 Spline Tool
Naval architects, highway engineers, illustrators and aircraft
designers use flexible metal or plastic rulers to draw smooth
curves connecting a series of points. The Spline tool provides
the ability to do the same thing in a PowerCADD drawing.
Splines can be reshaped by moving the handles.
A 'smooth curve' is not an easily defined entity; however,
for the purposes of this tool, an important requirement is that
a spline connecting points along a circle should match the curve
of a circle. Additionally, when the curve changes radius or direction,
the curve should transition smoothly. Curve fitting methods used
by many so-called 'powerful' CAD system are notoriously inadequate--many
depend on such crude methods of fitting a series of arcs, while
others depend on adjusting points that are well off the curve.
The curves produced are almost always lumpy, and they are difficult
to edit.
The Spline tool uses Bézier curve segments and automatically
calculates the control handle positions. Three spline methods
are provided.
To draw a spline, you draw with the same method that you use
to draw a polygon. When the drawing operation is complete, the
smooth spline is placed in the drawing. As shown above, there
is a handle at each point placed, and you can move these handles
around with the mouse and the curve automatically reshapes. You
can create a parallel spline with many different offsets with
the Parallel Offset tool, and these parallel objects behave just
like a normal spline.
Reshaping Splines with the Spline Tool
The Spline tool can be used to reshape existing splines and parallel
splines. This allows you to 'resume drawing' an existing spline,
add or delete points and close/open splines. To do this, press
and hold down the Option key. The cursor will change to an Arrow
cursor. Click on the object in the drawing. The spline will be
redrawn on the screen as a 'ghosted' object.
The action of the reshaping operation is the same as that of
the Polygon tool, except that you cannot drag a 'leg' of the spline
as you can with a polygon.
Converting Objects to a Spline
The Spline tool also allows you to convert an existing polygon
to a spline or to convert one type of spline to another. This
also works with Parallel Objects of the same base type. To do
this, press and hold down the Shift and Option keys. The cursor
will change to a Yin-Yang cursor. Click on the object in the drawing.
The object will be converted.
 B-Spline Tool
The B-Spline tool allows you to draw B-splines-commonly called
'smoothed polygons'. In addition, the tool provides a reshape
mode to add and delete points from existing B-splines and parallel
B-splines as well as the ability to convert polygons and parallel
polygons to B-splines.
To draw a B-spline, you draw with the same action as the Polygon
tool, that is, with a succession of clicks.
Reshaping B-Splines with the B-Spline Tool
The B-Spline tool can be used to reshape an existing B-spline
or parallel B-spline. This allows you to 'resume drawing', add
or delete points and close/open a B-spline. To do this, press
and hold down the Option key. The cursor will change to an Arrow
cursor. Click on the object in the drawing. The B-spline will
be redrawn on the screen as a 'ghosted' object. The action of
the reshaping operation is the same as that of the Polygon tool,
except that you cannot drag a 'leg' of the B-spline as you can
with a polygon.
Converting Objects to a B-Spline
The B-Spline tool can be used to convert a polygon, spline or
Parallel Object of the same base type to a B-spline. This allows
you to 'smooth' a polygon or parallel polygon. To do this, press
and hold down the Shift and Option keys. The cursor will change
to a Yin-Yang cursor. Click on the object in the drawing. The
object will be converted. |
