Dear Carsten, et al,
I just want to express a short 'thank you' for this information. Due to
other problems we still could not test it, but I intent to keep you
informed about success or failure.
thanks,
Martin
Carsten Neumann schrieb:
> Martin Wewior wrote:
>>>> [implementing headtracking]
>>> what does your setup look like, that is do you have an HMD, a (large)
>>> single screen, or a CAVE-like environment?
>> I'll provide some background information: We are developing a
>> cooperative visualisation tool, which is currently focused on desktop
>> rendering. ("We" are at the Regional Computing Centre of the University
>> of Cologne)
>>
>> This desktop tool should be enabled for VR-installations in general. But
>> the first step is a single screen (rear-projection, two projectors,
>> polarizing filters).
>> Currently we are using OpenSG 1.8. Using 2.0 is desired but not actually
>> planned.
>>
>>> What do you specifically want to know about the ProjectionCameraDeco?
>>> Basically it works by defining a projection surface in the coordinate
>>> system of the decorated camera and the user position relative to the
>>> decorated camera. So data from your headtracker influences the user,
>>> while to navigate around the scene you'd modify the camera's beacon.
>> We have implemented stereo projection using
>> ShearedStereoCameraDecorator-objects decorating the camera. Which works
>> as expected. Reading further, we came across this directions
>>> http://www.opensg.org/htdocs/doc-1.8/PageSystemWindow.html#PageSystemWindowCameraDecoratorsStereoProjection
>> In theory it is obvious, what needs to be done.
>> We studied
>>> http://www.opensg.org/htdocs/doc-1.8/classosg_1_1ProjectionCameraDecorator.html
>> and could not distil the relevant information:
>>
>> 1) According to the description the corners of the projection screen
>> have to be set. Which function needs to be used to to so?
>
> something like this should do it:
>
> Pnt3f screen_pnts[4];
> ProjectionCameraDecoratorPtr pcd;
>
> pcd->editMFSurface()->push_back(screen_pnts[0]); // lower left
> pcd->editMFSurface()->push_back(screen_pnts[1]); // lower right
> pcd->editMFSurface()->push_back(screen_pnts[2]); // upper right
> pcd->editMFSurface()->push_back(screen_pnts[3]); // upper left
>
>> Which
>> coordinate system/units have to be used?
>
> hm, I don't remember exactly, but using the same coord system/units that
> the tracking data for the users head is in would make sense.
>
>> 2) From the tracking system we obtain coordinates of the user's eyes in
>> mm from an arbitrary origin.
>
> this is arbitrary, but fixed and known?
>
>> This has to be passed to the system in coordinates relatively to the
>> camera. So there has to be a node, which is a child of the
>> camera-beacon. This is transformed(translated/rotated) corresponding to
>> the position of the tracked user to the centre of the screen?
>
> yes, create a Node (userBeaconN) with a Transform core, make it a child
> of your camera beacon and pass it as the user beacon:
>
> camBeacon->addChild(userBeaconB);
>
> pcd->setUser(userBeaconN);
>
> If you write your tracking data to that Transform core it is used as an
> offset from the camera position to give you the correct shape of the
> frustum.
> Basically the idea is that changing the camera beacon allows you to
> navigate your scene, while changing the "user" accounts for the head
> tracking.
>
>> There are private functions which seem connected to this (e.g. NodePtr
>> &getUser(void) ) but I do not see how the actual implementation should
>> be done, i.e. how and which functions need to be utilised.
>
> getUser() is public in ProjectionCameraDecoratorBase as well as the
> other field accessors (surface, width, height).
>
> Cheers,
> Carsten
>
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