Can I check for ʼDuplicateʼ lines that are sitting on top of each other in Rhinoceros 3D?

ByCADbrief Staff

Short Answer

Yes — in Rhino 3D, you can check for duplicate lines sitting on top of each other by using SelDup, which is the most common professional method for finding overlapping duplicate curves and objects. It quickly selects exact duplicates so you can review or delete them. Limitation: it only finds truly identical duplicates, not near-overlapping geometry.

What You Need to Know Before

Warning: SelDup only detects objects that are geometrically identical in the same location. If two lines look stacked but have tiny endpoint differences, different lengths, or are part of blocks, the command may not catch them as duplicates.

How to Check Duplicate Lines in Rhino 3D

  • Command: SelDup

  • Shortcut: SelDup

  • Quick Steps:

    1. In the command line, type SelDup and press Enter.
    2. When prompted, select the objects to check, or press Enter to search the whole model.
    3. Rhino will select the duplicate lines and overlapping duplicate curves; review them, then press Delete if they are unwanted.

  • Use the standard selection prompt carefully, especially if you only want to check one layer or a specific area of the model.

Variables & Settings

  • Key Setting: Selection scope

  • Expert Setting: Before running SelDup, isolate the target layer or preselect only the curve objects you want to test. This reduces false selections from other visible geometry and makes cleanup much faster in production files.

Why it Fails

  • Cause 1 (Geometry): The lines are not true duplicates — they may be visually overlapping but have slightly different endpoints, lengths, or Z-values.

  • Cause 2 (layers/Locks): Duplicate lines may be on locked layers or inside blocks, so they are not freely selectable or removable during cleanup.

  • Cause 3 (Command/Logic): SelDup finds exact duplicate objects, not partially overlapping collinear lines or near-duplicate geometry created by tolerance issues.

Quick Fix & Best Practice

  • Quick Fix: Run SelDup, then use Delete to remove the selected duplicates; if nothing is found, use What or endpoint object snaps to inspect whether the lines are actually identical.

  • Manager’s Verdict: Use SelDup as the first-pass cleanup tool in Rhino 3D because it is fast and reliable for exact duplicates. Avoid relying on it alone when importing DWG/DXF files, where near-duplicates and fragmented curves are also common.

FAQ

Can SelDup delete duplicate lines automatically?
No, it only selects them; you delete them manually.

Can SelDup find duplicate arcs and curves too?
Yes, it works on duplicate curves and other identical objects, not just lines.

Will SelDup find overlapping but different-length lines?
No, it only finds exact duplicates in the same position.

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