Inconsistent Bearing Calculation: Alpha Check vs. DCS Bullseye

[shaji-Dev]

Describe your issue

Hi,

We noticed inconsistent Alpha Check bearings with what appears in the F10 map, the further we are from the bullseye and bigger the margin of error.

These are our "ALPHA CHECK vs DCS F10 map BullsEye tool" results tested on Kola map:

- SkyEye: 016° for 36 nm
- DCS:  011° M/ 25° for 36 nm
Deviation: +4°
 
- SkyEye: 098° for 89 nm
- DCS:  092° M/ 107° for 89 nm
Deviation: 6°

- SkyEye: 036° for 227 nm
- DCS:  026° M/ 044° for 227 nm
Deviation: +10°

- SkyEye: 055° for 329 nm
- DCS:  043° M/ 063° for 329 nm
Deviation: +12°

Operating System

Windows

CPU

Ryzen 9950X

RAM

128GB

[dharmab]

What date is the mission set in? And what map is this on?

[shaji-Dev]

July 1st, 2025

[dharmab]

Does it happen as badly on other maps?

DCS uses a limited set of magnetic field data compared to SkyEye, I'm wondering if DCS's data is too old for 2025 missions, and the issue is more visible on Kola due to the high latitude.

When I'm back at a Windows PC I'll have to poke around DCS' data and see what the last date they have accurate magnetic data is.

(Incidentally, this issue is why runways in Canada use true bearings instead of magnetic bearings. Saves them from repainting the numbers so often.)

[shaji-Dev]

We only use Kola, but I'm pretty sure Kola would have the biggest declanation range that creates this huge margin of error given the proximity to the north pole and the size of the map (1000x1000 nm) and the variable and aggressive earth curvature in different areas of the map.

Most DCS maps are on the equator so I'm sure the margin of error between SkyEye's calculationa vs DCS is pretty small in maps like Syria and Sinai, I'm guessing that's why you didn't receive any reports about it since not a lot of servers run Kola.

But I agree, I personally prefer bearings as well instead of magnetic, but not realistic in most SOPs unfortunately.

Thank you @dharmab !

[dharmab]

Likely related to #618, workaround shipped in #634