In order to represent labels on parts of images, the Droplet format defines a number of types for representing geometry. In droplet, the coordinate space for an image is always 0-to-1 on both axes. This was chosen so that stored geometries are independent of the resolution of the image.
Since Droplet is a JSON-based serialization format, here we provide TypeScript-style type definitions for all of the serialized types. There are also language-specific bindings for operating on droplets; see the language-specific API documentation for more information.
A Point is a 2-dimensional point, generally representing a position on an image. A Point is considered invalid if either of its coordinates are outside the inclusive range [0, 1].
type Point = [x: number, y: number];A Rectangle is a 2-dimensional axis-aligned rectangle, defined by its top-left and bottom-right points. A Rectangle is considered invalid if either of its points are invalid or if its top-left point is not both strictly above and strictly to the left of its bottom-right point. (Zero-area rectangles are not considered valid.)
type Rectangle = [topLeft: Point, bottomRight: Point];A Polygon is a 2-dimensional simple polygon, defined as a list of its vertices. A Polygon is considered invalid if it has fewer than three points, if any of its points are invalid, or if it is self-intersecting.
type Polygon = Point[];A Mask is any 2-dimensional region. It may have holes and may be discontiguous. A Mask is defined by a collection of polygons, and inclusion is determined via the even-odd rule. A Mask is considered invalid if it doesn't have at least one polygon, if any of its constituent polygons are invalid, or if any pair of its constituent polygons intersect each other.
type Mask = Polygon[];