The tangency constraint makes the X axis of a constrained object tangent to a direction or curve. This is particularly useful for having an object follow a path’s direction, such as a roller coaster car following the tracks, or pitching an object (especially a camera) on a path.
Tangency is not a “real” constraint per se, but is available as a property (actually a low-level expression that determines which direction the object should point) of these other constraints: the Surface, 3-Point, Curve (Path), and Object to Cluster.
Because the tangency constraint is not a real constraint, you cannot view it as you do other constraints in a 3D view or the schematic view.
To set a tangency constraint
1. Select an object and apply any of these constraints which have a tangency property: Constrain > Surface, 3-Point, Curve (Path), or Object to Cluster.
2. In the constraint’s property editor, click the Tangency tab and select the Active option.
3. Use the Axis to Align controls to specify the axis to point along—X is the default. You can either click the axis buttons (positive and negative X, Y, Z) or enter 1 or -1 in the axis text boxes.
If two or more values are non-zero, the constrained object points along the resulting vector.
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