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## Degrees of Freedom

Each geometrical object is defined by its parameters, a point for example, by its 2D co-ordinates. The degree of freedom of a geometrical object is a parameter of the object that can be manipulated freely.
In SISCAD-P the individual geometrical objects can be defined with the following degrees of freedom:

- point - 2 degrees of freedom
  The two 2D co-ordinates.
- line (finite) - 4 degrees of freedom
  The sum of the degrees of freedom calculated from starting and end point.
- line (single infinite) - 3 degrees of freedom
  The sum of the degrees of freedom calculated from the base and the angle.
- line (infinite) - 3 degrees of freedom
  The sum of the degrees of freedom calculated from the base and the angle.
- circle (full circle) - 3 degrees of freedom
  The sum of the degrees of freedom calculated from center and radius.
- circle (arc) - 5 degrees of freedom
  The sum of the degrees of freedom calculated from center, radius as well as starting and final angle of the arc.

As described under Constraints within SISCAD-P, the constraints do not totally restrict geometrical objects but partially. So it is possible that an object which has some constraints may also have some degrees of freedom.

Depending on the number of degrees of freedom of a geometrical object the following terminology is used:

- underdetermined
  A geometrical object is underdetermined, in case it still has some degrees of freedom.

- exactly determined
  A geometrical object is exactly determined, when there are no degrees of freedom.

- overdetermined
  A geometrical object would be overdetermined, if one tries to state contra-dicting constraints.

- fixed
  With the constraint FIXING, a geometrical object is fixed. Other existent constraints of the object can be overlapped then.

The sum of the degrees of freedom of all geometrical objects of one part is the number of the degrees of freedom of this part. A part is underdetermined, when there are some degrees of freedom left and exactly determined, when there are no degrees of freedom left.
The number of the degrees of freedom is a decisive criterion to see how SISCAD-P behaves in parametric drawings when a manipulation is made.
If an object has no degrees of freedom left, SISCAD-P will not change this object for example after modifications of the dimensioning, which do not directly concern this object. If an object has some degrees of freedom left, SISCAD-P is free for modifications of the dimensioning and the object can be manipulated, if necessary.

Next: Working with Constraints Up: Constraints Previous: Constraints within SISCAD-P