[Sidefx-houdini-list] computing world space velocity

Antoine Durr antoine at floqfx.com
Tue Jul 8 14:46:42 EDT 2008


There's a new option in the object_merge SOP in H9.1, where you can  
transform the geometry into the space of a specified object.  I  
haven't tried it, but if you make yourself a world_object that has  
identity transforms, that /should/ work.

-- Antoine

On Jul 8, 2008, at 11:28 AM, Mark Elendt wrote:

> On Tuesday Jul 08 at 11:14, Michael K O'Brien wrote:
>>> -----Original Message-----
>>> From: sidefx-houdini-list-bounces at sidefx.com [mailto:sidefx- 
>>> houdini-list-
>>> bounces at sidefx.com] On Behalf Of Antoine Durr
>>> Sent: Tuesday, July 08, 2008 10:25 AM
>>> To: sidefx-houdini-list at sidefx.com
>>> Subject: Re: [Sidefx-houdini-list] computing world space velocity
>>>
>>> If you do an object_merge, and set the 'transform space' to '.', the
>>> geometry will now be in worldspace.  The trail SOP will work as
>>> expected, now.
>>
>> Sort of. The object merge needs to be in a network that has an  
>> identity OBJ
>> (not an animated OBJ) for it to correctly import the points in  
>> world space.
>> This is what led me to a separate SOP network to compute world-space
>> velocity, as I described below... which seems wrong.
>>
>> Is there any way to compute worldspace positions of points from  
>> within a
>> SOP? Is there any reason why that can't be done?
>
> I'm pretty sure the VEX ow_space() function(s) will transform from
> "object" (SOP) space to "world" (world) space.
>
> If you put down a
>
> Global(P)->Transform->Output
>
> Then set the parameters of the transform VOP to:
>     space:world
>     space:current
>
> (Yes, the VOP lies, space:world seems to work in SOPs just fine).
> you should get the world space location of the points.
>
> You can also transform "direction vectors" (i.e. velocity) the same
> way.  You may also be able to specify the full paths to objects, but
> don't quote me on that.
>
> But, to be honest, I'm not 100% sure this answers the original  
> question.
>
> If you want, there's also the "optransform" hscript expression
> function, but that way seems ridiculously difficult.
>
>>>> I'm sure I'm missing something fairly easy here.
>>>>
>>>> We have geometry that is imported by nodes that animate at the
>>>> OBJ level. I need to compute the velocity for use in a DOP. The
>>>> trail SOP computes velocity based on the object space positions.
>>>> How does one compute the world-space velocity?
>>>>
>>>> Right now, I'm creating another SOP network that imports the
>>>> original object, uses a trail on that node, and then uses a copy
>>>> attribute to apply it back to the original. This seems overly
>>>> clunky.
>
> -- 
> Please visit http://www.healemru.com/
>
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-- Antoine

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