Civil 3D 2013: 2D and 3D Polyline Conversion

While working on a grading I needed to change grades along a path that had been defined as a 2D polyline. Well, it is a fact that a 2D polyline cannot hold different elevations at different vertices. This is a property of a 3D polyline. So, is there a way convert the 2D polyline to a 3D polyline? Yes, there is!

I was reminded of two fantastic and very old tools that would let you do just that – Convert 2D polyline to 3D polylines and Convert 3D polyline to 2D polylines.

They are both found under Ribbon tab “Modify” > Expand “Design” Panel Title

After you convert the 2D polyline to a 3D polyline you can then assign different elevations to the vertices per your design.

And if you need to work with grades instead of vertex elevations, you can also convert the 2D polyline to a Civil 3D Feature line using the command Create Feature Line from Objects found under Ribbon tab Home > Design panel > Feature Line flyout.

However, there is one important thing to note when you convert a 3D polyline to a 2D polyline. The new 2D polyline takes the elevation of the start point. Which means you would lose individual vertex elevations of a 3D polyline. This is very similar to the flatten command, except the elevation of the first vertex is maintained instead of pushing everything down to “0” elevation.

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Gaurav Bagga
Ideate Infrastructure Solutions Application Specialist


Gaurav is a well rounded Application Engineer and Project Manager for Infrastructure Solutions at Ideate based out of San Francisco. He has over 15 years experience in construction industry and has been helping numerous small, medium and ENR 500 firms maximize their CAD investment for the last ten years. Gaurav is an Autodesk Certified Instructor and Autodesk Civil 3D Implementation Certified Expert. He has taught at several conferences, CAD Camps and Autodesk University. He has taught AutoCAD, Civil 3D, Land Desktop and Map 3D to thousands of students and helps Ideate develop the Infrastructure Services curriculum and courses. With his extensive CAD technology background he helps Bay Area engineering and surveying firms analyze and improve their design and drawing production process thereby improving productivity and the bottom line. Follow Gaurav on Twitter: @BeGeez

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