Constraint (computer-aided design)

[2] The plural form constraints refers to demarcations of geometrical characteristics between two or more entities or solid modeling bodies; these delimiters are definitive for properties of theoretical physical position and motion, or displacement in parametric design.

Concept of constraints is applicable for both two- (2D) three-dimensional (3D) sketches (including the ones used to create extrusions and solid bodies).

[3]: 29  In his work he argued that the usefulness of a technical drawing made by a computer program relied on their structured nature.

Compared to traditional drawings that lack this feature the virtual ones had advantages in keeping track of and recalculating dimensions of entities (lines, angles, areas etc.).

[5][1]: 203 More advanced 2D/3D CAD systems may allow application of mathematical relationships between constraints that help to save time on reshaping a model.

[1]: 213 In assembly modeling, constraints are widely used to control or restrict design parts movements or relationships between each other.

Some constraints forces models to respond to changes made in a separate part of a designed product.

When constraints are added into a sketch some system may be smart enough to apply additional ones based on pre-existing entities automatically.