CIRCLES & FREE-FORM SHAPES
Any circles oblique to the picture plane appear as ellipses.
To draw such a circle in a para line drawing, we must first draw
a para line view of the square that circumscribes the circle.
Then we can use either of two approaches to drawing the
circle within the square.
• The first is an approximate method. By dividing the
square into quadrants and drawing diagonals from each
corner to quarter points along the sides of the square, we
can establish eight points along the circumference of the
circle.
• The four-center method uses two sets of radii and a
compass or circle template.
·~---- From the m
idpoints of the sides of the square in the
para line view, we extend perpendiculars until they intersect.
With the four points of intersection as centers and with
radii rl and t2, we describe two.sets of arcs in equal pairs
between the origin points of the perpendiculars.
• It is often more convenient todraw aplan oblique rather
tha n an isometric of a circular or free-form plan because
the plan itself can be used as the base drawing and the
horizontal shapes remain true.
We can use agrid to transfer curvilinear or free-form shapes
from an orthographic view to the para line view.
~ __.;.......---
First, we construct a grid over a plan or elevation view of
the shape. This grid may either be uniform or correspond
to critical points in the shape. The more complex the shape,
~
the finer the grid divisions should be.
.______, Then we construct the same grid in thepara line view.
• Next, we locate the points of intersection between the grid
and the free-form shape and plot these coordinates in the
para line view.
• Finally, we connect the transferred points in the para line
view.
80/ ARCHITECTURAL GRAPHICS