Parametric Curves

The Sketcher can manipulate points, lines, circles and ellipses but can also manage splines and nurbs. This section is an overview of specific over-constrained and inconsistent problems on parametric curves.

This page discusses:

Curve Creation

These parametric curves can be created:

  • Through an intersection or projection of 3D geometry in the sketch. After isolating the resulting geometry, you can use constraints to change the position of the curve. The system is unable to directly modify the shape because the curve, which has no internal freedoms that the system can control, only has three degrees of freedom.
  • Using Spline . The curve is defined from other geometries. The parametric curve is said dependent. It is constructed so it passes through a series of control points.

Constraints and dimensions can be added between a dependent parametric curve and other geometries in the sketch.

Solving problems will occur:

  • If the position of the defining geometry depends upon the position of the parametric curve, either directly or indirectly.
  • When the other geometry of the constraint or dimension is an other parametric curve or dependent parametric curve.

Recommendations

Always use Constraint without dialog box to specify where the constraint must be created on the curve. When using this command, selection points are not taken into account.

On fully under-constrained sketches, the system can have difficulties in choosing between changing the shape and/or moving its defining geometry especially when it supposes to make large changes. Moving the geometry helps the system find a consistent solution in that case.