Advanced Annotation Tools

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Track Mode and Interpolation

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Understanding Tracks

• 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

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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

K        - Toggle keyframe on current frame
F        - Previous frame
D        - Next frame
V        - Next frame (while drawing)
C        - Previous frame (while drawing)

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Keyframes

• 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

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

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Interpolation Behavior

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

• Each vertex position independently
• Shape can morph smoothly

• Each keypoint position independently
• Natural pose transitions

• Masks (must set on each frame)
• Attributes marked as “immutable”
• Discrete properties (label, color)

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Interpolation Types

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

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

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Managing Track Visibility

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

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

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Object Propagation

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When to Use

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

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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

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Propagate vs Track

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Grouping Objects

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Purpose

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

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Creating Groups

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

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

G          - Toggle group mode
Shift+G    - Reset group (ungroup selected objects)
Shift+Click - Multi-select objects

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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

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Ungrouping

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

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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

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Merging Objects

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Purpose

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

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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

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Merge Behavior by Type

• Creates bounding box that encompasses all input rectangles

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

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

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

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Merge Shortcuts

M  - Toggle merge mode

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Limitations

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

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Splitting Tracks

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Purpose

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

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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

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Common Scenarios

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

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

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Split Shortcuts

Alt+M  - Toggle split mode

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Joining Tracks

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Purpose

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

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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

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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)

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Join vs Merge

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Slicing Objects

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Purpose

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

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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

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Slice Behavior

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

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

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Applications

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

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Attribute Annotation

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Understanding Attributes

• 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

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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

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Attribute Annotation Workspace

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

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

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Best Practices

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Copy, Paste, and Duplicate

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Copying Objects

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

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

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Copy Shortcuts

Ctrl+C  - Copy selected object
Ctrl+V  - Paste object
Ctrl+X  - Cut object (copy and delete)

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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

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Object Relationships

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Z-Order (Depth Ordering)

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

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

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Parent-Child Relationships

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

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Batch Operations

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Lock/Unlock All Objects

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

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Hide/Show All Objects

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

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Delete Multiple Objects

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

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Advanced Keyboard Shortcuts

K            - Toggle keyframe
O            - Toggle occluded
Q            - Toggle outside
P            - Toggle pinned
L            - Toggle lock
Ctrl+B       - Propagate object

G            - Group mode
Shift+G      - Reset group
M            - Merge mode
Alt+M        - Split mode
+/-          - Adjust Z-order
Ctrl+C/V/X   - Copy/Paste/Cut

T+L          - Lock all
T+H          - Hide all
Shift+Del    - Delete all on frame

V            - Next frame (while drawing)
C            - Previous frame (while drawing)
Tab          - Cycle through overlapping objects

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Best Practices for Video Annotation

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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

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Keyframe Strategy

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Tracking Difficult Objects

• More frequent keyframes
• Consider auto-tracking tools

• Mark “outside” during full occlusion
• Mark “occluded” during partial occlusion
• Keyframe before and after

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

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

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Troubleshooting

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Next Steps