Convert line to polyline and spline in AutoCAD

Updated on May 10, 2024 | By Jaiprakash Pandey | Category AutoCAD | min reading time

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At times you may need to convert line to polyline or polyline to a spline and sometimes Spline to a Polyline.

You can do all of these tasks using a few simple commands.

Let’s see the step-by-step method of converting these curves.

Convert Line to Polyline

You can convert a Line to a Polyline using the “Polyline Edit” tool of AutoCAD.

Using this tool you can also convert an arc or a spline into a polyline.

However, you can’t convert a circle, ellipse and elliptical arc into a polyline using this tool.

To start this, type PE on the command line and press Enter to start the “Polyline Edit” command.

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The command line will prompt you to select objects for making changes.

Click on the object which you want to change to polyline.

You can also select multiple objects by selecting Multiple from the command prompt.

Once you have made the selection a new prompt will appear on the command line stating that the “selected object is not a polyline do you want to convert it” as shown in the image below.

Type Y and press enter twice to convert the object into a polyline and exit this command.

Convert Polyline into Spline

To convert a polyline into spline type PE and press enter.

Then select the polyline which you want to convert and select spline from the prompt appearing on the command line.

Press enter to exit the polyline edit command.

This will convert your polyline into a “polyline spline” which looks like a spline but inherits properties of the 2D polyline.

To convert it into true spline type SPE on the command line and press Enter.

This will start the Spline Edit command, select “polyline spline” from the drawing area and press Enter.

The 2D polyline we created in the previous step will be converted into a true spline and it will also inherit all the properties of a spline.

Convert Spline into Polyline

To convert a Spline into a polyline type PE on the command line press enter then select the spline from the drawing area and press enter again.

The spline will be converted into a polyline.

Alternatively, you can also use Spline Edit (SPE) command to convert a “true spline” into a polyline by simply selecting the “Convert to Polyline” option from the command line options.

In this case when the command prompts you to specify the precision enter the default value 10 or any other value which you like.

The higher the value of precision more accurate will be the converted polyline with respect to the spline but it will also create a dense polyline.

The value of precision can be set between 0 and 99.

Making Polyline look like an Arc

You can convert polyline into set of tangentially connected 2D curve that look like arcs.

For this example I will use this drawing.

Double click on Polyline or use PEDIT to start Polyline edit then select Fit from options appearing on the command line.

The Fit option will convert your Polyline into series of tangentially connected arcs.

Control points will be added to the geometry at the position where initially vertices of original polyline were present.

You can modify this new geometry using those control points or grips.

In this case also the Polyline will geometrically change to series of connected arcs but it will still remain a 2D Polyline.

Your final geometry will look like the one shown below.


Converting line to polyline, polyline into spline and spline into polyline is a straight forward thing in AutoCAD but you should always keep precision in mind.

Don't add higher precision value if you don't intend to use it as it will eventually make your file size larger and drawing slower.

If you have questions related to this tip let me know in the comments area down below.

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About the Author

Jaiprakash Pandey is the published author of “Practical AutoCAD book” by Packt publication he is also an Autodesk AutoCAD certified professional and Autodesk expert elite community. He has been delivering CAD training to corporate clients for more than 8 years and his clients include Steel, Power, Automobile industries and also government organizations, fortune 500 companies and the military.

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