17 4 Macintosh
User's
Handbook
Now, let's create the ellipse using a reference rectangle.
Erase the two ellipses
just
created and
draw
a rectangle with the
same width
and
height. We will begin
and
end all ellipses
somewhere
on
the perimeter
of
this rectangle.
Draw
an
ellipse
by placing the cross hairs exactly
at
the
upper
left
corner
of
the
rectangle, and drag to the lower right corner. The exact posi-
tioning
of
the start and finish points
is
easy. Notice
that
the
cross hairs
turn
white as they pass over the black portions
of
the screen.
To
position them
on
the
upper
left corner, insure
that
the lower
and
right
arms
of
the cross hairs
turn
white
indicating
that
they exactly outline the upper left corner
of
the
rectangle. This
is
call the
dot
inversion technique. Now,
draw
the ellipse from
that
point to the opposite corner.
It
will exactly
fit within the rectangle. The reference rectangle has enabled
exact placement
of
the ellipse.
To
place
another
ellipse within the first ellipse, place the
cross hairs exactly
on
the left side
of
the reference rectangle
and
drag
to
the opposite side.
It
is
simple to
judge
center placement
since there
is
no question
that
the new ellipse will fit. The result
is
depicted in figure 6.10.
Though
it may be possible to judge one concentric ellipse
without the reference rectangle, it
is
much more difficult
to
judge multiple ellipses. A sample using this method
is
shown in
figure 6.11.
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