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Hi.

I have 3 OptiTrack cameras model FLEX:C120.

I have extended the grayscale sample in order to get the frame buffer of the 3 cameras.

I have modified the NP_OPTION_NUMERIC_DISPLAY_ON option, using a value of 2 (30 FPS), instead of the value 1 (60 FPS) in order to reduce the load of USB port.

The sample doesn�t work if I use the 3 cameras, but with 2 or 1 yes.

If I change the NP_OPTION_NUMERIC_DISPLAY_ON option using a value of 3, (15 FPS), the sample woks only during a moment. All displays show a little dot, (I suppose that it means that the camera works and send the frame buffer to the computer), and the cameras send the frame buffer to the computer. After a while the little dot of the display disappears and the camera stops sending the buffer.


What is the problem?
It is necessary to use any other option than the using in the example?


Thanks.

Regarding NP_OPTION_NUMERIC_DISPLAY_ON, do you mean NP_OPTION_FRAME_DECIMATION? Frame Decimation is the feature which controls transmitting only every Nth frame at the camera level.

Another thing you can do to optimize transfer greyscale data on a crowded USB bus is to slow the cameras down using the NP_OPTION_FRAME_RATE feature. It has the effect of spreading the frame transfer over a larger time period which reduces the load on the USB bus. I tested here and was able to get greyscale from 3 C120s on a USB hub (in the VC8b sample) using a frame rate value of 50% for each camera. Note that it will increase the amount of light the camera takes in, because it increases the duration of the exposure (you can reduce the exposure setting to compensate). You can use this feature in combination with NP_OPTION_FRAME_DECIMATION if you want to.

Another thing which can be done to improve the transfer performance is making sure the cameras are not sharing the same USB hub. Even better is spreading the cameras over separate root hubs or extra USB 2.0 cards.

You may also wish to review the FAQ entry on grayscale if you have not yet.
http://www.naturalpoint.com/optitrack/s ... q.html#q10

Hi.

Regarding NP_OPTION_NUMERIC_DISPLAY_ON, do you mean NP_OPTION_FRAME_DECIMATION?

Yes, I was wrong. The option is NP_OPTION_FRAME_DECIMATION.

I have change the option NP_OPTION_FRAME_RATE using a value of 50 (50%) and the sample works fine.

Thanks a lot.