Desktop VR

[eric.g]

My university group is working on a desktop VR system, which will use camera based tracking for interaction. I've looked through the available information about OptiTrack and it seems like a promising candidate for our needs, but I have a few questions about its capabilities:
How many 'objects' (i.e. markers) is the OptiTrack system capable of detecting?
Is it possible to maintain the 120fps frame rate when using multiple cameras?
Is there any extra processing that occurs when using multiple cameras?
When a new frame is acquired on a camera, what information is sent over the bus (e.g. just a notification, the entire image, just dot positions, etc)?
How is the synchronisation of multiple cameras handled?
At what frame rate can the images (if so desired) from the cameras be read?
Is there any news regarding the potential linux driver set?

[eric.g]

I'm a bit disappointed that this has not been answered in over 2 weeks considering other questions have been addressed.

[Birch]

Eric,
Let me see if I can address your questions :

• How many 'objects' (i.e. markers) is the OptiTrack system capable of detecting?The number of markers that the OptiTrack is capable of tracking depends on the size of the markers and the distance they are from the camera. For example, it can track at least 30 (if not more), 1/2 inch markers at a distance of 24 inches.
  .
• Is it possible to maintain the 120fps frame rate when using multiple cameras?
  Yes, the cameras maintain the 120 frames per second rate with multiple cameras arrayed.
  .
• Is there any extra processing that occurs when using multiple cameras?
  
  The marker information delivered by the SDK is not in X,Y,Z physical coordinate space, nor is the data from one camera correlated to data from another. The markers are delivered in X,Y imager pixel coordinates. So, there is no extra processing that is required for the basic marker acquisition when using multiple cameras. However, if you want to extract X,Y,Z coordinates from a marker which is seen by two cameras at the same time, then you will need to write an algorithm to resolve that information from the available data. --Note : You can use the Vector Tracking capability of the SDK to extract X,Y,Z,Roll,Pitch,Yaw information from a single cluster of three markers in a known configuration using a single camera.
  .
• When a new frame is acquired on a camera, what information is sent over the bus (e.g. just a notification, the entire image, just dot positions, etc)?
  
  Camera frames are delivered to the host PC as a 1 bit thresholded image. The marker position data is then computed from this information. It is possible to adjust the threshold value using the SDK.
  .
• How is the synchronisation of multiple cameras handled?
  
  There is no mechanism for exact camera synchronization, however the frames from multiple cameras will arrive for processing interleaved in the order in which they were received.
  .
• At what frame rate can the images (if so desired) from the cameras be read?
  
  The 1 bit thresholded image and/or tracked marker coordinate data can be extracted in real time at 120 frames per second from each camera. If you wish to sample at a slower rate, you may discard data.
  .
• Is there any news regarding the potential linux driver set?
  .
  We do not have any new information about the availability of Linux support at the moment, though we will share that information with our users if any becomes available.

[ August 20, 2005, 12:56 AM: Message edited by: NaturalPoint - Birch Zimmer ]

[yoshi]

Hi there,

I use six OptiTrack cameras with more than 30 markers. My system is Pentium 4, 3GHz, XP and I can get 120 fps from each cameras including the images without any problem. I got it to detect as many as 40 markers, I'm sure it can handle more, but I ran out of markers. I don't think there is synchronization mechanism. I record the system time as soon as the new frame comes in and use that to interpolate and get the approximate synchronization. Overall, this is a great product.

Hope this information is helpful.

[eric.g]

Thanks for the information. It seems like these cameras might be a good choice. Hopefully linux drivers will follow soon.