius,

we can also have a phone call if you want. I'll send you my number and email address via pm.

All the best

Daniel
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Re: UTM-Scaling in Target Statistics using Faro Scene

Post by smacl »

VXGrid wrote: Mon Nov 28, 2022 8:21 am do you need it in a system which has, which you don't consider?
[*]Do you want to apply the 0.9996 scale onto Z as well (since UTM is a map projection, the height is not defined)?
Just on this specific point, a commonly used solution in survey is to create a scale 1.0 project grid based on applying a 2d conformal transformation to the mapping grid using a local origin and inverse scale factor. I advise those doing this to remove the significant digits off the new local grid to avoid potential confusion between this and the original mapping grid at any point in the future. This works ok over small to medium size projects but falls foul of Earth curvature on larger projects, hence the need for Snake Grid.
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