Join and slice tools

In CVAT you can modify shapes by either joining multiple shapes into a single label or slicing a single label into several shapes.

This document provides guidance on how to perform these operations effectively.

See:

• Joining polygons and masks
• Slicing polygons and masks

Joining polygons and masks

The Join tool () works with both polygon and mask annotations.

This tool is useful in scenarios where a single object in an image is annotated with multiple shapes, and there is a need to merge these shapes into a single one. For polygons, you can join overlapping polygons or polygons that share at least one edge.

To join polygons or masks, do the following:

1. From the {{< ilink "/docs/annotation/annotation-editor/controls-sidebar#edit" "Edit" >}} block, select Join tool .
2. Click the shapes on the canvas that you want to join.
3. (Optional) To remove the selection, click the shape one more time.
4. Press J or click Join tool again to execute the join operation.

Upon completion, the selected shapes will be merged.

Notes about polygon merging:

• For the merge operation to be successful, polygons must overlap or share at least one edge.
• Disjoint polygons are kept as separate polygons.
• Merge is not supported if the resulting polygon would create an enclosed empty region.
• Self-intersecting polygons are excluded from the join operation.

{{% alert title="Tip" %}} The {{< ilink "/docs/annotation/manual-annotation/shapes/annotation-with-polygons/snap-tools" "Snap tools" >}} can help the join operation work best by making polygon borders and vertices align more precisely. {{% /alert %}}

Slicing polygons and masks

The Slice mask/polygon () is compatible with both mask and polygon annotations.

This tool is useful in scenarios where multiple objects in an image are annotated with one shape, and there is a need to slice this shape into multiple parts.

{{% alert title="Note" color="primary" %}} The shape can be sliced only in two parts at a time. Use the slice tool several times to split a shape to as many parts as you need. {{% /alert %}}

To slice mask or polygon, do the following:

1. From the {{< ilink "/docs/annotation/annotation-editor/controls-sidebar#edit" "Edit" >}} block, select Slice mask/polygon .
2. Click on the shape you intend to slice. A black contour will appear around the selected shape.
3. Set an initial point for slicing by clicking on the contour.
4. Draw a line across the shape to define the slicing path.

Hold Shift to add points automatically on cursor movement.

Note: The line cannot cross itself.

Note: The line cannot cross the contour more than twice. 5. (Optional)> Right-click to cancel the latest point. 6. Click on the contour (Alt+J) (outside the contour) to finalize the slicing.