GPS Flash device for precise timing

[admin]

Hi Steve,

most cameras do not report dropped frames from their SDK, meaning that any dropped frames reported by SharpCap are a result of the SharpCap code detecting something anomalous (timeout fetching frame data, etc). The exception to this is ZWO where the SDK does report dropped frames, although there is no guarantee of how this is implemented internally.

For QHY cameras with GPS, the frame has a sequence number, so SharpCap will flag a dropped frame if there are missing sequence numbers. In the QHY case, the sequence comes from the GPS hardware/FPGA, so we know it's not a number generated in software on the PC. I don't know if other cameras have this sort of feature (never really considered it before), but even if they do, unless it comes from the hardware it is not much use.

Note that SharpCap may flag dropped frames for a lot of causes not related to the camera (for instance if you have some image processing active and it takes longer to process a frame than the gap between consecutive frames). To see the details, you can check out the SharpCap log which records the number and types of different categories of dropped frames from time to time.

cheers,

Robin

[SteveP]

Robin,

This is very helpful - exactly what we need to know. In my view, the ideal metadata would be an exposure start clock time (based on the camera's internal clock). QHY's sequence number is the next best choice and very useful. The dropped frame count from ZWO might be useful but, as you say, we would need to know a lot more about the internal implementation.

One more related question:
Do many cameras include exposure duration or cadence (fps or time between exposure starts) as part of the metadata from the camera+driver? Or do you have to keep track of this in Sharpcap (via the camera settings) and "add" this metadata to the file?

Thanks again,
Steve

[admin]

Hi Steve,

basically the only cameras that provide any timing metadata at the moment are the QHY and Moravian cameras with the GPS built in (or the GPS addon - some QHY models). Everything else is sourced from within SharpCap. (Note - for clarity, frame index numbers on QHY camera are only available for the GPS models).

There may be some possibilities to get more data from the cameras in some cases - the ZWO SDK has some function calls to get GPS related info, although I have not yet seen a GPS enabled camera from them. The SDK used for ToupTek made cameras (which includes a number of other brands) has a way to get some additional info with each frame, but it's not clear whether all data is available for all models of camera or not - I would have to do some testing on that.

cheers,

Robin