[bos #29336] problem in inertia calculus

doc/salome/gui/GEOM/input/inertia.doc

@@ -8,7 +8,20 @@ This operation returns the axial moments of inertia for the selected geometrical
 
 The table displays:
 - 3*3 matrix of its own moments of inertia (in rows <b> 1:1, 2:1</b> and <b>3:1</b>) and  
-- the relative moments of inertia (in row <b>IX & IY & IZ</b>)
+- the main (principal) moments of inertia (in row <b>IX & IY & IZ</b>)
+
+\note 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.
+
+\note There is always a set of axes for which the products of inertia
+ of a geometric system are equal to 0. 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. The principal axes are not reported by this functionality.
+
+\br
 
 \note This dialog supports navigation through the selectable objects (in OCC 3D viewer only):
 - Scroll mouse wheel with pressed \em Ctrl key or press \em "S", \em "P" keys when input focus is
@@ -19,8 +32,8 @@ For more details, please refer to the \em "Functionality common for OCC and VTK
 of the GUI module's documentation.
 
 <b>TUI Command:</b> <em>geompy.Inertia(Shape),</em> where \em Shape is
-a shape for which the own matrix of inertia and the relative moments of inertia are
+a shape for which the own matrix of inertia and the main (principal) moments
-returned.
+of inertia are returned.
 
 See also a \ref tui_inertia_page "TUI example".