CULL

CULL is a section in the IPL file. It is used to create zones with different behaviour like mirrors or fixed camera positions. It can also influence the environment like disable rain within the zone and certain police behaviors.

GTA III / Vice City
Cull zones in GTA III and Vice City are built by a box which is controlled by various flags. By default, most of the cull zones are located in  for both games.

CenterX, CenterY, CenterZ, LowerLeftX, LowerLeftY, LowerLeftZ, UpperRightX, UpperRightY, UpperRightZ, Flags, Unknown

The first three parameters are odd since placing any values do not have an effect on the zone. They seem to act like identifiers rather than functions.

Flags
Flags are numbers which are build out of a collection of numbers formed by the power of 2-numbers lower than 230. Some are defining various behaviours of the zone. They can be combined by simply adding one flag value to another (see binary to decimal conversion).

San Andreas
GTA San Andreas has two different major formats in the game:

CenterX, CenterY, CenterZ, Unknown1, WidthY, BottomZ, WidthX, Unknown2, TopZ, Flag, Unknown3

CenterX, CenterY, CenterZ, Unknown1, WidthY, BottomZ, WidthX, Unknown2, TopZ, Flag, Vx, Vy, Vz, Cm

Coordinates are always rounded to the nearest world unit so that they are no longer floating point values, they are non-decimal integers.

Flags
Not all flags from the previous game are compatible with San Andreas.