12 ms·
3D scanning by dipping into a liquid
- skykooler 9y agoThis is a really clever solution!
- zellyn 9y agoI expected they'd be either visually watching the changing contours of an opaque liquid, or somehow using refraction to get multiple visual angles of the same features, but… …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?
- papercrane 9y agoIn their presentation they have a bit more info. For the elephant model they show the results at 100, 500 and 1000 dips. https://youtu.be/yHvyPnkuAiw?t=1m30s https://youtu.be/yHvyPnkuAiw?t=1m30s
- zellyn 9y agoAh, perfect. Thanks!
- 2_listerine_pls 9y agoWhy is it that all voices sound monotone when presenting a SIGRAP paper.
- npolet 9y agoNot everyone has loud, presentational voices.
- caio1982 9y agoWell... to be fair, if you wanna make sure your study reaches as many people as possible, you must eventually need to improve your presentational skills. Like, you know, we do for everything else. I understand you didn't imply this, but IMHO there is very little pride in wanting to sound introvert forever, intentionally. Now I just hope the parent didn't say that due to misogyny.
- seanmcdirmid 9y agoVoice presenting for a recording is more of a practical art than we really give credit for. Unless you do it a lot, you aren't going to be very good at it.
- annnnd 9y agoWhich is the same as with anything else really. You need to practice to be good at something.
- seanmcdirmid 9y agoYes, this is another case of the 10,000 hour rule.
- GuiA 9y agoGrad students don't have much budget for voice actors. 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.
- bsder 9y agoWhy are all the speakers at tech conferences so bad? And why do good presenters get invited to every conference on the planet? Public speaking is a skill. It takes work and practice. Most tech folks have neither the time nor desire to do so.
- 2_listerine_pls 9y agoIt's copycat behavior. They are imitating other presentations.
- Joe-Z 9y agoWho does? The bad one's or the good one's? Genuine question.
- bsder 9y agoBoth. 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.
- falsedan 9y agoThey're using computed tomography techniques, which is exactly the way I would expect.
- thearn4 9y agoIt's pretty cool. Based on the video, by dipping at various angles it looks like the process is solving an inverse problem in the Radon or Hough transform domains, something similar to what is done in medical tomographic imaging.
- dkonofalski 9y agoI just want to confirm that I understand what's going on here since you seem to get it. I have no background in this but am curious. 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?
- zellyn 9y agoFrom the video, it appears that they are dipping by 1cm, measuring volume, dipping by 1cm more, measuring volume, etc. So they end up, effectively, with a set of 1cm slices and the volume of each slice. For one orientation. Then they repeat, getting slices at a different orientation. 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.
- dkonofalski 9y agoYeah... I just wondered why they were 3D printing things instead of getting normal, everyday objects that they could dip like keys, cups, pens, etc. I have a feeling it's not detailed enough for those use cases yet.
- anoother 9y ago
- deepnet 9y agoAlso see 2007s Milk Scanner by Friedrich Kirschner http://www.instructables.com/id/Milkscanner-V1.0/ http://www.instructables.com/id/Milkscanner-V1.0/ https://www.youtube.com/watch?v=XSrW-wAWZe4 https://www.youtube.com/watch?v=XSrW-wAWZe4
- vernie 9y agoThis is completely different.
- anotheryou 9y agoHugged to death :/ 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.
- mrskeltal 9y agoBy dipping from various different angles
- anotheryou 9y agoI guess that would be possible, but one has to do some trickery to find false data. 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.
- agumonkey 9y agoIt's a bit like a fluid pet scan, each angle will give partial information, you "integrate" to gather the surface. Gives me ideas.
- samstave 9y agoThink of the intro to the Ghost in the Shell, where the android body is floating up through a bath, and the manufacturer layer on the body is dissolving and being removed. This method could detect that the material is 100% removed from the body as well as confirm that the body is created exactly to spec.
- falsedan 9y agoThey address this in the paper, but from the opposite angle (ho): 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.
- fredley 9y agocached: http://webcache.googleusercontent.com/search?q=cache:15m4DWEAMgYJ:irc.cs.sdu.edu.cn/3dshape/+&cd=1&hl=en&ct=clnk&gl=uk http://webcache.googleusercontent.com/search?q=cache:15m4DWE...
- tyingq 9y agoNo images, but doesn't hang on them like the Google cache: http://web.archive.org/web/20170711133251/http://irc.cs.sdu.edu.cn/3dshape/ http://web.archive.org/web/20170711133251/http://irc.cs.sdu....
- striking 9y agoThis one has at least a few images: https://archive.is/QuLKN https://archive.is/QuLKN
- papercrane 9y agoFound a presentation on this technique on youtube: https://www.youtube.com/watch?v=yHvyPnkuAiw https://www.youtube.com/watch?v=yHvyPnkuAiw
- perilunar 9y agoThanks. Video in the article kept timing out. Edit: it looks like it's the same video (same length and intro).
- deleted 9y ago[deleted]
- anfractuosity 9y agoWow this is very impressive. I was thinking originally they were using the milk scanning technique - http://www.instructables.com/id/GotMesh-the-Most-Cheap-and-Simplistic-3D-Scanner/ http://www.instructables.com/id/GotMesh-the-Most-Cheap-and-S...
- nom 9y agoDoes anyone here know if there is an original paper or where this technique originated? It has to be pretty old and I can't imagine nobody thought of it before, but I'm somehow unable to find anything else than the posts on instructable, hackaday and youtube.
- anfractuosity 9y agoI was wondering that too, I've not found an authoritative source.
- zeep 9y agoBut they should be able to improve the milk technique by using different dipping angles as shown here and in many cases it would probably be much faster then this technique (but in other cases impossible to get all the geometry).
- dre85 9y agoIs the software open sourced? This looks like it would translate into a fun hack-a-day project. At first sight, the required hardware seems pretty basic, or? It would be awesome if someone replicated it with a RaspPi or something and posted a step-by-step tutorial.
- simon_acca 9y agoHey, if you add a force sensor to the dipping arm couldn't you, in principle, obtain a 3d density map of the scanned object as well using archimede's principle?
- keithlfrost 9y agoNo, I don't think so. Archimedes' principle tells us that the decrease in force required to support the object is equal to the weight of the displaced liquid. The force of gravity on the object itself is the same, regardless of which portion of the object is submerged.
- deckar01 9y agoI'm not so sure. If the sensor was able to take a 2D measurement of the weight, the rotations could be used to calculate the 3rd dimension of density.
- simon_acca 9y agoIndeed, I also reached this conclusion upon thinking about it a bit more. 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.
- derefr 9y agoHow about if you're using a compressible fluid?
- proee 9y agoSee my other comment. It's an entirely novel approach to fluid scanning and includes 3d density scans. http://www.romansystemsengineering.com/our_product.html http://www.romansystemsengineering.com/our_product.html
- AndrewKemendo 9y agoThat is amazing. I think I've looked at every photogrammetry, desconstruction, hand modeling etc... technique for 3D reconstruction and this one takes the cake for ingenuity, quality and capability. 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.
- rsp1984 9y agoHow about firing air at an object through a series of nozzles, measure the resulting turbulence and then solve for shape ;-)
- JadeNB 9y ago> measure the resulting turbulence Just a quick solution of a million-dollar math problem (https://en.wikipedia.org/wiki/Millennium_Prize_Problems#Navier.E2.80.93Stokes_existence_and_smoothness https://en.wikipedia.org/wiki/Millennium_Prize_Problems#Navi...) and you're on your way!
- eru 9y agoYou don't have to solve the Navier Stokes equations analytical for this. You don't even have to solve them explicitly at all: I can see a grad student just getting a lot of experimental data and throwing it all at a neural net with good results.
- antman 9y agoThat seems equivalent to trying to get a joint distribution from its marginal distributions. So the constraint is probably that either it needs to be convex or you need to have a prior estimation of the object's cavities which means you need to know the 3d shape beforehand to have a mathematically guaranteed measurement.
- thebooktocome 9y agoNo such constraint exists for the Radon transform. There are limitations associated with limited data, but mathematically if you had perfect knowledge of the slices you could obtain a perfect reconstruction for any compactly supported generalized function (I'd usually say distribution but I don't mean the statistical object).
- dingo_bat 9y agoAwesome technique! But I cannot imagine this ever being a fast process. 1000 dips for a small model, and you cannot dip it with force.
- civilitty 9y agoAs long as the equipment is cheap, the speed isn't that big of a deal. Imagine a thousand $10k machines set up on a studio lot that is constantly scanning items - it would be a boon for the gaming and film industries where production takes months or years and they have several steps of increasing graphics and art work complexity. I bet you could also set up cameras and use the refractive index of the liquid to calculate textures while its scanning.
- hughes 9y agoLooks like they're doing 3 minutes per dip - that sums to over two days of continuous dipping.
- nom 9y agoHow does one come up with something like this? The method is everything but straight forward and not practical at all, but it still produces good results. Amazing work.
- rsp1984 9y agoNote that this only works for objects that don't have any flexible parts and don't interact with the water in any other way than pushing it aside (e.g. soak water).
- almostarockstar 9y agoThe same approach could be used with any liquids, and possibly gasses too. As a proof of concept, this is incredible. I can imagine a ton of applications too. Scanning fossils is the first that comes to mind. I'm sure there could be plenty of applications in forensics too.
- hemmer 9y agoI wonder how much of a role wetting/capillary effects play in this? The liquid interface will distort as it approaches the object, and will try to meet at a certain contact angle (based on surface tensions etc). Correcting for this might help improve the resolution of the scans?
- derefr 9y agoI would predict that it would be rather difficult to dip-scan a sponge. Might work if it was fully saturated (waterlogged) in advance, though.
- samstave 9y agoHow does it determine shape when measuring volume displacement? is it only measuring the displacement of the top surface-tension-layer of water as if it were a slice?
- jandrese 9y agoAs it dips the model into the liquid, it displaces an amount equal to the volume already measured plus one cross section at the current water level. By continuously measuring the dips you can determine the area of every slice. By dipping at different angles you can create a large number of those cross section datasets. By merging and doing some hairy math (but well understood, it's the same used for MRIs) you can work out the original shape. 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...
- jamesrom 9y agoSurface tension and evaporation would just show up as noise that would disappear with enough dips.
- gene-h 9y agoI once scanned myself at a maker fair in a similar manner. A swimming pool of blue dye with a camera facing above was used so that objects could be scanned by looking at their outline in the blue dye as they were dipped in(a different approach to the volume transforms presented here). Now to do this with a person involved strapping that person to a board and slowly dunking them in. Overall, the experience was unpleasant and what I imagine waterboarding is like, but hey at least I got a 3d scan of myself.
- catshirt 9y agoyou are being submerged in liquid? therefor holding your breath? therefor all together avoiding any of the torture induced by waterboarding? if you're interested in hammering out some science for us, waterboard yourself and report back. i think you might be surprised.
- gene-h 9y agoI did not mean for my post to make waterboarding seem to be simply unpleasant. It is not, it is horrible and inhumane practice whose use cannot be justified. 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.
- catshirt 9y agogot it. thanks mate. was an honest question. maybe negligent on my part, but i had something like a dunking booth in mind. wasn't considering a rush up the nose. definitely at least a bit closer to waterboarding than what i'd imagined. :)
- CobrastanJorji 9y agoFrom what I understand, which is admittedly not very much, waterboarding is a lot worse than being submerged. It's not so much dunking you into water as it is pouring water up your breathing passages.
- proee 9y agoMy friend created an advanced fluid scanner using a dodecahedron. His method is novel in that it: 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. See http://www.romansystemsengineering.com/our_product.html http://www.romansystemsengineering.com/our_product.html
- jamesrom 9y agoWhat property of a dodecahedron makes it useful for 3D scanning?
- nkurz 9y agoWow, this seems like an beautiful technique. 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." http://www.romansystemsengineering.com/hypothesis.html http://www.romansystemsengineering.com/hypothesis.html
- beagle3 9y agoIsn't this "dip transform" basically the (inverse) Radon transform[0] used in CT and MRI? [0] https://en.wikipedia.org/wiki/Radon_transform https://en.wikipedia.org/wiki/Radon_transform
- thethirdone 9y agoNot quite for two reasons: Displacement is integrated over all slices under the liquid (just take the derivative to reverse). And more importantly, CT reconstruction (can't speak for MRI) is often done slice by slice which cannot be done for this system because you are an area integral rather than a line integral; this means that to get a full reconstruction you have to rotate the object in more than one axis. There are certainly similarities though.
- xixixao 9y agoSuggestion for increasing applicability: Start with the optical scan, then only use the method to nail the occluded parts. And instead of just gathering data consider what angle will give you the biggest amount of new information next. Not sure if authors tried either.
- randyrand 9y agoI wonder if they are taking water cohesion into account. e.g, some of the water will stick to the sides of the object.
- ajuc 9y agoPre-dip the object.
- azernik 9y agoComment on the Hacker News system - most combinations of {edu,ac,gov,mil}.{$ccTLD} should probably be collectively treated as a TLD for site-display purposes. e.g. sdu.edu.cn (Shandong University) would be more descriptive than plan edu.cn (some academic institution in China).
- noja 9y agohttps://publicsuffix.org/ https://publicsuffix.org/
- Animats 9y agoThat is very clever. So slow you'd have to run it overnight, but that could be OK for some applications. 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.
- SubiculumCode 9y agoI half expected this to be tongue in cheek exposition on creating molds. I guess it was on my mind after watching a friend artist creates sculpture molds for pewter casting. https://www.joshhardie.com/fullscreen-page/comp-izfweszu/f59958ca-6f2d-4cb3-b33c-191bc8d851c5/2/%3Fi%3D2%26p%3Ddg5cd%26s%3Dstyle-izlvez77 https://www.joshhardie.com/fullscreen-page/comp-izfweszu/f59...
- joshontheweb 9y agoCan someone ELI5 as to how this gathers the spatial data for the samples? In my ignorance, it doesn't seem clear to me as to how this works. I get that you would be gathering different volume data with each dip but it seems to me that this information would look like a graph that rises and falls back to zero. In the video, they showed each dip as gathering an accurate 2d cross section of the object. For instance, the 2d slices of the elephant on each dip graph. They seem to be able to shape a closed 2d polygon slice per dip and it is mystifying to me. Am i missing a part of the process or what? Is there some imaging going on as well on top of the volumetric sampling? 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.
- taejo 9y agoNo, they only get a graph of the volume of each slice. They have to do this many times and compute something like a Radon transform (computed tomography) to reconstruct the shape.
- nullc 9y agoFun. So make a closed spherical assembly with lidar something to range the fluid height and put it in a three axis mount so the direction of down can be continually and smoothly changed, then drain the water very slowly. 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. :)
- dorianm 9y agoEpic!