Polyline

The polyline command draws a connected path of any number of straight segments, all stored as a single LWPOLYLINE entity. Because the entire path is one object, selecting it selects every segment at once — move, rotate, or scale the whole shape in a single operation. This is the key distinction from chained Lines, where each segment is an independent entity.

Polylines can also be closed: the Rectangle command uses the same LWPOLYLINE entity with a close flag set.

Drawing a polyline

1. Type polyline in the terminal or click the Polyline toolbar button.
2. Click the first point, or type X,Y and press Enter for an exact coordinate.
3. Click each subsequent point — each click adds a segment. Coordinate entry works at every step.
4. Press Enter or Space to finish (requires at least 2 points placed).

  ●──────●
  1st    2nd
          \
           \  segment 3 (in progress — cursor here)
            ●  ← click to add, Enter/Space to finish

Pressing Escape at any time discards all placed points and exits the command.

Coordinate entry

Instead of clicking, type an exact position for any vertex:

1. Type the X value.
2. Press , — the terminal shows [X], [Y{cursor}].
3. Type the Y value.
4. Press Enter to place the vertex.

Angle locking and exact segment length

The same 45° snap logic as the Line command applies between any two consecutive points. When locked to an axis:

Key	Action
0–9, .	Append digit to the segment length
-	Negative length — reverses direction along the axis (first character only)
Backspace	Delete the last typed character
Enter	Place the next point at the typed distance

The current accumulated length appears in the terminal prompt in real time. Clicking while locked projects onto the axis so the new vertex lands exactly on it.

Keyboard reference

Key	Action
0–9, ., -	Start X coordinate entry, or segment length when angle-locked
,	Lock X and move to Y entry
Backspace	Delete last typed character
Enter	Confirm typed coordinate or length, or finish the polyline if nothing is typed and ≥ 2 points exist
Space	Finish the polyline (same as Enter when no input is in progress)
Escape	Discard all points and exit

Grip editing — vertices and segment midpoints

A selected polyline shows two types of grips:

Grip	Position	What it does
Vertex	At each placed point	Drag to reposition that vertex; all connected segments stretch to follow
Segment midpoint	Centre of each segment	Drag to translate both endpoints of that segment together, keeping the segment length and angle intact

The segment-midpoint grip is unique to polylines — it lets you slide an individual segment sideways without changing its length. On a Line, the midpoint grip instead activates the Move command for the whole entity.

There is no single "move the whole polyline" grip. To move the entire path use the Move command.

Selecting polylines

Method	Behaviour
Click	Selects the polyline if the click lands within hit-test distance of any segment
Drag right (strict)	All vertices must fall inside the box
Drag left (crossing)	Any segment that crosses the box boundary selects the whole polyline

Because a polyline is one entity, a crossing selection that touches any segment selects all segments.

Supported edit commands

Polylines support all general transformations and offset, but not trim or extend (those are Line-only):

Command	What happens to the polyline
Move	Translates all vertices by the same displacement
Copy	Creates an identical polyline at a new position
Rotate	Rotates all vertices around the chosen base point
Mirror	Reflects all vertices across the mirror axis
Scale	Scales all vertices uniformly from the base point
Offset	Creates a parallel polyline at a fixed perpendicular distance
Delete	Removes the polyline from the drawing

Properties

When a polyline is selected the properties panel shows:

General

Property	Default	Meaning
Color	256 (ByLayer)	ACI color index
Layer	0	Layer assignment
Linetype	ByLayer	Named linetype pattern
Linetype Scale	1	Scale factor on the linetype pattern
Thickness	0	Extrusion thickness

Geometry

Property	Meaning
Closed	Whether the last vertex connects back to the first
Vertex Count	Total number of vertices
Vertices	Coordinate list of all vertices

Polyline vs Line — when to use which

	Polyline	Line
Entity count	One LWPOLYLINE for the whole path	One LINE per segment
Closed shape	Yes (close flag)	No
Trim / Extend	No	Yes — segment by segment
Segment-midpoint grip	Translates the whole segment	Activates Move for the entity
Best for	Outlines, contours, shapes you keep whole	Construction lines, geometry you'll trim

DXF — LWPOLYLINE entity

Polylines are saved as LWPOLYLINE entities in the DXF file. All properties — vertex coordinates, closed flag, color, layer, linetype, linetype scale, and thickness — round-trip without loss. Rectangles drawn with the Rectangle command also save as LWPOLYLINE (closed, four vertices) and are indistinguishable at the DXF level.

LWPOLYLINE entities from any DXF-compatible application (AutoCAD, LibreCAD, etc.) are read back as fully editable polylines in the editor.