What is a ʼPolylineʼ in Rhino?

ByCADbrief Staff

Short Answer

In Rhino, a polyline is a single curve made of multiple straight-line segments joined end to end, typically created with the Polyline command. It is the most common professional method for drawing connected linear paths quickly and cleanly. Limitation: polylines cannot contain true curved segments unless converted or rebuilt.

What You Need to Know Before

Warning: A polyline looks simple, but extra unwanted vertices can cause problems in offsets, joins, CNC toolpaths, and surface generation. If points are snapped imprecisely or duplicated, the object may stay technically valid while producing poor downstream results.

How to Create a Polyline in Rhino

  • Command: Polyline

  • Shortcut: Polyline or alias PL

  • Quick Steps:

    1. Start Polyline from the Curve menu or type PL in the command line.
    2. Click each point in order to place connected straight segments, using Object Snaps on the Osnap panel if needed.
    3. Press Enter to finish, or use the Close option in the command line to close the shape.

  • Common professional option: turn on Ortho or Planar when you need clean, controlled segment directions.

Variables & Settings

  • Key Setting: Close option in the Polyline command

  • Expert Setting: Use Close to create a closed polyline without manually snapping the last point back to the first. This reduces tiny endpoint gaps that often prevent clean joining, hatching, extrusion, or profile-based modeling.

Why it Fails

  • Cause 1 (Geometry): Vertices are placed slightly off-plane or too close together, creating messy segments or invalid downstream profiles.
  • Cause 2 (layers/Locks): The target layer is locked, or Osnaps are pulling points onto unintended referenced geometry.
  • Cause 3 (Command/Logic): Users expect a polyline to behave like a smooth curve, but it only creates straight segments between picked points.

Quick Fix & Best Practice

  • Quick Fix: Run SimplifyCrv or SelDup if the polyline has unnecessary points or duplicate geometry.
  • Manager’s Verdict: Use polylines for layouts, profiles, tracing, and fabrication-ready straight-edged shapes. Avoid them when the design intent requires smooth curvature, since control-point or interpolated curves are usually better.

FAQ

Is a polyline in Rhino one object or many?

It is usually one curve object made of multiple straight segments.

Can a polyline be closed in Rhino?

Yes, use the Close option while drawing or run CloseCrv later if applicable.

Can you turn a polyline into a smooth curve?

Yes, but you typically need commands like Rebuild or Convert depending on the result you need.

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