[chickenstu]

hi there,

i've been following the Houdini Technical Effects DVD's trail tutorial part 4
and for a unknown reason the emitted particle ID's don't stay even, they change here and then.

That causes a problem when i seperate my groups, as the id's change from even to uneven and vice versa.

would be great if somebody could have a look at my hipfile, i can't find my mistake.

http://www.manueltausch.com/trail_tutorial_part4.rar

regards,

Manuel

[CaptainHammy]

I haven't done the tutorial, but looking at the file, the problem is being caused by the fact the point order on the birth geometry is changing at different times in the scene. If you display the point numbers at frame 30, then step to frame 31 you can see that the point numbers for 0 and 1 change. This is caused by issues with the up vector combined with the deforming geometry points. If I either disable the up vector attribute, or move the transform to after the copy then I get proper results.

[chickenstu]

much obliged, thanks for finding the flaw!
it's a shame that there isn't much explanation about this up vector in the houdini help, this is the second time it caused me problems and i'm not really sure why.