---
title: "Basic Tutorial | Break line (Feature line) and sharp edge reconstruction"
slug: "cyclone-3dr-feature-border-fictive-lines"
updated: 2026-08-04T15:22:50Z
published: 2026-09-07T11:52:00Z
canonical: "rcdocs.leica-geosystems.com/cyclone-3dr-feature-border-fictive-lines"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://rcdocs.leica-geosystems.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Basic Tutorial | Break line (Feature line) and sharp edge reconstruction

The software provides tools to compute polylines following sharp edges, fillets or small radii on a mesh.

It is good to know that the curvature of a mesh can be negative or positive:

- A negative curvature has its center inside the mesh; the shape is convex.
- A positive curvature has its center outside the mesh; the shape is concave.

Two types of lines can be extracted from a mesh:

- The single **Break line** is the line on the sharp edge.
- The **fictive line** is the line which can be used to recreate the sharp edge (i.e. planar intersection line, imported line).

> [!WARNING]
> The extracted lines could also be useful for constraint meshing. See chapter [Meshing and mesh improvement](/v1/docs/cyclone-3dr-meshing-and-mesh-improvement).

- [Basic Tutorial | Extract a feature line or a break line from a mesh](/v1/docs/cyclone-3dr-exercice-extract-a-feature-line-from-a-mesh)