correct as-is Low HUD refresh rate

[FusRoPotato]

I've been noticing that the refresh rate of the HUD overall is really low. I've measured that the HMCS updates at 60 and the HUD updates at 20. I'm not sure if this is a graphical issue or not because some other modules I have show 3D object animation also playing at 20 Hz (like doors and panels opening/closing), which is strange to see when the rest of the game animates at 120. I've come across a small number of references that say the HMCS supplies a 60hz refresh rate to the pilot, so I have no quarrel there. However, the HMCS is not responsible for drawing the HUD, but it's a piece of hardware I can find specs on.

While this means nothing regarding what the HUD's rate itself should be, I know for a fact something's off because one of the components of this rate has a SPEC requirement. All data sent to these devices to be displayed in numerical form are spec'd to display at an update of 4 Hz for readability per a MIL SPEC unless direction is changed, in which case it will update no later than 12ms later and the refresh rate following it is rephased. So for example, if you are holding near perfect altitude or velocity and the value bounces back and forth, you could visually see a high refresh rate "flicker" values, but in continuous decay or increase, it will only update at 4 Hz. However, in DCS, if appears like entire package updates at 20hz including bearing tape, target boxes, and VVI, components that were mandated to update visually by at least 60 Hz minimum in the mid 70's. Additionally, all numerical values are updating far more quickly than they are supposed to. I could try to measure that to be accurate, but no point really because it's obviously not 60 or 30. Examples of this can be found on any YT video of a DCS F-16 by counting frames using <> keys and I linked one at the bottom. 

This obviously can't be proven with YT videos of RL HUD tapes uploaded at 30 fps, but 30 is still far better than 20 and I also linked one of those below. 

What I can't seem to find is, what the update rate of the HUD is supposed to be. I suspect it either has to be 60 or 72 but can't find design specs exactly, but I see a lot of suggestion it was also mandated shortly after the F-14 due to performance studies, requiring it to be 60 Hz minimum. This doesn't necessarily mean the bus feeding the HUD with data had to be updated at 60 Hz, but we do know it's interpolated with the F-18's HMCS to display smooth motion at 60 Hz when receiving data at 20 Hz, similar to the F-16's HMCS.

Is this something that I can fix with a graphics setting? Is it just an early development hitch?

What is the HUD refresh rate supposed to be and how do you know?

References

METRIC (aerospacelightinginstitute.com)

Using Helmet Mounted Displays to Designate and Locate Targets in the Urban Environment (tennessee.edu)

MIL-STD-1553 Designer's Guide (milstd1553.com)

In the above video, numerical data updates at 4 Hz, while everything else updates at 30. However, the video itself is only 30 Hz so a 60 Hz display would not be seen.

I just realized the previous video was from a bit of a newer model F-16, so here's a much earlier Block 30 showing the same measurement.

 

In the above video, some (not all) of the HMCS components update at 60 Hz but the HUD only updates at 20 Hz. Careful when measuring in this video because there are slo-mo sections that will give smaller results.

Edited January 16, 2023 by FusRoPotato

[grant977]

You want to see low refresh come over to the Tomcat dark side.

[LowGlow]

Interesting. I never thought about the Viper's HUD refresh rate. The Tomcat's HUD refresh is horribly low (like 4 FPS?), but that's what it was in the real Tomcat I guess. even though I have never seen 4 FPS on Tomcat HUD tapes.

What disturbs me more is that HUDs in DCS in general look somehow unrealistic in VR with any module. I don't know what it is exactly, but with a real HUD you can clearly visually distinguish the HUD lines spatially from other visual content outside. In DCS you can't. Is it uneven translucency with the real HUD? Is it the reflection of the HUD screen surface? It should not be the sharpness, right? Because real HUDs in jets are set to infinity distance as well.

[FusRoPotato]

Yea, poor Tomcat. I don't know about 4 fps though. IIRC they had a refresh rate of 30 for the screen itself and an update rate of about 8 Hz for the bearing tape, vvi, and pitch ladder. It depended on the source of data and how much load was on that source, plus they went through a series of upgraded that kept improving on that performance. Some things like bank and the data input from AIM-9's however would come in at a much higher rate, so you could have this mix of things looking both smooth and jumpy at the same time. 

I trialed the F-14 for a bit but never took the time to really look at the HUD and see if the game represents reality or not. Spent most of my time trying to figure out Jester's IQ, but I've seen enough complain about update rates to know they tried to recreate it to some extent. 

[BIGNEWY]

please stay on topic here - F-16 HUD refresh rate, if you have any more evidence please Pm me.

thank you

[NineLine]

These videos will not work as evidence as any HUD recording is recorded at the VCR Hz, so such a video does not indicate the actual HUD Hz. If you have any other evidence, we would be happy to take a look. Thanks. 

 

[FusRoPotato]

On 1/17/2023 at 1:55 PM, NineLine said:

These videos will not work as evidence as any HUD recording is recorded at the VCR Hz, so such a video does not indicate the actual HUD Hz. If you have any other evidence, we would be happy to take a look. Thanks. 

 

It doesn't matter what frequency the VHS recorded at. If the recording shows 1-1 time scale and the HUD components shift at 30 Hz, then the HUD update rate is equal to or greater than 30. Sure it doesn't prove it's 60, but it proves 20 is wrong.

Your F16 has color MFDs. Those didn't come until 1996, therefor MIL-HDBK-87213 applies.

[FusRoPotato]

On 1/17/2023 at 1:55 PM, NineLine said:

These videos will not work as evidence as any HUD recording is recorded at the VCR Hz, so such a video does not indicate the actual HUD Hz. If you have any other evidence, we would be happy to take a look. Thanks. 

 

Mover made comments on this again today in his videos. Unless you have evidence or proof the huds ran at 20hz, I think you should just change it as suggested. 

If a 30 hz video shows something moving once every 2 frames, that means it's updating at 15 hz. If it changes once every 6 frames, that means its updating at 5 hz. If it updates on every frame, that means it's at least 30. All you have to do is measure the time span between what is seen as changing and invert it. All hud tapes for F-16's have horizon lines updating every frame at 30hz (because they update at least that fast), and numerical indicators such as velocity update every 4 or 5 hz. 

Last thing you're going to do by fixing this is piss someone off.

Edited May 12, 2023 by FusRoPotato

[Alpiinoo]

I don't understand why this hasn't been done yet.

[FusRoPotato]

8 hours ago, Alpiinoo said:

I don't understand why this hasn't been done yet.

I'd say why but the honest answer is worth about 40 badboy forum points.

[Stroke 3]

Not only the F-16s hud refresh rate is low, also the hud is missing the gyroscopic effect that the Jf-17 and F-18 has on their huds. 

E.g. When you roll you can see the pitch ladder not instantly moving  accordingly same with pitch. 

Edited August 5, 2024 by Stroke 3

[FusRoPotato]

They were allowed a 100 ms response delay as a result of any filtering. I don't know if that is what the delay ended up being exactly IRL or what is measures to in DCS, but those displays ran at 60 hz while receiving data at 20 hz. This required using a 3 point interpolator as a visual aid based on MIL-STD requirements at the time to produce a dynamic display defined as visually continuous (no less than 55 hz). Interpolating a 20 hz signal requires at least 50 ms plus some computation and routing time, thus the delay should be between 50 ms and the 100 ms limit.

MIL-STD-1472D from 1989 describes all these requirements, including that gross numeric presentations must not exceed an update rate of 5 times per second.

In the DCS F-16C HUD, everything updates at 20 hz. This is wrong and we can likely guess where that number came from. The bearing tape, elevation bars, reticles and target boxes were updated at a smoothed 60 hz from their 20 hz data input. The numbers displayed in boxes ( Velocity, altitude, and bearing ), all updated at 5 hz. This is also true for the HMCS. All components displayed in motion were required to be appear continuous.

A 30 fps HUD tape that shows a new elevation bar location on every frame may not prove that a display component should be at 60 hz, but it is solid proof that 20 hz is incorrect. A 20 hz display recorded at 30 hz will always show elevation and bearing tapes that sometimes do not change from frame to frame.

Edited August 6, 2024 by FusRoPotato

[Stroke 3]

Hope this is seen by NineLine.

[Stroke 3]

  Here in this video you can clearly see the huds refresh rate is much smoother/higher @FusRoPotato

[Silver_Dragon]

Someone has papers? no videos.

[Alpiinoo]

If you ask a real viper driver I'm sure he would say the same thing. Please consult your SMEs

[Raven (Elysian Angel)]

What always struck me is that RAZBAM modules have a much higher HUD refresh rate than ED modules. I don't know which is more realistic, but I do know higher refresh rates *feel* better on our monitors/headset displays since it makes gameplay feel smoother.

[FusRoPotato]

18 hours ago, Silver_Dragon said:

Someone has papers? no videos.

Videos are enough and there's no excuse not to accept them, but I've already listed the names of 3 specific documents older than their block that contain the relevant regulations.

Edited August 8, 2024 by FusRoPotato

[SkateZilla]

On 5/12/2023 at 7:14 AM, FusRoPotato said:

Mover made comments on this again today in his videos. Unless you have evidence or proof the huds ran at 20hz, I think you should just change it as suggested. 

If a 30 hz video shows something moving once every 2 frames, that means it's updating at 15 hz. If it changes once every 6 frames, that means its updating at 5 hz. If it updates on every frame, that means it's at least 30. All you have to do is measure the time span between what is seen as changing and invert it. All hud tapes for F-16's have horizon lines updating every frame at 30hz (because they update at least that fast), and numerical indicators such as velocity update every 4 or 5 hz. 

Last thing you're going to do by fixing this is piss someone off.

 

Technically VHS was telecined 29.976 Hz w/ 3 Interlaced frames for every 2 progressive frames typically PIPII or PIPIP depending on recording hardware.,

So 3:2 Pulldown would apply. 30 Hz moving every 2 frames would mean 20 Hz.

[Stroke 3]

Will the gyro effect of the hud be at least added?

[Stroke 3]

  Hud looks smoother.

Edited August 17, 2024 by Stroke 3

[Alpiinoo]

Improved with 2.9.11.4686

• Improved HUD Limited Refresh Rate (made airspeed, altitude and acceleration update rates fixed at a set refresh rate. As such, faster rates of change will result in skipped values. The acceleration updates are slightly faster than velocity and acceleration).