The year have just begun :) On 4 June 2012 21:01, Guillaume Laforge <[email protected]>wrote:
> If there is a competition for the best answer of the year on this list, my > vote is for this one ! > > :) > > > On Mon, Jun 4, 2012 at 8:51 PM, Thiago Costa <[email protected]>wrote: > >> To the original question, you should be able to do it quite simply by >> seeding vortices particles (just flag them as vortices on emit), then >> computing the curl of the field. Finally you can use that as a force on >> each particle. >> >> To satisfy vortex equation [image: \vec \omega = \nabla \times \vec >> \mathit{u}.] each vortex particle (a random probability of being a >> vortex particle for simplicity), should give a spin axis (random) and a >> radius (might be random, but physically it shouldn't without more >> sophisticated volume conservation techniques). >> You then need to search for the closest vortex particles - using a large >> radius (normally the radius of the biggest vortex). Then compute the sum of >> all velocity perpendicular to the spin axis of the closest vortices. >> >> using lagoa you could probably set that as a force on each particle, and >> then let the integrator do the rest. >> >> >> Thiago >> >> On 4 June 2012 14:22, Byron Nash <[email protected]> wrote: >> >>> Thanks for the tips and example Andy (& everyone). I'll work on >>> implementing this into my approach. >>> >>> >>> On Mon, Jun 4, 2012 at 1:32 PM, Jonathan Laborde <[email protected] >>> > wrote: >>> >>>> I made 2 compounds that I use regularly to calculate velocity properly. >>>> You basically store the current point position and orientation at the >>>> beginning of every frame (first port in the stack). Even if you are say on >>>> frame 10, since it's the first thing being calculated in the stack the >>>> point position is still from frame 9. Then in post-simulation you do the >>>> actual calculation and store it in pointvelocity and angularvelocity, that >>>> way it won't affect the following frames. >>>> It works well, unless you are moving the points in post-simulation as >>>> they won't be calculated at the beginning of the next frame. >>>> Enjoy! >>>> --* >>>> **JONATHAN LABORDE* >>>> FX Artist >>>> >>>> www.rodeofx.com >>>> >>>> >>>> On Mon, Jun 4, 2012 at 12:25 PM, Grahame Fuller < >>>> [email protected]> wrote: >>>> >>>>> Verlet integration might be useful in these cases. With Verlet >>>>> integration, you store the previous positions and back-calculate the >>>>> velocity from that, instead of calculating the forward velocity as in >>>>> standard Euler integration. >>>>> >>>>> gray >>>>> >>>>> From: [email protected] [mailto: >>>>> [email protected]] On Behalf Of Andy Moorer >>>>> Sent: Sunday, June 03, 2012 02:18 PM >>>>> To: [email protected] >>>>> Cc: [email protected] >>>>> Subject: Re: ICE: Vortex and Lagoa >>>>> >>>>> Yeah I should have pointed that out... There's always a sacrifice >>>>> between the simplicity and emergent behavior of simulations and the >>>>> control >>>>> you can get by being more direct and specifying explicit positions per >>>>> frame. >>>>> >>>>> The more "custom" you get, the more you have to chase down and account >>>>> for this kind of thing. The motionblur problem with nonsimulated ICE >>>>> animations is the biggie - enough so that it might be advisable for the >>>>> softimage devs to implement some in-box solutions, like perhaps an option >>>>> for computing a per point velocity during caching, or writing special >>>>> "absolute" point position and velocity variables after the post-process >>>>> step... >>>>> >>>>> >>>>> On Jun 3, 2012, at 1:36 PM, Jonathan Laborde <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> Great answer Andy. But be careful with such a technique (blend between >>>>> simulation and manual positioning) as the point position will be as you >>>>> expect but point velocity will not be calculated properly. Your motion >>>>> blur >>>>> will be wrong in that case, and you will have tu manually set it in post >>>>> process. >>>>> Rock n' roll >>>>> -- >>>>> JONATHAN LABORDE >>>>> FX Artist >>>>> >>>>> www.rodeofx.com<http://www.rodeofx.com/> >>>>> >>>>> On Sun, Jun 3, 2012 at 11:33 AM, Andy Moorer <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> Byron hi there. Can't answer your questions about differences between >>>>> lagoa and "normal" reaction to forces, but the results you are seeing with >>>>> a combination of forces (one to move particles along a curve, the other to >>>>> draw particles towards a curve) is one I'm familiar with. It's easy to >>>>> fall >>>>> into the "simulation trap," where you drive yourself crazy trying to find >>>>> a >>>>> perfect balance of forces to get the results you want. >>>>> >>>>> There are a couple of suggestions I can give you... The first is to >>>>> clamp the maximum speed at which a particle is allowed to move: get >>>>> particle velocity, get "length" or magnitude of the vector (this is >>>>> "speed.") If the speed > a max value you set, new speed=max value. >>>>> Normalize your original velocity vector and multiply it by new-speed. >>>>> >>>>> The result, particles obey the forces you set, but never travel so >>>>> fast that they get flung away, and never develop enough momentum to get >>>>> out >>>>> of control. A drag force coupled with velocity can produce similar >>>>> results . >>>>> >>>>> Another option is to replace or blend your "suction" and "along curve" >>>>> forces with a setup which places each particle at a specific position in >>>>> relation to the curve, animated of course. I haven't tried this kind of >>>>> approach in this particular context, but in general the result is a hybrid >>>>> of a simulated look and an "absolute" look... particles are simulated to a >>>>> certain extent, blending to an absolute predetermined position. I've >>>>> attached a simple example of this kind of thing, a simple post-sim blend >>>>> between a simulation and goal positions on geometry. >>>>> >>>>> Cheers >>>>> Andy >>>>> >>>>> On Fri, Jun 1, 2012 at 9:32 AM, Byron Nash <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> I'm trying to make something along the lines of this video from >>>>> Firebird https://vimeo.com/29367269. It uses Lagoa and some of the >>>>> vortex techniques Brad showed in one of his videos. I can get it to move >>>>> somewhat but can't keep the points on the curve. They tend to fling off >>>>> despite increasing the "suction" controls. How does Lagoa respond >>>>> differently to forces than normal ICE particles? >>>>> >>>>> >>>>> >>>> >>> >> >
