# Dummy functions

Dummies are multipurpose objects. They can have very specific functions, or they can just be used as helper objects. Following dummy functions are common:

• Used as a point or reference system: This is the case when you want to track the position and/or orientation of a specific point in the scene. The dummy position can be matched to the position of a shape vertex for instance, and will allow to precisely positioning the shape: in the vertex edit mode, create a dummy from a vertex, then attach the shape to the dummy (make the dummy parent). Now you can manipulate/position the shape through the dummy which has the same position as the selected vertex.
• Used as proxy or supporting object for models: Models are defined by marking an object with the object is model base flag. Any object can be the base of a model, however dummies are the prefered objects for that.
• Used as marking points: When evaluating the work space of a robot for instance, a dummy could be positioned at the same coordinates as the robot's end-effector, at various time intervals, and finally the convex hull of all added dummies can be extracted and displayed. Refer to the section on convex hull calculation for more details.
• Used to specify end-effector, and end-effector target positions/orientations in inverse kinematics calculations: The inverse kinematics calculation module handles kinematic chains. Each chain is specified with a base object and a tip object. The tip object has to be a dummy, and often the user positions and orients the tip dummy to coincide with a robot's end-effector. At the same time, in order to move the kinematic chain in inverse kinematics mode, a target position/orientation for the robot's end-effector is required. There again, a dummy is used as the target object.
• Used to create loop closure constraints for mechanisms dynamically simulated: Refer to the section on designing dynamic simulations for more details.
• Used as path following objects: Dummy objects are the only objects that can be assigned to stay on a path (free on path, freely sliding) or to follow the path position (fixed on path, fixed along the path at its current intrinsic position). Following figure shows a dummy assigned to stay on a path:
• [Dummy assigned to stay on a path. The dummy's position and orientation is interpolated from the path's Bezier points]

### Recommended topics

• Dummies
• Dummy properties