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SimConnect Visual Frame Timing

P

pilotjohn

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32
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unitedstates
I'm pulling some data via RequestDataOnSimObject every visual frame. I'd like to know the exact time the data was "synthesized" within FSX to be able to interpolate between values (to both normalize and precisely calculate certain behaviors).

Locally timing arrival is the simplest method, but this may not always provide the correct results (network jitter etc.). SimConnect variables seem only to provide one second granularity (e.g. absolute time) which is useless when I'm getting 30+ events per second.

Pulling lat/lon and speed, and then calculating time between frames is also a possibility, but without knowing precisely when these are populated internally, it likely won't provide enough precision.

I also noticed SubscribeToSystemEvent Frame, which provides frame rate data, but again, it can arrive at delayed intervals and no guarantee to be in sync. with other SimConnect data. Also, the FPS measurement details are missing, so it's not known whether it is instantaneous (thus measuring the elapsed time from the last frame - which would be great) or averaged.

Has anyone looked at this problem and found a solution?
 
Hi,

You can't use per-frame to calculate trends as the frames are NOT guaranteed to be generated equally spaced.

You need to check the parameters from FS on a regular basis and independent of frame rate.

Best regards,
Robin.
 
3-2-1-Now said:
Hi,

You can't use per-frame to calculate trends as the frames are NOT guaranteed to be generated equally spaced.

You need to check the parameters from FS on a regular basis and independent of frame rate.

Best regards,
Robin.
Click to expand...

I'm aware of that, which is why I normalize the data based on the actual time difference between frames. However, this is where the problem starts. Measuring such frame delta time locally may not be valid because of propagation delays and jitter. Therefore I'm looking for some way to figure out what the frame delta might be from within FSX. Ideally, it would be nice if there were a "Milliseconds since Load" simulation variable, but there isn't. Thus my post asks if anyone has found a solution to reliably measuring frame delta.
 
Hmm - I appreciate your issue with the network delay, but I think you are asking a very difficult question. I know that previous it has been attempted to determine trend in real-time on the local computer in FSX with disastrous results because of the nature of the fact that neither FSX nor the OS are real-time.

Maybe you should request the data e.g. every 1/4 sec and use that? It will smooth out any jitter and make any trends more reliable, whilst continuing to use the per frame data for current state.

Best regards,
Robin.
 
Last edited:
3-2-1-Now said:
Hmm - I appreciate your issue with the network delay, but I think you are asking a very difficult question. I know that previous it has been attempted to determine trend in real-time on the local computer in FSX with disastrous results because of the nature of the fact that neither FSX nor the OS are real-time.

Maybe you should request the data e.g. every 1/4 sec and use that? It will smooth out any jitter and make any trends more reliable, whilst continuing to use the per frame data for current state.

Best regards,
Robin.
Click to expand...

There's definitely a difference in data between a networked client and a local client. A 1/4 second granularity is not adequate, but perhaps I can requests data at both at 1/4s intervals and every visual frame, and try to sync up. It might be worth some experimentation...
 
I do not know if it helps here, but I have used the invers of the frame rate returned from the frame event, and then smoothed with a function
time=a*newrate+(1-a)*time, with a=0.1 or whatever suits. This is a function that will not get out of control case a single frame gets far too late, but adaptes to trend changes fast enough.
 
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