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Wind direction (Mag vs True)


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#1 Jasper Bussemaker

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Posted 29 August 2010 - 01:28 PM

Hi Peter,

In a new program I am creating I am reading the wind direction.
In you manual, it states that because of compatibility reasons the wind direction is magnetic below the surface layer, and true above it.

So I did exactly as I was supposed to:
Read offset 0EEE (and convert it into feet and then add the ground altitude, because 0EEE is metres AGL).
Then I read the wind direction and do the conversion to normal degrees.
Then I check if the A/C altitude is lower than the surface wind layer, if this is true I add the magnetic variation to the wind direction.
This way I should get the true wind direction, above and below the surface wind layer.

However, it seems that FSUIPC is always transmitting the true wind direction, even below the surface layer!

I am running FSUIPC v3.90 for FS2004.
Can you confirm this bug?

Greetings,
Jasper
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#2 Pete Dowson

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Posted 29 August 2010 - 01:59 PM

In you manual, it states that because of compatibility reasons the wind direction is magnetic below the surface layer, and true above it.

That refers to the old FS98 offsets, the ones remaining compatible with FS6IPC and FS5IPC (the FS95 version).

So I did exactly as I was supposed to:
Read offset 0EEE (and convert it into feet and then add the ground altitude, because 0EEE is metres AGL).
Then I read the wind direction and do the conversion to normal degrees.
Then I check if the A/C altitude is lower than the surface wind layer, if this is true I add the magnetic variation to the wind direction.

Is this actually what you are "supposed to do"? How do you work that out?

What wind direction are you reading? That will make a lot of difference, because there are separate FS98 offsets for surface wind, lower, middle and upper layer winds. Obviously the correction for "magnetic" direction only applies to one of those. If you are reading the wind direction BEFORE checking the latitude, how on Earth can you make sure you read the correct offset for the direction?

However, it seems that FSUIPC is always transmitting the true wind direction, even below the surface layer!

FSUIPC transmits nothing. It merely provides access to FS values.

I am running FSUIPC v3.90 for FS2004.
Can you confirm this bug?

What bug? I think you need to check what you are doing. You need to check the altitude in order to determine which offset to read. either that or, for wind at aircraft, read the ambient wind data.

Pete
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#3 Jasper Bussemaker

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Posted 29 August 2010 - 04:16 PM

Ok I'll state it differently.

This is what I want:
A variable containing the true ambient wind direction.

This is how I am achieving this:
I am reading the offset 0E92, which is ambient wind direction.
Your "manual" states this:

Ambient wind direction (at aircraft), *360/65536 to get degrees
Magnetic or True.

For compatibility with previous FS versions, the direction is
Magnetic for surface winds (aircraft below the altitude set into
offset 0EEE), but True for all upper winds. See offset 02A0 for
magnetic variation and how to convert.

I want to have a value of the ambient wind direction which always contains the true heading of the wind.
So if I am not wrong (correct me if I am wrong):
If the A/C is flying below the surface layer (0EEE), I have to convert the value read from offset 0E92 to true degrees.

This is what I see:
Even if the aircraft is BELOW the surface layer, the offset 0E92 still contains a TRUE heading instead of a MAGNETIC heading which you manual states.
Can you confirm this?

FSUIPC transmits nothing. It merely provides access to FS values.

So? You understood me or not?

Jasper
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#4 Pete Dowson

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Posted 29 August 2010 - 04:25 PM

This is what I want:
A variable containing the true ambient wind direction.

at the aircraft? Okay. That is 0E92. Correct.

So if I am not wrong (correct me if I am wrong):
If the A/C is flying below the surface layer (0EEE), I have to convert the value read from offset 0E92 to true degrees.

Okay. Understood, now I know you are reading 0E92.

This is what I see:
Even if the aircraft is BELOW the surface layer, the offset 0E92 still contains a TRUE heading instead of a MAGNETIC heading which you manual states.
Can you confirm this?

Not at present. I would need to load up FS9, which I've not done for a long time. Nothing about any of this has changed in many years, but I'll re-check for you when I can. I only have FS9.1, not the original release though.

Regards
Pete
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#5 Jasper Bussemaker

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Posted 29 August 2010 - 04:33 PM

Not at present. I would need to load up FS9, which I've not done for a long time. Nothing about any of this has changed in many years, but I'll re-check for you when I can. I only have FS9.1, not the original bugy release though.


Ok so you can confirm that in FSX it works like in the manual?

Jasper
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#6 Pete Dowson

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Posted 29 August 2010 - 04:48 PM

Ok so you can confirm that in FSX it works like in the manual?

FSX? Of course. Also in FS9, as I've just tested. See the pic below, taken at Seattle (mag var about 20 degrees!):

Posted Image

I think you must be making an error someplace?

Pete
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#7 Jasper Bussemaker

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Posted 29 August 2010 - 05:28 PM

Wow this is weird.
I just tested it the way you did as in the screenshot, and it seems that 0E92 always contains the magnetic ambient wind direction :o
Because as you can see in the screenshot, you are above the surface layer, so according to the manual 0E92 should contain the true heading (which should be 173 instead of 153!).

Disregard: 0EEE is in metres :P

Update:
Hmm sorry to have bothered you, it seems that everything is working fine now... :S
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