Static scan or mobile mapping ?

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Ben
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Static scan or mobile mapping ?

Post by Ben » Wed May 18, 2016 1:30 pm

Hi,

is somebody here already test mobile mapping systems ?

For a long road scanning, what do you think ?
is it better to scan it with static scans (scanner faro x330 + tripod) or is it better to scan it with mobile mapping systems ?

I know it save time with mobile mapping. But what about precision ? What is better ?

Thanks

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Re: Static scan or mobile mapping ?

Post by Rikore » Wed May 18, 2016 2:59 pm

Ben,
Yes mobile mapping is faster. However you need to look at what accuracy you are trying to achieve. If cm accuracy, then static scanning is the way to go with targets and good survey control points. If all you need is 20 to 30 cm, then mobile. It is basically the accuracy and results for what you need.

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Re: Static scan or mobile mapping ?

Post by blazaj » Wed May 18, 2016 4:31 pm

Ben,

you can also mount a scanner on top of your vehicle and perform stop&go.

http://www.laserscanningforum.com/forum ... 69&t=10383

Switch the scanner with RTK GPS every couple of scans to get positions fixed. For scans between your georeferenced positions you can either use targets or rely on cloud to cloud if there is enough C2C friendly features along the road. You'll be faster then walking around with a tripod and the results will be more precise than full mobile.

Regards
Jiri

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Re: Static scan or mobile mapping ?

Post by Ben » Wed May 18, 2016 6:27 pm

interesting,

do you know the spacing between points, for mobile mapping ?

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Re: Static scan or mobile mapping ?

Post by ksyen » Wed May 18, 2016 8:55 pm

Ben,

The point density depends on the speed of the vehicle. (lower vehicle speed, higher density). The point density do fall off as it get further away from the mobile scanner. Typically, we keep it under 30 meter for accuracy and density reason.

Mobile scanner can get you 5 cm (95%) in z and about 2-3 cm (95%) without any ground control (+/-30m of the vehicle path). Error goes up, as the points are further away from the mobile scanner. You will likely get better vertical accuracy (cut by 1/2) with a single target / vertical adjustment.

With ground control (depending on the spacing), you can get 1.5 cm (95%) in z and about ~1 cm (95%) using a 150m to 200 m ground target spacing assuming you have good GNSS converge, GNSS base station (<15Km baseline), and good GNSS/IMU initialization.

If you need higher accuracy, use static scanning.

Kin

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Re: Static scan or mobile mapping ?

Post by blazaj » Thu May 19, 2016 8:01 am

Nice result Kin, better than I would expect from a mobile system. Did you compare to static LS and/or to total station survey?
Thanks
Jiri

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Re: Static scan or mobile mapping ?

Post by richard_m » Thu May 19, 2016 8:46 am

Hi,

how long is the road and what do you need to deliver?

This usually decides for us which tech we use as both have advantages and disadvantages..

Richard.

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Re: Static scan or mobile mapping ?

Post by Ben » Thu May 19, 2016 9:38 am

Hi,

project lenght is around 15km.

We don't really care about time to scan. We need high precision and high density for totality of road surface.
We also need to make updates. For example, if a project was made with static scans, we can delete a scan in software, and change it by a new one. Can we do that with a pointcloud from mobile ?

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Re: Static scan or mobile mapping ?

Post by CWhyman » Thu May 19, 2016 4:18 pm

If your interested in learning more about mobile mapping technology - download the white paper/buyers guide that Chris Cox has written - we have just published it online.

http://www.3dlasermapping.com/mobile-ma ... ers-guide/

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Re: Static scan or mobile mapping ?

Post by richard_m » Fri May 20, 2016 8:52 am

15km is far into the mobile mapping option for me!

Some quick and dirty calculations, for a small road you could "zig-zag" along the route in maybe 1000 scans but I suspect this is a bigger road and so you will have to scan up one side and down the other, allowing for stretching the spacing a little then you have maybe 1500 scans, or put another way about 2 months scanning. A mobile mapper will do this in a morning. Obviously there could be a day or two mobilising / repositioning the auto and whichever method you use there is a few days for a field team with gps to co-ordinate some line markings etc to provide control and quality assurance points.

If your client is willing to wait months and pay for 2 months scanning then great - do it, could be very profitable. Mobile mapping will be much cheaper and quicker but therefore not as profitable..

The two methods will produce slightly different results, static scanning will theoretically be more "accurate" (for a single scan but not necessarily for 1000 scans.) but will pick up countless thousands of passing vehicles whereas the mobile solution should be much cleaner. Point spacing / resolution is dependant on the travel speed and hardware. We run 2x scanners in overlap on our scan-autos for maximum resolution which helps, be careful with single scanner mobile mappers. Of course the mobile-mapper will also produce a georeferenced 360deg photo record of the route which can be viewed online very easily, clients don't often ask for this but love it when they have it.

Updating the data depends on how you store the data but if you intend to update your pointclouds this is not a problem for either method really. If you take out a single terriestrial scan then little will actually remove from the combined pointcloud because you will have almost total overlap with other scans so you will have to remove quite a few scans to make a hole in the data. With a mobile-mapper pointcloud you can fence the area to remove and delete it. Then make a single scan or arbitrary registration of scans for the new data and simply cloud-constrain this new (terrestrial) data into the exising (mobile) data - you can easily mix-and-match.

You haven't said what your deliverables are.

If you are interested in knowing more about the mobile option please drop me a mail with some details at r.merrin[at]fugro.com and I can ask my colleagues in France to give you a call. Our scan autos are based in NL but travel widely and I assume we would use field / management resources locally. Or yours.

Nice project, keep us updated.

Richard.

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