Open CASCADE Technology 6.6.0
Public Member Functions | Protected Attributes
GProp_GProps Class Reference

Implements a general mechanism to compute the global properties of
a "compound geometric system" in 3d space by composition of the
global properties of "elementary geometric entities" such as
(curve, surface, solid, set of points). It is possible to compose
the properties of several "compound geometric systems" too.

To computes the global properties of a compound geometric
system you should :
. declare the GProps using a constructor which initializes the
GProps and defines the location point used to compute the inertia
. compose the global properties of your geometric components with
the properties of your system using the method Add.

To compute the global properties of the geometric components of
the system you should use the services of the following classes :
More...

#include <GProp_GProps.hxx>

Inheritance diagram for GProp_GProps:
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Public Member Functions

 GProp_GProps ()
 The origin (0, 0, 0) of the absolute cartesian coordinate system
is used to compute the global properties.

 GProp_GProps (const gp_Pnt &SystemLocation)
 The point SystemLocation is used to compute the gobal properties
of the system. For more accuracy it is better to define this
point closed to the location of the system. For example it could
be a point around the centre of mass of the system.
This point is referred to as the reference point for
this framework. For greater accuracy it is better for
the reference point to be close to the location of the
system. It can, for example, be a point near the
center of mass of the system.
At initialization, the framework is empty; i.e. it
retains no dimensional information such as mass, or
inertia. However, it is now able to bring together
global properties of various other systems, whose
global properties have already been computed
using another framework. To do this, use the
function Add to define the components of the
system. Use it once per component of the system,
and then use the interrogation functions available to
access the computed values.

void Add (const GProp_GProps &Item, const Standard_Real Density=1.0)
 Either

Standard_Real Mass () const
 Returns the mass of the current system.
If no density is attached to the components of the
current system the returned value corresponds to :

gp_Pnt CentreOfMass () const
 Returns the center of mass of the current system. If
the gravitational field is uniform, it is the center of gravity.
The coordinates returned for the center of mass are
expressed in the absolute Cartesian coordinate system.

gp_Mat MatrixOfInertia () const
 returns the matrix of inertia. It is a symmetrical matrix.
The coefficients of the matrix are the quadratic moments of
inertia.

| Ixx Ixy Ixz |
matrix = | Ixy Iyy Iyz |
| Ixz Iyz Izz |

The moments of inertia are denoted by Ixx, Iyy, Izz.
The products of inertia are denoted by Ixy, Ixz, Iyz.
The matrix of inertia is returned in the central coordinate
system (G, Gx, Gy, Gz) where G is the centre of mass of the
system and Gx, Gy, Gz the directions parallel to the X(1,0,0)
Y(0,1,0) Z(0,0,1) directions of the absolute cartesian
coordinate system. It is possible to compute the matrix of
inertia at another location point using the Huyghens theorem
(you can use the method of package GProp : HOperator).

void StaticMoments (Standard_Real &Ix, Standard_Real &Iy, Standard_Real &Iz) const
 Returns Ix, Iy, Iz, the static moments of inertia of the
current system; i.e. the moments of inertia about the
three axes of the Cartesian coordinate system.

Standard_Real MomentOfInertia (const gp_Ax1 &A) const
 computes the moment of inertia of the material system about the
axis A.

GProp_PrincipalProps PrincipalProperties () const
 Computes the principal properties of inertia of the current system.
There is always a set of axes for which the products
of inertia of a geometric system are equal to 0; i.e. the
matrix of inertia of the system is diagonal. These axes
are the principal axes of inertia. Their origin is
coincident with the center of mass of the system. The
associated moments are called the principal moments of inertia.
This function computes the eigen values and the
eigen vectors of the matrix of inertia of the system.
Results are stored by using a presentation framework
of principal properties of inertia
(GProp_PrincipalProps object) which may be
queried to access the value sought.

Standard_Real RadiusOfGyration (const gp_Ax1 &A) const
 Returns the radius of gyration of the current system about the axis A.

Protected Attributes

gp_Pnt g
gp_Pnt loc
Standard_Real dim
gp_Mat inertia

Detailed Description

the dimension (length, area or volume)


Constructor & Destructor Documentation

GProp_GProps::GProp_GProps ( )
GProp_GProps::GProp_GProps ( const gp_Pnt SystemLocation)

Member Function Documentation

void GProp_GProps::Add ( const GProp_GProps Item,
const Standard_Real  Density = 1.0 
)
  • initializes the global properties retained by this
    framework from those retained by the framework Item, or
  • brings together the global properties still retained by
    this framework with those retained by the framework Item.
    The value Density, which is 1.0 by default, is used as
    the density of the system analysed by Item.
    Sometimes the density will have already been given at
    the time of construction of the framework Item. This
    may be the case for example, if Item is a
    GProp_PGProps framework built to compute the
    global properties of a set of points ; or another
    GProp_GProps object which already retains
    composite global properties. In these cases the real
    density was perhaps already taken into account at the
    time of construction of Item. Note that this is not
    checked: if the density of parts of the system is taken
    into account two or more times, results of the
    computation will be false.
    Notes :
  • The point relative to which the inertia of Item is
    computed (i.e. the reference point of Item) may be
    different from the reference point in this
    framework. Huygens' theorem is applied
    automatically to transfer inertia values to the
    reference point in this framework.
  • The function Add is used once per component of
    the system. After that, you use the interrogation
    functions available to access values computed for the system.
  • The system whose global properties are already
    brought together by this framework is referred to
    as the current system. However, the current system
    is not retained by this framework, which maintains
    only its global properties.
    Exceptions
    Standard_DomainError if Density is less than or
    equal to gp::Resolution().
gp_Pnt GProp_GProps::CentreOfMass ( ) const
Standard_Real GProp_GProps::Mass ( ) const
  • the total length of the edges of the current
    system if this framework retains only linear
    properties, as is the case for example, when
    using only the LinearProperties function to
    combine properties of lines from shapes, or
  • the total area of the faces of the current system if
    this framework retains only surface properties,
    as is the case for example, when using only the
    SurfaceProperties function to combine
    properties of surfaces from shapes, or
  • the total volume of the solids of the current
    system if this framework retains only volume
    properties, as is the case for example, when
    using only the VolumeProperties function to
    combine properties of volumes from solids.
    Warning
    A length, an area, or a volume is computed in the
    current data unit system. The mass of a single
    object is obtained by multiplying its length, its area
    or its volume by the given density. You must be
    consistent with respect to the units used.
gp_Mat GProp_GProps::MatrixOfInertia ( ) const
Standard_Real GProp_GProps::MomentOfInertia ( const gp_Ax1 A) const
GProp_PrincipalProps GProp_GProps::PrincipalProperties ( ) const
Standard_Real GProp_GProps::RadiusOfGyration ( const gp_Ax1 A) const
void GProp_GProps::StaticMoments ( Standard_Real Ix,
Standard_Real Iy,
Standard_Real Iz 
) const

Field Documentation

gp_Pnt GProp_GProps::g [protected]

The documentation for this class was generated from the following file:
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