DOPs grouping problem

[ehsan parizi]

Hi all,

I have a problem with grouping my RBD GLUE object.

I have a scene(which is attached) in which a rbd sphere that is animated by a motion node, collides with a rbd glue obj. the problem is I don't want my gravity to affect the whole glue obj, and I tried to group my rbd objects that are hit by the sphere, they all have Impacts data. but there are a few problems here.

1. The Impacts data, comes into the data sheet just when the collision happens! if you look at the group2_impacts node, after frame 41, the number of objects in this groups varies, which makes sense, because we're just saying that add those pieces that have impacts subdata, but there's nothing like preserve group in POPs! so, my first question is how to make the group to preserve the pieces that come into the group?

2. although we're telling the gravity node to just work on the group_impacts, it's affecting other parts too! as you can see, all the streetPc pieces fall down! why is this happening?

3. Since I don't know how to preserve the group, I tried to use dopfield expression, and use the velocity field, but it didn't work out! do you know how I can use that expression to make a group of the pieces that have a velocity !=0?

btw I noticed that the pieces that seems like are not moving, have velocity! (for example see the piece53, and disable the gravity, in the viewport, it looks like that piece stands still, but the vel in options is changing after frame 40 and it's not [0,0,0] anymore!

if you have the answer for each one of my questions, that would be great or if you have a better way to achieve that effect. right now I'm painting all the pieces that I don't wanna move and add them to a group and use it in an Active Value node, but it's not the best way, because if I change my cracks map, I have to paint again, YES! it takes only a few seconds, but still, I prefer a procedural way to do that.

Edited April 3, 2011 by ehsan parizi

[ehsan parizi]

The file

RBD_groups_problem.hip

[Macha]

Could you give the pieces an appropriate attribute in the sop context? (like mass or something like that, perhaps even use a sopsolver)

Or could you use a mask for the gravity?

Edited April 4, 2011 by Macha

[ehsan parizi]

I probably can give the pieces an attribute on SOP level, but the problem is how to use that attribute in DOPs? We already have all these subdata in dop level, and like I said, I can use the dophassubdata to use them, but I don't know how to keep the pieces in a group.

by masking gravity you mean using group? if so, I'm exactly trying to do that! if there's another way please let me know.

thanks.

[Macha]

You can use a mask dop (use a sop scalar field to define it) and then plug it onto the green part of the gravity node. It's a little tricky because I think the field has to include all points but it kind of works. The problem is that if pieces fall into it the gravity also disappears from them.

With attributes, I think just setting the mass will work (just call it mass and give it the appropriate value).

If I find time today I'll try and post a hip file but I can't promise. Attribute should work.