BGL File Format
Introduction
The information contained in this wiki comes from different sources:
- "FSX File structure" by Winfried Orthmann
- This is the first document about BGL file format. It describes the generic format of a BGL file and the content of some important sections like Airport, Scenery Objects,etc.
- Some reverse engineering work on the TmfViewer and BglComp applications.
BGL Common Format
All BGL files share the same generic format. A BGL file is made of a header, sections, subsections and subsection data. Subsections are children of sections. The sections are here to help us locate the subsections in the file. Data specific information is contained in the subsections data and their format is dependent on the section type.
A BGL file is really a big container where all kind of information can be stored (in the subsection).The meaning of the data contained in the subsections is known only by the application using it. Th only contraint is for the file to comply to the generic format described below.
A BGL file always start with a header (Size = 0x38 bytes), followed by a list of section pointers. The number of section pointers is defined in the header.
File Header
The header consists of 0x38 (56) bytes. It contains the number of sections defined in the file as well as the bounding geographical coordinates of the covered squared area.
| Offset | Number of bytes | Description |
|---|---|---|
| 0x00 | 4 - DWORD | Magic Number #1 – Must be 0x01, 0x02, 0x92, 0x19 |
| 0x04 | 4 - DWORD | Header size : 0x38 |
| 0x08 | 4 - DWORD | dwLowDateTime of the FILETIME structure. Date and Time the file was created The FILETIME structure represents the number of 100-nanosecond intervals since January 1, 1601 |
| 0x0C | 4 - DWORD | dwHighDateTime of the FILETIME structure |
| 0x10 | 4 - DWORD | Magic Number #2 – Must be 0x03, 0x18, 0x05, 0x08 Maybe to identify the FS version |
| 0x14 | 4 - DWORD | The number of sections following this header. |
| 0x18 | 32 | Array[8] of unsigned integers (DWORD). Each value describes the bounding coordinates of a squared subarea. Even if 8 slots are provided, it is not necessary to have all 8 values filled. The list stops at the first null (0x00000000) value. |
Example
For example, in CVX2815.bgl :
| Offset | Values | Description |
|---|---|---|
| 0x00 | 01 02 92 19 |
Magic Number #1 |
| 0x04 | 38 00 00 00 |
Header size |
| 0x08 | EF 82 DF E2 |
Low = 3806298863 |
| 0x0C | E8 C7 C6 01 |
High = 29804520 => February 27, 2007 |
| 0x10 | 03 18 15 08 |
Magic Number #2 |
| 0x14 | 01 00 00 00 |
1 section following this header |
| 0x18 | E8 07 02 00 |
MinLatitude(Deg) = 46.40625 MaxLatitude(Deg) = 47.8125 MinLongitude(Deg) = -75.0 MaxLongitude(Deg) = -73.125 |
| 0x1C | E9 07 02 00 |
MinLatitude(Deg) = 46.40625 MaxLatitude(Deg) = 47.8125 MinLongitude(Deg) = - 73.125 MaxLongitude(Deg) = -71.25 |
| 0x20 | EA 07 02 00 |
MinLatitude(Deg) = 45.0 MaxLatitude(Deg) = 46.40625 MinLongitude(Deg) = -75.0 MaxLongitude(Deg) = -73.125 |
| 0x24 | EB 07 02 00 |
MinLatitude(Deg) = 45.0 MaxLatitude(Deg) = 46.40625 MinLongitude(Deg) = -73.124 MaxLongitude(Deg) = -71.25 |
| 0x28 | 00 00 00 00 |
|
| 0x2C | 00 00 00 00 |
|
| 0x30 | 00 00 00 00 |
|
| 0x34 | 00 00 00 00 |
You’ll notice that only 4 subareas are defined (on a possibility of 8) and the last 4 available slots are empty (Value = 0)
So the bounding coordinates of the area covered by cvx2815.bgl are:
- MinLatitude(Deg) = 45.0
- MaxLatitude(Deg) = 47.8125
- MinLongitude(Deg) = -75.0
- MaxLongitude(Deg) = -71.25
Sections
Following the header, at offset 0x38, there are as many sections as defined at offset 0x14 of the header. A same file may contain sections of different type. Each section has a size of 20 bytes and has the following structure:
| Relative Offset | Number of bytes | Description |
|---|---|---|
| 0x00 | 4 - DWORD | Section type (as defined by Microsoft Flight Simulator): one of the following values:
|
| 0x04 | 4 - DWORD | Unknown |
| 0x08 | 4 - DWORD | Number of subsections in the section. |
| 0x0C | 4 - DWORD | File offset = position in the file where the first subsection starts. |
| 0x10 | 4 - DWORD | Total Size (in bytes) of all the subsections. This value should be equal to : 16 * nbSubSections |
Note that a cvx*.bgl file have at least a section of type 101 (0x65) = TerrainVectorDb.
Example
For example, in cvx2815.bgl, the only one section, at offset 0x38, has this:
| Offset | Values | Description |
|---|---|---|
| 0x38 | 65 00 00 00 |
TerrainVectorDb = 101 = 0x65 |
| 0x3C | 01 00 00 00 |
Unknown |
| 0x40 | 8D 07 00 00 |
0x078D = 1933 subsections in the section |
| 0x44 | 01 CD 1F 00 |
0x1FCD01 = File offset = position in the file where the first subsection starts. |
| 0x48 | D0 78 00 00 |
Size (in bytes) =0x78D0 = 30928 bytes |
Subsections
A subsection contains information about the geographical area it covers. If also contains the file offset of the subsection’s data. All subsections of a same section are contiguous meaning that they are following each other in the file.
A subsection has the following structure:
| Relative Offset | Number of bytes | Description |
|---|---|---|
| 0x00 | 4 - DWORD | Bounding coordinates of a squared area covered by this subsection. See Annexe A. |
| 0x04 | 4 - DWORD | Number of records contained in the subsection's data. It is 0 for TerrainVectorDb (which actually means only 1 record). |
| 0x08 | 4 - DWORD | File Offset = Position in the file of the subsection’s data |
| 0x0C | 4 - DWORD | Size of the subsection’s data |
The interpretation of the section data depends on the section type.
Example
| Offset | Values | Description |
|---|---|---|
| 0x1FCD01 | 00 FA 81 00 |
Bounding coordinates:
|
| 0x1FCD05 | 00 00 00 00 |
Number of records = 0 |
| 0x1FCD09 | 4C 00 00 00 |
0x4C = File Offset = Position in the file of the subsection’s data. |
| 0x1FCD0D | DD 00 00 00 |
Size of the subsection’s data = 0xDD = 221 bytes. |
