NavVis VLX - wearable mapping

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Jaakko Tawast
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Re: NavVis VLX - wearable mapping

Post by Jaakko Tawast »

GeorgSchroth wrote: Tue Dec 01, 2020 9:34 am Shane and Dennis from LSF but for sure many many others outside the LSF have already done extensive accuracy evaluations of the VLX (thank you for that). But not everyone had the chance to compare the VLX scans against a ground truth scan.

As you know building a reliable ground truth is not a quick scan, and the team working on this project realized that as well:
To get a reference, we first scanned a hallway at NavVis with a TLS (that many of us own) and used cloud to cloud registration. However, the resulting point cloud showed clear artifacts from incorrect registrations.

So we decided to go an get the most precise scanner out there (afaik) and used a total station to precisely position the scans with respect to each other (which took us a full day overall together with a trusted surveying customer of ours)

The result of the comparison is pretty good I would say ;) Actually a lot better than the VLX accuracy spec. This is not too surprising since we made and will continue to add quite a few enhancements to our algorithms & software. So all the devices out there are getting better and better with every release.

But have a look for yourself and let me know what you think or would need in addition (point clouds can be downloaded here https://navv.is/2HS4LM0 )


youtu.be/dzCFEkd9GzQ
This kind of videos are quite misleading, modern scanners like RTC do colour scans in 2-3 min and usually colours are not used so it's more like 1-2 mins per scan. It would take less than 1 hour.
In many cases surveying control point network can be the most difficult part of work, sometimes even crew of 2-3 is needed. I guess with mobile scanners you need to pay even more attention to control points as drift can occur and digital imu perfomance doesn't match compensator (noticed on RTC). Having precise elevation is usually required at least on our indoor projects, so P40 would win this comparison ;)
For floor area calculations we have some standards in Finland and mobile scanners don't exceed those requirements.

VLX is still a great product, specially for topographic surveys or fast scans on renovation projects.
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Re: NavVis VLX - wearable mapping

Post by GeorgSchroth »

Jaakko Tawast wrote: Thu Dec 03, 2020 1:05 pm
This kind of videos are quite misleading, modern scanners like RTC do colour scans in 2-3 min and usually colours are not used so it's more like 1-2 mins per scan. It would take less than 1 hour.
In many cases surveying control point network can be the most difficult part of work, sometimes even crew of 2-3 is needed. I guess with mobile scanners you need to pay even more attention to control points as drift can occur and digital imu perfomance doesn't match compensator (noticed on RTC). Having precise elevation is usually required at least on our indoor projects, so P40 would win this comparison ;)
For floor area calculations we have some standards in Finland and mobile scanners don't exceed those requirements.

VLX is still a great product, specially for topographic surveys or fast scans on renovation projects.
Comparisons on speed are always tough since you would first need to define a very clear application that you need the scan for. But then there are soo many different applications and requirements that you can address only most of them.
Like you said: if you dont need colors in your application, you dont need to take panos with the VLX and just use the intensity cloud, right?
This will almost double the speed of scanning with the VLX.

However, when I look at customers like larger companies and enterprises in the manufacturing industry: Only few can work with point clouds and they ask for 2D DWGs. But what they get are immersive webtools like NavVis IV or Faro Scene that let them take their own measurements as if they where in site via the panos. Also they exchange and collaborate on that basis and use this for project mgmt. This is where more panos are better and where a lot of growth potential lies for our industry.

On the need for total stations: For a project of that size, only few would use a total station in addition to a TLS, right? Registration with spheres is usually very accurate and I would say, if done properly, good enough?
Same with VLX: for a project of that size there is no need for a total station. As you see in the clouds the drift is very limited and hardly noticable.
In this evaluation we used a TLS to assure we have a ground truth reference and indeed the TLS + TS approach took as like 6 hours.

On the leveling: Yes I heard that RTC360 has/had issues with leveling but that doesnt mean that other products that are fast have that problem as well. Check out the VLX datasets or talk to one of hour customers about this point. BTW: what are the requirements in Finnland? Is there a document that specifies that like with the USIBD?

Last: I know the race is a bit of an apples and oranges comparison but it also sparked a vivid discussion that helps us to continue to improve & learn. So thanks for the feedback :)
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Re: NavVis VLX - wearable mapping

Post by RobM »

Well now this thread is interesting.
I was just using Trimble Timms for a week (rental unit) and came acros the NaVis VLX on here... After watching a few videos and reading on here I must say I am getting kind of curious... Will download the sample data now. Are there rental units available too? And whats the price range for buying one?
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Re: NavVis VLX - wearable mapping

Post by cjmackenzie »

RobM wrote: Thu Dec 03, 2020 6:11 pm Well now this thread is interesting.
I was just using Trimble Timms for a week (rental unit) and came acros the NaVis VLX on here... After watching a few videos and reading on here I must say I am getting kind of curious... Will download the sample data now. Are there rental units available too? And whats the price range for buying one?
Morning Rob, I am glad that we were about to spark your curiosity. A person from our team will reach out to you to answer your questions. Thanks, Charles
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Re: NavVis VLX - wearable mapping

Post by Jaakko Tawast »

GeorgSchroth wrote: Thu Dec 03, 2020 2:05 pm Comparisons on speed are always tough since you would first need to define a very clear application that you need the scan for. But then there are soo many different applications and requirements that you can address only most of them.
Like you said: if you dont need colors in your application, you dont need to take panos with the VLX and just use the intensity cloud, right?
This will almost double the speed of scanning with the VLX.

However, when I look at customers like larger companies and enterprises in the manufacturing industry: Only few can work with point clouds and they ask for 2D DWGs. But what they get are immersive webtools like NavVis IV or Faro Scene that let them take their own measurements as if they where in site via the panos. Also they exchange and collaborate on that basis and use this for project mgmt. This is where more panos are better and where a lot of growth potential lies for our industry.

On the need for total stations: For a project of that size, only few would use a total station in addition to a TLS, right? Registration with spheres is usually very accurate and I would say, if done properly, good enough?
Same with VLX: for a project of that size there is no need for a total station. As you see in the clouds the drift is very limited and hardly noticable.
In this evaluation we used a TLS to assure we have a ground truth reference and indeed the TLS + TS approach took as like 6 hours.

On the leveling: Yes I heard that RTC360 has/had issues with leveling but that doesnt mean that other products that are fast have that problem as well. Check out the VLX datasets or talk to one of hour customers about this point. BTW: what are the requirements in Finnland? Is there a document that specifies that like with the USIBD?

Last: I know the race is a bit of an apples and oranges comparison but it also sparked a vivid discussion that helps us to continue to improve & learn. So thanks for the feedback :)
We are using real height systems in most projects so surveying at least elevation to scan area is usually needed. In typical office buildings we bring elevation to all storeys. Working without control is against good practices. Btw do you have video how VLX is working with control, can you give "weight" to control like in cyclone and is target recognition automatic?

In general i think VLX would be good enough for calculating floor area, it's surely better in complex spaces than simple distance meter. In finnish standard 4 digits must be used in calculation and in drawing attached measurements are rounded like 2405mm->2410mm. If area is under 100 sqm result is given in 0.5 accuracy, otherwise 1 sqm accuracy. With bad luck some 2-3 cm errors could result incorrect rounding. IMO the standard is outdated, it doesn't include scanning and is only mentioning single measurements.

Interested seeing VLX in real life action some time :)
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Re: NavVis VLX - wearable mapping

Post by GeorgSchroth »

Here you go:


youtu.be/PfGCcIhNP6g

And you might want to check the accuracy whitepaper for the VLX (from beginning of this year -> so the results have improved further).
https://navv.is/2IbW3bD

VLX is NOT a 2-3cm or rough mapping system. In the exemplary evaluation above, one sigma (68%) of the points have been better than 3mm and two sigma better than 11mm.

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Re: NavVis VLX - wearable mapping

Post by scankukai »

Hi,

We just did some tests. The overall accuracy is very good indeed. However, data are more noisy, and the VLX has a tendency to produce rounded edges.
This would make the system not suitable for industrial environments (small pipes and structures).
Doing a flatness / slope analysis would also be harder.
But it is perfect for floorplans and classical BIM.

Slice. Blue: VLX ; Red: TLS
Edges.jpg
Flatness VLX
2020-12-04_14-57-40.JPG

Flatness TLS
2020-12-04_14-57-48.JPG
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Re: NavVis VLX - wearable mapping

Post by GeorgSchroth »

Thanks for the feedback and extensive analysis! Yes, we haven' t tested VLX for floor flatness applications and I would not recommend that as of now (by that I mean local floor flatness of in the range of mm as you have shown in the screenshots).

When comparing the edges, keep in mind that the bulge of the door that you show above has a thickness of just over 2cm. But fair point on which we can improve further :)
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Re: NavVis VLX - wearable mapping

Post by jedfrechette »

yankoch wrote: Fri Dec 04, 2020 2:30 pm the VLX has a tendency to produce rounded edges.
It seems like this is a significant challenge for this type of workflow:
GeorgSchroth wrote: Thu Dec 03, 2020 2:05 pm However, when I look at customers like larger companies and enterprises in the manufacturing industry: Only few can work with point clouds and they ask for 2D DWGs. But what they get are immersive webtools like NavVis IV or Faro Scene that let them take their own measurements as if they where in site via the panos.
When users are making measurements, it seems likely that more often than not the points they want to measure between will be edges or corners which will be the least accurate portions of a highly post-processed point cloud like this. Having the point cloud show smooth flat walls is great (assuming they actually are smooth), but how often are you making measurements between the middle of those surfaces rather than say the corners of a room or a window/door frame?

We run in to much the same issue meshing point clouds. On the one hand you want to retain sharp features, but it's often not trivial to distinguish between real features and noise.
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Re: NavVis VLX - wearable mapping

Post by GeorgSchroth »

Hi Jed,

we are looking here at the bulge of a door frame of an elevator of about 2,4cm thickness.
Small details like these with two edges right next to each other are challenging for the VLX until now.
Using the TLS scan recorded from close distance as a reference, the error on that bulge is between 5,9 to 8,44mm (in the screenshot below read the ΔXY values to get the horizontal distances).
The single/normal edges look better IMO with 5,4mm deviation on the upper right edge.

Certainly we keep working on the software to get better on those fine details (e.g. with double edges) but for many use cases (especially those where you pick points on edges ;) ) this should be quite ok?

VLX PC of the elevator doors with the bulge around the frame.
Screenshot 2020-12-06 at 10.14.34.png

15cm section of the TLS PC (in red) as well as the VLX PC (in white)
Screenshot 2020-12-06 at 11.31.48.png

zoomed in with a few measurements (read the ΔXY values to get the horizontal distances)
Screenshot 2020-12-06 at 11.52.17.png

One more thought as mentioned above: The video above should rather have been called: VLX AND TLS. Clearly every tool has its sweet spots and limits.
Measuring the size of a door bulge is not VLX terrain. So far ;)
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