PLEA FILE
Plane Equation Array - Level File

Hex	Translation	Meaning
01 41 02 00	577	00577-.PLEA
01 00 00 06	3	level 3
AD DE	dead	not used
F2 34 00 00	13554	13554 packages follow (one package is edged in black)
Below follows the first package.
00 00 00 00	0.000000	x-part of the normal vector
00 00 00 00	0.000000	y-part (height) of the normal vector
00 00 80 3F	1.000000	z-part of the normal vector
00 00 19 44	612.000000	x-, y- or z-position; it's the value that doesn't change

Plane equation The canonical equation for a plane in 3D is : a * x + b * y + c * z + d = 0 where (a, b, c, d) are 4 real numbers. The plane is the set of points (x, y, z) verifying that equation. It is likely that the four floats in one of a PLEA's packages are exactly the (a, b, c, d) of the above definition. In that case, the first package of the above example defines the plane (0 * x + 0 * y + 1 * z + 612 = 0), i.e., the vertical plane z = -612. It is possible, however, that the definition used is different, e.g. : a * x + b * y + c * z = d . In that case, the first package of the above example defines the plane (0 * x + 0 * y + 1 * z = 612), i.e., the vertical plane z = 612. Front/back The 4 numbers (a, b, c, d) can also serve to define whether a 3D point (x, y, z) is on the "front" side of the plane or in the "back". "points are in front of the plane if a * x + b * y + c * z >= d" (from commented Myth source) That would mean the plane equation is a * x + b * y + c * z = d , not a * x + b * y + c * z + d = 0 . It's rather easy to check (just flip the "normal" of the plane equation for a known axis-aligned quad). The oriented "plane inequation" can be used for: culling; collision.

Back to File Types