If the get was a GetObjects() and the mouse was used to select the objects,
then the returned rect has left < right and top < bottom. This rect
is the Windows GDI screen coordinates of the picking rectangle.
RhinoViewport.GetPickXform( pick_rect, pick_xform )
will calculate the picking transformation that was used.
In all other cases, left=right=top=bottom=0;
RhinoCommon (in RhinoCommon.dll)
public Rectangle PickRectangle()
Public Function PickRectangle As Rectangle
The picking rectangle; or 0 in the specified cases.