# Working with Multiple Curves

This system allows you to design and work on a number of curves at the
same time on the drawing canvas.

Design the first curve has no mystery. Just follow the procedure described
in **Creating Curves**. To design the
second and all subsequent curves, use the same procedure:

- Select
**Curve**, followed by
**New Curve Segment**, followed by
the type of curve you want.
- Select a degree (if it is a B-spline or NURBS curve) and put a
number of control points on the drawing canvas.
- Select
**Curve**, followed by
**Show Curve Segment**, followed by
the type of knots (*i.e.*, clamped, open or closed) you want.
Then, a second curve will appear on the canvas.

Therefore, creating the second and all subsequent curves is essentially the
same as creating the first one.
The left figure below is a Bézier curve of degree 6. Then, follow the
above procedure to design a B-spline curve of degree 4. This is shown in the
right figure .

### Switching Among Curves

Now we have more than one curves on the drawing canvas. We really need some
way to select and work on one of them. This comes the concept of the
*current curve*. The current curve is the curve you can edit
and transform. If there are more than one curves on the drawing canvas, the
current curve is always thicker with brighter color. When you create a new
curve, that curve is the current curve. For example, in the right figure
above, when the B-spline curve of degree 4 is created, it becomes
the current curve.

Since only the information about the current curve (*i.e.*, type, degree
and knot vector) are shown in various buttons and sliders, you can work on
the current curve only.

In the system, all curves are stored in the order they are created. Thus,
given any curve, one can always find its next and previous ones. The next
(*i.e.*, previous) curve of the last (*resp.*, first) curve is the
first (*resp.*, last) curve on the canvas. There are two ways for
changing the current curve. The first one uses the menu items, while the
second uses the *Display & Tracing Options Window*.
Select **Curve**, followed by
**Next Curve Segment**
(*resp.*, **Previous Curve Segment**)
to make the next (*i.e.*, previous) curve the current curve.

Or, you can bring up the *Display & Tracing Options Window*
by selecting **Window** followed by
**Display & Tracing Options**. Near the
bottom, you should see two buttons
**Next Curve** and
**Prev Curve** as shown in the figure
above. Clicking on the former moves to the next curve, while clicking the
latter moves to the previous curve.