> For the complete documentation index, see [llms.txt](https://docs.imerit-prod.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.imerit-prod.io/annotation-tool/key-features/split-merge-and-extend-3d-polylines.md).

# Split, Merge and Extend 3D Polylines

The Split, Merge and Extend Polyline feature gives users fine-grained control over editing polylines—making it easy to break a line into segments, join two polylines together, or extending an existing line. This leads to **more accurate annotations**, **faster editing**, and **leaner workflows** by reducing the need for redraws and manual corrections. It’s especially valuable when working with long or branching path structures that evolve frame by frame.

{% hint style="success" %} <img src="/files/qchq9tcQpS8cX7YBw03I" alt="" data-size="line"> Split, Merge, and Extend Polylines is an all-round feature that enables high-quality annotations, delivered quickly - ensuring the process is efficient.
{% endhint %}

<figure><img src="/files/PmNG32fBmuwqTqXrSZS2" alt=""><figcaption></figcaption></figure>

***

## Use Cases

* **Road or path segmentation** in autonomous driving datasets where line breaks indicate intersections or stop zones.
* **Crop row or field boundary adjustments** in agri-tech, especially when shapes change across time or due to occlusions.
* **Splitting or connecting wiring paths** in industrial inspection or utility mapping annotations.

***

## Benefits

* **Good**: Increases annotation precision by letting users restructure lines without redrawing from scratch.
* **Fast**: Saves time in editing by using quick gestures to split, merge, or extend existing work.
* **Cheap/Lean**: Minimizes the need for repetitive actions and simplifies quality control by maintaining continuity of attributes during edits.

***

## Steps to Use Split, Merge and Extend Polylines

### **Split Polyline**

1. Select the polyline to split.
2. Hold **Shift** and hover over an edge.
3. A red blade icon appears when the tool is ready to split.
4. **Right-click** on the edge.
5. A confirmation prompt appears.
6. On confirming, you're prompted to enter **class, instance, and attribute** values for the new lines.
   * The tool retains selection on the split polyline for quick attribute entry.

### Merge Polylines

1. Hover over the first or last vertex of a polyline.
2. Hold **Alt**—the edge visually latches to your cursor.
3. Release **Alt**; the latching remains active.
4. Hover over the vertex of the second polyline (start or end).
5. Press **Alt** again.
6. An **'M'** icon appears, indicating the merge option.
7. **Left-click** to confirm merge.
8. A confirmation prompt appears.
9. Polylines are merged.
   * The resulting polyline inherits the **class, instance ID, and attributes** of the first line.

### Extend Polyline

* Hover over the first or last vertex of a polyline.
* Hold **Alt**—the polyline end latches to your cursor.
* Let go of **Alt**; extension mode remains active.
* Left-click to place new vertices and continue drawing.

> Tip: This feature works seamlessly with **free and snapped vertex modes**, allowing for precise control while extending.

### Remove the Extended Line Incrementally

<figure><img src="/files/rkxkAGQ13MMBdCJQvLXq" alt=""><figcaption></figcaption></figure>

To undo the last segment added while extending a polyline (before saving):

**Press Ctrl + Z**&#x20;

This will remove the most recently added vertex or line segment during extension, allowing fine-tuned corrections before committing your changes.

> Note: This only works before saving or finalizing the extended polyline.

### Remove the Extended Line Entirely

<figure><img src="/files/JGOxv8aBF8uqr9VFT9vU" alt=""><figcaption></figcaption></figure>

To discard the entire extension made to a polyline before saving:

**Press Esc**

This will cancel the full extension operation, removing all newly added vertices and reverting the polyline to its original state.

> Note: Must be done before saving or submitting changes.