[simpits-tech] "Big sim" visit, and 25 frames per second.............

[Matt Bailey]

Now that makes some sense.....I bet I could cook up a plugin for
X-Plane that gives me a nice graph of time between frames. X-Plane has
a time-differential readout (sim time vs real time) but it is not
useful for observing trends. I could not handle 15fps I'm afraid! I
like my down-low VFR flying too much. :) Actually 45+ in X-Plane 10
looks great, even on a big projection screen.

The big sim I was seeing was keeping its FPS within 0.2 at all
times....quite impressive.

Matt

On Mon, 5 Aug 2013 18:36:45 +0000 (UTC)
wledzian1 at comcast.net wrote:

> The sims may only show 25 frames per second, but one of the
> requirements for certification of sim visuals is that this frame rate
> is rock-solid and reliable. Our home flight simulators don't have
> this requirement, so they can get away with stutters. You may see the
> frame counter telling you that you've got 40 fps, but you may get a
> few fast frames that look really smooth, with moments that it drops
> to 10-15 fps. Your eyes most definitely notice the difference. I
> typically run my sim locked at 15 fps even though it will routinely
> display 30FPS peaks, knowing that at 15 it will be steady, and will
> be an even divisor of the 60hz display frequency. It looks choppy
> when I'm low and fast, but then I'm not usually flying low and fast. 
> 
> Can I see a difference above 25fps? Sure. I used to play a lot of FPS
> games, and I could easily tell the difference between 60 and 100 fps.
> (aside - I really miss my ViewSonic CRT that could reliably do
> 1024x768 at 120hz). For the simulation world, slow and steady beats
> fast and choppy. 
> 
> -Wayne 
> ----- Original Message -----
> From: "Matt Bailey" <dabigboy at cox.net> 
> To: simpits-tech at simpits.org 
> Sent: Sunday, August 4, 2013 2:54:59 PM 
> Subject: [simpits-tech] "Big sim" visit, and 25 frames per
> second............. 
> 
> So this past week I spent probably an hour and a half climbing around 
> some big sims with the senior sim tech. It was REALLY cool, I gained
> a lot of insight and learned a lot about how these sims operate. The
> one thing that had me dumbfounded, however, was some of the
> frequencies the sims were running at. Most processes were running 7
> to 15hz (which is fine for something like radio tuning, or updating
> cockpit switch positions, for instance). The graphics, however, are
> running at a blazing 25fps. The graphics computer for this particular
> sim was running at 2 ghz (I didn't catch how many CPUs it had) and
> had 2g RAM. The sim tech was insistent that 25 is all the human eye
> can really see, and that yes, indeed, this was literally only putting
> 25 unique images on the screen per second. 
> 
> Now I have heard folks say no one can see the increase in rates above 
> 30fps or so, but I have always dismissed this, as I can assure you
> that 25fps on a PC flight simulator looks not-very-good. 40 is nice,
> but 60+ is what I really like to see. Above that, yep, can't tell
> much difference. I will say, however, that I have seen animations
> running at extremely high FPS that seem incredibly real because of
> their high refresh rates....this may have something to do with other
> graphic effects (like good antialiasing), but it seems to happen only
> with very high FPS animations (like the DirectX graphics tests, for
> instance). 
> 
> This has me stumped. Is it possible that our computers are lying to
> us? Could it have to do with the inconsistency/variation in frame
> rate (that is, not a consistent 25fps)? I have flown some of these
> big sims, and I don't recall the graphics looking slow or stuttery at
> all. 
> 
> I considered one other option, and this could be a clever way to gain 
> FPS: could it be that the actual graphic generators for these sims
> are intelligently adding frames? In other words, your main graphics 
> processor only has to calculate geometry, lighting, etc 25 times per 
> second, but the final piece of the graphics pipeline could be looking 
> at the most recent frames, and generating new frames based on the
> trend of the past few frames. Could this explain it? It doesn't seem
> likely, as the sim tech was quite insistent that 25fps is about all a
> human could detect, and was all they were running. Puzzling! 
> 
> Or, it could just be that the big sims would indeed look slow and 
> stuttery if they were stuck on a sharp, bright monitor instead of
> over a big projection system that blurs the image just a little
> bit...... 
> 
> Matt 
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