How to draw a keypoint line from the tangent at some point on an existing curve or between two curves, or perpendicular to some point on an existing curve.
Draw a line tangent to a curve
The Line Tangent to Curve tool calculates the end point for the line to be tangent to that curve.
Draw a tangent line between two curves
The Line Tangent from/to Curve tool calculates the line tangent to both curves.
I want to edit the coordinates, parallel distance, or angle after I create a line?
Choose Windows > Information > Information Window and change the parallel distance or angle.
The relationships between keypoint curves are maintained until you manually reshape one of the curves.
The tool does not create a true 3D tangent?
The tangent lines are only tangent in the current view. It is only a true 3D tangent if the curve and start point are planar.
To get a true 3D tangent, use the Line tool with curve snapping to place the first point on the curve, then snap to the tangent guideline.
Draw a line perpendicular from a curve
A set of 6 buttons appear in the active window: True|Projected, From Curve|To Curve, Next|Change Settings. The settings from the option box show as active buttons. (See Line Perpendicular Options.)
A keypoint line is created that extends from the point selected on the first curve (to which it is perpendicular) to the location closest to the point selected. If the second item selected was a curve, the line meets the curve at the point closest to where you clicked.
Draw a line perpendicular to a curve
A set of 6 buttons appear in the active window: True|Projected, From Curve|To Curve, Next|Change Settings. The settings from the option box show as active buttons. (See Line Perpendicular Options.)
A keypoint line is created that extends from the selected point to the selected curve and is perpendicular to the curve.
If no perpendicular line can be found on the curve to the specified point, linear extensions are built at the start or end of the curve, and the perpendicular is built from those.