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Symmetries
Symmetries (Arrays)
Symmetries are called arrays in some other CAD systems. Symmetry is property of an Object. The Symmetry
property represents geometrical symmetries of the model.
Using symmetries greatly increases productivity of modeling. If a section has a symmetry the object
will be rendered as multiple copies of the same object placed in different
location and probably with different orientation in space.
One of the main properties of symmetry is the repeat count. If for example
the repeat count equals to 2 than there will be rendered two additional
copies of the object. Location and orientation of the copies are determined by
the type of symmetry and its parameters.
Currently there are three types of symmetries:
 Axial Symmetry
 Mirror Symmetry
 Translation Symmetry
Common properties of symmetry include: repeat count, enable flag,
visible flag and Include Children flag. If the visible flag is on, a correspondent graphic element will
be drawn ( the axis in the case of an axial symmetry) to visualize properties of
the symmetry. Include Children flag indicates whether the current section's
children will be included in additional copies.
An object can have multiple symmetries of different types. Symmetries of a
object are arranged in an array. This array can be edited in 3D Debugger
by using "Current Object">Symmetries dialog. (See
Symmetries Editor topic). The order of the array is important.
The second symmetry is applied to the result of the first one.
This means that for the second symmetry the object,
which should have multiple copies, is whole set of objects generated by the first
symmetry. The resulting number of copies of the original object will be equal
to:
( Repeat count of the symmetry one + 1 ) x ( Repeat count of the symmetry two
+ 1 ).
Generally, changing order of symmetries leads to a different geometry
of the object.
Axial Symmetry
When a object has a single axial symmetry the secondary copies of the
object are created by rotation of the original (primary) one by a fixed angle,
which is a parameter of the symmetry. The axis of the symmetry and angle of the
rotation can be edited with 3D Debugger or accessed via
IAxialSymmetry interface programmatically. Note that the axis of an axial symmetry can be any
axis in 3D space. The axis is determined by a point of its origin and a nonzero direction vector.
Mirror Symmetry
Mirror symmetry adds another single copy to the primary object, which is
obtained by symmetric reflection respective to a plane. The plane of the
symmetry is an arbitrary plane in 3D. Its location and orientation can be
defined in 3D Debugger or by using IAxis interface, which can be queried
from the correspondent ISymmetry. In this context IAxis represents normal of the
plane of the symmetry. Origin of the axis is a point where the plane passes
through. This point can be managed by using GetLocation and SetLocation methods
of the base class ILocation of IAxis.
Translation Symmetry
Translation symmetry is defined by its translation vector. Secondary copies
will be created by parallel translation of the primary object by the translation vector. To get access to the translation vector programmatically
it is necessary to query ILocation interface from the correspondent
ISymmetry.
Programming Symmetries
Common properties of a symmetry are managed by ISymmetry interface. The
array of
symmetries of an object is managed by ISymmetries
interface, which can be queried
from ISection. By default the array is empty. An individual symmetry can be
retrieved from ISymmetries with
GetSymmetry method.
ISymmetries
is a readonly interface. To add or delete a symmetry it is necessary to obtain
IArray2
interface form ISymmetries and use its InsertNew
or RemoveAt methods. type parameter
of InsertNew must be 1, 2 or 3, for axial,
mirror or translation symmetry, which are the valid values of the ESymmType
enumeration.
Note that the above query ISymmetries>IArray2
is a contextdependent
query. It means that between two steps ISection>ISymmetries and
ISymmetries>IArray2
there must not be any other queries from the ISection
interface.
