The real question about range..

[dcacioppo]

I think the Faro Premium is always scanning at it's max range regardless of the version that you have (70, 150, or 350). By "upgrading" to the 150 or 350 versions, Faro is simply allowing you to see the data that was captured beyond 70m. In essence, removing the "filter" that allows you to see the data beyond 70m. I think that the benefit to the 150 over the 70 would be to help during the registration process if you are typically scanning larger areas. I know that we usually trash the data beyond 300 ft.

I too wonder what this Range setting is actually doing internally.
From Faro Premium Manual:

Distance Range - The Distance Range setting configures the scanner to increase the quality of the points captured at specified distances.

Normal - Select this to scan most objects.

Near - Select this to scan objects that are near the scanner, especially when the objects are reflective. (Not available with the FARO Core scanner.)

Far Distances - Select this when scanning outer-lying spaces, where the scan surfaces are located at distances of greater than 20 meters from the scanner. This setting is not recommended for indoor scanning.

[Augusto 3D]

I wonder if the previous version scanner focus and focus plus are the same in terms of how they achieve the range - via firmware installed at the factory depending on what you ordered

[jedfrechette]

Based on their description, I would guess Faro’s distance settings have more to do with varying the power output of the laser to try and improve the signal to noise ratio, but I don’t really know.

Faro’s spot size is going to be a little over 3cm at 100m and 9cm at max range, and I think that’s probably the biggest reason the data looks “fuzzy” at range compared to what you’re used to seeing close up. There’s only so much signal processing magic you can do when you’re sampling an ingressingly large area.

To my knowledge, nobody let’s you adjust beam diameter, it’s probably just not worth the extra complexity of essentially putting a zoom lens in front of the laser aperture. I believe Optech was working on a system with focusable optics at one point that would let yet you adjust the distance to the beam waist, but I don’t think that ever made it in to a product that was released.

[gsisman]

Lieven's description of why you might want a long range scanner is perfect. Basically they allow you to capture data if you can't get close to your subject. Scanning at shorter ranges will always be better though if you can.

One thing I'll add that often gets neglected when talking about the accuracy of long rang scans are the effects of beam diameter. If Lieven is doing a long range scan, the diameter of the laser beam he's recording points with is going to be about 20 cm at his scanner's maximum range of 800 m. Switch to a VZ-6000 though and its optics reduce that diameter to only 11 cm at 800 m. At its maximum range of 6 km though the VZ-6000'a beam diameter is still going to be a whopping 75 cm. The scanners often let you set their point spacing much smaller than the beam diameter so you can oversample (often by alot), but beam diameter still ends up being a pretty fundamental constraint on the smallest features you're able to resolve.

Since the VZ-6000 has a smaller beam, and will therefore be more accurate than a VZ-400 at range why not always use the VZ-6000 (if cost was no object)? It should be more accurate everywhere right? Unfortunately no, in order to perform well at long range its optical system needs to make trade-offs that make it perform worse at short distances. In particular, at a distance of 0, it's beam diameter is still 15mm so it will have trouble capturing detailed objects even at very short distances. Riegl doesn't seem to provide the beam exit diameter of the VZ-400, but for comparison something like a Faro will have an exit diameter of ~2mm so if I had to guess the VZ-400 is probably something like 3-5mm.

We do more civil type scans than structural engineering scans but on the few we have done we have rented or hired an operator with a P series (P20, 40) I did have a demo with a Leica P50 and some some impressive scans down with one on a bridge over the Ohio River (Scanned from each bank). What I saw first hand was that in order to get the max res out of something like a P50 (1km @ 80% reflection) is has to move real slow, I believe it was about 1 hour for a full dome when I saw it.

P 50 Specs.JPG

This to meet the specs they quote in the spec sheet, which is still about 13mm distance accuracy at that range, but the angular accuracy could throw as much as 5-6cm into it (if my math is correct) , which is actually pretty dang close for stuff you would want to capture at that range, rock faces, quarry walls or even a city top-scape from several high top roof corners. I do know with the BW targets and Leica's scanners you need 9-10 scan lines on the target for the SW to algorithmically select the target and we tested that. That is the big reason for the Window/Intense targets scan option on the P series- one of the things sorely lacking on the BLK & RTC. That is why we pretty much always scan Hi-Res on the BLK -to get the most range to our targets (and for Archival capture not as much for Production). We've recently ordered 6 inch targets which will hopefully extend our range a little for the BLK and provide even further on the RTC or other mobile scanner if and when we get one. I think where the traversing mode come in very handy with the Dual axis compensated scanners is when you have long linear scans with a lot of uniformity that makes C2C more difficult and the precise location of the scan station is not as dependent on the quality of the C2C fit but more help to align the rotation of the scan set.

[Augusto 3D]

Good input. We are ordering targets and our local vendor only has 4.5" in stock but I have been wanting 6" just to have a "better chance" of detection. We don't have a leica scanner we have a Faro S+ and the team really likes the quality of the b/w panos. Target detection may be a little different but larger targets always help.

Do you put your targets on a full size pole or do you deploy a tripod and tribrach for each?

[Daniel Wujanz]

Dear colleagues,

one short remark: the maximum range specified in all spec sheets always refers to a certain quotient of reflection. In many cases the maximum range refers to a SnG-scenario (Siegfrid 'n Roy that is). Hence, the reference target is pretty "white".

Let's say you're standing 100 metres from a facade (@ 50% quotient of reflection - qor) that you'd like to capture. If your scanner is capable to capture surfaces up to 150 metres (@80% qor), you will likely not capture anything since the object's surface munches the majority of the signal.

I've attached this excerpt from a Riegl spec sheet. It shows a function that correlates the object's qor to the corrsponding maximum range. Nice and meaningful in my opinion!

Riegl-Spec-sheet.PNG

Long story short: The maximum range specified in the spec sheet is most likely not the maximum range in the field.

All the best

Daniel

P.S. Here are also some thoughts on scanning spec sheets: https://www.linkedin.com/pulse/taming-e ... el-wujanz/

[smacl]

one short remark: the maximum range specified in all spec sheets always refers to a certain quotient of reflection. In many cases the maximum range refers to a SnG-scenario (Siegfrid 'n Roy that is). Hence, the reference target is pretty "white".

As those who have used a reflectorless total station at range can testify, sometimes pigeons and seagulls are your friends

Another issue is angle of incidence of the beam to the target, which will be nice and flat if surveying a distant object, but very narrow if surveying a tall building or mine shaft from the ground. Sample below from a mine shaft where the spacing and point size are adversely affected by narrow scan angle at distance.

shaft.jpg

[Justin Richards]

Good input. We are ordering targets and our local vendor only has 4.5" in stock but I have been wanting 6" just to have a "better chance" of detection. We don't have a leica scanner we have a Faro S+ and the team really likes the quality of the b/w panos. Target detection may be a little different but larger targets always help.

Do you put your targets on a full size pole or do you deploy a tripod and tribrach for each?

I wouldn't go farther than necessary. The most common situation that I need to capture far away targets (but usually still within a 70M range) is when scanning from the roof to the ground to connect them on a job that has a bit higher error tolerance between the two connections. I do go ahead and set the latitude when when doing extended distance scans.

We only carry up to 150 scanners now besides a RTC360 that we don't use. The most I have ever used was about 400' when scanning buildings and we do send sample data before doing any extended scans to see if the Faro scanners will meet their needs or if we need a P series.

With the Faro S+, use a detail scan to capture your targets.



This is the setup I use. With the 250mm sphere the smaller stakeout poles aren't as stable outside but they are good to have. If you're setting up on a point just adjust the Z to the center of the sphere or target. (or you could do global transformation after applying control if you want to do it the lazy way).