[Sidefx-houdini-list] DOPs Impact question

Craig Hoffman craigleehoffman at aol.com
Wed Jan 12 19:16:08 EST 2011


 That otl rocks!  Thanks so much!

The Odforce write-up mentions the help card, but that doesn't seem to work for me (I got the last one from the thread).  What exactly is "Number of Configurations?




-----Original Message-----
From: Graham Thompson <captainhammy at gmail.com>
To: sidefx-houdini-list <sidefx-houdini-list at sidefx.com>
Sent: Wed, Jan 12, 2011 2:32 pm
Subject: Re: [Sidefx-houdini-list] DOPs Impact question

This is all really as I would expect it.  Most if not all of the time

your impacts will occur during sub frames.  Depending on your objects

velocity and the amount of substepping and such the simulation might

not recognize that your objects are impacting the ground until they

have part way through, which is why your impact points appear below

the ground plane.  This also explains why you can have a large number

of impact points as a point is generated at each impact during each

subframe.  Looking at the time field of the data can show what happens

during each step.  By increasing the number of minimum substeps you

can get around this problem by increasing the accuracy of the

collisions so it detects the impact right away, though this will

introduce longer sim times and might not be ideal if your sim is

already looking good.  An alternative would be to use a Ray SOP to ray

the points up to the ground plane where you want them.

As for the data showing up after the impact actually occurred, well

that is related to what I just mentioned.  Your impact occurs during

say frame 21.765342 but since you are using integer frames you can not

really expect to see anything until the next whole number frame in

which case the simulation has advanced and your object probably isn't

impacting anymore.

Finally, your source object isn't actually a DOP object.  It is a

digital asset that is creating a bunch of data, in the case of the

glue object it is creating a bunch of objects which are then simulated

and receive impact data as they hit individually.  As far as the

simulation engine is concerned there is no "sphereObject1" in your

actually simulation you could attach the data to. As for getting the

data from all your piece objects usually people will use a SOP setup

with some copy + stamping using dopnumrecords and dopfield to get at

the data for each record or each object.  Here is a scripting solution

I've posted a couple times on odforce that dramatically simplifies

this and even lets you attach some attributes as well.


On Wed, Jan 12, 2011 at 12:40 PM, Craig Hoffman <craigleehoffman at aol.com> wrote:




>  Hi guys,


> I am doing a DOPs simulation and getting the Impact data out to drive particle 

systems where impacts happen and am having some issues.


> The DOPs sim looks really accurate- no interpenetrations or anything, but the 

"Impact" positions coming out of DOPs aren' exactly where I would expect them to 

be.  Some are a fair bit below the groundPlane collision plane (although others 

are pretty close).  Is there a way to get more accurate Impact data since the 

actual simulation seems pretty accurate?  Also, they seem to show up a frame 

after I would expect them to.  Is "Impact" data generated for the frame after a 

collision is detected?


> Also, I am using a Glue Object, so the Impact Data I want shows up on 

"piece1", "piece2", etc. and not on the source object "sphereObject1".  Is there 

some way to get all the Impact data from the entire simulation rather than 

having to collect it for each piece at a time using expressions like 

"dopnumrecords" and "dopfield" (which don't take wildcards).


> Thanks for any help.

> Craig




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