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Q: Building Gas Fields, Masks, Custom Forces
char replied to char's topic in General Houdini Questions
Hoping this topic picks up and more people engage in the conversation as well @ikoon That's interesting, haven't really been looking into vortex confinement too much so seeing this is encouraging enough to try and dissect it later. I'm guessing a\ll that (curl, grad,...) is essentially a representation of Rotation, Magnitude, Direction and then normalization in a simulation, correct me if I'm wrong. Been watching Khan videos on Gradients and Curl yesterday, really wish I found his content earlier, loads of gems right there. The examples from 2011 are still quite relevant in H16.5, all opens up normally and I did have a quick peek just now, so recommending it to anyone learning like me.- 5 replies
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Q: Building Gas Fields, Masks, Custom Forces
ikoon replied to char's topic in General Houdini Questions
Hi char, I would also like to know more about these deep things, so I hope other users will also contribute. My know-how is unfortunately not enough to explain these things. But if you have time and mood to "dig", then the gasvortexconfinement is really nice combination of Gas Match Fields, Analysis (Curl then Length then Gradient, then Normalize) and then Gas Cross, Gas Combinations, Gas VOP. It "applies" calculated result to the vel. From the docs about gasvortexconfinement: The Gas Vortex Confinement DOP applies vortex confinement to a velocity field. This is a force which amplifies existing vortices with the intent of undoing the diffusion that occurs during the diffusion stages of the fluid solver. You can also look at videos from 3Blue1Brown or Khan Academy, so you know how these nodes together "find" and amplify the Vortex direction: https://www.khanacademy.org/math/multivariable-calculus/multivariable-derivatives/curl-grant-videos/v/2d-curl-intuition https://www.khanacademy.org/math/multivariable-calculus/multivariable-derivatives/curl-grant-videos/v/3d-curl-intuition-part-1- 5 replies
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Q: Building Gas Fields, Masks, Custom Forces
char replied to char's topic in General Houdini Questions
Hi @ikoon & @loudsubs Thanks a lot for both of your replies. Where on earth have you been all this time, that's probably the most useful script that exists, thanks so much for sending out the links. I've watched the masterclass and a few other videos, some of which you posted are still new so I'll surely adding them to my watch later list. Would you mind if I continue this topic a bit further? Both clarifications helped to understand the whole thing quite a lot. So let's say in your example, you have a Gradient built from the surface of your FLIP sim, where / how would that vector field be used? Would this just be a case of filling the Gas Calculate > Dest Field with vel and your Source Field with the name of the field created and using a specific Calculation method? Even the quote from that fluid masterclass : "advect velocity by velocity" is messing with my head at this point. I'm only aware of a method where you feed a certain field to control where for example GAS Turbulence affects the simulation but even that is not really intuitive because in order to use a mask in a simulation you need to put the name of the field into Gas Turbulence > Bindings > Density Field and I'm finding it a bit hard to understand why that should be placed there in order to work. An example for that would be a dotproduct of the gradient and velocity to mask only the top part of the smoke (if it's moving up), but again, I've read about it but there isn't much of an explanation why certain things are done the way they are. Second question would be; to understand Curl, Gradient, Laplacian a bit more than just the document explanation: "The simple case of a scalar field results in a vector field which points in the direction of increasing scalar values." would it be worth just watching a few Khan Academy videos on physics to really get a grasp of all these aspects? I'm pretty comfortable with most of the aspects of Houdini, but understanding a few things above was my goal for the past year of researching. Thanks again! -
Q: Building Gas Fields, Masks, Custom Forces
ikoon replied to char's topic in General Houdini Questions
Hi, the mentioned masterclass is probably this: https://vimeo.com/42988999 I also like this tutorial: https://vimeo.com/119694897 Matt Estela has great tutorials: http://www.tokeru.com/cgwiki/index.php?title=HoudiniDops# http://www.tokeru.com/cgwiki/index.php?title=Smoke_and_Pyro I don't know if there is any new video tutorial, which describes the low-level principles. I learn by digging into the "shelf" solutions https://forums.odforce.net/topic/41800-gas-analysis/?do=findComment&comment=199863 https://forums.odforce.net/topic/42101-how-do-pyro-collisions-work/?do=findComment&comment=201007 Btw, when I am digging, I use this script "Find all parms referencing this parm". http://lex.ikoon.cz/find-all-parms-referencing-this-parm/ Here is an attachment, microsolvers_dev.rar with lots of experiments, just for an inspiration. Unfortunately lots of it is outdated (it is from the year 2011) https://forums.odforce.net/topic/13748-learning-microsolvers/?do=findComment&comment=101666- 5 replies
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POPs Alpha based on point proximity (distance between neighbours)
MaximumsProductions replied to kio0o's topic in Effects
Hey this is just neighbors based. I'm not exactly sure how I'd go about distance, except by per point, add the sum of all the distance from pts found in its vicinity and store in each and normalize for the whole cloud. I'm not very good at point clouds so I would end up doing something silly like creating all the prims, and measuring those and summing them haha. But if you want based on neighbors beside them. just refit the number of neighbors found and play with that normalized value? Cheers, hope this is a step in the right direction. MM_Send_AlphaPointProximity.hiplc -
The connection part is precisely what I wanted to try in houdini. In my previous use it was semi manual. A script attached to each wheel with a link to the previous wheel, with known radius and position. It was for "real" machines. For my "try" it will be more a UI exercise. How generate the gear : Giving two points and a number of gear to create in between ? Give a random (or not) grid of point and generate gear on these ? random size or not ? other ? And then generate all the links and speeds. And then I probably discover it's not so easy The gear building itself is done and almost "pure" VEX
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hi flcc, no- I'm not in a hurry but this thing has been giving me a trouble for a week and i just want a good solution to it. I do have numTeeth attribute, and i am able to match gear rotation with previous one... but i just don't know how to generate it automatically in Houdini and for the file... i wonder if its not showing up because I'm still using free learning edition.. well basically the connection is very similar to hip file thats in the link above (http://deborahrfowler.com/MathForVSFX/GearRatio.html) well thanks for your time! and i would love to see how you have treated this problem in your way too
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Other than the ones on the SideFX website I have no idea. Or you could look at the built in rigs too. In the object context theres 3, Simple Biped, Simple Fe/male, Toon Character. They'll all be slightly different, as will the rig you create from the Rigging Series (6).
- Yesterday
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Q: Building Gas Fields, Masks, Custom Forces
loudsubs replied to char's topic in General Houdini Questions
Gas match field will let you create a new field and gas analysis will do a specific calculation, such as find the gradient or curvature. It's similar to the vdb analysis. Then gas calculate lets you do math operations, such as combining fields by adding or multiplying, etc. So if you had a FLIP sim, you could use a gas match field to create a new field, using the flip surface field as reference. Then you could calculate the gradient of the surface, and store it in that newly created field. Make sure to pick the right class of field for the new field, based on the operation you'll do with the gas analysis. Ie: to store a gradient calculation, it needs to be vector. Now you have a vector field, based on the gradient of the flip surface. You can use a gas calculate or gas linear combination (preferable for simple operations) to add that field to vel. Also, there's a masterclass called 'building fluid solvers" or something like that. definitely worth checking out.- 5 replies
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Ok, I understand. Need to just try to understand when to animate in which context. I guess its just a matter of creating the project and keep track of the best way to organize your structures from the beginning. Sometimes I feel like it can be a bit messy with the structures, node levels.
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Hi, Clear, can you, please, advise any particular if I am interested in creating simple character rigs of humans, probably with the autorigging system?
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preflight allows you to find the path of the missing textures, but not the name of the materials who use them. It was the purpose of the question. That say its usefull too.
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Animation of what and for what? All workflows can be pretty subjective, but your mileage may vary. If you're animating a character Houdini is geared towards doing all that in the Object context, not in the geometry context. Check out rigging tutorials. If you're creating procedurally animated geometry involving lots of SOPs that's better to do in a single (or several sensibly organized) Object.
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Thank you Weish!
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The issue is related to UV. Add uvproject to both meshes. Should fix it.
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There is also the preflight scene option (Use the Render ▸ Preflight menu item to find references in the current scene file to resources outside the project)
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Just a quick update, I can actually break constraints using targetv and pop force...it's just requires "big" values and constraints should be "somehow" easy to break (e.g. if I break some constraints, then the rest won't be able to withstand the force)...I guess, using a collision object is the safest and easiest way to break constraints... Seems like the only way to break constraints is either manually by placing them in broken group or a colliding object...
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Do you know what the brightest values in the HDR are? If they're crazy-high it could give you problems like that. A max value of 6.0 is pretty good - maybe try a max value of 3.0 to see if that solves it. Definitely keep it below 20.0 whatever you do, that's just begging for trouble. Blurring it could also be the answer ; to get rid of hot spots. You'll have to take the HDR into something like Nuke to do this ( did Photoshop ever make this kind of work possible? I avoid it like the plague ) *edit, Houdini has its own comper, maybe you can use that, I don't know how - 10 is really high for light samples - I've almost never needed more than 1, 10 must be super-slow
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hello I have a simple rbd sim exploding outwards that I want to turn into vellum grains as they explode. I have a simple set up working but the issue is that my source is emitting grains at every frame due to the creation frame being at $F. Is there a way where I can emit the grains on only one frame as the rbd is exploding ? I tried a length function to try and delete slow moving pieces but it is still emitting for a good 10 frames. I am trying to get it to emit once when the rbd piece is moving the fastest. The idea is to make the rbd pieces look like it is breaking up into a finer sand. I hope this is not a very complicated issue. I will attach my scene file for anyone that wants to take a look. Thank you rbd_into_grains.hip
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Are you in a hurry? Because I was about to post a gear generation asset with a gear connexion part. I already do this but in another software. Unfortunately, I'm really in a hurry to finish a job an I can't dive inside for now (not in yours, not in mine). I don't think I can get back to it for another week or two. What I can say for now is the "connexion" is fairly simple and is more a UI problem. I think the for-each approch is not the best (but it's just a quick opinion). At least the iteration use, cause the gears speeds is just about teeth numbers. You should create an attribute "numTeeth" and use it. And by the way I get an "incomplet asset" message. At the object level I just see a line.
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Hi, If you have glue constraints network (using Bullet), it's possible to break them using a colliding object (e.g. a moving sphere that is flagged as animated static). However, is it possible to break them using abstract forces (e.g. using field or fluid forces, or even uniform force)? I've tried many types of forces, but regardless of their strength they don't break constraints. I've noted that packed pieces don't have "F" attribute, neither the Glue primitives (i.e. impacts = 0)? I only get impacts if I use collision geo, and "F" I apply POP forces... Another related question: in addition to breaking constraints by colliding object, sop solver, and geometry wrangler, Is there another way to break glue constraints? Thanks
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Hi guys I'm trying to use rop file output node in for loop. I want to render multiple frame using for loop However It only renders last frame with rop file output node. When with file node's write mode, it works fine I need help. Any comments will be appreciated!! Thanks I attached hip file. Render Button is in the <rop_volume_texture1> node read smoke_39.bgeo at 'file1' node Questionfoorloop.hip smoke.39.bgeo
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hi guys I'm new to the Houdini, and I'm having hard time understanding how to make loop nodes what i want to do is to create a gear generator, which allows me to spawn connected gears with correct rotation speed something based on the link below, but using loop iteration number as gear name and doing the adding and multiplying based on previous gears information http://deborahrfowler.com/MathForVSFX/GearRatio.html where I'm stuck is figuring out the previous gears name and adding new gears info in it. any help will be appreciated!!! thank you in advance! GearGenearatorWIP3.hipnc
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Hi Guys, my very first try on Houdini Rigging and Muscles, is it possible to make a muscle with one loose end? I need a rig dynamic udder. (cow) The other thing I experiencing is when I ad a "Muscle Displace" and connect muscles it strongly deform my skin.. Why?? Thanks.
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