Constraint

Introduction
In FreeCAD the word "Constraint" is normally used to refer to a "rule" to draw geometrical shapes inside a Sketch ( class). A constraint limits the position of a certain geometrical element in different ways, for example, it can specify whether the element is horizontal, vertical, tangent, parallel, perpendicular, coincident with a point, concentric to another object, etc.

There are two big types of constraints:
 * define characteristics of the shapes without specifying exact dimensions, for example, horizontality, verticality, parallelism, perpendicularity, and tangency.
 * or define characteristics of the shapes by specifying dimensions, for example, a numeric length or an angle.

See the information in the Sketcher Workbench for a list of all constraints that can be applied. Some of them apply to lines, some to curves, and some to vertices. See also the basic sketcher tutorial.

Usage

 * 1) Create a sketch either from the Workbench_Sketcher.svg Sketcher Workbench or through the Workbench_PartDesign.svg PartDesign Workbench.
 * 2) Press
 * , or
 * 1) * followed by.
 * 2) Double click the created sketch to enter its edit mode.
 * 3) Draw a series of lines using.
 * 4) Pick one of the lines, and use.
 * 5) Pick one of the lines, and use.
 * 6) Pick the vertical line, and use ; assign a distance.
 * 7) Pick the horizontal line, and use ; assign a distance.