Magdec BGL File
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Introduction
The Magdec.bgl file is located in the ..\Scenery\Base\Scenery subfolder (FS2004, FSX and all P3D versions). It provides the basis for magnetic variation (declination) calculation by the simulator at current aircraft position.
By convention, East magnetic variation values are POSITIVE, while west values are NEGATIVE.
See this Wikipedia article for some basics regarding magnetic declination meaning.
File length is 130468 bytes in FS2004 (offsets 0x0 to 0x1FDA3) and 130456 bytes in FSX and P3D (offsets 0x0 to 0x1FD97)
File structure
Magdec.bgl file includes a header, a latitude/longitude table and optionally (FS2004 only) an ending string.
File header
File header is 136 bytes long (offsets 0x0 to 0x87) and has the following structure
| Offset | Length | Description | Content |
|---|---|---|---|
| 0x00 | 1 - BYTE | World set number | 0X01 |
| 0x01 | 127 - ? | Unknown | All 0, except 0x80 at offset 0x6E |
| 0x80 | 2 - WORD | Number of longitude values | 0x168 (360) |
| 0x82 | 2 - WORD | Number of latitude values | 0xB5 (181) |
| 0x84 | 1 - BYTE | Reference date day (?) | 0x01 |
| 0x85 | 1 - BYTE | Reference date month (?) | 0x01 (FS2004) - 0x11 (FSX/P3D) |
| 0x86 | 2 - WORD | Reference date year (?) | 0x1993 (FS2004) - 0x2006 (FSX/P3D) |
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References
Translation - Ask Fr. Bill.
