[Sidefx-houdini-list] DOPS and scale

Robert Kelly isstuff at gmail.com
Tue Jan 18 17:08:34 EST 2011


woops I see you said what not why.....

there are plenty of values that are sensitive one way would be to make
some shelf smoke as cm and another as meters and compare the values on
them.

On 18 January 2011 14:06, Robert Kelly <isstuff at gmail.com> wrote:
> you fall at a rate of 9.8 m/s² if your unit scale is  1 unit = 1 meter
> then you put in your gravity force 9.8
> BUT !
> if your unit scale is 1 unit = 1 center meter other wise known as 1
> unit = .01 Meters then your gravity force gets a value of 980.
>
> There are other real world values that are unit sensitive.
>
> http://en.wikipedia.org/wiki/Equations_for_a_falling_body
>
> On 18 January 2011 13:50, Alex Czetwertynski <disciple1 at gmail.com> wrote:
>> Thanks for the answers...
>>
>> What nodes are scene unit sensitive?
>>
>> Thanks
>> Alex
>>
>> On Jan 18, 2011, at 1:46 PM, Robert Kelly wrote:
>>
>>> if your doing DOPs you want to set your unit scale before putting down
>>> any DOP nodes. They change values on the nodes that are scene unit
>>> sensitive on creation. So if your not careful you can make a scene
>>> with some values made for meters and some set for center meters.
>>>
>>> On 18 January 2011 09:08, Michael K. O'Brien <mobrien at pixar.com> wrote:
>>>> Hola~
>>>>
>>>> There are several constants in physics simulations that have dependencies on
>>>> distance that aren't exposed (like damping factors). If you try to do really
>>>> large or small scale simulations, float precisions starts to creep in as
>>>> well.
>>>>
>>>> We usually scale the world down so something that is 1 unit == 1m when
>>>> possible. We've had problems with changing the units.
>>>>
>>>> MO
>>>>
>>>>> -----Original Message-----
>>>>> From: sidefx-houdini-list-bounces at sidefx.com [mailto:sidefx-houdini-
>>>>> list-bounces at sidefx.com] On Behalf Of Peter Bowmar
>>>>> Sent: Monday, January 17, 2011 8:19 PM
>>>>> To: sidefx-houdini-list at sidefx.com
>>>>> Subject: Re: [Sidefx-houdini-list] DOPS and scale
>>>>>
>>>>> I believe 1 unit defaults to 1 metre and 1 weight unit is Kg (forget
>>>>> exactly). It's in the Preferences->Miscellaneous section. So the
>>>>> "smaller object" would have lower mass and therefor less force
>>>>> required to accelerate it.
>>>>>
>>>>> Unless I've really badly forgotten my highschool physics :) in which
>>>>> case I blame the antibiotics...
>>>>>
>>>>> Cheers,
>>>>>
>>>>> Peter B
>>>>>
>>>>> On 17 January 2011 19:00, Alex Czetwertynski <alex at franktheplumber.com>
>>>>> wrote:
>>>>>> When modeling objects to be used in DOPS, does one have to pay
>>>>> attention to scale?  I noticed a wind force had a much stronger
>>>>> influence on a smaller object, but I'm not sure what the rule of thumb
>>>>> is in terms of getting things to be in a good mid-range?
>>>>>> staying within the range of the initial grid maybe?
>>>>>>
>>>>>> Thanks
>>>>>> Alex
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>>>>>
>>>>>
>>>>>
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>> ---
>> http://www.disciplefilms.com
>> http://www.aenhancers.com
>>
>>
>>
>>
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