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Jasper Bussemaker

Weird values when accessing Whiskey Compass offset

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Hi Pete,

I today decided that the GPS60 should get an update.

One of these updates include the heading:

I want to use the Whiskey Compass value instead of the Heading value, because the Whiskey Compass gives the correct heading when viewing it in Google Earth.

BUT:

When I access the 02CC value (Whiskey Compass), which does display right in FSInterrogate!, I get a value waaaaayyy to high. :?

And when I examined it further, the value seemed to depend on the altitude!

When I climbed, the value increased, when I descended, the value decreased.

I access the 02CC value the same as I do for the Longitude value (which is also a FLT64).

And this is where the next weird thing comes in:

In FSInterrogate, the lat and lon display wrong values. :o

But my GPS60 does log the flight at the right place, so apparently the GPS60 ís getting the correct lat and lon values...

So:

GPS60 gets wrong Whiskey compass value, FSInterrogate gets the right.

GPS60 get right lat/lon value, FSInterrogate gets wrong values.

Weird!!

FSInterrogate also states that the format of the Whiskey Compass value is just plain degrees, but I think that is wrong.

Can you confirm this?

Greetings,

Jasper Bussemaker

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I want to use the Whiskey Compass value instead of the Heading value, because the Whiskey Compass gives the correct heading when viewing it in Google Earth.

But that compass reads incorrectly when you are turning, or banking. it is only reliable when flying level.

For a correct Magnetic Heading you should take the True heading and adjust it using the Magnetic Variation, exactly as documented.

When I access the 02CC value (Whiskey Compass), which does display right in FSInterrogate!, I get a value waaaaayyy to high. :?

You are not reading it correctly then. As documented, it's a 64-bit (i.e. 8-byte) double floating point value. Are you reading into such a variable?

And when I examined it further, the value seemed to depend on the altitude!

When I climbed, the value increased, when I descended, the value decreased.

Yes, because it's a magnetic disk floating in oil or alcohol and is influenced by G-forces etc. fly straight and level to get a proper reading, as in reality!

I access the 02CC value the same as I do for the Longitude value (which is also a FLT64).

No, the Longitude value at 0568 is NOT a FLT64, it is a 64-bit integer (__int64, or a long long, depending on your compiler).

In FSInterrogate, the lat and lon display wrong values. :o

FSInterrogate cannot handle 64-bit integers, so it shows you the upper 32 bits, dividied out, and separately the adjustment in the other 32 bits.

Weird!!

No. You are simply not reading the documentation properly. There's a lot of difference between 64 bit floating point and 64-bit integers, just as there is between 32-

FSInterrogate also states that

Why on Earth are you using some data files concocted for FSInterrogate as documentation when I spend so many hours making sure that the true documentation for the offsets is complete, accurate and up to date! PLEASE USE THE DOCUMENTATION SUPPLIED!

Regards

Pete

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Hi Pete,

Here, when I use the true hdg, I get this in Google Earth:

GEWrong_TrueHDG.jpg

And as you see, this is wrong...

But I found out it was a calculation error in my code :( :roll:

So now it is working correctly...

I'm sorry again for making myself stupid. :(

Greetings,

Jasper Bussemaker

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