PEDIT: Convert Lines to Polylines

In AutoCAD, it’s common to inherit drawings where geometry looks clean but behaves poorly. Imported CAD files, exploded blocks, or older drawings often contain collections of individual lines that visually form a shape but aren’t actually connected. These drawings work — until they don’t.

Commands like OFFSET, HATCH, FILLET, and STRETCH all work more reliably when geometry is combined into a single polyline instead of many individual line segments. Converting lines to polylines is one of the simplest ways to clean up drawings, reduce object counts, and make geometry easier to edit.

The most direct way to do this is with PEDIT, but there is also a second, often-overlooked method using FILLET that behaves very differently — and in some cases works when PEDIT does not. Understanding the difference between these two approaches is the key to choosing the right tool for the situation.

What Actually Changes When Lines Become a Polyline

When lines are converted into a polyline, AutoCAD does not change their location or dimensions. The geometry stays exactly where it was. What changes is how AutoCAD treats that geometry.

Instead of multiple independent LINE objects, AutoCAD creates a single POLYLINE object that contains multiple segments. Those segments can include straight lines, arcs, or a combination of both. From that point forward, AutoCAD treats the shape as one continuous object.

This matters because many Modify commands behave differently with polylines. OFFSET works more predictably, FILLET applies consistently, and HATCH can detect boundaries without manual intervention. Grip editing also becomes more powerful because vertices can be moved without breaking the shape into pieces.

Converting lines to polylines doesn’t redraw your work — it simply organizes it in a way AutoCAD prefers.

Method 1: Convert Lines to a Polyline Using PEDIT (Endpoint-Based)

PEDIT is the most explicit and controlled way to convert lines into polylines. It is also the method most users are familiar with — and the one most tutorials stop at.

Step-by-Step Workflow

Start the PEDIT command and select a line. Because a line is not a polyline, AutoCAD prompts you to convert it. Accept the conversion. That single line is now a polyline.

Once one object is a polyline, you can use the JOIN option within PEDIT to add additional line segments. Each line you join becomes part of the same polyline, creating one continuous object.

This process works well when geometry is already clean.

PEDIT prompts to convert a selected line into a polyline before editing

PEDIT JOIN combines connected line segments into one polyline

The Critical Limitation of PEDIT / JOIN

PEDIT with JOIN has an important constraint that is easy to overlook:
The line and polyline must already share an endpoint.

PEDIT does not trim, extend, or adjust geometry to make connections. It assumes the endpoints already touch — or are close enough to fall within the fuzz distance tolerance.

If one line overshoots another, stops short, or appears connected but actually has a tiny gap, JOIN will fail. Increasing fuzz distance can help in some cases, but fuzz distance does not fix geometry that fundamentally does not meet.

Key takeaway:

PEDIT joins geometry that already connects. It does not make geometry connect.

Method 2: Convert and Join Lines Using FILLET (Trim/Extend-Based)

FILLET behaves very differently than PEDIT — and that difference is exactly why it sometimes succeeds when PEDIT fails.

When the FILLET command is applied between a polyline and a line, AutoCAD does three things automatically:

1. Trims or extends the objects so they meet
2. Converts the line into a polyline
3. Joins everything into a single polyline

This mirrors how FILLET works when joining two lines, but with an added benefit: all resulting geometry becomes part of one continuous polyline.

Important distinction

This workflow uses the standalone FILLET command, not an option within PEDIT. While PEDIT includes a JOIN feature (which behaves slightly differently than the standalone JOIN command), PEDIT does not include a fillet option. The trimming, extending, and automatic conversion described here occur only when using the actual FILLET command. FILLET operates independently of PEDIT and applies its own geometric rules before joining objects into a polyline.

FILLET with Radius = 0 (Sharp Corner)

When the fillet radius is set to zero, AutoCAD trims or extends the objects so they meet at a sharp corner. No arc is created, but the objects are still joined. The line is converted into a polyline and becomes part of the existing polyline.

FILLET with a Radius (Arc Created)

When a fillet radius is specified, AutoCAD trims or extends the geometry and creates an arc. That arc is not a separate object — it becomes another segment of the polyline. The result is a single polyline containing straight segments and curved segments, all connected cleanly.

FILLET trims or extends geometry, converts the line, and joins it to the polyline

Why FILLET Works When PEDIT Does Not

PEDIT / JOIN	FILLET
Requires shared endpoints	Trims or extends geometry
Does not modify geometry	Actively modifies geometry
Explicit conversion step	Conversion happens automatically
Best for clean geometry	Best for imperfect geometry

Key takeaway:

FILLET creates the joint first — then joins the geometry into a polyline.

Common Problems When Converting Lines (and How to Fix Them)

One of the most common frustrations with PEDIT is geometry that looks connected but refuses to join. Zooming in often reveals tiny gaps, overlapping endpoints, or lines that stop just short of each other.

Imported drawings frequently contain Z-value mismatches, where objects appear aligned in plan view but are technically on different planes. In these cases, JOIN may fail even though everything appears correct.

Tiny gaps between endpoints prevent lines from joining into a polyline

When geometry is nearly correct, fuzz distance may help. When geometry clearly does not meet, FILLET is often the better tool because it trims or extends objects as part of the operation.

If neither method works, cleanup may be required — but understanding why a join fails makes that cleanup far more efficient.

When You Should (and Should Not) Convert Lines

Good Candidates for Conversion

• Closed boundaries
• Profiles
• Shapes used for OFFSET or HATCH
• Geometry intended to behave as a single object

When Conversion Is Unnecessary

• Construction geometry
• Temporary layout lines
• Intentional segmented drafting

Polylines are powerful, but not every line needs to become one.

CAD Master Coach Tip: Choose the Tool That Matches the Geometry

• Use PEDIT when geometry already connects cleanly and you want precise control.
• Use FILLET when geometry needs trimming or extending anyway.

AutoCAD commands overlap by design. The fastest workflows come from choosing the command that matches the condition of the geometry — not forcing one tool to do everything.

Related Commands You’ll Use with Converted Polylines

Command	Why It Matters
PEDIT	Edit vertices, widths, joins
JOIN	Combine already-connected geometry
FILLET	Trim, extend, and join geometry
OFFSET	Create parallel geometry
TRIM	Clean intersections
HATCH	Detect closed boundaries

Frequently Asked Questions (FAQ)