Skyrim Mod:Mod File Format/CELL

CELL records contain the data for either interior (CELL top group) or exterior (WRLD top group) cells. They follow the same format in both cases. The CELL record is followed by a group containing the references for the cell, organized into subgroups. Persistent references are defined in the 'persistent children' subgroup while temporary references are defined in the 'temporary children' subgroup. The 'persistent children' subgroup must occur before the 'temporary children' subgroup.

The block and sub-block groups for an interior cell can be determined either by the label field of the group headers of the block and sub-block, or by the last two decimal digits of the Form ID. For example, for Form ID 0x138CA, which is 80,074 in decimal, 4 indicates that this is block 4, and the 7 indicates that it's sub-block 7.

The block and sub-block groups for an exterior cell can be determined either by the label filed of the group headers of the block and sub-block, or by the X, Y coordinates of the cell from the XCLC field. Each block contains 16 sub-blocks (4x4) and each sub-block contains 64 cells (8x8). So, to get the sub-block number, divide the coordinates by 8 (rounding down), and the block number can be determined by dividing the sub-block numbers by 4 (again, rounding down). Thus, a cell with the X, Y coordinates 31, 50 would be in floor(31 / 8) = 3, floor(50 / 8) = 6, so sub-block 3, 6. Dividing again, only this time by 4, it would be in block 0, 1.

Record header flags:

0x00000400 - Persistent Cell?

0x00020000 - Off Limits

0x00080000 - Can't Wait

C	Field	Type	Info
-	EDID	zstring	Cell editor ID
-	FULL	lstring	In game name of the cell. Only in interior cells.
+	DATA	uint16	flags - Sometimes the field is only one byte long 0x0001 - Interior 0x0002 - Has Water 0x0004 - not Can't Travel From Here - only valid for interior cells 0x0008 - No LOD Water 0x0020 - Public Area 0x0040 - Hand Changed 0x0080 - Show Sky 0x0100 - Use Sky Lighting
-	XCLC	struct	(X, Y) grid location of the cell followed by flags. Always in exterior cells and never in interior cells. int32 - X int32 - Y uint32 - flags (high bits look random) 0x1 - Force Hide Land Quad 1 0x2 - Force Hide Land Quad 2 0x4 - Force Hide Land Quad 3 0x8 - Force Hide Land Quad 4
-	XCLL	struct	92 byte structure - Lighting rgb Ambient rgb Directional rgb Fog Near float Fog Near float Fog Far int Rotation XY int Rotation Z float Directional Fade float Fog Clip Dist float Fog Pow rgb Ambient X+ rgb Ambient X- rgb Ambient Y+ rgb Ambient Y- rgb Ambient Z+ rgb Ambient Z- rgb Specular Color? not shown in CK - assumed from LGTM float Fresnel Power? not shown in CK, usually 1 - assumed from LGTM rgb Fog Far float Fog Max float Light Fade Distances Start float Light Fade Distances End uint32 Inherit flags - controls which parts are inherited from Lighting Template 0x0001 - Ambient Color 0x0002 - Directional Color 0x0004 - Fog Color 0x0008 - Fog Near 0x0010 - Fog Far 0x0020 - Directional Rot 0x0040 - Directional Fade 0x0080 - Clip Distance 0x0100 - Fog Power 0x0200 - Fog Max 0x0400 - Light Fade Distances this field has only 64 bytes in NavMeshGenCellDUPLICATE001
-	TVDT	684 bytes
-	MHDT	1028 bytes
-	XCGD	struct	Only found in Xbox360 and PS3 official DLC, not supported by CK 1.8.151.0. uint32 - Count of substructures? Seems plausible, but doesn't always seem to match up. uint32 - String length, including null-terminator (like bzstring, but with a uint32 length) char[String length] - File name (looks to always be .nif files) ? - Other data here, but unclear what it is or what delineates the next file.
+	LTMP	formID	The lighting template for this cell.
-	LNAM	4 bytes
+	XCLW	float	Non-ocean water-height in cell, is used for rivers, ponds etc., ocean-water is globally defined elsewhere. 0x7F7FFFFF reserved as ID for "no water present", it is also the maximum positive float. 0x4F7FFFC9 is a bug in the CK, this is the maximum unsigned integer 2^32-1 cast to a float and means the same as above 0xCF000000 could be a bug as well, this is the maximum signed negative integer -2^31 cast to a float
-	XNAM	1 byte
-	XCLR	formID[]	Regions containing the cell (assumed from Oblivion).
Fields below this line can appear in any order.
-	XLCN	formID	The location for (of?) this cell.
-	XWCS	uint32	Size of XWCU/16 - CK changes this into use of XWCN Always has the value three in Skyrim.esm.
-	XWCN	uint32	Size of XWCU/16 Only one occurrence - 0x04
-	XWCU	struct[]	Water Current, series of 16 byte structures, minimum 3 float X float Y float Z float? unknown Unclear how structures are matched up to "Linear Velocity" and "Angular Velocity" shown in CK
-	XCWT	formID	The water for (of?) this cell.
-	XOWN	formID	Owner NPC or Faction (assumed from Oblivion). Only in interior cells.
-	XILL	formID	ID of an NPC_ or FLST. Only in interior cells.
-	XWEM	zstring	Water Environment Map only interior cells
-	XCCM	formID	Climate if interior cell behaves like exterior cell (assumed from Oblivion). Only in interior cells.
-	XCAS	formID	The acoustic space for this cell.
-	XEZN	formID	A reference to an encounter zone.
-	XCMO	formID	The music type for this cell.
-	XCIM	formID	The image space for this cell.

The last four bytes in XCLC do not appear to be a form ID. The following values appear 100 or more times in those last four bytes:

Count	Value
100	53bd00
279	53ba00
360	53d400
586	0
586	53d200
5881	53fd00
8397	53d100

The less frequent values show a distribution of values that makes them look like a bitmap.