| | Describes a circle in 3D space.
A circle is defined by its radius and, as with any conic
curve, is positioned in space with a right-handed
coordinate system (gp_Ax2 object) where:
- the origin is the center of the circle, and
- the origin, "X Direction" and "Y Direction" define the
plane of the circle.
This coordinate system is the local coordinate
system of the circle.
The "main Direction" of this coordinate system is the
vector normal to the plane of the circle. 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 circle.
The "main Direction" of the local coordinate system
gives an explicit orientation to the circle (definition of
the trigonometric sense), determining the direction in
which the parameter increases along the circle.
The Geom_Circle circle is parameterized by an angle:
P(U) = O + R*Cos(U)*XDir + R*Sin(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,
- R is the radius of the circle.
The "X Axis" of the local coordinate system therefore
defines the origin of the parameter of the circle. The
parameter is the angle with this "X Direction".
A circle is a closed and periodic curve. The period is
2.*Pi and the parameter range is [ 0, 2.*Pi [.
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1.6.3