If you’re trying to turn a corner and transition smoothly from a circle to a square (for example) the morphing option in the Spirix plugin will do this for you. As an example, start with a template of the circle and square. In this case, construct the circle using 24 segments and group the result. Create the square using four lines and group it as well. Position the groups in the X/Z plane along the x-axis at the radius of curvature you want (18" in this case):
In order to use the plugin to morph one shape into another, the profiles must be created in sequence and made into groups using the Create Group option in the Spirix plugin. To create the circular profile, create an arc using 12 segments from C1 to C3 with the height at C2. Then create a second arc from C3 to C1 using C4 as the height. Use the Spirix Create Group and name this “circle”. Now create a line from S1 to S2 and then use the right-click context to divide it into 6 segments. Create a second line from S2 to S3 and divide it as well. Continue for two more lines ending with S4 to S1 divided. Use the Create Group function and name this one “square”. Now run the Create Surface option with the following:
The Spirix plugin can be found here: spirixcode