Scanstation P20 & Registration Accuracy

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Re: Scanstation P20 & Registration Accuracy

Post by Scan-Ninja » Mon Jul 07, 2014 9:43 pm

tbwester wrote:
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!
Thanks Tbwester. I was impressed by it as we really never used the scanner in traverse mode, and it's our first project with our new P20. It's definitely a beast. Saying goodbye to the days of playing Angry birds in the truck while scanning. Can't keep with how fast, accurate that scanner is.

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Re: Scanstation P20 & Registration Accuracy

Post by matu78 » Tue Jul 08, 2014 7:53 am

I have found that traversing with the P20 is fine aslong as you are using predetermined control points, i.e. measured by total station. When using the P20 to traverse to unknown points I found the misclosure to generally be good x/y but poor in z, usually around +/- 5-7mm.
You can measure your control stations after you have occupied them but then you have to do a bit of messing around with your scanner imported registration. Cyclone doesn't seem to like this too much and the whole point is to try and minimise your post processing. If you go down the resection route I would make sure that your control is very tight and reject the setup and try again if you don't get good results first time. Also always use 3 or more points, which may be tricky assuming that you will not be exceeding the recommended 50m range!
I would also use carriers with optical plummet+plate level and be exceedingly careful when determining your target heights. I would definitely recommend working out your vertical offsets beforehand!!
I'm not trying to put you off the idea but based on my experiences I would use the traverse functions on lower accuracy jobs and even then with some caution.
As with the previous posts its a 'horses for courses' choice depending on your accuracy requirements

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Re: Scanstation P20 & Registration Accuracy

Post by Matt Young » Tue Jul 08, 2014 8:37 am

Matt Young wrote: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.
Sorry to quote myself... but if you don't follow the correct registration procedure then you will get those level differences/errors. If you do full 360 degree scans in traverse mode and then run cloud 2 cloud afterwards you will rule out the majority of the Z errors, especially if you work in a closed loop traverse. The C10/P20 are both locked in Z axis and this process of adjustment works very well.
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Re: Scanstation P20 & Registration Accuracy

Post by pburrows145 » Tue Jul 08, 2014 9:22 am

You should really only scan P20 targets up to about 50m away... C10 targets are fine up to over 100m.

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Re: Scanstation P20 & Registration Accuracy

Post by Matt Young » Tue Jul 08, 2014 11:49 am

I would recommend 25 to 35m for both, but that's just my opinion.
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Re: Scanstation P20 & Registration Accuracy

Post by tbwester » Tue Jul 08, 2014 12:26 pm

Matt Young wrote:I would recommend 25 to 35m for both, but that's just my opinion.
I agree. Only when I get in a bind do I use points beyond 20 meters for the p20 and 50m for the C10.

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Re: Scanstation P20 & Registration Accuracy

Post by dbianculli » Wed Aug 27, 2014 4:51 pm

What kind of targets do you use for this project? I have been tested P20 for high accuracy 3D targets automatic recognition using spherical white targets (6" diameter) and hemispherical 5" with magnetic drift nest to reposition accurately the targets in a well defined network of points in the space that has to be scanned. The overall accuraly of registration taking into account only the targets is below 1mm. I would say 0.2-0.4 mm for targets-station distances beyond 5/6m. Never tried for large distances beyond 25 meters but I guess it should be precise either way. Anyway the bottom line is a cloud to cloud registration is based on non conventional targets (the surfaces of the environment you scan). The targets based registration is done on well known targets (surface, shape, dimension) and is the best accurate way to do this job. Of course it requires a bit more time to scan each targets for each of the station you foresee to place.

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Re: Scanstation P20 & Registration Accuracy

Post by tbwester » Wed Aug 27, 2014 5:01 pm

dbianculli wrote: The targets based registration is done on well known targets (surface, shape, dimension) and is the best accurate way to do this job.
True, but c2c has the best possible target geometry - which increases accuracy over using targets alone.

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Re: Scanstation P20 & Registration Accuracy

Post by hypsometric » Thu Aug 28, 2014 5:02 am

dont believe of word of this till Phil chimes in....

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Re: Scanstation P20 & Registration Accuracy

Post by Matt Young » Thu Aug 28, 2014 8:45 am

If you use a total station to record your targets then your registration is only as good as your total station.

If you set up over known points that have been recorded with your total station then your registration is only as good as your total station.

If you use cloud 2 cloud after either of the above methods then your registration should be better than your total station, provided that you do it right.

There is a balance between geometry, target placement and post scan processing. It takes a long time to find that balance and it works very well when you have found it.
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