FIGURE 1.23 Sketch motion is becoming more constrained.
In addition to sketch relations. dimensions applied using the Smart Dimension tool are also part of the parametric scheme. If you apply an angle dimension (by clicking the two angled lines with the Smart Dimension tool) about the origin and try dragging again, as shown in Figure 1.24, you see that the only aspect that is not locked down is the length of the sides. Notice also that when the angle dimension is added, another line turns black.
FIGURE 1.24 Open degrees of freedom can be dragged.
Finally, adding length dimensions for the unequal sides completes the definition of the sketch, as shown in Figure 1.25. At this point, all lines have turned black. This is the state that we call “fully defined.” Between the dimensions and sketch relations, there is enough information to re-create this sketch exactly.
It is considered best practice to fully define all sketches. However, there are times when this is not practical. When you create freeform shapes, generally through the use of splines, these shapes cannot easily be fully defined, and even if they are fully defined, the extra dimensions are usually meaningless, because it is impractical to dimension splines on man- ufacturing drawings. BEST PRACTICE
It is the idea of reacting to change that is of most concern regarding parametric sketching. There are other factors that can also drive the sketch, such as equations, other model geometry that is external to the sketch, and even geometry from another part in an assembly, as you shall see later.