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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