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

# Advanced Annotation Tools

> Master interpolation, track mode, attribute annotation, object propagation, grouping, merging, and splitting

CVAT provides powerful advanced tools that significantly accelerate video annotation and enable sophisticated annotation workflows. These tools leverage temporal continuity, object relationships, and intelligent algorithms.

## Track Mode and Interpolation

### Understanding Tracks

Tracks are temporal annotations that represent the same object across multiple video frames:

* **Single identity**: One track = one object throughout its appearance
* **Keyframe-based**: You define object position at keyframes
* **Automatic interpolation**: CVAT calculates positions between keyframes
* **Efficient**: Annotate once every N frames instead of every frame

<Info>
  Interpolation can reduce annotation time by **5-10x** for videos compared to frame-by-frame annotation.
</Info>

### Creating Tracks

1. Select any drawing tool (rectangle, polygon, etc.)
2. Choose a label
3. Click **Track** (instead of Shape)
4. Draw the object on the current frame
5. Navigate forward several frames
6. Adjust the object position if needed (creates a new keyframe)
7. Repeat until the object disappears or leaves the frame

<CodeGroup>
  ```text Track Navigation Shortcuts theme={null}
  K        - Toggle keyframe on current frame
  F        - Previous frame
  D        - Next frame
  V        - Next frame (while drawing)
  C        - Previous frame (while drawing)
  ```
</CodeGroup>

### Keyframes

**Keyframes** are frames where you explicitly set the object's position and shape:

* **Manual keyframes**: Created when you adjust the object
* **Automatic keyframes**: First and last frame of track
* **Visual indicator**: Diamond icon in the objects sidebar
* **Toggle keyframe**: Select object and press `K`

**When to add keyframes**:

* Object changes direction
* Speed changes significantly
* Shape deforms
* Object enters/exits occlusion
* Camera motion changes
* At least every 30-60 frames

<Tip>
  **Rule of thumb**: Add a keyframe whenever you notice the interpolated position is inaccurate. The more keyframes, the more accurate the interpolation, but more work required.
</Tip>

### Interpolation Behavior

CVAT interpolates different properties:

**For all shapes**:

* Position (x, y coordinates)
* Size (width, height)
* Rotation angle

**For polygons and polylines**:

* Each vertex position independently
* Shape can morph smoothly

**For skeletons**:

* Each keypoint position independently
* Natural pose transitions

**Not interpolated**:

* Masks (must set on each frame)
* Attributes marked as "immutable"
* Discrete properties (label, color)

### Interpolation Types

CVAT uses **linear interpolation** by default:

* Smooth, constant velocity between keyframes
* Works well for most objects
* Simple and predictable

For complex motion:

* Add more keyframes at motion changes
* Consider using auto-tracking tools

### Managing Track Visibility

**Outside Property** (`Q`):

Mark a track as "outside" when the object leaves the frame:

1. Navigate to the frame where object exits
2. Select the track
3. Press `Q` or toggle "Outside" in sidebar
4. Object disappears from this frame onward
5. Toggle off when object re-enters

<Info>
  "Outside" is frame-specific in tracks. An object can be outside on frames 50-100 and visible again on frame 101.
</Info>

**Occluded Property** (`O`):

Mark frames where the object is hidden but still in the scene:

1. Select the track
2. Press `O` on frames where object is occluded
3. Visual indicator appears
4. Useful for datasets that distinguish visibility states

***

## Object Propagation

Propagate copies an object to subsequent frames:

### When to Use

* Object is stationary or moves slowly
* Faster than creating a track for short durations
* Initial annotation before refinement

### Using Propagate

1. Select an object (shape or track)
2. Press `Ctrl+B` or right-click → "Propagate"
3. In the dialog:
   * **Up to frame**: End frame number
   * **Propagate as**: Shape or track
4. Click OK
5. Object is copied to all frames in range

<Tip>
  Propagate as **shape** to create independent copies on each frame. Propagate as **track** to create a single interpolated track.
</Tip>

### Propagate vs Track

| Feature      | Propagate (shapes)          | Track                                |
| ------------ | --------------------------- | ------------------------------------ |
| Independence | Each frame separate         | Single object                        |
| Editing      | Edit each copy individually | Edit keyframes, interpolates between |
| Use case     | Static objects              | Moving objects                       |
| Efficiency   | Good for few frames         | Excellent for many frames            |

***

## Grouping Objects

### Purpose

Group multiple objects that logically belong together:

* Parts of a single entity (car + wheels)
* Related objects (person + accessories)
* Maintain relationships across frames
* Export as single composite object

### Creating Groups

**Method 1: Group Mode**

1. Press `G` to enter group mode
2. Click objects to add to group (or select first)
3. Click "Group" button or press `G` again
4. Selected objects are now grouped

**Method 2: Shift-Click Selection**

1. Select first object
2. `Shift+Click` additional objects
3. Right-click → "Group"

<CodeGroup>
  ```text Grouping Shortcuts theme={null}
  G          - Toggle group mode
  Shift+G    - Reset group (ungroup selected objects)
  Shift+Click - Multi-select objects
  ```
</CodeGroup>

### Group Properties

* **Group ID**: All grouped objects share a group ID
* **Color**: Can set uniform color for group
* **Selection**: Clicking one object highlights the group
* **Operations**: Some operations affect entire group

### Ungrouping

1. Select any object in the group
2. Press `Shift+G` or right-click → "Ungroup"
3. Objects become independent

### Best Practices

* Group **related objects** that move together
* Use **consistent grouping** across all frames (for tracks)
* **Document grouping** rules in annotation guidelines
* Consider if **hierarchical labels** might be better than grouping

***

## Merging Objects

### Purpose

Combine multiple separate annotations into a single object:

* Merge over-segmented regions
* Combine parts annotated separately
* Fix duplicate annotations
* Combine tracks that represent the same object

### Using Merge Mode

1. Press `M` to activate merge mode
2. Click objects to merge (minimum 2)
3. Selected objects are highlighted
4. Click "Merge" or press `M` again to complete
5. Objects combine into one

<Info>
  Merged objects take the label of the first selected object. Attributes may need manual reconciliation.
</Info>

### Merge Behavior by Type

**Rectangles**:

* Creates bounding box that encompasses all input rectangles

**Polygons**:

* Combines into a single polygon (may have complex boundary)
* Handles overlapping regions

**Masks**:

* Performs pixel-wise union
* Perfect for combining segmentation regions

**Tracks**:

* Merges track histories
* Useful for fixing tracking errors where same object has multiple IDs

### Merge Shortcuts

```text theme={null}
M  - Toggle merge mode
```

### Limitations

* Cannot merge different shape types (e.g., rectangle + polygon)
* Merging tracks requires temporal overlap consideration
* Attributes from only one object are retained

***

## Splitting Tracks

### Purpose

Divide a track into two separate tracks at the current frame:

* Fix tracking errors (wrong ID continuation)
* Split tracks when objects separate
* Correct annotation mistakes

### Using Split Mode

1. Navigate to the frame where you want to split
2. Press `Alt+M` to activate split mode
3. Click the track to split
4. Track divides:
   * **Before current frame**: Original track
   * **Current frame onward**: New track with new ID

<Warning>
  Splitting is irreversible without undo. Make sure the split point is correct before confirming.
</Warning>

### Common Scenarios

**ID Switch**:

* Two objects cross paths
* Tracker assigns wrong ID
* Split both tracks at crossing, then join correctly

**Object Separation**:

* Single object splits into multiple (e.g., flock disperses)
* Split track, annotate each resulting object separately

### Split Shortcuts

```text theme={null}
Alt+M  - Toggle split mode
```

***

## Joining Tracks

### Purpose

Combine two separate tracks into a single continuous track:

* Fix fragmented annotation of same object
* Connect tracks across occlusion
* Correct tracking gaps

### Using Join

1. Click the **Join** tool in controls sidebar
2. Click the first track (earlier in time)
3. Click the second track (later in time)
4. Tracks merge into one continuous track
5. Object maintains single identity across both track segments

### Requirements

* Tracks must be **same shape type**
* Tracks should be **temporally sequential** (or overlapping)
* Both tracks must have **same label** (or you'll be prompted to choose)

### Join vs Merge

| Feature  | Join                              | Merge                        |
| -------- | --------------------------------- | ---------------------------- |
| Purpose  | Combine sequential track segments | Combine simultaneous objects |
| Input    | 2 tracks                          | 2+ objects                   |
| Result   | Single continuous track           | Single object                |
| Use case | Fix fragmented tracking           | Combine over-segmentation    |

<Tip>
  **Workflow for fixing tracking gaps**:

  1. Object is tracked incorrectly, creating multiple track IDs
  2. Split incorrect tracks at error points
  3. Join correct segments to form proper continuous tracks
</Tip>

***

## Slicing Objects

### Purpose

Cut an object into multiple parts using a line:

* Divide over-segmented regions
* Split connected components
* Create separate annotations from one

### Using Slice Mode

1. Click the **Slice** tool in controls sidebar
2. Select the object to slice
3. Draw a line across the object:
   * Click to place line vertices
   * Press `N` or double-click to finish line
4. Object splits into multiple objects along the cut line

### Slice Behavior

**For polygons**:

* Creates 2+ separate polygons based on where line intersects
* Each new polygon becomes an independent object

**For masks**:

* Divides mask into connected components
* Each component becomes a separate mask

### Applications

* Separate touching objects annotated as one
* Divide regions after approximate annotation
* Fix over-segmentation from auto-annotation
* Create part-based annotations

***

## Attribute Annotation

### Understanding Attributes

Attributes are properties associated with objects:

* **Defined per label**: Each label has its own attributes
* **Types**: Checkbox, radio, select, number, text
* **Mutable vs Immutable**:
  * **Immutable**: Same value across all frames in track
  * **Mutable**: Can change per frame

### Setting Attributes

1. Select an object
2. Expand **DETAILS** section in objects sidebar
3. Set attribute values
4. For mutable attributes in tracks:
   * Navigate to frames where value changes
   * Update attribute value
   * CVAT tracks changes per frame

### Attribute Annotation Workspace

For efficient attribute annotation:

1. Switch to **Attribute Annotation** workspace
2. Interface shows:
   * Large object view
   * Attribute controls
   * Object and frame navigation
3. Keyboard shortcuts for attributes
4. Rapid annotation workflow

**Workflow**:

1. Navigate to object (Tab or sidebar)
2. Set attributes with keyboard or clicks
3. Press `Ctrl+Enter` to save and move to next object
4. Repeat

<Tip>
  **Keyboard shortcuts** for attributes are automatically assigned:

  * Number keys (1-9) for radio/select options
  * Enter to confirm
  * Tab to next object
</Tip>

### Best Practices

<CardGroup cols={2}>
  <Card title="Immutable Attributes" icon="lock">
    Use for properties that don't change (object color, vehicle type, etc.)
  </Card>

  <Card title="Mutable Attributes" icon="arrows-rotate">
    Use for time-varying properties (door open/closed, lights on/off)
  </Card>

  <Card title="Consistent Values" icon="check">
    Maintain consistency across similar objects
  </Card>

  <Card title="Documentation" icon="book">
    Document attribute definitions clearly in project guidelines
  </Card>
</CardGroup>

***

## Copy, Paste, and Duplicate

### Copying Objects

**Within same frame**:

1. Select object
2. `Ctrl+C` to copy
3. `Ctrl+V` to paste
4. Adjust position of pasted object

**Across frames**:

1. Copy object on one frame
2. Navigate to target frame
3. Paste with `Ctrl+V`
4. Useful for objects that appear multiple times

<Tip>
  Pasted objects inherit **all properties** from the source: label, attributes, size, shape. Only position may need adjustment.
</Tip>

### Copy Shortcuts

```text theme={null}
Ctrl+C  - Copy selected object
Ctrl+V  - Paste object
Ctrl+X  - Cut object (copy and delete)
```

### Use Cases

* **Repeated objects**: Copy-paste-adjust faster than drawing from scratch
* **Similar objects**: Copy, paste, change label
* **Template annotation**: Copy object with attributes set, paste to new instances

***

## Object Relationships

### Z-Order (Depth Ordering)

Control which objects appear in front when overlapping:

**Change Z-Order**:

* `+` or `=`: Bring selected object forward
* `-`: Send selected object backward
* `Ctrl++`: Bring to front
* `Ctrl+-`: Send to back

**Z-Order Layers**:

* Objects sidebar can display objects grouped by Z-order layer
* Higher Z-order = rendered on top
* Useful for organizing complex scenes

### Parent-Child Relationships

Some label configurations support hierarchical relationships:

* **Skeleton sublabels**: Keypoints belong to skeleton
* **Part annotations**: Wheels belong to vehicle
* **Nested structures**: Building parts, room elements

Parent-child relationships are defined in label configuration.

***

## Batch Operations

### Lock/Unlock All Objects

* `T+L`: Toggle lock for all objects on current frame
* Prevents accidental edits
* Unlock to edit again

### Hide/Show All Objects

* `T+H`: Toggle hide for all objects on current frame
* Clear canvas for easier viewing
* Objects still exist, just hidden

### Delete Multiple Objects

1. Select multiple objects (`Shift+Click`)
2. Press `Del` or `Backspace`
3. All selected objects are removed

<Warning>
  Batch delete is immediate and can only be undone with `Ctrl+Z`. Be careful when deleting multiple objects.
</Warning>

***

## Advanced Keyboard Shortcuts

<AccordionGroup>
  <Accordion title="Track and Interpolation">
    ```text theme={null}
    K            - Toggle keyframe
    O            - Toggle occluded
    Q            - Toggle outside
    P            - Toggle pinned
    L            - Toggle lock
    Ctrl+B       - Propagate object
    ```
  </Accordion>

  <Accordion title="Object Operations">
    ```text theme={null}
    G            - Group mode
    Shift+G      - Reset group
    M            - Merge mode
    Alt+M        - Split mode
    +/-          - Adjust Z-order
    Ctrl+C/V/X   - Copy/Paste/Cut
    ```
  </Accordion>

  <Accordion title="Batch Operations">
    ```text theme={null}
    T+L          - Lock all
    T+H          - Hide all
    Shift+Del    - Delete all on frame
    ```
  </Accordion>

  <Accordion title="Navigation During Annotation">
    ```text theme={null}
    V            - Next frame (while drawing)
    C            - Previous frame (while drawing)
    Tab          - Cycle through overlapping objects
    ```
  </Accordion>
</AccordionGroup>

***

## Best Practices for Video Annotation

### Efficient Workflow

1. **First pass**: Create tracks for all objects with keyframes every 30-60 frames
2. **Review pass**: Navigate through interpolated frames, add keyframes where needed
3. **Refinement pass**: Adjust boundaries, set attributes
4. **Quality check**: Review entire video for consistency

### Keyframe Strategy

<Steps>
  <Step title="Start and End">
    Always annotate first and last frame where object is visible
  </Step>

  <Step title="Motion Changes">
    Add keyframe whenever object changes direction or speed significantly
  </Step>

  <Step title="Occlusions">
    Keyframe before entering and after exiting occlusion
  </Step>

  <Step title="Shape Changes">
    For polygons/skeletons, keyframe when shape deforms
  </Step>

  <Step title="Regular Intervals">
    Even for smooth motion, add keyframes every 30-60 frames to prevent drift
  </Step>
</Steps>

### Tracking Difficult Objects

**Fast motion**:

* More frequent keyframes
* Consider auto-tracking tools

**Occlusions**:

* Mark "outside" during full occlusion
* Mark "occluded" during partial occlusion
* Keyframe before and after

**Camera motion**:

* Background motion affects interpolation
* More keyframes needed
* Use stabilization if available

**Deformable objects**:

* Use polygons or skeletons
* Frequent keyframes
* Each vertex interpolates independently

***

## Troubleshooting

<AccordionGroup>
  <Accordion title="Interpolation looks wrong">
    * Add more keyframes at motion changes
    * Check that keyframes are properly set (press K to toggle)
    * Ensure "outside" flag is not incorrectly set
    * Consider if object motion is too complex for linear interpolation
  </Accordion>

  <Accordion title="Can't merge objects">
    * Objects must be same type (all rectangles, all polygons, etc.)
    * Both objects must be on the same frame
    * Check that merge mode is active (M key)
  </Accordion>

  <Accordion title="Track split in wrong place">
    * Use Undo (Ctrl+Z) immediately
    * Navigate to correct frame before splitting
    * Consider joining tracks instead
  </Accordion>

  <Accordion title="Grouped objects behave unexpectedly">
    * Ungroup (Shift+G) and regroup
    * Check that all intended objects are selected
    * Some operations may not support groups
  </Accordion>

  <Accordion title="Propagate created too many objects">
    * Delete propagated objects and try again with shorter range
    * Consider using track mode instead
    * Use Ctrl+Z to undo if just completed
  </Accordion>
</AccordionGroup>

***

## Next Steps

<CardGroup cols={2}>
  <Card title="Manual Annotation" icon="hand" href="/annotation/manual-annotation">
    Basic annotation workflows and techniques
  </Card>

  <Card title="Auto-Annotation" icon="wand-magic-sparkles" href="/annotation/auto-annotation">
    Use AI tracking to automate interpolation
  </Card>

  <Card title="Quality Control" icon="shield-check" href="/projects/quality-control">
    Review and validate annotations
  </Card>

  <Card title="Export Data" icon="file-export" href="/datasets/import-export">
    Export your completed annotations
  </Card>
</CardGroup>