Job: Modifying the tangency conditions at the endpoints (curve interpolation points)

Modifying the tangency conditions at the endpoints

To modify the tangency condition at the end points when editing a curve with the Curve through Interpolation Points command, you can proceed in one of the following ways:

To move the end point leaving the tangency condition as it is:
Click on the tangent vector in a position close to the end point. Drag the end point to the new position and release the mouse button.
To modify the tangent vector applying the current Rule:
- Set the current rule:
  - Click More Options
  - Select the desired option in the Rule drop-down list
- Right-click on the tangent vector and select Apply End Condition Rule
  or
- Click on the tangent vector middle way between the selected end point and its middle point. The current Rule will be applied:
  - Natural — the section of the curve near the end point has null curvature: it coincides with the tangent to the spline at the end point
  - Circular — the section of the curve near the end point coincides with a circle passing through the three interpolation points nearest to the end point
  - Quadratic — the section of the curve near the end point coincides with the curve of degree 2 through the three interpolation points nearest to the end point.
  - Cubic — the section of the curve near the end point has the shape of the cubic curve through the four interpolation points nearest to the end point.
To modify the tangent vector direction, while keeping its magnitude unchanged:
- Right-click on the tangent vector and select Set Tan Direction
  or
- Click on the tangent vector close to its middle point. The tangent vector starts moving along as you move the mouse. Click in the position defining the new desired direction for the tangent vector.
To modify the tangent vector magnitude, while keeping its direction unchanged:
- Right-click on the tangent vector and select Set Tan Magnitude or
- Click on the tangent vector middle way between its middle point and its far end point. The tangent vector extension changes as you move the mouse. Click in the position defining the new desired length.
To modify both direction and magnitude of the tangent vector:
- Right-click on the tangent vector and select Set Tangent
  or
- Click on the tangent vector close to its far end point. The tangent vector starts moving along as you move the mouse. Click in the position defining the new desired direction and magnitude for the tangent vector.

You can modify the tangent vectors of more than one curve contemporarily, so that they become either parallel or with the same magnitude or even both parallel and with the same magnitude.

1	Select the two curves and apply the Curve through Interpolation Points command.
2	Select the first and the second vector (holding down the SHIFT key)
3	Click: Middle way between the end point and the middle point to apply the current Rule (shortcut menu: Apply End Condition Rule). Close to the middle point of the second vector to change the magnitude of the first vector to the one of the second (shortcut menu: Set Tan Magnitude). Middle way between the middle point and the far end point of the second vector to change the direction of the first vector to the one of the second (shortcut menu: Set Tan Direction). Close to the far end point of the second vector to change both the direction and the magnitude of the second vector to the ones of the first (shortcut menu: Set Tangent).