[Paraview] VRPN Setup

[Aashish Chaudhary]

Hi Sean,

On Tue, Jul 24, 2012 at 10:39 AM, Sean Delaney <sdelaney at cp.dias.ie> wrote:
> Hi Aashish,
>
> Thanks for your comments. To my knowledge, there is no reason why the eye
> separation must be specified in the same units as the raw tracking data.

Lets suppose they are not in the same units, in that case we would
have to provide an API to inform an user what these numbers mean. Also
any time we perform any calculation, we would have to check the units
first before we
compute any numbers. Now if we provide an API to set eye in mm or cm,
but internally always store it in meters (and hence everything else),
that could be worked out as well. When you are not tracked, an eye
separation of 0.06 assumes that your data is in meters but when you
are tracked they both need to be in same reference system or else it
would not be a good experience for the user.  In a VR environment, you
mostly always have a real measurement (feet, inches, or meters are
most common).

> Paraview never uses my tracking data in its raw state. The tracking data is
> transformed to my chosen "world" coordinates before it is used for graphical
> calculations. These "world coordinates" are the ones in which my screen
> geometry is defined. I believe that the eye separation should be defined in
> these "world" coordinates.

It is. If you transform your tracker data, then you would have to
adjust your eye separation as well.

>
> I agree that the scene should be scaled to fit the world coordinates, and
> then the eye separation will fit automatically.

>
> In practice, it doesn't matter whether Paraview requires the eye separation
> to be specified in tracker units or world units because the two are related
> by a fixed scale factor. Users simply need to know which units Paraview
> expects.

Like I said ParaView has no notion of units. So  it really depends on
the user to define a system and stick with it.

 In my opinion, it's simpler if everything is defined in world
> coordinates. Of course, many users use the same units as the tracker for
> their world coordinates, in which case, the point is moot.

Sure.

>
> Would you agree with the above? Or have I perhaps overlooked something? I'm
> not coming from a graphics background, so I may have misunderstood
> something.

No problem. Hope my explanation makes sense. Let me know if I miss something.

>
> Seán
>
>
>
>
>
> On Tue, Jul 24, 2012 at 2:29 PM, Aashish Chaudhary
> <aashish.chaudhary at kitware.com> wrote:
>>
>> Hi Sean,
>>
>> >>
>> >> By the way, I may have found a bug / feature. It seems like I have to
>> >> specify the eye separation value in mm, even though I have transformed
>> >> my
>> >> tracker units to metres in the state file. Perhaps this is another
>> >> mistake
>> >> in my configuration though. Please let me know if that's the case.
>>
>> If you tracker data is in meters, you should keep the eye separation
>> in meters too. In general I keep the eye separation to 0.06 meters (6
>> centimeters). Now if your object is tiny, you may feel like too much
>> eye separation because now the object has to be really close to your
>> eyes and hence larger eye separation. I would recommend that you scale
>> you scene (objects) appropriately (to make them of a particular size
>> in terms of bounds).
>>
>> Hope this helps.
>>
>> Thanks,
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>



-- 
| Aashish Chaudhary
| R&D Engineer
| Kitware Inc.
| www.kitware.com