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Technical Discussion » Creating an elliptical orbit with varying velocities
- bentway23
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That gets the shape, but not the changes in velocity–what I'm looking for is the acceleration at the perigee and deceleration at the apogee. I tried basic trig early on, but couldn't translate that into varying velocities.
Technical Discussion » Creating an elliptical orbit with varying velocities
- bentway23
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What I'm looking for is an object to follow an elliptical curve, accelerating near the perigee and decelerating near the apogee. Theoretically I could wrestle with magnet forces and do a sim for this, but I feel that (1) that'd be unnecessarily complicated, and (2) that this is going to be a collider for another sim, and that might muck it up.
I've tried follow path and using primuv, but I have not been able to find a way to accelerate and decelerate them as they follow the curve.
I've tried something, attached, that is MOSTLY working. I get velocities from the tangent normals of the orbit curve, and a velocity multiplier based on the min and max x positions along the curve, so at the perigee the velocity multiplier is 1 (or whatever), and at the apogee it's 0.1. Using a solver SOP, each frame I transfer the curvevel attribute to the ball orbiting object at its current location, and then use @P += @curvevel. This actually works for the most part, except the orbiting object keeps going further and further out, creating a spiral orbit. Furthermore, even though I have a wrangle setting its initial position to be at point 0 of the path curve, starts farther away.(Also, I will need to figure out a way to orient it so it's always looking forward, but that will be easy enough, methinks.)
I assume I'm missing something obvious within the solver SOP. This might be easy and dumb, so thanks for any help. (Also, if there's just a way better way to do this, I'm open to suggestions!)
I've tried follow path and using primuv, but I have not been able to find a way to accelerate and decelerate them as they follow the curve.
I've tried something, attached, that is MOSTLY working. I get velocities from the tangent normals of the orbit curve, and a velocity multiplier based on the min and max x positions along the curve, so at the perigee the velocity multiplier is 1 (or whatever), and at the apogee it's 0.1. Using a solver SOP, each frame I transfer the curvevel attribute to the ball orbiting object at its current location, and then use @P += @curvevel. This actually works for the most part, except the orbiting object keeps going further and further out, creating a spiral orbit. Furthermore, even though I have a wrangle setting its initial position to be at point 0 of the path curve, starts farther away.(Also, I will need to figure out a way to orient it so it's always looking forward, but that will be easy enough, methinks.)
I assume I'm missing something obvious within the solver SOP. This might be easy and dumb, so thanks for any help. (Also, if there's just a way better way to do this, I'm open to suggestions!)
Edited by bentway23 - Jan. 20, 2020 13:16:02
Technical Discussion » Make line length match width of object directly underneath
- bentway23
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Thanks for the pointers! Actually, I did not want the line to intersect, just to change its length accordingly. Also, the reference shape was a lumpy riverbed, not just a flat plane, so intersection was possible. What I ended up doing (based on some other pointers from odForce–and not unlike some of the pointers above) was to resample the hell out of my line, ray it down onto the riverbed, use intersect analysis to create points, used an add to create a line from those points, sorted the points, and then used a wrangle to kill everything but the first and last points. That didn't keep the line above the riverbed/reference shape, but at that point it was easy enough to throw a transform there and lift it back up.
There are some points above that are new to me, so I'll dig in now. Thanks again!
There are some points above that are new to me, so I'll dig in now. Thanks again!
Technical Discussion » Make line length match width of object directly underneath
- bentway23
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I have a line hovering above another object (in this example, it's just a grid, but it's more irregularly shaped in what I need). I would like it so that the line length matches the width of the object directly underneath, without reorienting the line, and preferably without actually snapping it to the new point (in y).
Ideally, if I could extract a bbox D_XMIN (/MAX) (or a getbbox min.x), but only at the point in z where the line is, then I could just translate the points to that location. I'm sure this is super-simple, but I'm not quite sure how to go about it.
A ray SOP gets me in the ballpark, but presents some problems, as in the pics.
Thanks!
Ideally, if I could extract a bbox D_XMIN (/MAX) (or a getbbox min.x), but only at the point in z where the line is, then I could just translate the points to that location. I'm sure this is super-simple, but I'm not quite sure how to go about it.
A ray SOP gets me in the ballpark, but presents some problems, as in the pics.
Thanks!
Edited by bentway23 - Oct. 21, 2019 13:35:00
Technical Discussion » Help/F1 now just pulls up Google
- bentway23
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I usually hit F1 for help. I just hit the question mark in the upper right hand corner for the first time, and now “help” no longer pulls up “help,” but a tab that searches Google instead of the Houdini help. Since that happened, now it does the same for hitting F1. I've shut down and restarted and it's still doing it. (The tab also tells me it's using an older version of Chrome, which my outside-of-Houdini browser is not.)
How can I get Help to start showing, well, Help again?
I'm running Houdini Indie 17.5.
Thanks!
How can I get Help to start showing, well, Help again?
I'm running Houdini Indie 17.5.
Thanks!
Technical Discussion » Grouping points in cached FLIP sim?
- bentway23
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I have a pre-simmed/cached FLIP sim. I would like to create a group of a section of the particles of the sim so I can mesh them separately and apply different shaders to them later. Re-simming is difficult and slightly impractical, so I would love to be able to do this with the cached points as-is(/are).
I can create a group of points, but it looks like point numbers are not constant in FLIP sims, as the group changes over the course of the sim (frame to frame, actually). Is there a way to create a group that then remains constant and flows with the existing sim? Or even a way to create a new group of particles that is advected by the existing cached sim? (I'm pretty sure it's no longer a “volume” by then, so I'm guessing a straightforward advection by volume POP wouldn't work.) Or a way to do some sort of “sort” operation to compel points to retain point numbers, which I could then group? Or advecting another form to follow the sim, and I could then use that as a bounding volume to create my group? (Point deforms with FLIP sims as the deformer seem to get really messy really quickly.)
Thanks for any help!
I can create a group of points, but it looks like point numbers are not constant in FLIP sims, as the group changes over the course of the sim (frame to frame, actually). Is there a way to create a group that then remains constant and flows with the existing sim? Or even a way to create a new group of particles that is advected by the existing cached sim? (I'm pretty sure it's no longer a “volume” by then, so I'm guessing a straightforward advection by volume POP wouldn't work.) Or a way to do some sort of “sort” operation to compel points to retain point numbers, which I could then group? Or advecting another form to follow the sim, and I could then use that as a bounding volume to create my group? (Point deforms with FLIP sims as the deformer seem to get really messy really quickly.)
Thanks for any help!
Technical Discussion » Flyaway particles in viscous FLIP
- bentway23
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I'm running a FLIP sim that I would like to make fairly viscous (read: blood from a wound). If I crank the viscosity high (2500 - 5000) I can see some general slowdown, but the problem is I still get lots of little flyaway particles and after meshing the result still looks very particle-y. I've toyed with surface tension, but have found that it either makes no apparent difference or it just makes the sim explode. Any idea on how I can make my viscous fluid more “stringy”/viscous? The emitter is very small as the scene is fairly small–I actually had to scale up the imported alembics so that the character's head is about a meter high, as “real life” size was too tiny for me to get anything useful out of FLIP. I'm testing at a particle separation of 0.002, doing more detailed tests at 0.0005. Could it just be a matter of cranking those down to ridiculous sim times for it to look less like popcorn? (Unfortunately posting the file isn't do-able, any more info needed I'm happy to supply.)
Boosting reseeding to oversampling 48/bandwidth 3 seems to help with the overall feel, but just delays the flyaways, doesn't eliminate them.
Thanks for any help!
Boosting reseeding to oversampling 48/bandwidth 3 seems to help with the overall feel, but just delays the flyaways, doesn't eliminate them.
Thanks for any help!
Technical Discussion » Meshed FLIP sim as deforming "solid" RBD collider--not working as expected
- bentway23
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I have a meshed FLIP sim (cached out, .bgeo files read back in) that I want to use as a “solid” object and have a rigid body rest on top of it (the idea is that something solid “ripples” psychedelically and the objects resting on top of it move as the ripples go underneath–but the original object is still a solid, and the objects don't sink into it). I just can't get it to hold up, however–when the RBD object is initially “dropped” onto the fluid mesh, it bounces and settles as expected, and does okay with simple early movement, but eventually the collisions become less and less precise and the RBD object just sort of sinks in. How can I get the mesh to read as just a run-of-the-mill deforming object?
I've tried RBD solver, bullet solver (obviously doesn't work with the shape of the mesh), volume and surface collisions, jacking up collider volume resolution to make sure all the little waves are getting captured, and boosting the substeps, but the result has been pretty consistent (except more substeps = super jittery RBD as it's reading all of the little pre-big-movement mesh ripples). On the attached setup (a simpler version of the project giving me trouble) I even ran the meshed surface through a “clean” just in case any of the lingering velocity attributes were throwing it off, but that didn't help either. I'm wondering if the fact that the topology itself changes so much might be the problem, but if so I'm not sure how to fix that.
Thanks for any suggestions!
I've tried RBD solver, bullet solver (obviously doesn't work with the shape of the mesh), volume and surface collisions, jacking up collider volume resolution to make sure all the little waves are getting captured, and boosting the substeps, but the result has been pretty consistent (except more substeps = super jittery RBD as it's reading all of the little pre-big-movement mesh ripples). On the attached setup (a simpler version of the project giving me trouble) I even ran the meshed surface through a “clean” just in case any of the lingering velocity attributes were throwing it off, but that didn't help either. I'm wondering if the fact that the topology itself changes so much might be the problem, but if so I'm not sure how to fix that.
Thanks for any suggestions!
Technical Discussion » Create group of edges by angle for creasing?
- bentway23
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Aha–turns out that, since it was imported as an alembic, I had to run it through a convert before it would work right. Thanks for your help, that's a good thing to know!
Technical Discussion » Create group of edges by angle for creasing?
- bentway23
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I apologize if the answer to this is somewhere obvious–through Googling I've found some of people asking this over the last 15 years, but no answers that work.
I have a model that I need to crease before subdividing. Manually selecting the edges is impractical–too many round buttons with flat tops. How can I automatically select/group just the edges joining faces with right-ish angles? I've tried the “include by edges” and setting min and max edge angles, but that doesn't appear to do anything unless you chose “Edge Angle Uses Angle Between Edges,” in which case it selects pretty much everything.
Thanks!
I have a model that I need to crease before subdividing. Manually selecting the edges is impractical–too many round buttons with flat tops. How can I automatically select/group just the edges joining faces with right-ish angles? I've tried the “include by edges” and setting min and max edge angles, but that doesn't appear to do anything unless you chose “Edge Angle Uses Angle Between Edges,” in which case it selects pretty much everything.
Thanks!
Technical Discussion » Where are SOP to DOP Bindings in Volume Source (vs. old Source Volume)?
- bentway23
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I'm trying to create a custom velocity field for a FLIP tank (so I can “pin” part of it down with 0 velocity, while part of it sims all over the place). I'm following this tutorial:
https://www.youtube.com/watch?v=xm404aavXrY [www.youtube.com]
–but it's from a version or two ago, and when he brings in the volume he created with the velocity attributes into his DOP network, he uses “source volume” and brings in the fields via SOP to DOP bindings (at about 12' into the video).
I've crudely sussed out how to use a Volume VOP in the bit where the volume is created to add noise, but not how I could add the velocity at that level (if in fact that's how it's done).
Following this model:
https://www.youtube.com/watch?v=8UaDetbvMAs [www.youtube.com]
I have had success–grouping the FLIP particles in a SOP Solver and using a wrangle to set a custom velocity–but to my knowledge doing it that way won't produce a falloff–it's a very clear line in the tank between the 0-velocity particles and the non-custom particles.
Thanks for any help!
https://www.youtube.com/watch?v=xm404aavXrY [www.youtube.com]
–but it's from a version or two ago, and when he brings in the volume he created with the velocity attributes into his DOP network, he uses “source volume” and brings in the fields via SOP to DOP bindings (at about 12' into the video).
I've crudely sussed out how to use a Volume VOP in the bit where the volume is created to add noise, but not how I could add the velocity at that level (if in fact that's how it's done).
Following this model:
https://www.youtube.com/watch?v=8UaDetbvMAs [www.youtube.com]
I have had success–grouping the FLIP particles in a SOP Solver and using a wrangle to set a custom velocity–but to my knowledge doing it that way won't produce a falloff–it's a very clear line in the tank between the 0-velocity particles and the non-custom particles.
Thanks for any help!
Technical Discussion » Where is the checkerboard pattern living these days?
- bentway23
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That's great, thanks! More complicated than it apparently used to be, but I'm assuming that had to do with them retooling how shaders/materials are handled.
The place I saw this done, where he just drags it off the palette, is at 5:09 at:
https://app.pluralsight.com/player?course=disintegration-teleportation-reintegration-effects-houdini-2322&author=jeff-wolverton&name=disintegration-teleportation-reintegration-effects-houdini-2322-m2&clip=0&mode=live [app.pluralsight.com]
The place I saw this done, where he just drags it off the palette, is at 5:09 at:
https://app.pluralsight.com/player?course=disintegration-teleportation-reintegration-effects-houdini-2322&author=jeff-wolverton&name=disintegration-teleportation-reintegration-effects-houdini-2322-m2&clip=0&mode=live [app.pluralsight.com]
Technical Discussion » Where is the checkerboard pattern living these days?
- bentway23
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Yup, dragged it on and confirmed that the material path was showing.
I'm sure this is something dumb and obvious–for instance, is there an equivalent of hitting 6 in Maya? I made sure that show materials is turned on, and if I modify the base color it works, it just doesn't accept anything from the pattern.
I'm sure this is something dumb and obvious–for instance, is there an equivalent of hitting 6 in Maya? I made sure that show materials is turned on, and if I modify the base color it works, it just doesn't accept anything from the pattern.
Technical Discussion » Where is the checkerboard pattern living these days?
- bentway23
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That doesn't produce any sort of result–everything stays grey (see attached–both are just off-the-shelf objects with a UVunwrap thrown on for good measure). Clearly I'm doing something wrong there, just trying to figure out what.
Image Not Found
Technical Discussion » Where is the checkerboard pattern living these days?
- bentway23
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I don't mean the node, I mean the actual material, under “patterns” in the material palette. Here's a screenshot (annotated) of the moment in the tutorial when the gent grabs it.
Edited by bentway23 - Aug. 24, 2019 22:26:35
Technical Discussion » Where is the checkerboard pattern living these days?
- bentway23
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So a few older tutorials I have been following have people dragging the Checkerboard from the Material palette onto an object. I thought maybe the checkerboard just was no more since the material system changed, but I recently saw a Houdini 17+ tutorial where someone did the same thing. My material palette has no Checkerboard pattern on it. Where can I find it? Is it something I have to opunhide?
Technical Discussion » Increase FLIP viscosity with particle age?
- bentway23
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Thanks! The add ID attribute, aside from being big and obvious, worked like a charm.
I'll have to play with the Gas Temperature Update DOP a bit when I have the time–it works, just very very quickly. It's always good to know an alternate solution.
I'll have to play with the Gas Temperature Update DOP a bit when I have the time–it works, just very very quickly. It's always good to know an alternate solution.
Technical Discussion » Increase FLIP viscosity with particle age?
- bentway23
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How would one increase FLIP viscosity based on particle age, to get a thickening/coagulating effect? My searching only found one how-to from 2012, which doesn't work in H17+. I understand setting viscosity by attribute, but it appears FLIP particles don't have an age attribute, so I'm not sure how to shoehorn one in there.
Thanks!
Thanks!
Technical Discussion » FLIP colliders flickering on and off
- bentway23
- 100 posts
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In case someone else runs into this, the incomparable Atom offered the solution on odforce. Using a polyfill node, set to single polygon, ensures that any holes in the topology (eyes, nose, clothes, whatever) are closed and not confusing the collider cook. This did the trick.
Technical Discussion » FLIP colliders flickering on and off
- bentway23
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So after a very lengthy FLIP sim I'm finding that my colliders are arbitrarily flickering in and out and disappearing altogether. I had done various tests–this happened a lot with lower res settings but seemed to stabilize at the final sim resolution–until frame 240 (of 250).
The problem appears to be in the static object itself creating the collision geo. It's set to use volume collisions, mode is volume sample, division method by size at 0.005 division size. The object is an animated person at scale (about two units = 2 meters tall), this setting was about as large as I could go and not lose details.
The .abc itself is imported and unpacked. The same object is used elsewhere to drive a pyro sim and it's working fine there.
How can I ensure that my colliders don't just disappear?
The problem appears to be in the static object itself creating the collision geo. It's set to use volume collisions, mode is volume sample, division method by size at 0.005 division size. The object is an animated person at scale (about two units = 2 meters tall), this setting was about as large as I could go and not lose details.
The .abc itself is imported and unpacked. The same object is used elsewhere to drive a pyro sim and it's working fine there.
How can I ensure that my colliders don't just disappear?
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