Scanning cliff from above ...

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Scanning cliff from above ...

Post by vislaw »

Hi all. I received an inquiry regarding acquiring a scan of a cliff at Lands End in San Francisco. This is a National Park and Wildlife Preserve so that there is NO flying (drone, helicopter or fixed wing) over the location. The base of the cliff is completely inaccessible but I can access the edge of the cliff at the top. The topography is such that I could get a decent scan provided I can figure out how to extend the scanner out over the edge in order to capture a point cloud. My first thought was to consider getting a jib designed for cinematography since I've shot some stuff over the edge of buildings with pretty expensive cameras. I'd appreciate any thoughts, suggestions, ideas from anyone here who has had a similar problem to solve...

Mark
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Re: Scanning cliff from above ...

Post by Scott »

You might try using a collapsable extension ladder: 15.5' long when fully extended, with plenty of sandbags. It's easy to firmly attach a Focus3D to the top rung. Use WiFi to control it. The photo shows the scanner vertically, but it would not be difficult to rotate the scanner 90º for horizontal use.
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Re: Scanning cliff from above ...

Post by vislaw »

Scott wrote:You might try using a collapsable extension ladder: 15.5' long when fully extended, with plenty of sandbags. It's easy to firmly attach a Focus3D to the top rung. Use WiFi to control it. The photo shows the scanner vertically, but it would not be difficult to rotate the scanner 90º for horizontal use.
Brilliant. I truly appreciate this great suggestion.
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Re: Scanning cliff from above ...

Post by RobM »

I honestly don't like the ladder idea at all. Not saying that it is a bad idea, but I'd be to scared of dropping my scanner.
I knew I've seen that picture before and I think there are a lot of great other approches in the thread I saw it in, so you might want to check this out:

https://laserscanningforum.com/forum/vi ... 8&start=10
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Re: Scanning cliff from above ...

Post by richard_m »

Thats some pretty rough cliffs as I remember, with serious surf at the bottom. This is the park by the military hospital(?) I'm assuming but I haven't been in several years.

Can you access the top of the cliffs by vehicle? if so I'd rent something like this:

http://www.genielift.com/en/products/bo ... /index.htm

Its pretty simple to mount a scanner inverted under the basket with redundant safety features, it can easily get you 20ft out and you can operate both the scanner and boom from safely on land and very quickly.

For me a ladder or boom is fine for a scan or two (with extreme care) but those cliffs are big and very irregular so you'll need lots of scans and from some precarious locations. Using such a machine means you can position the scanner slightly above the clifftop level so you can still see targets on the clifftop. Each scan will be very similar and have little or no hard detail so targets will be your friend here..

Given its a park it may be tricky to negociate machine access but here in Europe safety usually overrules everything else.

Good luck.

Richard.
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Re: Scanning cliff from above ...

Post by richard_m »

Just as another p.o.v..

We use our 'Boat-Map' system, this basically means we strip the kit from the roof of a 'Drive-Map' scan-auto and mount it on a boat.

Useful for waterside perspectives and we often use it in conjuction with sidescan to get the full above and below waterline 3d picture or structures and quays. In this case it would be possible to mount a mobile mapping system on an inshore-coded charter boat (JetRIB etc) and scan the cliffs from the water, maybe with large targets on the clifftop. Could be tricky if the water conditions are not kind.

I could get this done for you in conjuction with one of our more local offices but realistically the mobilisation cost from Europe would be crazy for a 1 day project and delays for weather could add up. Is there someone more local with a demountable mobile mapper? or would someone allow you to take a rented Pegasus2 (etc) on the water?

Just a thought.

Hmm who do we know who has a $250k pegaus backpack, a jetski and is more than a little crazy.. anyone? ;)


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Re: Scanning cliff from above ...

Post by vislaw »

Thanks for all of this great discussion. Very much appreciated and worth considering.

The boat suggestion, while innovative and worth considering for future projects, is a no-go here because the park is a wildlife sanctuary with a one-mile approach limit for watercraft (not to mention the conditions off shore being problematical with lots of shoals, currents and dangerous wind).

Really too bad that I can't put a drone up. Since I haven't been to the site personally I intend to do a preliminary assessment using a 20-foot fiberglass camera pole to get some static images over the edge. Depending on how things look, how accessible the precipice is and whether or not there may be ledges or surfaces lateral to the subject area that could support scanning, I'll keep an open mind and report back with more information hopefully.

Many thanks!
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Re: Scanning cliff from above ...

Post by Attreyu »

If you're able to get a high-mpx camera on a pole over the edge, and if you are able to achieve visibility towards all spots, and IF you'd be able to do this across the whole length of the cliff, your might, in theory do a photogrammetry-based scan. Just a thought.
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Re: Scanning cliff from above ...

Post by 3DForensics »

Hi Mark,

A while back, Jonathan Coco posted about using telestrut. I used this on a project scanning silos and it is a wonderful piece of hardware that you can pick up at Home Depot and configure very easily for various scanning situations. I can only imagine what the cliff looks like but telestrut allows you to create just about any length you want and you could even rig a few pieces together to create a kind of bipod off the side of the cliff.

I would make sure to tie down the scanner/jig with some rope as a safety precaution. You can secure a steel rod in the ground or tie down to some other structure like a tree or whatever isn't going to easily move.

Would be happy to chat about it but if you know what the cliff looks like, what kind of access you have and what kind of structures are around, a quick visit to Home Depot and you'll imagine something pretty quick.

Cheers,

Eugene
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Re: Scanning cliff from above ...

Post by vislaw »

Attreyu wrote:If you're able to get a high-mpx camera on a pole over the edge, and if you are able to achieve visibility towards all spots, and IF you'd be able to do this across the whole length of the cliff, your might, in theory do a photogrammetry-based scan. Just a thought.
That's something I've been curious about. Would love to try to get a photogrammetry-derived cloud. Probably not practical but I'm going to definitely give it some thought when I get to the scene to start getting references. THANKS
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