Surface Flatness, Surface Levelness

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laserg
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Surface Flatness, Surface Levelness

Post by laserg »

Hi everyone,

I am currently conducting a study to implement laser scanner to find 2mm defect on the concrete slab & wall, when I am exploring Cyclone 3DR, i get confused by Surface Flatness and Surface Levelness. May I know what is the difference between them and what is the algorithm behind? Another one is accuracy of a leica p50 laser scanner, how can I estimate its confident interval in conducting a highest density and quality with multi scanworld? Is 2mm 3D positional accuracy really achievable?

Thank you all.
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Re: Surface Flatness, Surface Levelness

Post by badam »

laserg wrote: Tue Dec 28, 2021 6:30 pm Hi everyone,

I am currently conducting a study to implement laser scanner to find 2mm defect on the concrete slab & wall, when I am exploring Cyclone 3DR, i get confused by Surface Flatness and Surface Levelness. May I know what is the difference between them and what is the algorithm behind? Another one is accuracy of a leica p50 laser scanner, how can I estimate its confident interval in conducting a highest density and quality with multi scanworld? Is 2mm 3D positional accuracy really achievable?

Thank you all.
I've never used/seen 3dr, but based on the wording. The difference is that the flatness is create a best fit plane to the selected points and gives out i suppose the Mean/Max dist to that fitted plane. (plane not required to be level it can be a wall, roof etc...)

Levelness will go a step further and check how much that plane/points differ from a perfectly leveled plane (XY plane in the coord system)...

Leica could give you more detailed information on those, but will not give you the algorithms...


As for precision/quality 2mm is a little bit too low... maybe if you are scaning from only 1 scan location... If you measure in the 120m/270m mode then you will have 1.2mm + 10ppm over full range, and there is a range noise as well which is around [email protected] So it is almost impossible to measure with 2mm error if you require multiple setup...

But correct me if I'm wrong. I'd say that 5mm can be achieved (not easy) but it really depends on the size of the plant, how many targets/setups will be used, etc...
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Re: Surface Flatness, Surface Levelness

Post by gilles_3DR »

Hi,
A surface can be flat but not levelled!

Levelness is very simple to define: on each point, you measure the distance to a horizontal plane. This horizontal plane is always the same for all the points.

There are many ways to define flatness on the other hand.
The way it is implemented in Cyclone 3DR is that local planes are fitted on regular grids. And then, each points are compared against their local planes.

Do not hesitate to hit F1 in each command in Cyclone 3DR to know more!

Hope this helps
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Re: Surface Flatness, Surface Levelness

Post by laserg »

gilles_3DR wrote: Wed Dec 29, 2021 5:01 pm Hi,
A surface can be flat but not levelled!

Levelness is very simple to define: on each point, you measure the distance to a horizontal plane. This horizontal plane is always the same for all the points.

There are many ways to define flatness on the other hand.
The way it is implemented in Cyclone 3DR is that local planes are fitted on regular grids. And then, each points are compared against their local planes.

Do not hesitate to hit F1 in each command in Cyclone 3DR to know more!

Hope this helps
Is there any formula for the algorithm to illustrate the analysis function? I am writing a academic paper to implement laser scanner to find 2mm defect on the concrete slab & wall and wondering if a well-calibrated P50 and controllable environment can detect 2mm detect on a concrete surface by utilizing surface flatness and levelness. Thanks!
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Re: Surface Flatness, Surface Levelness

Post by VXGrid »

laserg wrote: Thu Jan 20, 2022 1:45 pm
gilles_3DR wrote: Wed Dec 29, 2021 5:01 pm Hi,
A surface can be flat but not levelled!

Levelness is very simple to define: on each point, you measure the distance to a horizontal plane. This horizontal plane is always the same for all the points.

There are many ways to define flatness on the other hand.
The way it is implemented in Cyclone 3DR is that local planes are fitted on regular grids. And then, each points are compared against their local planes.

Do not hesitate to hit F1 in each command in Cyclone 3DR to know more!

Hope this helps
Is there any formula for the algorithm to illustrate the analysis function? I am writing a academic paper to implement laser scanner to find 2mm defect on the concrete slab & wall and wondering if a well-calibrated P50 and controllable environment can detect 2mm detect on a concrete surface by utilizing surface flatness and levelness. Thanks!
If you conduct the measurements with at least 2 scans I'd say your 2mm will go down in "noise" aka registration error.
When your scanner position is within 1mm this accumulates depending on the distance to your target (the overlapping area of both scans does not form a single plane anymore).

Even if we are talking about single scan measurements (don't know the point accuracy of the P50), this will be pretty hard to find with a good confidence - imho.
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Re: Surface Flatness, Surface Levelness

Post by laserg »

How about the control point that was provided for the scanning task? I assumed that established a series of control points by total station and use direct geo-referencing (the scanner sitting on the control point, like a total station) will give a better result compared to an in-direct geo-referencing method, right?
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Re: Surface Flatness, Surface Levelness

Post by pmalatzky »

laserg wrote: Sun Jun 12, 2022 6:57 pm How about the control point that was provided for the scanning task? I assumed that established a series of control points by total station and use direct geo-referencing (the scanner sitting on the control point, like a total station) will give a better result compared to an in-direct geo-referencing method, right?
Well not necessarily, you'll likely get a "better" result from well-positioned scan location/s that have multiple, accurately coordinated targets (i.e established by total station), within each scan.

Also, you can/should refer to ASTM E1155 for more information on FF and FL.
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Re: Surface Flatness, Surface Levelness

Post by smacl »

pmalatzky wrote: Wed Jun 15, 2022 8:28 am
laserg wrote: Sun Jun 12, 2022 6:57 pm How about the control point that was provided for the scanning task? I assumed that established a series of control points by total station and use direct geo-referencing (the scanner sitting on the control point, like a total station) will give a better result compared to an in-direct geo-referencing method, right?
Well not necessarily, you'll likely get a "better" result from well-positioned scan location/s that have multiple, accurately coordinated targets (i.e established by total station), within each scan.

Also, you can/should refer to ASTM E1155 for more information on FF and FL.
Agreed, for high accuracy work you should also consider a digital level on the control in addition to total station. Thanks for the ASTM links, must have a read of them.
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Re: Surface Flatness, Surface Levelness

Post by landmeterbeuckx »

smacl wrote: Wed Jun 15, 2022 10:09 am
pmalatzky wrote: Wed Jun 15, 2022 8:28 am
laserg wrote: Sun Jun 12, 2022 6:57 pm How about the control point that was provided for the scanning task? I assumed that established a series of control points by total station and use direct geo-referencing (the scanner sitting on the control point, like a total station) will give a better result compared to an in-direct geo-referencing method, right?
Well not necessarily, you'll likely get a "better" result from well-positioned scan location/s that have multiple, accurately coordinated targets (i.e established by total station), within each scan.

Also, you can/should refer to ASTM E1155 for more information on FF and FL.
Agreed, for high accuracy work you should also consider a digital level on the control in addition to total station. Thanks for the ASTM links, must have a read of them.
Digital level is teh way to go. XY with a ts, Z with a level.
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Re: Surface Flatness, Surface Levelness

Post by laserg »

smacl wrote: Wed Jun 15, 2022 10:09 am
pmalatzky wrote: Wed Jun 15, 2022 8:28 am
laserg wrote: Sun Jun 12, 2022 6:57 pm How about the control point that was provided for the scanning task? I assumed that established a series of control points by total station and use direct geo-referencing (the scanner sitting on the control point, like a total station) will give a better result compared to an in-direct geo-referencing method, right?
Well not necessarily, you'll likely get a "better" result from well-positioned scan location/s that have multiple, accurately coordinated targets (i.e established by total station), within each scan.

Also, you can/should refer to ASTM E1155 for more information on FF and FL.
Agreed, for high accuracy work you should also consider a digital level on the control in addition to total station. Thanks for the ASTM links, must have a read of them.
Is direct geo-referencing more accurate than in-direct geo-referencing. Although I cannot find any literature about this statement, I still want to consult the expert in this forum, according to your experience.
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