Hi.

I need to conform a volume particle stream to a curve.

I tried using Position with path option but it just places all particles in same place. I am looking for curve flow effect as found in Maya.

Dave

how about the Follow POP?
a null animated along the curve as Leader?

That cannot work, as the stream is continiois over long period of time. It has been tried. Follow is for flocking not stream contouring. Imagine volume particle stream, now conform it to a curve.

Dave

well I'm sure there is a better solution…
but I think it would work…depending on the shot.
a very long curve, or better yet, one that simply loops…

You could append two position POPs to your source.

The first Position POP is set to Path mode. The object will be your curve you want the particles to follow. Your position along the curve could be $LIFE or something like that.

The second Position POP will be the offset so your particles don't all go in a straight line. For this POP you could set each particle's position to be
$TX + (rand($PT)-.5) * some_scale
where some_offset is a scaling value to control how far away the particles could be from the curve.

You could probably replace the first Position POP and use a Creep POP too.

jim.

Thank you. But something is not working with this method, and I don't know.
I am distressed that something that sounds straightforawrd is so impossible to do. I thought that this just bunch of POPs strung together, and that I did not know them. Its looking that noone here knows how to do that, hence it must be unreasonable complicated. I can't even get the Creep'ing particles to move at consistent speed across the creep surface. THey start slow, speed up, then slow down, as if they have a velocity curve, which they don't.
I am about ready to throw in the towel in POPs and VEX. I can't learn them. They don;t make sence at all. The tutorials are simplistic, and when I try to go beyond them everything stops working. My nanuals are V3 and in japanese, and the PDF's on learning CD's don't contain comprehensive instructions. I cannot find the concise list of expression commands, and hence I can't learn the syntax.

DaveR

I can't offer much more than shots on the dark as I have not really used POS at all…
but the ‘start slow, spped up, slow down’ bit sounds alot like what happens in Maya if your curve/surface has an uneven topology > the CVs not evenly distributed…

as for the docs…I think many of us have come to Houdini at a real transition point, the software has advanced faster than the documentation and we're waiting for them to catch up…, should be soon by all indications but that doesn't help you if you're trying to get a shot done right now….

david,
maybe you can try this.
place the source at the begining of the curve.
now with the curve add a pointSOP and go to the force folder. now add ‘radius’, ‘f scale’, ‘radial f’ and ‘edge f’…you will need to play/experiment with these parameters according to the effect you are after.
go into POPs and bring in the source for your particles. then add an attractor and use the pointSOP of the curve for this. add a dragPOP and play with the parameters. this will get your particles following a curve, as well as much more…….this works for me.
hope it helps
b

Thank you Betty

I've been messing with PointSOP with varying degrees of success. USing your explanation, I am getting no where near the flow of particles along a curve. To me the rational solution would be a Position POP using Path option, with randomizing value. Yet that POP is , I don't know. All particles, regrdless of when they were created, are pleaced on same position. So a popnet with 10,000 points appears as single point, and POP has no options to randomize it, or even make it appear like a stream on path. I just don't get what the intention of engeeneers was with this POP. What I don't see is a rational relationship between values in those fields and project units. Sometimes a very low value works, sometimes a high value. Sometimes a .001 change in value has large effect , sometimes100's are needed. It seems to be random, and inconsistent. There is no ‘apparent’ frame of reference. What are the units, Newtons, gravity (9m/s^2)? This is the aspect of Houdini that is grating me. Everything is so cryptic. The icon pop-ups are , well I am sorry, but they are not usefull. The glossary, is like wise weak on explanation.
All this talk about how Houdini is in transition is great, but in practical terms, it is very hard, if not impossible to learn for a user with no access to proffessional education. For example, I need a comprehensive guide to expression syntax, yet I can't find it anywhere. No on CD's not at sidefx.com. Where is it? I have these examples, and I see in them these complex expressions, and I can't make head or tails what the variables mean, so the rest formula is meaningless to me.

DaveR

DavidRindner
I can't even get the Creep'ing particles to move at consistent speed across the creep surface. THey start slow, speed up, then slow down, as if they have a velocity curve, which they don't.
DaveR

Refine or resample the Curve in SOPs.

jim.

I tried it with hi and low CV count creep surfaces. Tried both Bezier and NURBS. There is no change in particle velocity. Its still slow in the beggining, speeds up towards the center, slows down to a crawl towards the end.

Dave R