# [ODE] How to shift the center of mass of a Geom using Transform Object - Some questions

Jon Watte (ODE) hplus-ode at mindcontrol.org
Sat May 12 10:35:22 MST 2007

```You can either use the geom-offset functions, which are new in ODE 0.8,
or you can use the GeomTransform geom, which has existed since the dawn
of time.

Cheers,

/ h+

PKS123 wrote:
> But, doesn't the ODE Engine itself place the Geom at the body's position and
> visa-vis on its own.
> That is, if i place a body at (x,y,z) using dBodySetPosition() function,
> doesn't the geom get placed at (x,y,z) autometically. Thats what the
> documentation says. So, how can i offset the Geom position with respect to
> the body??
>
> Thanks and Regards
> PKS123
>
>
> Jon Watte (ODE) wrote:
>
>> Actually, as of ODE 0.8, there is a simpler way: you can set the offset
>> of each geom instead. So to lower the center of mass, just raise each of
>> the geoms. The center of the body and the center of the mass is always
>> the same thing in ODE -- the "offset" part of the mass is ignored.
>>
>> If you want a sample for how to use geom transforms (the old way), check
>> out the RayCar sample: http://www.mindcontrol.org/~hplus/raycar/
>>
>> Cheers,
>>
>>              / h+
>>
>>
>> PKS123 wrote:
>>
>>> I know that this is a hackneyed question and there are posts which give
>>> the
>>> answers, but none of them give the answer to my satisfaction. So, i'll
>>> again.
>>>
>>> My question is how do I lower the center of mass of a ODE Body. The
>>> that I know of is, "by using the ODE transform object". But I have some
>>>
>>> 1. The Transform object claims to change the point of reference of a
>>> body.
>>> Do point of reference and center of mass mean the same thing in ODE?
>>>
>>> 2. Is there any example anywhere of how to use the Transform Object. Its
>>> not
>>> there in any of the ODE demos.
>>>
>>> 3. Will the transform object inherit all the geometrical properties
>>> (sides
>>> in case of a box) and behave exactly the same was as a (box) geom would
>>> have, or is there an unsaid difference of behavior somewhere.
>>>
>>> Thanks and Regards
>>> PKS123
>>>
>>>
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>>
>>
>>
>
>
```