Couldn't Capture Synchronous frames from two Realsense Depth cameras D435i
We are using two Intel Realsense Depth Cameras D435i for capturing the synchronous frames.
Trying to capture the same picture of the milli second timer running on our mobile camera with both the cameras while applying the external sync signal.
Our understanding is that both the camera's will capture the frame at the same time at the rising edge of the external sync pulse (>100uS pulsewidth)
We could set RealSense devices into different modes (Master, Slave, Full Slave, GenLock) easily but we couldn't able to capture the images at the same time on both the cameras with an accuracy of few milli seconds either with internal / external sync signal.
Always we are observing a difference of 50 to 100 milli seconds in the captured mobile timer image when cameras are set with 6FPS.
There are some whitepapers available in the Intel website and we are exactly sending the external sync signal inline with the website details yet we couldn't able to capture the frames from two cameras at the same time.
https://dev.intelrealsense.com/docs/external-synchronization-of-intel-realsense-depth-cameras
Could some one help us to understand the exact method to capture the synchronous frames using the external sync signal.
Thank you,
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Hello Sandeep,
There are several things you can try:
- Make sure to use the latest FW. There was a bug in older FWs that 6fps sync does not work. Or use a higher frame rate, e.g. 15 fps.
- Use Master and Slave for the two D435i. Don't use Genlock mode.
The difference between the two cameras should be less than 1us.
Sincerely,
Jesus G.
Intel Customer Support -
Hello Jesus,
Thank you for your reply.
Could you please provide your feedback on the below 4 queries:
1) By using Master and Slave, Do you mean connecting the two cameras using the external connectors Pin 5 (Sync ) and Pin 9 (GND)2) If we are syncing 4 cameras, then which is more recommended, setting cams to master/slave or all in full slave mode or genlock.3) Is there any dependency of sync on librealsense sdk version. we are using version2 so hopefully it should be fine4) Could you please confirm on the color to color stream sync.It is mentioned that it will be less than 1usec. Could you please confirm if it holds true for color to color streamThank you,
Best Regards,
Sandeep
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Hello Jesus,
Additional to above 4 points, i missed to mentioned the below point:
5) We connected two real sense cameras earlier using the external connector Pin 5 (sync) and Pin 9 (GND). One camera is set as master and another as Slave / Full slave. Both were set with 6FPS.
In this case, the captured images are not in sync . We will try to repeat the same with the higher frame rate.
https://dev.intelrealsense.com/docs/multiple-depth-cameras-configuration#section-e-external-trigger
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Hello Sandeep,
I apologize for missing a very important detail in your first post. It is impossible to sync RGB streams across D435-based cameras because the RGB sensor is physically on a separate board from the depth sensors and the sync pin is not connected to it. On D435/D435i cameras, only depth streams can be synced across multiple cameras.
You should use the latest version of librealsense.
Sincerely,
Jesus G.
Intel Customer Support -
Hello Jesus,
Thank you for your feedback.
Can you please suggest any other possible work around to sync the RGB colour frames for D435/D435i cameras. It is quite important for us in the current stage to sync the RGB streams using the Realsense Depth cameras D435iAdditionally, Could you please suggest a method to test the sync of depth frames from 2 cams?Is there any other version of D435/D435i cameras where we can sync the colour frames ?Thank you for your support,Best Regards,Sandeep -
Hi Sandeep,
It is impossible to sync the RGB color frames for D435/D435i camera since the RBG and Depth Sensor are on different PCB. The D435 only has depth sync. There is no other version of the D435/D435i camera that can do that. This is only possible with the D415 camera since the RGB and Depth Sensors are on the same PCB board.
Regards,
Aznie
Intel Customer Support -
Hi Sandeep,
You can refer to this article on how to sync the D435 via hardware. Hence, there is a whitepaper on External Synchronization of Intel® RealSense™ Depth cameras that might be helpful to you.
Regards,
Aznie
Intel Customer Support -
Hello Aznie,
Thank you for your feedback. I am sorry if my question is bit confusing. I will try to further elaborate.
We are clear about the hardware sync procedure (Connecting multiple cameras together and also with external sync) right from the beginning.
We have gone through the whitepapers multiple times related to the external sync and also have applied the external sync exactly as per the recommendation from the whitepaper. We have also connected two cameras via the external sync connector and have set one as master and other as slave.
We were actually looking for RGB sync and It is clarified in this thread that the RGB colour sync is not possible with D435 / D435i and only depth sync is possible by connecting multiple cameras.
My query is that how could we ensure that the depth sync is working after connecting the multiple cameras (by setting one as master and others as slaves)
Thank you for your support,
Best Regards,
Sandeep
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Hi Sandeep Tammana,
In section 3 of the Multi-Camera Configuration paper explains:
Now to the somewhat counterintuitive aspect of time stamps. If NO HW sync is enabled, the timestamps will now surprisingly appear to be perfectly aligned. This is because each individual ASIC is counting the exact same number of cycles between frames, and then sending them off. So according to their own timelines, they are sending frames at say, exactly 33.333ms intervals, for a 30fps mode. By contrast, if HW Sync is enabled, the timestamps will actually drift over time. You might expect this drift to be on the order of less than 1ms/minute. Knowing this, you can actually validate that your sync is working by looking at the drift in the difference of the timestamps. If you see NO DRIFT, then there is NO HW sync. If you see DRIFT, then the units are actually HW synced.
Regards,
Aznie
Intel RealSense Customer Support
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