Can I extend a line until it meets another curve in Rhinoceros 3D?

Short Answer

Yes — in Rhinoceros 3D, you can extend a line until it meets another curve using the Extend command, which is the most common professional method for this task. Select the line, define the boundary curve, and Rhino extends it to the nearest valid intersection. It will not work if the objects cannot intersect in their current plane or direction.

What You Need to Know Before

Warning: Rhino 3D extend operations often fail when the line and target curve are not truly coplanar, even if they look aligned in the viewport. A very common mistake is trying to extend toward a trimmed edge or object snap illusion rather than actual intersectable geometry.

How-to

• Command: Extend

• Shortcut: Extend

• Quick Steps:

  1. Start Extend from the command line or type Extend, then select the boundary curve the line should meet and press Enter.
  2. Click the line end you want to extend toward that boundary.
  3. Confirm the result; if needed, use the Type=Line or normal extend behavior depending on the object and keep Input=Trimmed or the current object selection logic in mind.

Variables & Settings

• Key Setting: Type

• Expert Setting: In Rhino 3D, the Type option inside extend-related workflows can affect how the result is created or interpreted with some object types. Also verify you are selecting the correct boundary object first, because Rhino uses that geometry as the extension limit.

Why it Fails

• Cause 1 (Geometry): The line and target curve do not actually intersect in 3D space or are not coplanar.
• Cause 2 (layers/Locks): The line, boundary curve, or referenced object is on a locked layer, preventing modification or proper selection.
• Cause 3 (Command/Logic): The wrong object is selected as the boundary first, or the chosen line end is pointing away from the target curve.

Quick Fix & Best Practice

• Quick Fix: Run ProjectToCPlane or verify object elevations, then use Extend again with the correct boundary curve.
• Manager’s Verdict: Use Extend for fast 2D drafting and clean curve edits in Rhino 3D, but avoid forcing it in messy 3D geometry; when alignment is uncertain, check planar consistency before editing.

FAQ

Can Rhino extend a line to a surface edge?

Yes, if the selected edge is a valid boundary target and the geometry supports the extension.

Why does Extend not reach the curve I clicked?

Usually the line is not aimed toward that curve end, or the objects do not truly intersect in space.

Can I extend multiple lines at once in Rhino?

Yes, if you use Extend with appropriate boundary selection and compatible geometry.

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