Polygon annotation

When to use it

• Segmentation masks for irregular objects
• Land parcels, roofs and roads in imagery
• Cell outlines in microscopy
• Documents and layout regions

What your file looks like

Each row links one image, as with boxes. Aerial and medical images work well here because outlines are rarely rectangular. A file like this is enough:

id,image
1,https://example.com/aerial/001.jpg

What reviewers see

The image, label buttons and a Close shape button. Clicks add corner points, Undo removes the last one, and each finished shape is listed.

What a reviewer submits

A polygon is a list of corner points, each a pair of fractions of the image width and height, with a label. At least three points and non-zero area are required.

{
  "answer": {
    "polygons": [
      {
        "label": "building",
        "points": [
          [
            0.1,
            0.2
          ],
          [
            0.4,
            0.2
          ],
          [
            0.4,
            0.5
          ],
          [
            0.1,
            0.5
          ]
        ]
      }
    ]
  }
}

What you get back

Polygons are the same object when the overlap of their filled shapes is at least 0.5 and the label matches. The exported polygon is the first one of the agreeing group.

{
  "n": 3,
  "value": [
    {
      "label": "building",
      "points": [
        [
          0.1,
          0.2
        ],
        [
          0.4,
          0.2
        ],
        [
          0.4,
          0.5
        ],
        [
          0.1,
          0.5
        ]
      ]
    }
  ],
  "agreement": null,
  "tie": false
}

Quality checks

• Majority filtering removes shapes only one reviewer drew.
• Say how to treat holes and touching objects in your instructions.
• Use boxes first if you only need locations; polygons cost more time per object.

Tips

• Tell reviewers how many points are enough. Twenty to thirty points outline most objects.
• Use fewer images per reviewer session. Polygons are slower than boxes.
• Keep shapes simple: a polygon needs at least three points and an area above zero.

Limits

Up to 50 polygons per image and 200 points per polygon. Up to 20 labels. Brush masks and holes inside polygons are not supported.