---
title: "Replace a Portion"
slug: "cyclone-3dr-replaceaportionc"
updated: 2026-09-07T11:51:19Z
published: 2026-09-07T11:51:19Z
canonical: "rcdocs.leica-geosystems.com/cyclone-3dr-replaceaportionc"
---

> ## 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.

# Replace a Portion

![CmdPolylineReplaceAPortion.svg](https://cdn.document360.io/820e11db-8ed5-45ae-ac86-f6b77dcb2aa7/Images/Documentation/CmdPolylineReplaceAPortion.svg)

This command replaces a portion of a polyline with a segment or a 3D curve.

> [!TIP]
> ### Requirements
> 
> Select the polyline to process and optionally the mesh to project onto and launch the command.

1. Define the portion of the polyline you want to replace:
  1. Click both extremities of the restriction.
  2. Click a third point to define which part of the polyline you want to replace (when the polyline is closed).
  3. Press **Enter** to validate or **Delete** to delete a point.
2. Choose the portion type you want to use:
  1. **Straight** will replace the portion with a straight segment.
  2. **Curve** will replace the portion with a 3D Curve. Drag and drop the control points to adjust the junction shape.
3. In Curve mode, select the option **Keep tangency direction** to lock the movement of starting control points in the tangency direction.
4. Select the option **Project on the mesh** to enable the 3D closest projection of the portion on the chosen mesh. By default, this option is checked if a mesh has been selected.