# `Geometry`

Any one of the six geometries, sent as the GeoJSON geometry it holds.

[Geospatial](types.md#geospatial); not ordered; since Jadpo 0.1.0.

## Make one

Pick one of its variants and give its fields, `Geometry.point { point: ... }`.

These operations give one: `geo.from_geojson` and `geo.from_wkt`.

## Variants

| Variant | Fields |
|---|---|
| `point` | `point`: [`Point`](type-point.md) |
| `line_string` | `line_string`: [`LineString`](type-line-string.md) |
| `polygon` | `polygon`: [`Polygon`](type-polygon.md) |
| `multi_point` | `multi_point`: [`MultiPoint`](type-multi-point.md) |
| `multi_line_string` | `multi_line_string`: [`MultiLineString`](type-multi-line-string.md) |
| `multi_polygon` | `multi_polygon`: [`MultiPolygon`](type-multi-polygon.md) |

## Text, JSON and storage

It has no single text form, so `text.from` and `text.parse` don't take it. JSON sends a GeoJSON geometry, its positions longitude first.

| JSON |
|---|
| `{"type":"Point","coordinates":[-0.1276,51.5072]}` |
| `{"type":"LineString","coordinates":[[0,0],[1,1]]}` |
| `{"type":"Polygon","coordinates":[[[0,0],[1,0],[1,1],[0,1],[0,0]]]}` |
| `{"type":"MultiPoint","coordinates":[[0,0],[1,1]]}` |
| `{"type":"MultiLineString","coordinates":[[[0,0],[1,1]]]}` |
| `{"type":"MultiPolygon","coordinates":[[[[0,0],[1,0],[1,1],[0,1],[0,0]]]]}` |

It is stored in one column named for the field, of type `geography`. `{"type":"MultiPoint","coordinates":[[0,0],[1,1]]}` is stored as `'SRID=4326;MULTIPOINT (0 0, 1 1)'::geography`.

## Shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `{"type":"Point","coordinates":[-0.1276,51.5072]}` | `51.5072° N, 0.1276° W` |
| `{"type":"LineString","coordinates":[[0,0],[1,1]]}` | `(0°, 0°; 1° N, 1° E)` |
| `{"type":"Polygon","coordinates":[[[0,0],[1,0],[1,1],[0,1],[0,0]]]}` | `((0°, 0°; 0°, 1° E; 1° N, 1° E; 1° N, 0°; 0°, 0°))` |
| `{"type":"MultiPoint","coordinates":[[0,0],[1,1]]}` | `(0°, 0°; 1° N, 1° E)` |
| `{"type":"MultiLineString","coordinates":[[[0,0],[1,1]]]}` | `((0°, 0°; 1° N, 1° E))` |
| `{"type":"MultiPolygon","coordinates":[[[[0,0],[1,0],[1,1],[0,1],[0,0]]]]}` | `(((0°, 0°; 0°, 1° E; 1° N, 1° E; 1° N, 0°; 0°, 0°)))` |

## Operations

- `geo.bounding_box(shape: T) -> BoundingBox`: The smallest box of parallels and meridians holding the shape, an edge's highest or lowest point counted, across the antimeridian when that box is narrower; a shape holding a pole runs from -180 to 180.
- `geo.centroid(shape: T) -> Point`: The shape's centre on the sphere, as PostGIS's `ST_Centroid(x, false)` finds it: each point a unit vector, weighted by area, length or count by the shape's kind, summed, and back to latitude and longitude. It may lie outside a concave polygon.
- `geo.contains(a: T, b: U) -> Bool`: Whether no point of `b` lies outside `a`, edges included. `a` may be a `BoundingBox`, whose sides are compared directly, or a `Circle`, holding the points within its radius of its centre.
- `geo.from_geojson(text: Text) -> Geometry`: The geometry GeoJSON text (RFC 7946) writes, each position longitude first: `{"type":"Point","coordinates":[-0.1276,51.5072]}`, any of the six, held as the `Geometry` of its kind, each ring wound by the right-hand rule. A coordinate out of its range fails with `out_of_range`, and text that isn't one of the six geometries, a polygon whose rings aren't valid or a geometry mixing altitudes included, with `malformed`, which the call's `attempt` maps.
- `geo.from_wkt(text: Text) -> Geometry`: The geometry WKT or EWKT text writes, longitude first: `POLYGON((-0.2 51.49,-0.05 51.49,-0.05 51.54,-0.2 51.49))`, any of the six, with `Z` for an altitude, held as the `Geometry` of its kind. `SRID=4326;` may lead; another system, or a coordinate out of its range, fails with `out_of_range`, and text that isn't one of the six geometries, a polygon whose rings aren't valid included, with `malformed`, which the call's `attempt` maps.
- `geo.intersects(a: T, b: U) -> Bool`: Whether the two share at least one point, edges included.
- `geo.to_wkt(shape: T) -> Text`: The shape as WKT, longitude first, as PostGIS's `ST_AsText` writes it: `POINT(-0.1276 51.5072)`, `POINT Z (-0.1276 51.5072 35)` with an altitude, each ring in the order it holds its points.
- `geo.within(a: T, b: U, distance: Length?) -> Bool`: `geo.contains(b, a)`; or, with `distance:`, whether two points are at most that far apart, as `geo.distance` measures them.

Like every standard type, it also has the contract's own operations: `text.format`, `json.read`, `json.write` and `==`. It isn't ordered, so `<` and sorting don't take it. [Every standard type meets one contract](../topics/every-standard-type-meets-one-contract.md) says how they work.