Commands

3DPOLY command in AutoCAD : Creates a 3D polyline

If you need a clear, step-by-step guide to using the 3dpoly command in AutoCAD, this article explains what the command does, how to use it, common problems and fixes, alternative commands, practical tips for efficient work, and a short FAQ to answer additional reader questions.

What is the 3DPOLY command?

The 3dpoly command (type 3DPOLY at the command prompt) creates a 3D polyline — a connected series of straight-line segments defined in three dimensions (X, Y, Z). Unlike a 2D polyline (PLINE), a 3D polyline stores a Z coordinate for each vertex, so it can represent non-planar paths such as terrain lines, wire routes, or structural members.

Key characteristics:

  • Creates only straight segments (no arc segments).
  • Stores vertex coordinates with X, Y, Z values.
  • Useful for modeling paths, guide curves for sweeps, and reference geometry for 3D modeling workflows.
  • A 3D polyline is not a surface or solid; use extrusion or other modeling commands to convert it into volume or faces.

How to use 3dpoly (Step by step)

Follow these steps to draw a basic 3D polyline:

  1. Start the command:

    • Type 3dpoly (or 3DPOLY) and press Enter.

  2. Specify the start point:

    • Click in the drawing area or type coordinates (for example: 100,50,0).

  3. Specify each subsequent vertex:

    • Click for the next point or enter coordinates including a Z value (for example: 200,75,10).
    • You can use relative coordinates (for example: @50,0,5) to specify a point relative to the last vertex.

  4. Finish the polyline:

    • Press Enter or Esc to end the command when your last vertex is placed.
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Quick tips while drawing:

  • Enable Object snap (OSNAP) to snap to existing geometry when placing vertices.
  • Turn dynamic input (DYN) on to see and enter coordinates directly at the cursor.
  • Ensure Ortho is off if you need oblique or custom Z movement.

Options, editing and examples

  • Shortcut: Type 3DPOLY and Enter.
  • During command: you will typically see a prompt like Specify next point or [Undo]:. The common option available while in the command is Undo to remove the last segment you placed.
  • Editing a 3D polyline:
    • Use grips to move vertices directly.
    • Use standard modify commands (Move, Rotate, Scale) on the entire polyline.
    • To edit vertex-by-vertex in greater detail, you can explode the 3D polyline into individual line segments (use the EXPLODE command) and then edit those lines; note this converts the polyline to separate line objects.
    • Use the Properties palette to view or manually edit vertex coordinates (select the polyline and open Properties).
  • Example use cases:
    • Draw a terrain breakline by snapping successive points to survey elevation points (enter Z values to match elevations).
    • Create a path for a 3D sweep: draw the 3D polyline as the path, then use SWEEP with a profile to create a pipe or railing.

Why 3dpoly sometimes doesn’t work — common issues and fixes

If the 3dpoly command seems not to work or gives unexpected results, check the following:

  • Layer is frozen or locked:

    • Fix: Ensure the target layer is on and unlocked.

  • You’re in the wrong drawing space:

    • Fix: Make sure you are in Model space (or the correct layout) where you intend to draw.

  • Ortho mode or Polar constraints limiting movement:

    • Fix: Turn Ortho or Polar tracking off if they restrict desired direction (type ORTHO or F10/F11).

  • Coordinates entered without Z value:

    • Fix: Include the third coordinate (Z) when you need vertical positioning, e.g., x,y,z or use relative @dx,dy,dz format.

  • Dynamic Input or UCS orientation hides vertical component:

    • Fix: Turn on Dynamic Input (DYN) to see coordinate fields while you pick, or adjust your UCS so you’re working in the expected plane.

  • OSNAP not active (can’t snap to points with Z):

    • Fix: Enable Object Snap (F3) and enable the appropriate snap modes (e.g., Endpoint, Intersection).

  • Command is mistyped or not recognized:

    • Fix: Type 3DPOLY exactly. If AutoCAD says “unknown command”, check your version or command aliases.

  • Object appears invisible or extremely thin:

    • Fix: Verify visual styles, zoom extents, and that the object isn’t on a non-printing layer. Also check coordinate scale/units.
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Alternatives and related commands

Depending on your goal, these commands may be more appropriate:

  • PLINE (POLYLINE) — 2D polyline for planar polylines (supports width and arc segments). If you need arcs or widths in a single planar polyline, use PLINE.
  • SPLINE / 3DSPLINE — Create smooth curves in 2D or 3D (useful if you need curved paths rather than straight segments).
  • LINE — Simple straight segments; you can join multiple lines later.
  • 3DFACE — Create triangular faces for mesh-like surfaces.
  • REGION + EXTRUDE / PRESSPULL — Convert closed planar curves into regions or solids.
  • SWEEP — Use a 3D polyline as a path to sweep a profile and create a 3D solid or surface.
  • POLYSOLID — Quickly build walls/solid members with thickness and height (architectural use).
  • Use EXPLODE to break a 3D polyline into lines if you need to edit segments individually.

Choose the alternative based on whether you need planar vs. non-planar, straight vs. curved, or object vs. surface/solid results.

Practical tips and best practices

  • Always work with a consistent UCS and know whether you’re entering world coordinates or user coordinates.
  • Use DYN and OSNAP for precise vertex placement.
  • When exact Z values are critical (survey, structural), enter coordinates numerically — avoid relying only on graphical picks.
  • If you need closed loops in 3D, draw the final segment explicitly back to the start point using exact coordinates.
  • To use a 3D polyline as a path for modeling, keep the geometry clean: avoid overlapping vertices and duplicated segments.
  • Use layer naming and color conventions to keep 3D polylines organized (e.g., Breaklines, Conduits, Paths).
  • Consider converting to other types (explode to lines, or sweep to solids) before advanced edits that 3D polylines don’t support.
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FAQ

How do I close a 3D polyline so it becomes a loop?

To close a 3D polyline, draw the final segment so the last vertex matches the first vertex (enter the exact coordinates of the start point). There is no dedicated “Close” option like in PLINE, so you must explicitly connect the last point to the start.

Can I create curved segments with 3dpoly?

No — 3dpoly supports only straight-line segments. For smooth curves in 3D, use 3DSPLINE or create a series of short segments to approximate a curve, or draw a 2D spline on a UCS-aligned plane and then place it in 3D.

How can I convert a 3D polyline into a 3D solid or surface?

A 3D polyline itself is just a wire. To create solids or surfaces, use it as a path for SWEEP, or use planar closed curves (convert or redraw) and use EXTRUDE, PRESSPULL, or create 3DFACE/Region and build solids from those. If necessary, convert the polyline to lines (EXPLODE) and rebuild closed profiles on a plane.

Why can’t I move vertices in the Z direction?

If moving vertices in Z doesn’t work, check that Ortho is off and that you’re not constrained by the current UCS. Use grips to move points, or enter the exact new coordinates including Z (e.g., type @0,0,10 to move up 10 units relative to the selected vertex).

Is 3dpoly available in all AutoCAD versions?

Most full AutoCAD releases support 3dpoly. If the command isn’t recognized, verify your product version and command aliases. Some specialized or older versions may have different command availability or limited 3D functionality.

How do I edit a single vertex of a 3D polyline precisely?

Select the polyline and use grips to drag the vertex, or open the Properties palette to edit vertex coordinates numerically. If you need very detailed vertex editing, consider exploding into lines and editing individual segments.

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