Geometric Constraints

Geometric constraints allow you to fix a position of an element inside the Boolean tree. Whenever a shape of the solid is changed, the position of constrained elements is redefined according to a new shape.

Definition of Constraints

Constraints may be defined:

• If a new object is created and its location is defined
• If objects are inserted from a file or clipboard and their location is defined
• If an object is selected for transformation. In such a case, you may select an element from the Boolean tree (for instance, a hole). Constraints are defined within an existing solid. Or, you may select one or more entire solids. Then, the constraints may be defined only if you perform an additional Boolean operation and these solids are add to or cut from an existing root solid. The constraints are defined within such a complete solid.

Constraints cannot be defined:

• If you select the entire solid and a solid element.
• If you select multiple elements belonging to multiple solids.
• If an object is inserted from a mechanical part library.
• If the selected element belongs to a Boolean tree, but the other elements are only blendings.
• If you select multiple elements and they are already constrained in different groups.
• If you perform complex solid editing.

To define a constraint, click the inner part of corresponding object’s axes. Optionally, you may click an icon in the Constraint panel. To edit a constraint, click the outer part of an axis. Then you may select:

• Delete the constraint.
• Highlight the constraint.
• Edit a distance used in the constraint (not available for all types of constraints)

You may work with constraints within a function transforming solids or their elements, see Additional Boolean Operation, Constraints Definition. The constraints can be created or edited after the location is defined. Another option is to skip a location definition:

Geometric Constraints, CST

This function works with constraints without necessity to define a location.

Either for the function “Solid Transformation” or “Geometric Constraints”, transformations necessary for a particular constraint are always performed. It is more convenient to define a location and then to switch to constraints definition than to define a location only within the constraint definition. Transformation possibilities within the constraint definition are limited.

Constraint definition, Constraint panel

Constrained Objects

Constraints fix a constrained object in its movement along an axis or in rotation around the axis. The constraining is performed for the insertion point of the object. You may change a location of the insertion point until constraints are defined. Then you may change the location of the insertion point only temporarily within the current function. The change is not accepted permanently.

Also, you cannot change permanently a location of the insertion point, if the corresponding element is an anchor for another constrained object and this object is constrained right to the insertion point.

Selecting Constrained Objects

This option, which is available for objects selection, allows you to select an entire constrained group.

If you select elements of a solid for transformation, the complete constrained group is detected. You cannot change a location of a single element of the constrained group individually.

Automatic detection of a constrained object is displayed at the cursor:

Cursor	Use
	A constrained group or constrained object is detected
	The already constrained object cannot be selected for the current constraint definition

Constraining Multiple Objects

You may select multiple objects for constraining. The insertion point is the point of the first selected object. If you need to add a new object into a constrained group, select the group and a new object (or multiple new objects). They are added automatically.

This option, which is available in the Constraint panel, allows you to remove an object from the constrained group.

Cancel All Constraints

This option, which is available in the Constraint panel, cancels all constraints of the currently defined group.

Types of Geometric Constraints

All constraints are related to a specified axis. Direction of the axis may be selected along or against to a normal or another axis in dependence on a particular situation.

Definition of a constraint rewrites all existing constraints whose fix any axis of the object the same way as the new constraint. Fixed movements, fixed rotations or defined directions for the constrained object are displayed in the upper part of the Constraint panel.

Available Types of Geometric Constraints

Distance to solid's insertion point. Constrained object is at a defined distance from the insertion point of a selected object (another solid element). Distance may be both positive or negative (along or against the axis arrow), or zero. This type of the constraint is often used for definition of a distance between holes or other solid elements.

Distance from a patch, the axis is not directed. Intersection between the axis and the selected patch is calculated. The constrained object is fixed at a specified distance from the intersection.

Location at a patch, the axis is not directed. This constraint is similar to the previous, but the distance is always zero.

Location at a patch, the axis is directed according to a normal. The nearest point at a patch is found. Then the object is moved to the nearest point and the corresponding axis is directed against or along the normal of the patch at the location. This type of the constraint fixes the object at a surface and adjusts always its orientation. It can be used often for location of a hole – the object is always at the surface and the axis is always oriented perpendicularly to the surface.

Location at a circle center, the axis is directed according to the normal of a planar surface. This constraint is especially usefull for joining pipe or shaft segments.

The axis is directed according to a plane normal. This constraint is performed always as first before the other constraints. It defines orientation of the constrained object. Only one axis can be oriented this way.

The axis is directed according to a rotation axis. The axis is parallel to the axis of the rotation surface.

Object is constrained at a distance from a rotation axis. An axis selected from the remaining two axes is simultaneously directed according to the rotation axis.

Removing Constraints According to Corresponding Axes

Clicking an outer part of object’s axes, you may select deletion of the corresponding constraint (see above). If you need to cancel the constraining of a selected axis, use following options:

Constraint fixing movement along the axis is deleted.

Constraint fixing rotation around the axis is deleted.

Constraint fixing alignment of the axis is deleted.

Chain of Constraints

Constraints within a solid cannot be defined without a limitation. Basically, if an object A is constrained to an object B, then the object B cannot be constrained to the object A. All objects can be constrained to an object which is not constrained further.

If the object A is constrained to the object B (for instance, fixed at a distance from a patch of the object B), and the object B is constrained to the object C, a sequence of objects A, B and C creates a constrained chain.

Regarding the already existing constraints, you cannot anchor a constrained group at an object, if:

• The object is from a different solid.
• The object is from a different chain of constraints,
• The object is constrained at the currently defined group, not only directly, but also over multiple constrained links.

System automatically blocks the selection of anchors, if the constraint is not possible. The cursor is automatically changed at such a situation (see Selecting Constrained Objects

Chain of constraints

Fixed Object within Constraints

When the position of constrained elements is redefined according to a new shape, it may be moved inconveniently. For instance, you may define a chain of constraints within a shaft. After changing a length of a segment, all remaining segments are moved. You may want objects to be moved in opposite direction. You can fix a selected element from the entire solid. Then the element remains always in the same position – it is not translated or rotated. If no element is fixed then elements without constraints remain at the same location.

This option, which is available in the Constraint panel, allows you to fix a selected element to the current location.