Scanstation P20 & Registration Accuracy

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gmanca
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Scanstation P20 & Registration Accuracy

Post by gmanca »

Hi all,
Is there anyone out there who can provide some information about the accuracy of a registration using the traverse function of the P20? We are planning to use the P20's traverse option instead of the more conventional "total station + targets" method, but we're not sure about the final result; we work with hundreds (sometimes thousands) of scans and our customers require registration errors <5 mm: We managed to achieve this result using a total station to survey the targets coordinates, but will it be possible using the traverse option?

Thanks,
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Giuseppe
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Re: Scanstation P20 & Registration Accuracy

Post by Jamesrye »

There is a good thread on the subject here:

http://www.laserscanningforum.com/forum ... =43&t=3034

For the best accuracy I'd go with resection, otherwise you'd likely have to 'augment' the registration with cloud to cloud - and then adjust target weights etc...
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Re: Scanstation P20 & Registration Accuracy

Post by pburrows145 »

Use the field set up method, create a registration on board, unfreeze the registration (which requires you to delete the modelspace) and then use auto-add cloud constraints to tighten up the entire registration... I have used this route successfully many many times.

However, it's up to you which route you go with. I also like working with existing control and setting up the scanner and targets over them (with heights etc), enabling the known-backsight function for 1 target registration in the field.

Saying that, I love using no targets and using cloud-to-cloud too - so quick! :)
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Re: Scanstation P20 & Registration Accuracy

Post by Matt Young »

With the correct procedures you should achieve a mean average of around 1 or 2mm for your overall registration result. You must use the cloud 2 cloud function after the traverse in order to achieve this type of accuracy, and you must adjust constraints within the registration after the cloud 2 cloud process.

I always prefer using coincident targets with scans - as Paul suggests using no targets is fast but not reportable in the same way as traverse or coincident targets.

If you have a project with thousands of scans then don't try and do it all in one registration, it will be slow going. Try to break the project up into manageable areas. Two or three hundred scans max per registration is usually my preference.
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Re: Scanstation P20 & Registration Accuracy

Post by pburrows145 »

Also, remember that targets should only be used up to 50m away with the P20. Up to 100m-150m (Though Steve says he's managed >170m before) with the C10.
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Re: Scanstation P20 & Registration Accuracy

Post by Matt Young »

I find the optimal range for targets is between 30 to 40m - you can scan them at further ranges but tend to lose accuracy a little.
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Re: Scanstation P20 & Registration Accuracy

Post by Scan-Ninja »

I have found that the P20 is as accurate as the total station, getting the same type of error as the total station when used on a traverse mode.
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Re: Scanstation P20 & Registration Accuracy

Post by tbwester »

I find that the p20 looses accuracy on target acquisition after 20-25m or so.

I've done long traverses (~800 feet), and when I went to close the loop, I was off by several inches (maybe 6 inches, I can't remember exactly). Once I closed the loop in registration it was perfect, so it just comes down to having a robust methodology in the field.

One thing that amazes me with the P20 is the cleanliness of the data. When you check your registrations, it looks like there is a fair amount of error (between overlapping scans) , but when you measure it - its a lot less than you expect. I attached an image as an example. It looks like clear mis alignment - but the distance between the clouds is less than 1/4 inch.

I like the p20 a lot, but c10 is better for projects that require significant data capture past 75-100 feet.
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Last edited by tbwester on Mon Jul 07, 2014 9:35 pm, edited 1 time in total.
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Re: Scanstation P20 & Registration Accuracy

Post by Scan-Ninja »

we have recently used the P20, using the traverse mode at the maximum distance (100 to 120m for targets), and we were able to get as good of a closure @6mm error.
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Re: Scanstation P20 & Registration Accuracy

Post by tbwester »

Scan-Ninja wrote:we have recently used the P20, using the traverse mode at the maximum distance (100 to 120m for targets), and we were able to get as good of a closure @6mm error.
nice work!
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