BGL File Format

Applicable
FSX

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 See http://support.microsoft.com/kb/188768
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. I don’t know what these subareas are used for. To compute the bounding coordinates, please see Computing the bounding coordinates from a DWORD value. To get the bounding coordinates of the square area covered by the file, just keep the minimal and maximal values of each bounding coordinates.

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