Curve Edit > Create > Combine Curves

Creates a 3D curve from two planar curves representing orthogonal projections.

Use this tool to create 3D curves from traditional “plan and elevation” type drawings.

Combine Curves Options

Automatic Direction: Try to figure out the projection axes for the two curves automatically. Leave this option on unless Combine curve guesses wrong and you must set the axes manually.

In some cases, the Combine curve tool cannot automatically figure out the projection directions (for example, if the two curves are in the same plane). In these cases, type the projection axes for the first and second profile curves.
Create History: Save the Combine curve history for later editing. If you turn on Create History, you can edit the profile curves and the combined curve automatically updates.