| | Describes a parabola in 3D space.
A parabola is defined by its focal length (i.e. the
distance between its focus and its apex) and is
positioned in space with a coordinate system
(gp_Ax2 object) where:
- the origin is the apex of the parabola,
- the "X Axis" defines the axis of symmetry; the
parabola is on the positive side of this axis,
- the origin, "X Direction" and "Y Direction" define the
plane of the parabola.
This coordinate system is the local coordinate
system of the parabola.
The "main Direction" of this coordinate system is a
vector normal to the plane of the parabola. The axis,
of which the origin and unit vector are respectively the
origin and "main Direction" of the local coordinate
system, is termed the "Axis" or "main Axis" of the parabola.
The "main Direction" of the local coordinate system
gives an explicit orientation to the parabola,
determining the direction in which the parameter
increases along the parabola.
The Geom_Parabola parabola is parameterized as follows:
P(U) = O + U*U/(4.*F)*XDir + U*YDir
where:
- P is the point of parameter U,
- O, XDir and YDir are respectively the origin, "X <br>
Direction" and "Y Direction" of its local coordinate system,
- F is the focal length of the parabola.
The parameter of the parabola is therefore its Y
coordinate in the local coordinate system, with the "X <br>
Axis" of the local coordinate system defining the origin
of the parameter.
The parameter range is ] -infinite, +infinite [.
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1.6.3