What are Constraints?

There are times when simple sketches are adequate for your design process, but you will often need to work on more complex sketches requiring a rich set of geometrical or dimensional constraints.

The Sketcher workbench provides constraint commands which allow you to fully sketch your profiles.

Sketcher constraints are of two types:


The location you click when selecting the elements to constrain is taken into account to create the constraints (it is used to position the constraints accurately). Therefore, when selecting the elements to constrain, it is important that you click where you want the constraint to be positioned. The software will then position the constraint according to the area where you clicked. This is especially true when creating constraints on certain types of curves (complex curves like splines, for example). In some cases, if you don't click in the right place when selecting the curve to constrain, the constraint and the geometry will be inconsistent.

Topics discussed are:

Related Topics
Using Colors
What about Constraint Visualization?

Geometric Constraints

A geometric constraint is a relationship that forces a limitation between one or more geometric elements.

For example, a geometric constraint might require that two lines be parallel. If you select three lines, or two lines and a point, these elements will automatically result parallel to each others, as illustrated in the table further down.

You can set a constraint on one element or between two or more elements.

Number of Elements Corresponding Geometric Constraints
One Element Fix

Horizontal

Vertical
Two Elements Coincidence

Concentricity

Tangency

Parallelism

Midpoint

Perpendicularity
Three Elements Symmetry

Equidistant Point

When creating a constraint, remember that:


  • A green constraint is a valid constraint by default.

  • Conversely, a yellow constraint indicates that the definition is not valid.

The software lets you customize the colors and more generally the style of the constraints you use. To have details about these capabilities, see the Sketcher customization section of this guide.

When you position the cursor on constraint symbols, the software calls your attention on the elements involved in the constraint system.

Dimensional Constraints

A dimensional constraint is a constraint whose value determines geometric object measurement.

For example, it might control the length of a line, or the distance between two points.

You will use Constraint to finalize your profile. The Constraint command allows you to set dimensional or geometric constraints but you will mainly use it to set dimensional constraints.

You can combine dimensional constraints to constrain a feature or sketch.

You can set a dimensional constraint on one element or between two elements.

Number of Elements Corresponding Geometric Constraints
One Element Length Radius/Diameter Semimajor axis Semiminor axis
Two Elements Distance Angle

You can apply a diameter constraint between two lines provided one of these lines is an axis line.

Important: The application does not take into account negative values.

What about Constraining While Sketching?

Provided you previously activated Constraint , sketching certain elements automatically generates constraints although you did not specify that you wanted these elements to be actually constrained.

Creating a Constraint Between a 2D and a 3D Element

When you need to create a constraint between a 3D element and a line, it may result impossible. You will therefore have to use manually the projection operators.

When you need to create a constraint between a 3D element and a line, for example, this creation may result impossible. This is the case when the projection or intersection resulting use-edge does not give a unique solution. In other words, the use-edge (projection of one side of a pad) corresponds to several limit edges of the side.

As a result, you will not be able to select this 3D element when creating the constraint. You will therefore have to use manually the projection operators.

What is SmartPick?

SmartPick is an intuitive, easy-to-use tool designed to make all your Sketcher creation and edition tasks as simple as possible.

SmartPick dynamically detects the following geometric constraints:


  • support lines and circles
  • alignment
  • parallelism
  • perpendicularity
  • tangency
  • concentricity
  • horizontality and verticality
  • midpoint

Constraints and Geometrical Supports

When you apply constraints on curves, lines, circles and ellipses, the complete geometrical support is taken into account.

In the example below, SmartPick is active as you are creating a line. This capability detects a coincidence constraint between the line and the support of the arc.