3D scanning by dipping into a liquid
irc.cs.sdu.edu.cn
irc.cs.sdu.edu.cn
…they're repeatedly dipping it, and using the volume displacement to reconstruct the shape. Amazing. The site is hammered right now so I can't get more details: anyone see how many dips are required to get the highest-detail models they show on the landing page?
That being said, they still make efforts. When I was in grad school, I was routinely asked to do voice overs for videos that accompanied paper submissions by students who had strong accents when speaking English.
Public speaking is a skill. It takes work and practice. Most tech folks have neither the time nor desire to do so.
The good ones snarf ideas from other good presenters when they see something useful.
A lot of bad ones imitate other presentations as the "minimum standard" because creating a good speech takes a LOT of work.
I'm also going to point out that a lot of tech speakers aren't native speakers of English. If you made me, a native English speaker, give a presentation in French or Chinese, I'm guaranteed to be a bad speaker.
/s
They're dipping this thing into liquid multiple times in different ways and then measuring how much the volume has changed from the initial touch of the liquid to the volume of the object as fully submersed? Also, it seems that they are first 3D printing a 3D model, dipping, and then comparing the scan to the original 3D model? Is there any chance that the types of models they're choosing are skewing the accuracy of the results? They seem to be choosing models that don't have a lot of surface texture or much fine detail and I'm assuming that's a limit for all 3D scanning tech right now?
Edit: Also, how does this thing handle 3D scanning of something like a sponge or box that might absorb the liquid? I imagine that's just not possible with this kind of scan, right?
Not only would it not work with something absorbent, but (per other comments below) does not (currently) work with shapes that trap air or catch liquid.
I think they're 3D-printing test shapes because it's the simplest way to generate interesting test structures. Otherwise they'd have to manufacture (for example) a bunch of columns plus a ball using metalwork or wood or something. Some of their models look like they were originally scanned from small sculptures -- although in this day and age, it's possible they were just created as 3D models in the first place.
If they were to use real world objects, any comparison would have to use another scanner, which would introduce its own bias.
My initial interest was that it would bring the cost down a lot, but they don't seem to bring great precision and they require a moving robot with at least 3 axes which is unlikely to be very cheap for precision material.
Your idea also requires precision hardware to move the sphere.
It's a better idea than dipping with a robot arm. And also faster.
Not sure how practical it is right now, but I wonder if you could do this with air volume at a high enough delta measurement resolution you might get some amazing results.
Just a quick solution of a million-dollar math problem (https://en.wikipedia.org/wiki/Millennium_Prize_Problems#Navi...) and you're on your way!
Yes, to be sure you are right. It was just a silly (and, as you point out, mathematically inaccurate) joke.
How about shining a normal light though and just inverting the shadow calculations.. hmm.. has that been done?
Elsewhere in this thread, 'proee' links to what might be an even more interesting technique, which restrains the object in a dodecahedral "cage" (to allow for precise angular positions) and then measures the amount of liquid necessary to create a set predetermined rise in liquid level. http://www.romansystemsengineering.com/hypothesis.html.
Combining some aspects of the two, it might make sense to start with the object at the bottom of an empty container (in a cage or otherwise restrained) and add liquid at a known constant rate (as for a titration). Then generate a 2D graph of time against liquid height for a number of known angles, and solve in the same manner as this paper describes.
I believe this is isomorphic to the draining mechanism described in their paper.
I also wonder if instead of using discrete angles and multiple fills (or drainings) one could just tilt the container, possibly even slowly rotating it continuously. Add a squirt, measure the liquid level for a 360 rotation, then add another.
Edit: just saw your other comment suggesting similar things!
1. Does not require rotation of the DUT, but instead uses just rising fluid level.
2. Uses permeable fluid so it achieves full density scans.
He spent a number of years trying to get the product to market as a startup, but ran out of personal funding.
He believes Archimedes may have used the Roman dodecahedron as a fluid scanner to test the quality of their projectiles to improve accuracy.
Apparently, it's not that the dodecahedron is uniquely suitable, rather it offers the best compromise between competing factors. In this process, it mostly serves as a cage to hold the object for immersion, although it has some other useful properties as well:
"There is no other 3d platonic structure that has a higher fill-factor (volume that can be inscribed within a sphere of rotation) relative to the entrance hole (i.e. face area), while minimizing periphery length."
"Intuitively, one might suspect that both the dodecahedron and the icosahedron are reasonable choices of structure for the given constraints, with their subjective scores of 4.6 and 4.0 respectively. The dodecahedron offers increased fill factor, aperture size, and minimizes the periphery length, and is simple to manufacture."
Edit: it looks like it's the same video (same length and intro).
if you're interested in hammering out some science for us, waterboard yourself and report back. i think you might be surprised.
That being said getting a good scan required me lying on my back holding still as I was slowly lowered into the water. At the end of the scan I had water going into my nose. Holding my breath was unable to prevent this. Certainly not as bad as waterboarding, but certainly enough to elicit a coughing fit.
The procedure is terminated quickly once the person is entering distress due to lack of oxygen.
The first few times it's done on a person, it's very frightening. Later, it becomes very annoying, especially if they wake you up at 4 AM for another go.
You make it sound like the DoD, Amnesty International and the Red Cross had a couple of meetings on this and came up with a humane way of doing this.
So a force sensor on the arm would only be good as a way of measuring what they are already measuring, that is, the volume of the displaced liquid.
There are certainly similarities though.
Then change the fluid for something with less surface tension (hurray more uses for chlorofluorocarbons), and put it in a 20g centrifuge, and perhaps scanning times will be reasonable. :)
e.g, some of the water will stick to the sides of the object.
How do they handle overhangs that trap bubbles?
Maybe shaking and scanning in reverse? (can stall cause weird effects when the air can't get back in, but should be more detectable.
Maybe correlating the exact oposite dip works: Dipping a bowl shows a negative volume then the bowl begins to fill. A dome (reversed bowl) will show additional volume of trapped air at the same point.
Gives me ideas.
It should be noted that our dipping scheme assumes that the
object has no vertical _caps_ in any orientation. A cap is a vertical
cavity that forms a vessel, in which water can be accumulated if
the object is elevated vertically and air can be trapped, generating
air pockets when the object is dipped in the opposite orientation.
Most caps, if they exist, would be small and would have a minor
effect akin to noise on the dip transform. Nevertheless, caps can be
detected by dipping and then lifting back the object with the liquid
trapped in the cap, yielding two different water levels. Flipping the
object vertically allows detecting air pockets as they become caps.> It should be noted that our dipping scheme assumes that the object has no vertical _caps_ in any orientation. A cap is a vertical cavity that forms a vessel, in which water can be accumulated if the object is elevated vertically and air can be trapped, generating air pockets when the object is dipped in the opposite orientation. Most caps, if they exist, would be small and would have a minor effect akin to noise on the dip transform. Nevertheless, caps can be detected by dipping and then lifting back the object with the liquid trapped in the cap, yielding two different water levels. Flipping the object vertically allows detecting air pockets as they become caps.
maybe I should look into how to add custom CSS rules to a particular site (HN), can you do that native in firefox, or does it need a plugin?
Edit: I should add that this really impresses me regardless of how they do it. Ive always thought it was a pretty big bummer how optical 3d scanning looks so incomplete in a lot of cases.
A good test: run it on an auto throttle body. Those have lots of voids and holes, and some people need to duplicate existing ones.
It's a clever technique, but undoubtedly slow since it requires on the order of 500-1000 careful dips of an object to get a reasonable level of detail. I'm guessing they probably aren't using plain old water since then they'd have to worry about surface tension, evaporation, etc...