| | Describes a right-handed coordinate system in 3D space.
A coordinate system is defined by:
- its origin (also referred to as its "Location point"), and
- three orthogonal unit vectors, termed respectively the
"X Direction", the "Y Direction" and the "Direction" (also
referred to as the "main Direction").
The "Direction" of the coordinate system is called its
"main Direction" because whenever this unit vector is
modified, the "X Direction" and the "Y Direction" are
recomputed. However, when we modify either the "X <br>
Direction" or the "Y Direction", "Direction" is not modified.
The "main Direction" is also the "Z Direction".
Since an Ax2 coordinate system is right-handed, its
"main Direction" is always equal to the cross product of
its "X Direction" and "Y Direction". (To define a
left-handed coordinate system, use gp_Ax3.)
A coordinate system is used:
- to describe geometric entities, in particular to position
them. The local coordinate system of a geometric
entity serves the same purpose as the STEP function
"axis placement two axes", or
- to define geometric transformations.
Note: we refer to the "X Axis", "Y Axis" and "Z Axis",
respectively, as to axes having:
- the origin of the coordinate system as their origin, and
- the unit vectors "X Direction", "Y Direction" and "main <br>
Direction", respectively, as their unit vectors.
The "Z Axis" is also the "main Axis".
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1.6.3