Geometry & modeling
Geometric constraint solver
Definition
A geometric constraint solver calculates the positions and dimensions of sketch geometry so declared relationships, such as parallel, perpendicular, tangent, equal, coincident, and fixed dimensions, are satisfied together. It lets a designer define intent instead of calculating every coordinate by hand.
Also known as: constraint solver, sketch solver, geometric solver
Updated
The solver and the constraints are different things#
A sketch constraint is one rule, such as making two lines parallel or setting a distance. The solver is the system that finds geometry satisfying all the rules at once. As constraints are added, it removes degrees of freedom until the sketch is fully constrained.
Zoo's May 2026 sketch-mode announcement describes this process in Design Studio: rough geometry can be dimensioned, related, and fixed until it can no longer move. The solver is integrated with both point-and-click sketching and KCL.
Underconstrained and overconstrained sketches#
An underconstrained sketch still has one or more free movements, so a later edit can move geometry in an unintended way. An overconstrained sketch contains redundant or conflicting rules that the solver cannot satisfy cleanly.
CAD systems expose those states differently. Onshape's constraint documentation, for example, uses sketch colors and constraint indicators to show whether geometry is underconstrained, fully constrained, or in conflict.
Why the solver matters#
A solver turns geometric intent into repeatable behavior. It is what lets a designer say that two edges remain parallel or that a hole stays centered when the surrounding dimensions change. A valid result still depends on good constraints: the solver can enforce the relationships it receives, but it cannot decide which relationships the design should have.
Sources
Related terms
Sketch constraint
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.
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.
KCL
KCL is Zoo's text-based programming language for parametric CAD. It is the source representation behind Zoo Design Studio models, so point-and-click actions and Zookeeper prompts can produce code that people can read, edit, reuse, and track with version control.