OBD:PLEA
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Offset  Type  Raw Hex  Value  Description 

0x00  res_id  01 41 02 00  577  00577.PLEA 
0x04  lev_id  01 00 00 06  3  level 3 
0x08  char[20]  AD DE  dead  unused 
0x1C  int32  03 00 00 00  13554  array size 
First element (black outline)  
0x00  float  00 00 00 00  0.000000  'a' coefficient of the plane equation (x component of plane's normal) 
0x04  float  00 00 00 00  0.000000  'b' coefficient of the plane equation (y component of plane's normal) 
0x08  float  00 00 80 3F  1.000000  'c' coefficient of the plane equation (z component of plane's normal) 
0x0C  float  00 00 19 44  612.000000  'd' coefficient of the plane equation 
 Plane equation
 The canonical equation for a plane in 3D is
 a * x + b * y + c * z + d = 0,
 with (a, b, c, d) being 4 real numbers and (a, b, c) forming a nonzero vector (the plane's "normal").
 The set of points (x, y, z) verifying a * x + b * y + c * z + d = 0 are said to be in the plane or at the plane.
 The set of points (x, y, z) verifying a * x + b * y + c * z + d > 0 are said to be in front of the plane.
 The set of points (x, y, z) verifying a * x + b * y + c * z + d < 0 are said to be behind the plane.
 N.B. If a=b=c=0, then the equation is degenerate and applies either to the whole space (if d=0) or to no points at all (if d is nonzero).
 As a further convention, if (a,b,c) is normalized at unit length (i.e., a*a + b*b + c*c = 1) then d is the distance from the plane to the world's origin, along the normal vector.
 The four floats in each element of a PLEA are exactly the (a, b, c, d) of the above definition.
 In the above example, the first element defines the plane (0 * x + 0 * y + 1 * z + 612 = 0), i.e., the vertical plane z = 612.
 What planes are for and how they are referenced
 Planes are used for environment culling, collision detection and BSP.
 The plane equations stored in PLEA are referenced from such data as ABNA, AKBP, AKBA and AGQC by means of a 32bit array index.
 However, the high bit of those 32bit references is not part of the array index, instead it indicates whether the facing of the plane should be flipped.
 If the high bit is not set, then the 4 values (a, b, c, d) are used as described above.
(If referencing the above example without a high bit, then any points with z >  612 will be in front of the plane, whereas points with z < 612 will be behind the plane.)  If the high bit is set, then the plane equation coefficients become (a, b, c, d).
(If referencing the above example with a high bit, then any point with z >  612 will be behind the plane, whereas points with z < 612 will be in front of the plane.)
 If the high bit is not set, then the 4 values (a, b, c, d) are used as described above.
 This means that the actual array index is a 31bit value (i.e., there can "only" be up to 2,147,483,648 distinct planes in a level), but the same array element can be used for two different facing directions.
ONI BINARY DATA 

OTLF << Other file types >> PNTA 
PLEA : Plane Equation Array 
Level file 