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F10 map Bullseye offset bug.


ron533

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Hi,

Maybe it was reported before, but I couldn’t find it...

I recently tried an offset from bullseye training which gave me a huge error using the F10 map in the Caucasus area. It did not repeat in the Persian Gulf map.

 

For example, Bullseye is west of Zugdidi in a small island in the river by default,

via the F10 map ruller I draw a line to the practice airfield below Kobuleti,

The heading and distances is 170 for 40 miles.

Offseting that in the CDU gave me the offest mission point west of the airfield,in the sea...

way to far for the expected error.

Hook from bulls in TAD - showed a correct Heading/Distance.

 

As mentioned before, PG map was handling it fine.

 

Is it known and reported? Any workarounds /fixes ?

 

Thanks!

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I used offset mode in a campaign mission a few days ago (latest beta) and it worked so it may be more complicated, ie sometimes works sometimes has you issue.

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Are you sure you have the major grid coordinates right? Caucuses spans 37T and 38T.

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Are you sure you have the major grid coordinates right? Caucuses spans 37T and 38T.

 

 

 

Sorry thatvdoesnt make sense but still maybe relevant. Maybe the bug is when the offset spans a major grid?

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I recently tried an offset from bullseye training which gave me a huge error using the F10 map in the Caucasus area. It did not repeat in the Persian Gulf map.

 

Did you account for magnetic variation?

 

In the Caucasus region, the magnetic variation is mostly +6 degrees.

 

The F10 map gives something that is close to True Headings, whereas all of the aircraft systems will be affected by magnetic variation and will show Magnetic Headings.

 

So with bulls 170 for 40 NM based on True North, that should give you bulls 164 for 40 based on Magnetic North.

 

Does that work better?

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Did you account for magnetic variation?

 

In the Caucasus region, the magnetic variation is mostly +6 degrees.

 

The F10 map gives something that is close to True Headings, whereas all of the aircraft systems will be affected by magnetic variation and will show Magnetic Headings.

 

So with bulls 170 for 40 NM based on True North, that should give you bulls 164 for 40 based on Magnetic North.

 

Does that work better?

 

I see your point,

but I would have thought the F10 map would already compensate for that...

Also, the actual bulls of 170/40 gave me bulls more to the West, in the sea...

don't have in front right now , but about 173+- and not 164

 

What is the MagVar of the PG map then? and why I don't see it happening there as well?...

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I see your point,

but I would have thought the F10 map would already compensate for that...

 

Magnetic Variation changes over time. If this was incorporated into maps like the F10 map in DCS, these maps all would need to be adjusted every couple of years to account for MagVar.

 

It makes more sense IMO to have maps show true north and then let pilots (or navigators, more generally) account for MagVar themselves. I believe that's typically how it's done IRL.

 

Also, the actual bulls of 170/40 gave me bulls more to the West, in the sea...

don't have in front right now , but about 173+- and not 164

 

You said the ruler on the F10 map gave you 170 for 40, correct? Then 164 for 40 should be correct after accounting for MagVar, though I haven't actually tested it. But it sounds about right, since this would shift the target point a bit further east. And IIRC, you said with 170/40 in the pit, you were looking too far west, at the Black Sea, so unless I have an error in my calculations, I think 164/40 should be okay.

 

What is the MagVar of the PG map then? and why I don't see it happening there as well?...

 

I just googled for an airport chart for Dubai International. Hit #1 was a Jeppesson chart, which states Mag Var 1.4°E. I'm guessing in this case the MagVar of 1.4° was too small to be noticed.

 

Of course the offset between True and Magnetic shows more strongly the further you go away from the bullseye, so if it was XYZ/10, even in the Caucasus the offset wouldn't be terribly noticeable, whereas XYZ/150 would show a fairly big difference even in the Persian Gulf. :smartass:

 

Do you have the Nevada map? You should try it there. At 11° to 12°, the effect is really pronounced over there. ;)

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You said the ruler on the F10 map gave you 170 for 40, correct? Then 164 for 40 should be correct after accounting for MagVar, though I haven't actually tested it. But it sounds about right, since this would shift the target point a bit further east. And IIRC, you said with 170/40 in the pit, you were looking too far west, at the Black Sea, so unless I have an error in my calculations, I think 164/40 should be okay. ;)

 

Hi,

I'm attaching a combined picture to demonstrate my point better, sorry for the bad quality, but that's what I have right now at work... :)

 

You can see the ruler (black line) from the Bullseye in Zugdidi area to the target area "Expected Offset" (the small unused airport). you get 170/40.57 ,

 

so in the offset from bullseye I typed 170.41 as seen in the CDU picture.

And the markpoint was actually in the sea, a few miles to the West "Actual mission offset" as seen in the picture, which is wrong...

opposite of what you calculated to be (to the East).

 

If this is due to MagVar or something else is still not clear to me, and I have no clue in the map as to what offset should I consider or calculate to compensate for this deviation.

That's why I expect to use the ruler and get the correct/corrected heading right away.

 

Thanks :)

 

 

jwwnM7E.jpg

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If this is due to MagVar or something else is still not clear to me, and I have no clue in the map as to what offset should I consider or calculate to compensate for this deviation.

 

Okay, let me try once again, although it would probably work best if someone else explained it in their own words; maybe then it would become clearer.

 

Anyway, here we go.

 

There's a geographic north pole and a geographic south pole, with virtual lines connecting these two, called lines of longitude.

 

Maps are usually aligned along these lines of longitude from geographic south to geographic north.

 

However, the earth's magnetic field is not perfectly aligned with these lines. In fact, the magnetic north pole is currently located somewhere in Northern Canada as far as I know.

 

In turn, a compass will show you the exact direction towards magnetic north (well... barring any other magnetic fields that would affect a compass, but let's leave that aside ;)). But when the earth's magnetic field doesn't point straight to geographic north, then there's an offset between geographic north (what you see on a map) and magnetic north (what the compass shows).

 

This offset, or difference, is called "Magnetic Variation", and in order to navigate by magnetic compass, you will need to know the magnetic variation at your current location.

 

Like I said, magnetic variation in the Caucasus region is roughly 6°E, so any direction read from a magnetic compass is actually +6° in comparison to true north.

 

In order to get the correct heading/bearing, you need to subtract these 6° from your map readings (*) in order to align them with map readings, and then you should be good to go.

 

I just created a sample mission, placed the bullseye in the spot you described so that my map gave me 170/41 as well, and then flew the mission in the A-10C.

 

I created 2 offset waypoints (3, actually), one based on the true north readout from the map called "uncorrected", and then another with a heading -6°, called "corrected". The "corrected" waypoint turned out to be still too far west, so I created another waypoint 170 -7, and that was almost spot-on.

 

So if you don't trust me, by all means just try it out in a mission: subtract 6 or 7 degrees from any map reading, and it should align nicely when seen from the aircraft.

 

And of course, there's further reading, like the Wikipedia article on True North.

 

I hope that clears things up a bit.

 

TL;DR: Not a bug, simply the effect of magnetic variation that is correctly modeled in DCS.

 

Edit: (*) My bad, I had written "you need to subtract these 6° from your magnetic readings" but that's wrong of course, they need to be subtracted from the map readings. Bonus points for anyone who figured this out before the correction. ;)

mag_var_bullseye_offset.trk


Edited by Yurgon
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Thank you for the elaborate explanation.

It sounds right and checks out as you described which is good enough of course... :)

 

At first I thought you were explaining from what you BELIEVED is implemented rather than actually KNOW what is really implemented, for the cause of this.

(also pointing me to what I misunderstood as the other direction - added to my confusion...)

that is why I kept nagging about it...

Nevertheless - your explanation seats well within scientific reason and should cover it.

 

As I mentioned before, I would have expected from ED to add this basic information to the map (could be in the title bar), like every map which has this info...

 

Cheers! :thumbup:

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