Hello,
So, I have a character flipping over a table. I animate a constraint so the table's corner is constrained at the appropriate time when his hand is doing the flipping motion. Works great! However, it's too slow. I don't want to change the timestep for the whole DOP network though. Ideally, I want to multiply the velocity (which I see clearly in the Details view) for the Constraint data.
In SOPs, a Point SOP would do it almost instantly. How do I do it in DOPs?

Cheers

Peter B

I don't understand what you want to do with the Veocity information? Where is th velocity information coming from and what would you like to apply it to? Is this all within DOPs? Do you want to modify the velocity point attributes of the table geometry within a DOP simulation? If so you can use a SOP Solver on the table and dop expressions to access the velocity from the person (using the dopvelatpos expression). But it doesn't sound to me like this is what you want to do…

Mark

Hi Mark,
Since this is Houdini, I've already got what I want by using a Stretch CHOP. The Dynamics CHOP rocks, by the way.
However, as an academic exercise ) In the Details view of the DOPnet, in the Constraint section, I see a velocity vector. It is 0,0,0 until the constraint becomes active. The velocity is, I presume, the delta between frames that the contstraint is applying to the table. What I want to do is multiply (speed up) the velocity that is being applied to the table, so that the table “flies away” faster, for artistic reasons…

Cheers,

Peter B

Hey Peter,

This may not be such a good idea because it will probably affect the whole sim including the way your character moves off of the table, but could you maybe alter the table's mass/density for a short amount of time so that it flies away faster? I know this isn't what you're wanting and is a cheap hack, but thought I'd throw it out there.. I'm still interested in your original question though. (i.e. how we can affect these properties/attributes we see in the details view like a point sop would be doing in sops..)

Yah, I'm curious about this too. I'm suspecting the notion of slinking in there and hacking the velocity manually like that would break the sim in a number of ways - it's all interrelated and simply upping the vel would cause other things to behave differently, thus defeating the purpose of simply speeding or slowing that precise sim. Might be wrong, but I'm interested in the answer to that.

Cheers,

J.C.

Huh, I didn't even know that Velocity value existed in the Constraint data That's part of why I was confused by your first post…

Anyway, since that velocity value has a parameter associated with it on the DOP node that created it (though the parameter is inside a locked subnet), it is probably safe to set it however you see fit. It may produce “unrealistic” results, but if that's the look you're going for then that's a perfectly valid thing to do. I was recently shown a hip file where point velocities on a deforming object were multiplied by ten so that anything hitting the object would act like it had been hit by something moving much faster. In the context of that file, this gave the desired look, even though the “real” physics of it was highly dubious.

Anything you see in the Details View can be modified using a Modify Data DOP or a Script Solver DOP. Being able to hand-tune features of a simulation in a non-realistic way is one of the big strengths of DOPs. So don't be shy about tweaking whatever you want to get the results you want. The RBD solver in particular was designed to be extremely robust in terms of having objects modified in arbitrary ways from one timestep to the next precisely so that you could make these kinds of changes without worrying about “breaking” the simulation.

Mark

Hi Mark,
Modify Data sounds perfect, and yes, who cares about physics? We're making movies!

Sadly, and this is I'm sure my own deficiency, how do I make it go? Please see attached, have I got the Data name right? I still am really confused by Data names etc. Based on what I see here, should I not have a velocity of 1,1,1? It appears to have no effect…


RFE Data browser for Object Merge, Dynamics CHOP and anywhere else you reference data directly from DOPs. It's too hard to keep track of the syntax to have to type it all in…

Cheers,

Peter B

The full path to the “vel” field in the Detail view can be broken down into several parts:

Object Name - table
Data Name - Constraints/Anchor_rbdconstraint1_constraint1_3
Record Name - Options
Field Name - vel

So the Data Name in the Modify Data DOP should be set to the Data Name listed above. The Record Name does not need to be specified because the Modify Data DOP can only work on the record named “Options”. And then you have the Field Name (Valu 0 Name) set correctly. The only other thing you may want to do is change the Group of the Modify Data to “table” so that the Modify Data will only affect the object named table.

The RFE you suggest has already been submitted in a slightly different form. The idea is that DOP objects and DOP data would appear as child branches off the DOP Network in the regular tree browser that the Object Merge already uses.

Mark

hey peter,

i don't *think* you need the /Options as the vel data is attached to the anchor itself…

ahh, i see mark beat me to it.. and explains it a lot more as well.. thanks for all the clear up on this mark, i've learned a ton!