Surface constraints are available only for free form surfaces. Local constraints for free form surfaces include Position, Tangent, Curvature, and Normal. You can create new constraints by referencing one of the following entities:

You can use the Align tool to define new constraints or modify existing constraints for a surface. You can use the four collectors on the Align tab to define new or modify existing constraints. The four collectors are Side 1, Side 2, Side 3, and Side 4. Each of the collectors corresponds to a natural boundary of the surface. A surface can have a maximum of four natural boundaries. If any of these boundaries is completely trimmed away by a trimming curve, then the corresponding collector is not available and you cannot create a constraint for that boundary. Only boundaries coincident to the surface’s natural boundaries can be aligned.

By default, any two surfaces that share a two-sided edge each have a position constraint defined at that boundary. You can remove this constraint or change it to a more specific constraint, such as, Tangent, Normal, or Curvature. You can change an existing constraint to any of the other constraints or completely remove them by deleting the reference for the constraint.

All surface constraints except position are of primary-secondary type. The surface that is being aligned follows the reference surface. Only the secondary surface is modified to satisfy the applied constraint.

The Align tool does not allow you to create incompatible constraints. When creating a new constraint, you cannot select any reference that would create a constraint incompatible with other constraints of the surface.

If a surface is aligned to a surface boundary of another base-node branch, the surface constraints are not remembered, that is, their history is not maintained by IDD. Only constraints created by aligning surfaces belonging to the same base-node branch are stored with the surface. However, this is not applicable if the reference geometry is a curve. Constraints created using curve references are never stored, even if they do belong to the same base-node branch.

When you align two surfaces that belong to the same component, the Wireframe of that component is modified accordingly. All surface constraints result in the creation of a two-sided Wireframe piece represented in green, and tangent or curvature surface constraints additionally result in the creation of a tangency condition on the corresponding Wireframe piece. Similarly, if you remove an existing surface constraint, the corresponding piece of the Wireframe is removed.

Tangency, curvature and normal constraints defined by the align tool restrict modification of the aligned surface. However, they do not restrict modification of the primary or reference surface, so it is possible to invalidate the constraint by modifying the reference geometry.

Update of the surface constraints is not dynamic. Hence, modification of reference geometry may result in unsatisfied constraints. To reapply the constraints of a surface, select the surface and use the Align tool again. This automatically modifies the surface to satisfy its existing constraints, assuming the existing constraints are still valid.