This function finds the smallest rectangle (with sides parallel to
the coordinate axes) that contains all the given objects.

For a window (object of class `"owin"`

), the bounding box
is the smallest rectangle that contains all the vertices of the
window (this is generally smaller than the enclosing frame,
which is returned by `as.rectangle`

).

For a point pattern (object of class `"ppp"`

or `"lpp"`

),
the bounding box
is the smallest rectangle that contains all the points of the pattern.
This is usually smaller than the bounding box of the window of the
point pattern.

For a line segment pattern (object of class `"psp"`

)
or a linear network (object of class `"linnet"`

), the
bounding box is the smallest rectangle that contains all endpoints
of line segments.

For a pixel image (object of class `"im"`

), the image will
be converted to a window using `as.owin`

,
and the bounding box of this window is obtained.

If the argument is a list of several objects, then
this function finds the smallest rectangle that contains
all the bounding boxes of the objects.