Daggerfall's BSA File Formats

This is a description of the format of the various .BSA files found in the ARENA2 directory of Elder Scrolls:Daggerfall by Bethesda. The information here is not complete or 100% percent accurate, although the basic formats appears to be well understood. For more information, corrections, or comments, e-mail me at the above address. Check out The UESP: Daggerfall for the latest version of this document and other DF goodies.

Contributors

General BSA Files

There are five BSA files in Daggerfall's ARENA2 directory (ARCH3D, MAPS, MONSTER, MIDI, and BLOCKS). Although they contain different data, their overall structure is the same. This format has been derived from all these five files. The following description appears to be complete.

General File Layout

BSA Header
...BSA Records...
BSA Directory

This is the first 4 bytes found at the start of a BSA file and gives information about the BSA directory at the end of the file.

	[Bytes 0-1] short DirectoryCount;
		Gives the number of entries in the directory at the end of the 
		file.
	[Bytes 2-3] short DirectoryType; 
		Gives the type of directory at the end of the BSA file (See
		BSA Directory below).
			0x0100 = Directory has records of 18 bytes in size
				 consisting of a 14 byte filename and a long
				 record length.
			0x0200 = Directory has records of 8 bytes in size
				 consisting of long ID and a long record size.

BSA Records

This data will depend on the actual BSA file. The basic contents for the five known BSA files are as follows:

ARCH3D: 3D Object Information
BLOCKS: Dungeon/town block information
MAPS: Location information (towns, dungeon, houses, temples, etc...)
MONSTER: Monster data (no images)
MIDI: HMI formatted music

BSA Directory

The directory contains the information needed to access the various data records in the BSA file. The contents of each record depends on the BSA file. In general, the directory gives an identification number/string and a record length for each record. There are two known types of directories identified by the DirectoryType bytes in the BSA header (0x0100 and 0x0200).

BSA 0x0100 Directory (Name)

The 0x0100 type directory consists of records 18 bytes in size and give a record size and 13 byte name for each BSA record.

	
	[Bytes 0-13] char FileName[14];
		The filename which identifies this data section.  Filenames
		are in the usual DOS 8.3 format.
	[Bytes 14-17] long DataSize;
		The size of the data in bytes.  The first record starts at 
		offset 4 in the file, ignoring the 4 bytes of the BSA Header.
		The subsequent section offsets can be calculated from this.

BSA 0x0200 Directory (Number)

The 0x0200 type directory consists of records 8 bytes in size and give a record size and long identifier for each BSA record.

	[Bytes 0-3] long RecordID;
		A long number which assumbly identifies the record somehow.
	[Bytes 4-7] long DataSize;
		The size of the data in bytes.  The first entry starts at 
		offset 4 in the file, ignoring the 4 bytes of the BSA Header.
		The subsequent section offsets can be calculated from this.

Appendix A - REGION NUMBERS

Appendix B - LOCATION TYPES

Dungeons

Towns

Temples

Homes

Appendix C - BLOCK INDICES

File chars fill in the first two ?? and the file index fills in the last two ??. A value of "A/B/G, L/M/S" means the file characters could be one of AL, AM, AS, BL, BM, BS, GL, GM, or GS. The descriptions given are a rough guess based on the RMB file name. The known values for the file chars as given in location post records in MAPS.BSA are shown below.

Appendix D - COORDINATE LIMITS

Coordinates are roughly in centimeters as given in the game by using the ' cheat key for quest info. Coordinates are 256 times smaller than the coordinates used for the 3D objects.

Appendix E - UV TEXTURE COORDINATES

Daggerfall handles UV coordinates a little differently than most 3D programs and require some explanation. The TextureU and TextureV in the plane sub- records hold the texture coordinate data for the face point but, depending on the face, the UV coordinates have different meaning:

Since all points on the face after the 4th have no UV values, this indicates that we must find a relationship between the XYZ point and the UV coordinate, which is detailed below.

The units of DfUV texture coordinates are relative to the size of the texture image. A value of 1024 represents 64 pixels of image data. The conversion between DfUV and standard UV coordinates is detailed below.

CONVERTING XYZ to UV Coordinates

Unfortunately, as of this point, there is no simple way to compute the UV coordinate of a point from its XYZ location, but the best current method is explained as follows. We first assume that the relationship is linear and of the form:

Normal UV coordinates are based on a value of 1.0 equaling the texture width or height and are usually used in 3D modelling programs. These equations appear to give the correct texture coordinates for most 3D objects.

Appendix F - LAND CREATION NOTES

Steps to create a map 'block' or pixel. The entire DF map is composed of 1000x500 land pixels, each of which is further divided into 5x5 subpixels as per the WOODS.WLD data. Each pixel can contain only one town or dungeon and has a given terrain type, texture, and roughness.