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[BUG] - wrong altitude


apocom
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Hi,

 

a small bug I've found while testing the radar. My altitude is displayed false. Maybe that has ingame reasons, but I don't think there is a way that the altitude of my target should be displayed correctly. Both planes are set to 5000m ASL and I'm flying over the sea (which shouldn't matter at this altitude)

2015-11-08_00003.thumb.jpg.283829a4f70a5f508cae03071f01b1e8.jpg


Edited by apocom
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This may or may not be a bug. It depends on what method the tracking system uses to measure altitude.

 

I may have this backwards but I believe that the Mission Editor, external F2 view, and what your image shows as the target's altitude are barometric altitude reported as QNE. In the cockpit, in its default setting, your baro altimeter and (consequently) the HUD display barometric altitude as QNH. The former uses standard pressure as the reference point. The latter uses mean sea level.

 

The question, of course, is what reference point does the tracking system use. And, of course, there's the added possibility that I'm completely off base and all these discrepancies are bugs. :)

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Just to confuse things further, the barometric altimeter, when calibrated to QFE, can under certain circumstances show a different altitude to the HUD... :huh:

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Just to confuse things further, the barometric altimeter, when calibrated to QFE, can under certain circumstances show a different altitude to the HUD... :huh:

:) No confusion. QFE is a height (above a specific location), not altitude, calculation. :)

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:) No confusion. QFE is a height (above a specific location), not altitude, calculation. :)

 

Ah, OK, I didn't know that but it makes perfect sense that QFE is used at airfields as they're by definition fixed positions, hence it helps when you're taking off or landing at one to get the pressure / altitude measurement above that fixed position.

 

Thanks, that's really clarified for me what QFE is supposed to be :thumbup:

 

Edited to add: So, I just read the wikipedia article on Q codes and now I'm even more confused :confused: I can understand that quoting QFE to a pilot on approach to an airfield makes perfect sense, but for a pilot about to take off shouldn't the tower use QNH instead?


Edited by DarkFire

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...I can understand that quoting QFE to a pilot on approach to an airfield makes perfect sense, but for a pilot about to take off shouldn't the tower use QNH instead?

I don't know. The QFE would be useful to have in case of an emergency return to the runway, I suppose. But I'm afraid we're hijacking poor apocom's bug report.

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I don't know. The QFE would be useful to have in case of an emergency return to the runway, I suppose. But I'm afraid we're hijacking poor apocom's bug report.

 

Ah, yes we are :doh:

 

That's definitely a bug given that the two aircraft are at the same altitude.

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Ah, yes we are :doh:

 

That's definitely a bug given that the two aircraft are at the same altitude.

:) Only if the radar tracking system and cockpit baro altimeter are supposed to be using the same "Q" reference. That's what we don't know.

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:) Only if the radar tracking system and cockpit baro altimeter are supposed to be using the same "Q" reference. That's what we don't know.

 

Ok, we don't know this, but it just makes no sense to use different values here.

The Su27 handbook references for your own altitude with barometic altitude, and for the target simply with target height.

 

8 – Высота цели.

9 – Высота барометрическая текущая

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Ok, we don't know this, but it just makes no sense to use different values here.

The Su27 handbook references for your own altitude with barometic altitude, and for the target simply with target height.

 

8 – Высота цели.

9 – Высота барометрическая текущая

 

Высота цели instead of bысота барометрическая цели. The difference could just be to save space in the diagram or it could be a meaningful difference.

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Just for chuckles, I've been playing around with the ME in an effort to understand why the values are different. What I've discovered is that the ambient temp set for the mission makes a big difference in how divergent the ME and F2 View values are from what's displayed in the cockpit. It also effects the direction of the divergence.

 

In other words, the cockpit barometric altimeter takes different temperatures into account. The ME and F2 views do not. The latter use a standard value of around 14 C. I have not taken the time to check if the reported locked target altitude follows suit.

 

If you change the mission temperature to 14* C, everything matches through 3830 meters. After that things diverge slightly. At 8000 meters, you'll see 8020 m in the cockpit. Above and below the 14 C temperature, the two diverge. The greater the mission temperature differs from 14 C, the greater the divergence between the ME/F2 values and the cockpit values.

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That makes sense I guess - the aircraft's instrument presumably is impacted by temperature (in turn affecting measured atmospheric pressure), but the ME & F2 are just telling you where the object is.

Do they diverge the right way - does the altimeter read low if it's cold & high if it's hot ?

Equally interesting - does the weather engine impact the displayed altitude - does barometric altitude hold result in different true altitudes if you fly from a 'high' to a 'low' placed in the ME ?

Cheers.

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That makes sense I guess - the aircraft's instrument presumably is impacted by temperature (in turn affecting measured atmospheric pressure), but the ME & F2 are just telling you where the object is.

That's what I'm thinking as well. I haven't checked yet to see if the same applies to the OP's "bug".

Do they diverge the right way - does the altimeter read low if it's cold & high if it's hot ?

They do diverge in the right direction but it's the opposite of what you're thinking. Higher baro pressure with cold air and lower with warm. And that's what happens in the sim with the crossover point being 14 C.

Equally interesting - does the weather engine impact the displayed altitude - does barometric altitude hold result in different true altitudes if you fly from a 'high' to a 'low' placed in the ME ?

That would be interesting to check. :)

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In F2 exterior view i don´t know the reference DCS is taking. The same for the editor but incockpit the Indicated Altitude never would be corrected-affected by exterior temperature. A change in the editors temperature never could change the HUD-Altimeter Indicated Altitude at the same QNH.

Correctly or incorrectly, the cockpit altimeter is effected by the temperature set in the ME. And that's what has been puzzling me. I couldn't find any reference to indicate that temperature should play the factor it does.

 

The ME uses 14 C as a "standard temperature" when setting turn point altitudes. And that seems to be what is displayed in the F2 View as well.

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Correctly or incorrectly, the cockpit altimeter is effected by the temperature set in the ME. And that's what has been puzzling me. I couldn't find any reference to indicate that temperature should play the factor it does.

 

The ME uses 14 C as a "standard temperature" when setting turn point altitudes. And that seems to be what is displayed in the F2 View as well.

 

14* is very close to being the seal level temperature value of an ICAO standard atmosphere. I wonder if that's what the game engine as a whole is calibrated to?

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14* is very close to being the seal level temperature value of an ICAO standard atmosphere. I wonder if that's what the game engine as a whole is calibrated to?

I noticed that, too. But why not use 15 which is the ICAO standard? In fact, 15 was the 2nd number I experimented with. 0 C was the first.

 

EDIT: So it appears that our "junior member" apocom might just be right and there is a bug. :)


Edited by Ironhand

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Realized this morning that what we are seeing is more or less correct. I've just been conceptualizing it backwards. I also found an interactive website that allowed you to enter the altimeter displayed altitude and sea level temperature and it provided your real altitude. While the numbers don't match exactly, it basically agreed with what we see in the sim.

 

Weta43,

 

Used the dynamic weather in the ME this morning and placed my aircraft at different points on the map. There were definite variations on the baro altitude displayed as I moved around the pressure systems.


Edited by Ironhand

YouTube Channel: https://www.youtube.com/channel/UCU1...CR6IZ7crfdZxDg

 

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Realized this morning that what we are seeing is more or less correct. I've just been conceptualizing it backwards. I also found an interactive website that allowed you to enter the altimeter displayed altitude and sea level temperature and it provided your real altitude. While the numbers don't match exactly, it basically agreed with what we see in the sim.

 

Weta43,

 

Used the dynamic weather in the ME this morning and placed my aircraft at different points on the map. There were definite variations on the baro altitude displayed as I moved around the pressure systems.

 

Oooh that sounds useful! Could you post the URL for the web site?

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Oooh that sounds useful! Could you post the URL for the web site?

Altimeter Error Calculator You'll have to do some converting because, while it used Celsius for temperature, it used feet for altitude. Like I said, it's not an exact match for what we see in the sim but it's all in the right direction. Set the airport altitude to "0" and type in the cockpit baro altitude in the "Indicated Altitude" block. The answer approximates what we see in F2 or, if you're low enough, the radar altimeter.

 

I checked this morning and saw that the radar altimeter and F2 values are identical. I take that to mean that the ME, F2, and radar altimeter are all displaying the "real" sim altitude based on a "standard" temperature (of some sort).

 

And judging from the OP's screenshot, so does the radar. That being the case, why go through all the extra calculations? It seems that it would use the baro altimeter value and, with angle and range information, compute the target's altitude. If that were the case, then the target in the screenshot should have the same altitude value we see on the HUD. Unless, of course, I'm missing something important. I feel like I've been all over the map with this as I've tried to learn enough to know how all the pieces fit together.

 

Since my previous post I've run into another great looking site that I have yet to fully explore: Luizmonteiro.com/Altimetry. Be sure to check the tabs on the left. Some interesting stuff there.


Edited by Ironhand

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Very interesting, thanks! :thumbup:

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  • 3 years later...

So basically the ME's altitude is simply the vertical axis position, or "radar altitude"

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So basically the ME's altitude is simply the vertical axis position, or "radar altitude"

 

Depends on what you choose: AGL or MSL.

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