[Imstk-developers] Rendering interpolation/extrapolation

[Sreekanth Arikatla]

Hi Alexis, Nick,
                 In our case i think the first thing we should do, which is
easy, is to make the time step dT used by the physics module adaptive. It
should be the set to the delta T that is measured in terms of the wall
clock time between two successive physics solves. Once this is done we
encounter the problem that Nick had mentioned.

In that case:

   1. If the lowest frame rate amongst all of physics objects is more than
   30 Hz then we shouldn't observe much of a difference (unless we are dealing
   with haptics).
   2. If the lowest frame rate amongst all of physics objects is less than
   30 Hz then we will observe something like stop motion animation. In that
   case we need to probably use one of the options suggested from the link:
   extrapolation or interpolation. Extrapolation might work if there is no
   sudden and drastic change in direction of motion of parts of the scene else
   you will see artifacts. If we choose interpolation, then i think we are
   forced to lag by one time step and also choose the linear interpolation
   constant (slope) adaptively. This could work but I myself have never tried
   this. One problem I see is that if the frame rates are really low like 4fps
   then if the user tries to interact with the objects, they will observe the
   lag of one time step enforced by the method. If it is not interactive it
   should be fine I guess.

Implementation wise adaptive time step and interpolation/extrapolation
should not be very difficult. Its a good discussion to have. Let me know
what you guys think.

Thanks.



On Tue, Nov 29, 2016 at 11:39 AM, Alexis Girault <alexis.girault at kitware.com
> wrote:

> Sreekanth, what's your take on our possible update rate for the physics
> modules?
>
> Alexis Girault
> R&D Engineer in Medical Computing
> Kitware, Inc.
>
> http://www.kitware.com
> (919) 969-6990 x325
>
> On Tue, Nov 29, 2016 at 11:02 AM, Milef, Nicholas Boris <milefn at rpi.edu>
> wrote:
>
>> How are we handling different update rates from the physics modules in
>> the rendering? I imagine this will be a pretty severe problem for physics
>> modules with low update rates.
>>
>> http://gamedev.stackexchange.com/questions/12754/how-to-inte
>> rpolate-between-two-game-states
>>
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-- 
Sreekanth Arikatla, Ph.D,
Senior R&D Engineer,
Kitware, Inc. <http://www.kitware.com>, Carrboro, NC.
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