# 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" %} Split, Merge, and Extend Polylines is an all-round feature that enables high-quality annotations, delivered quickly - ensuring the process is efficient.
{% endhint %}
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## 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.
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## 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.
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## 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
To undo the last segment added while extending a polyline (before saving):
**Press Ctrl + Z**
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
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.
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