I am trying to build a raspberry pi device that will take a stereoscopic picture of a moving conveyor belt by simultaneously taking a photo from two separate cameras. Since the image is constantly changing, the images need to be taken close to simultaneously. What is the best way to accomplish this with a raspberry pi? I would like to use picameras, but I am limited by the single CSI port. I have been researching ideas such as:

Which of these options should I purchase and explore further? Do you have any incite into using any of these options? Do you have any other ideas that could accomplish this goal?

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    You need to define the scale of "simultaneously". I believe relativity theory implies there is no such thing in meaningful terms ;) So, within a nanosecond? Within 100 ms? Even a device with two cameras attached may not be able to guarantee that they take a picture "simultaneously". The context implies that wireless communication between separate devices should be fine -- it is certainly "instantaneous" on a human scale. – goldilocks Jun 8 '17 at 16:45
  • It does not need to be perfectly simultaneous. I only need an error less than roughly one tenth of a second. Until I test one these methods, I will not be able to know exactly how small that error needs to be. I just want to know if anyone here has any relevant experience or useful insight into any of the aforementioned technology. – RaptorT Jun 8 '17 at 20:36
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    You can check your network latency with, e.g., ping. Here I notice it's ~2 ms roundtrip from my laptop via air, through a router to a wired pi. So if you wanted a latency of ~100 ms, doing it over a network like that would not cost much time. – goldilocks Jun 8 '17 at 20:40
  • The compute module is basically simultaneous. When the two cameras are started, they are in near perfect sync, and the two CSI ports simultaneously stream frames to the GPU. Eventually they'll drift out of sync because both cameras are using their own clock (there's no central clock controlling them both) but the drift is sufficiently slow that it takes hours to be noticeable and simply restarting the dual-cameras re-syncs things. – Dave Jones Jun 9 '17 at 8:55
  • Thank you for that input. The device needs to be able to work without a network connection, and it needs to run for many hours on end (ideally 24) taking pictures as frequently as every 5 seconds. Could you re-sync the cameras in that 5 second interval? It's alright if it has to take a minute break every hour or so to restart, but I want to know if it's capable of avoiding that. Thanks. – RaptorT Jun 9 '17 at 14:01

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