| | Describes the common behavior of surfaces which
have a simple parametric equation in a local
coordinate system. The Geom package provides
several implementations of concrete elementary surfaces:
- the plane, and
- four simple surfaces of revolution: the cylinder, the
cone, the sphere and the torus.
An elementary surface inherits the common behavior
of Geom_Surface surfaces. Furthermore, it is located
in 3D space by a coordinate system (a gp_Ax3
object) which is also its local coordinate system.
Any elementary surface is oriented, i.e. the normal
vector is always defined, and gives the same
orientation to the surface, at any point on the surface.
In topology this property is referred to as the "outside <br>
region of the surface". This orientation is related to
the two parametric directions of the surface.
Rotation of a surface around the "main Axis" of its
coordinate system, in the trigonometric sense given
by the "X Direction" and the "Y Direction" of the
coordinate system, defines the u parametric direction
of that elementary surface of revolution. This is the
default construction mode.
It is also possible, however, to change the orientation
of a surface by reversing one of the two parametric
directions: use the UReverse or VReverse functions
to change the orientation of the normal at any point on the surface.
Warning
The local coordinate system of an elementary surface
is not necessarily direct:
- if it is direct, the trigonometric sense defined by its
"main Direction" is the same as the trigonometric
sense defined by its two vectors "X Direction" and "Y Direction":
"main Direction" = "X Direction" ^ "Y Direction"
- if it is indirect, the two definitions of trigonometric
sense are opposite:
"main Direction" = - "X Direction" ^ "Y Direction"
More...
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1.6.3