Data formats
============

This document describes the various data formats that are used in the system.

Raw annotation data
-------------------

The client sends raw data for image annotations in a JSON format which is a list
of shapes. Each shape is a dictionary with the following keys:

* `type`: The type of the shape which can be:
  * `bbox` (bounding box, rectangle)
  * `polygon`
  * `polyline`
  * `point`
* `shape`: The shape data. Its format depends on the shape `type`:
  * For `bbox` it is a dictionary with keys x, y, w, h:
    ~~~json
    {"x": x, "y": y, "w": w, "h": h}
    ~~~
  * For `polygon` and `polyline` it is a list of points; each point is a
    dictionary with keys x and y:
    ~~~json
    [{"x": x1, "y": y1}, {"x": x2, "y": y2}, ...]
    ~~~
    The only difference between `polygon` and `polyline` is that the former is
    supposed to be closed so the last point is connected to the first one.
  * For `point` it is a dictionary with keys x and y:
    ~~~json
    {"x": x, "y": y}
    ~~~
  * All coordinates are floating-point numbers in the range [0, 1] and relative
    to the image size, with the origin in the top-left corner.
* `object`: The ID of the type of object (label) depicted in the shape. This ID
  is a human-readable string that must be registered in the system before
  being used on shapes.

The server sends the same data back to the client, to use to show the existing
annotations for an image.

### Example

~~~json
[
    {
        "type": "bbox",
        "shape": {"x": 0.1, "y": 0.1, "w": 0.5, "h": 0.5},
        "object": "Cat (Felis catus)"
    },
    {
        "type": "polygon",
        "shape": [{"x": 0, "y": 0}, {"x": 1, "y": 0}, {"x": 0, "y": 1}],
        "object": "Slice of pizza margherita"
    },
    {
        "type": "point",
        "shape": {"x": 0.5, "y": 0.5},
        "object": "Cat (Felis catus) - left eye"
    }
]
~~~

Query format
------------

The query format is based on YAML and used to query for pictures in the system.

### Structure
The root can have 3 keys:
* `want`: A list of rules that the images must satisfy. If not provided, no
  filtering is done.
* `exclude`: A list of rules that the images must not satisfy. If not provided,
  no filtering is done.
* `include_obsolete`: If true the query may return images with a designated
  replacement. If false (default) this won't be possible.

`want` and `exclude` are lists of rules. Each rule is a dictionary with a single
key (this is to allow multiple rules of the same kind). Accepted rules are:
* `has_object: [object1, object2, ...]`: The image must contain any of the
  objects in the list.
* `nature: [nature1, nature2, ...]`: The image must have one of the natures in
  the list. Natures are strings like "photo" that indicate the source of the
  image.
* `licence: [licence1, licence2, ...]`: The image must have one of the licences
  in the list. If possible, licence IDs are SPDX identifiers, non-standard ones
  are prefixed with `X-`.
* `author: [author1, author2, ...]`: The image's author's username must be in
  the list.
* `title: query`: Search for titles (`ilike`).
* `description: query`: Search for descriptions (`ilike`).
* `origin_url: query`: Search for origin URLs. The query matches the beginning
  of the URL excluding the protocol. (like `commons.wikimedia.org`)
* `above_width: width`: The image must have a width greater than or equal to
  the given value, in pixels.
* `above_height: height`: The image must have a height greater than or equal to
  the given value, in pixels.
* `below_width: width`: The image must have a width less than or equal to the
  given value, in pixels.
* `below_height: height`: The image must have a height less than or equal to the
  given value, in pixels.
* `before_date: timestamp`: The image must have been uploaded before the given
  Unix timestamp.
* `after_date: timestamp`: The image must have been uploaded after the given
  Unix timestamp.

`ordering`, `offset` and `limit` can be specified as query parameters in the
URL. `ordering` can be one of `date-desc`, `date-asc`, `title-asc`, `title-desc`,
`number-regions-desc`, `number-regions-asc`, `random`. `offset` and `limit` are
integers that specify the number of images to skip and the maximum number of
images to return, respectively.

### Example
~~~yaml
# Restrictions for queried images
want:
    # This means that the image must contain both rules, so both a cat and a dog
    - has_object: ["Cat (Felis catus)"]
    - has_object: ["Dog (Canis lupus familiaris)"]
    # Or we can put them in a list to mean that the image can contain any of the
    # objects in the list
    - has_object: ["Grass", "Flower"]
    # So the image must contain a cat and a dog, as well as either grass or
    # a flower
    # The following rule restricts the images to those with a certain source,
    # like a camera or a drawing; omitting this rule means that the images can
    # be of any source
    - nature: ["photo", "computer-3d-art"]
    # The following rule restricts the images to those with a certain licence
    - licence: ["CC-BY-1.0", "CC-BY-2.0", "CC-BY-3.0", "CC-BY-4.0", "CC0-1.0",
                "Unlicense", "WTFPL", "MIT", "BSD-2-Clause", "BSD-3-Clause",
                "Apache-2.0", "X-informal-attribution", "X-informal-do-anything",
                "X-public-domain-old", "X-public-domain"]
# Prohibitions for queried images
exclude:
    # This means that the image must not contain any of the objects in the list
    - has_object: ["Human"]
    # This excludes images uploaded before the given date
    - before_date: 1546300800
    # This requires images to have a minimum resolution
    - below_width: 800
    - below_height: 600
# In summary, we want images that contain both a cat and a dog, either a grass
# or a flower, but not a human, taken after 2019-01-01, must be a photo or a
# 3D render, must carry one of certain permissive licences and have a resolution
# of at least 800x600 pixels.
~~~