mic Posted March 19, 2009 Share Posted March 19, 2009 Hello! i have some fast moving object (as file sequence, but it doesn't matter) and i want to take it to dops. i want to emit SPH from it, and apply attracting field forces.. the problem is that as everything is ok in static, when moving cause of the very fast motion emitted fluid particles don't stay on the surface. ehat hints maybe there except increasing the substeps?.. thank you! Quote Link to comment Share on other sites More sharing options...
Jason Posted March 19, 2009 Share Posted March 19, 2009 Hello!i have some fast moving object (as file sequence, but it doesn't matter) and i want to take it to dops. i want to emit SPH from it, and apply attracting field forces.. the problem is that as everything is ok in static, when moving cause of the very fast motion emitted fluid particles don't stay on the surface. ehat hints maybe there except increasing the substeps?.. thank you! Substeps only really count if your object moves correctly at subframes. In other words, turn off your playbar's "Integer Frame Values" and slowly drag between frames. If your object motion smooth moves/interpolates in the fractional frames, you're good to go to substepped simulation because when the sim asks for a fractional frame, your object has indeed moved correctly. If not: Do you have a consistent point-count in your object? Or do you have velocity vectors? If you have either of these, you can build a tiny network that will allow your object to animate correct at sub-frames. The former is best for objects/characters because you don't have to store velocity, the latter is better for particle systems written out to disk. Look at the attached hipfile - hit the Geo ROP to output the frames. Investigate the nodes. Hope this helps, Jason PS. This is something that all FX-houses end up building into HDAs for themselves. It's a very common issue, and a little surprising Houdini doesn't support it in the FileSOP directly. subframe_reads.hip Quote Link to comment Share on other sites More sharing options...
michael Posted March 19, 2009 Share Posted March 19, 2009 I thought for sure there was a new node to do this...ed pointed me to it... of course I can't find it now... and of course we use our own here... Quote Link to comment Share on other sites More sharing options...
johner Posted March 19, 2009 Share Posted March 19, 2009 I thought for sure there was a new node to do this...ed pointed me to it...of course I can't find it now... and of course we use our own here... Isn't that what the TimeBlend SOP is supposed to do? Assuming you have constant point counts I mean... Quote Link to comment Share on other sites More sharing options...
Jason Posted March 19, 2009 Share Posted March 19, 2009 Isn't that what the TimeBlend SOP is supposed to do? Assuming you have constant point counts I mean... Ahh; that was it:) The second example I gave is good for particles, then. The docs for TimeBlend are skinny - does it only blend point position (P)? Or does it blend attributes too? It would be nice if it got some other features, like "Blend Along v Attribute" and spline interps, like Monotone Cubic Interpolation and such. In any case I will probably update our inhouse tools to use this instead. EDIT: ah no, maybe I won't - it doesn't support supplying another time index. I'd want a $FF exposed there so I can shift around. Quote Link to comment Share on other sites More sharing options...
mic Posted March 20, 2009 Author Share Posted March 20, 2009 thank you very much, Jason, Michael and Johner! =) Quote Link to comment Share on other sites More sharing options...
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