Geometry & modeling
Sketch constraint
Definition
A sketch constraint is a rule applied to 2D sketch geometry, such as coincident, parallel, tangent, equal, or a fixed dimension. When a sketch is fully constrained, nothing in it can move freely, which makes later edits predictable.
Also known as: geometric constraint, fully constrained sketch, sketch constraints, sketch relations
Updated
Constraint status#
CAD programs show how constrained a sketch is. In Onshape, sketch colors show the status: blue means underconstrained, black means fully constrained, and red means a constraint problem such as overconstraint.
An underconstrained sketch can still produce a valid part, but it can change shape unexpectedly when an upstream dimension moves. Fully constraining sketches, with dimensions that match how the part is made and inspected, is one of the simplest habits that keeps a parametric model stable.
Sources
Related terms
Parametric modeling
Parametric modeling builds a CAD model from dimensions, constraints, and an ordered list of features, so changing a value regenerates the geometry. It is the default approach in SolidWorks, Fusion, Onshape, Creo, NX, and FreeCAD Part Design.
Design intent
Design intent is the reasoning built into a model's structure: which dimensions drive others, what stays centered or symmetric, and what should move when something changes. Two models that look identical can behave very differently when edited because of how their intent was captured.
Feature tree
A feature tree is the ordered list of operations, such as sketches, extrudes, cuts, fillets, and patterns, that builds a parametric CAD model. Editing an early feature replays every feature after it, which makes controlled changes possible and also makes the model depend on each earlier step.