Graphics Programs Reference
FIGURE 2.8 The Sketch tab's Constrain panel
Coincident This constraint is by far the most common. It can be placed between
endpoints, between midpoints, and even between a point and a curve or line. If
you want a point to maintain a relationship with just about anything, Coincident
will do it.
Collinear This simply tells lines to be aligned with one another.
Concentric For a Concentric relationship to be placed, you need to have at least
one arc and one circle. Two arcs or two circles will also work. This is essentially
a specialized Coincident constraint used only for the centerpoint of a radius.
Because an ellipse also has a centerpoint, it will work with that shape as well.
Fix The Fix constraint enables you to hold a position on a point. It can be use-
ful for positioning critical points while others are allowed to move freely around
them. Fixing a point is sometimes referred to as grounding the point. You can
also use Fix on lines, arcs, circles, and so on.
Parallel This constraint is also commonly applied while sketching. Like all
constraints, it's maintained until it's removed. If one of the members of the con-
straint relationship changes direction, the other does as well.
Perpendicular This constraint creates a relationship between line segments
that keeps them at 90 degrees. It's commonly placed automatically while
Horizontal and Vertical These two constraints can occasionally catch you off
guard. It's important to remember the orientation to the coordinate system.
Vertical relates to the Y axis of the active sketch, and Horizontal relates to the
X axis. These constraints are used for far more than keeping lines oriented. You
can constrain a point to be vertical or horizontal to another point. This can aid
in aligning critical points as you develop around them. A keyboard shortcut is
available for the Vertical constraint: while in a sketch, pressing the I key starts
the constraint placement.
Tangent You can create this condition between lines and arcs, arcs and splines,
and circles and other circles.