Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

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nyterydur
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Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by nyterydur »

I'm looking to improve our workflow and accuracy of our scan data. My company often has projects that involves laser scanning large scale facilities. Most of these are congested with production equipment, others are newly acquired spaces that a empty or generally wide open. That being said the focus of this post will be on controlling the accuracy of 3D laser Scans in a Large moderately congested INTERIOR Space.

I would like to hear how other people do it, especially when you traverse through many (potentially)small doorways, from room to room (or warehouse to warehouse), and through stairwells to other levels. I hear these large LS firms scan sometimes thousands of scans in an interior space but never how they can prove the accuracy of said scans.

Is it common practice to utilize a survey total station to shoot in points in an interior environment? Limitations to this are you can't really set pins in a plant finish floor, and reflectorless surveying (if you are shooting in checkerboards on vertical surfaces) to my knowledge is not as accurate, but I'm not a surveyor.

Anybody have additional insight into this or experience. I did some brief searches on here and I'm not finding anything that stands out as obvious to answer my question, I apologize if I missed a thread covering this topic.

Thanks in advance
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by Ioannis »

Hire a licensed surveyor in order to apply control to each project you can not push a button and do registration and also scanning it's a philosophy behind the buttons that requires surveyors' knowledge to do righ right.
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by stutosney »

As above, either hire a surveyor or have the know how yourself to control the data. Whilst I agree a survey background is beneficial (I myself have a survey background), I do think that scanning and surveying are becoming separate industries in themselves. It depends on what you are using the scanner for at the end of the day. If you are producing survey drawings, these should meet the survey standards and specification which usually means getting in a certified/experienced surveyor to control the job.
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by badam »

Well, if you want to increaae accuracy without controll, you need a lot of loop closure. For example if the building has 4 stairs register/link all of them. If you have a multifloor space then register the scans which has overlap. If the building has balcons then register the balcons setups to the exterior scans. If you have opportunity open the window and place the scans in the window and register them to the exterior scans. Scan the flat roofs and connect it with as many stairs as you can and also with the exterior scans.

However, this is only works where you have exact controll, which setups are linked together, like cyclone register/register360. It is not gonna work with recap, faro scene and as far as i know not works in trw. (Let me know if í'm wrong.)
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by jaredmatthews »

To answer your questions bluntly - yes you require a total station (TS).

You do not necessarily need to set pins inside these environments. You just need some semi-permanent reference points that you can scan in with your scanner. These can be as simple as stickers. I sometimes use blank white barcode labels as they are easy to remove afterwards, and they can be written on. Just stick them where ever you need them, draw a big + with the point reference name under the +.

Then its just a matter of capturing these points with a TS and then scanning them in with the scanners.

Though you mentioned that you are not a surveyor, so I doubt you would have a TS.

You never mentioned what scanner you are using either...
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by Augusto 3D »

jaredmatthews wrote: Wed Jun 29, 2022 5:16 pm To answer your questions bluntly - yes you require a total station (TS).

You do not necessarily need to set pins inside these environments. You just need some semi-permanent reference points that you can scan in with your scanner. These can be as simple as stickers. I sometimes use blank white barcode labels as they are easy to remove afterwards, and they can be written on. Just stick them where ever you need them, draw a big + with the point reference name under the +.

Then its just a matter of capturing these points with a TS and then scanning them in with the scanners.

Though you mentioned that you are not a surveyor, so I doubt you would have a TS.

You never mentioned what scanner you are using either...
So far this has been the best and more imformative post to answer the OPs question. I thikn that we are also in the same boat and are looking to hire a surveyor part-time to help us with control and we also deal with the same constraint on larger interiors. The reality is that as much as you wish, something you just can't close the loop (for many reasons) , be it time, budget or access.

I like the idea of drawing the a cross of the label paper, we have done something similar with small adhesive targets we have made (and stick them on the floor). However the caviat is that you need to make sure that you are scanning them at a "good" angle. What we are going to try for the next job is to use the floor points as our TS control network and then shoot wall targets. This is what a surveyor we hired did. The challenge with working a TS is the time it takes to move from setup to setup. Down a hallway is not problem with a Robot, but when you have to go in an out of rooms its a PITA and add a lot of time to the whole operation. at least from what I have seen, I am happy to be corrected.
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by nyterydur »

jaredmatthews wrote: Wed Jun 29, 2022 5:16 pm To answer your questions bluntly - yes you require a total station (TS).

You do not necessarily need to set pins inside these environments. You just need some semi-permanent reference points that you can scan in with your scanner. These can be as simple as stickers. I sometimes use blank white barcode labels as they are easy to remove afterwards, and they can be written on. Just stick them where ever you need them, draw a big + with the point reference name under the +.

Then its just a matter of capturing these points with a TS and then scanning them in with the scanners.

Though you mentioned that you are not a surveyor, so I doubt you would have a TS.

You never mentioned what scanner you are using either...
Thanks for your insight. We are using 2 Faro S70 units. I agree with your approach and we do have what we call checkerboard targets and stickers to be used in this situation. I guess from a surveying standpoint however, that's considered a reflectorless shot. This means that we are not shooting a prisim on a rod like normal and the signal is not being reflected back to the receiver to be "corrected". You are only relying on what your eyeball sees as far as aligning the crosshairs of the TS to be as exact as possible on the checkerboard. I'm being told that reflectorless shots on a TS are not as accurate, but maybe that's because our TS (which we do own) is quite dated. Not sure if newer technology has improved this.
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by nyterydur »

Augusto 3D wrote: Wed Jun 29, 2022 8:22 pm
So far this has been the best and more imformative post to answer the OPs question. I thikn that we are also in the same boat and are looking to hire a surveyor part-time to help us with control and we also deal with the same constraint on larger interiors. The reality is that as much as you wish, something you just can't close the loop (for many reasons) , be it time, budget or access.

I like the idea of drawing the a cross of the label paper, we have done something similar with small adhesive targets we have made (and stick them on the floor). However the caviat is that you need to make sure that you are scanning them at a "good" angle. What we are going to try for the next job is to use the floor points as our TS control network and then shoot wall targets. This is what a surveyor we hired did. The challenge with working a TS is the time it takes to move from setup to setup. Down a hallway is not problem with a Robot, but when you have to go in an out of rooms its a PITA and add a lot of time to the whole operation. at least from what I have seen, I am happy to be corrected.
Agreed, surveying aside, the going in and out of all the rooms will always induce minor error which will compound over time. Doorways are the weakest link in any scan. We do 3 scans thru every doorway to reduce issues, but closing loops during scanning is not always possible or practical. It will almost always potentially significantly increase scan time if that has to occur.

This is not a new issue of ours, line of sight in a moderatly congested building could be a huge issue inside and the whole multiple setups just take forever unfortunately.
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by Augusto 3D »

nyterydur wrote: Wed Jun 29, 2022 10:19 pm
Augusto 3D wrote: Wed Jun 29, 2022 8:22 pm
So far this has been the best and more imformative post to answer the OPs question. I thikn that we are also in the same boat and are looking to hire a surveyor part-time to help us with control and we also deal with the same constraint on larger interiors. The reality is that as much as you wish, something you just can't close the loop (for many reasons) , be it time, budget or access.

I like the idea of drawing the a cross of the label paper, we have done something similar with small adhesive targets we have made (and stick them on the floor). However the caviat is that you need to make sure that you are scanning them at a "good" angle. What we are going to try for the next job is to use the floor points as our TS control network and then shoot wall targets. This is what a surveyor we hired did. The challenge with working a TS is the time it takes to move from setup to setup. Down a hallway is not problem with a Robot, but when you have to go in an out of rooms its a PITA and add a lot of time to the whole operation. at least from what I have seen, I am happy to be corrected.
Agreed, surveying aside, the going in and out of all the rooms will always induce minor error which will compound over time. Doorways are the weakest link in any scan. We do 3 scans thru every doorway to reduce issues, but closing loops during scanning is not always possible or practical. It will almost always potentially significantly increase scan time if that has to occur.

This is not a new issue of ours, line of sight in a moderatly congested building could be a huge issue inside and the whole multiple setups just take forever unfortunately.
but that is how a TS works. You have set it up everytime you move it. They are not cloud-to-cloud LOL or shot-to-shot, not yet anyway.
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Re: Controlling Accuracy of 3D laser Scans in a Large INTERIOR Space

Post by VXGrid »

nyterydur wrote: Wed Jun 29, 2022 3:07 pm [...]

Anybody have additional insight into this or experience. I did some brief searches on here and I'm not finding anything that stands out as obvious to answer my question, I apologize if I missed a thread covering this topic.

Thanks in advance
If you want to read more about it I can highly recommend the "Taming Errors" Series by Daniel Wujanz:
viewforum.php?f=153
nyterydur wrote: Wed Jun 29, 2022 10:19 pm
Augusto 3D wrote: Wed Jun 29, 2022 8:22 pm [...]
Agreed, surveying aside, the going in and out of all the rooms will always induce minor error which will compound over time. Doorways are the weakest link in any scan. We do 3 scans thru every doorway to reduce issues, but closing loops during scanning is not always possible or practical. It will almost always potentially significantly increase scan time if that has to occur.

This is not a new issue of ours, line of sight in a moderatly congested building could be a huge issue inside and the whole multiple setups just take forever unfortunately.
Loop closure does not mean to do additional consecutive scans to close loops, but to place scans, so you are able to not only connect the previous and next scan with the current scan, but possibly with other scan groups.
If you are scanning the exteriour & interiour of a building, don't just use the front- and backdoor as loops, include scans through open windows to connect the outside and inside. Especially if you have multiple stories it makes sense to do that (of course if feasable/possible), because than you can correct the staircase errors ;)

If going over 200 scan stations a total station geodetic point net is a must (in my opinion).
Reflectorless measurement of checkerboard targets is no issue, the accuracy of these points will still be a lot higher than the one of the laser scanner.
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