# Applying Constraints

Constraints are the restrictions applied to the degree of freedom of a free object. Applying specific types of constraints to elements enables you to conveniently and successfully model a complex geometry.

Constraint tools let you fix various dimensions that control the location and/or orientation of elements on a profile, and also let you fix geometric components relative to each other, so that they remain correctly located even if the underlying geometry or feature is modified.

There are primarily two types of constraints based on what geometry they are applied to:
• 2D Constraints
• 3D Constraints
Both 2D and 3D constraints can be of two types:
• Dimensional - Dimensional Constraints define the exact dimensions of a construction. The dimensional constraining tools let you fix the different dimension of a profile while you can convert them to 3D models honoring your desired dimensions. Also, they let you control the inter-planar dimensions between different components of your built 3D elements.

Using the dimensional 2D constraints tools, you can constrain Length of an Element, Distance between two points, Angle between two line segments, distance between three or more coplanar line segment - making them equal, area of a closed profile, and perimeter of a profile.

Using the dimensional 3D constraint tools, you can constrain the distances between the various components (vertices, edges, and faces) of two 3D elements.

These operations provide you with great potential of controlling the dimensions in your design and hence let you achieve your intent of modeling complex geometries eventually.

• Geometric - Geometric Constraints are non-numerical relationships between the parts of geometric figures which controls the shape of the profile.

Using the geometric constraining tools, you can constrain the different components of an element to be parallel, perpendicular, coincident, concentric, tangent, fixed and equal. These constraints can be applied either to a 2D profile before building it to 3D element, or to the completed 3D elements.

Note: Unlike 2D Constraints, 3D constraints application will not deform a geometry, instead it will transform it. For example, if you apply coincident 3D constrain to a line, which is between two solids, to join the vertex of these two solids, the constraint application will try to relocate the participating geometries to satisfy the coincident constraint but will not change the original length of the line.
Note: When you animate a 3D Constrained geometry the animation sequence will respect the applied 3D constraints.
Tip: 3D constraints can apparently be applied to any entity that can act as one of the faces, edges, or vertices of an element. For example, following entities also participate in 3D constraints:
• Axis of Cones, Cylinders and Tori
• Center point of spheres
• Central axis and edges of circular or elliptical wires
These entities are edges and vertices effectively.
This makes constraining workflow very effective and intuitive. Following figure shows such example where you can constrain holes by the center rather than the edge.