Positions as iterable of coordinate values on geobase

[navispatial]

Related to #129, #133 and #134.

The geobase package has position class hiearchy:

• Position
  • Projected (x, y, z, m)
  • Geographic (lon, lat, elev, m)

In some interfaces position coordinates are handled as Iterable<num> (a list or other iterable implementation).

For data management it might be handy if some classes support at the same both both representations.

For this a new set of coordinate classes:

/// A geospatial position as an iterable collection of coordinate values.
///
/// Such position is a valid [Position] implementation and represents
/// coordinate values also as a collection of `Iterable<num>` (containing 2, 3,
/// or 4 items).
abstract class PositionCoords extends Position implements Iterable<num>;

/// A projected position as an iterable collection of coordinate values.
abstract class ProjectedCoords extends PositionCoords
    with IterableWrapperMixin<num>
    implements Projected;

... and also implementations.

[navispatial]

Implemented in 0.3.0-dev.1 with main parts as:

/// Geospatial coordinate values as an iterable collection of double values.
///
/// See also sub classes:
/// * [PositionArray]: coordinate values of 0 to N positions in a flat structure
/// * [PositionCoords]: coordinate values of a single position
/// * [BoxCoords]: coordinate values of a single bounding box
abstract class Coordinates extends Iterable<double> implements Positionable {}

/// Coordinate values of geospatial positions as an iterable collection.
///
/// The collection implements `Iterable<double>` with coordinate values of
/// positions as a flat structure (each position containing  2, 3, or 4 values).
///
/// Position data is also accessible as position coordinates via [data]. You can
/// also use [dataTo] to map coordinate values to custom position types.
///
/// See [Position] for description about supported coordinate values.
class PositionArray implements Coordinates {}

/// A base class for positions as an iterable collection of coordinate values.
///
/// See [PositionCoords] for a concrete implementation.
///
/// See also specialized sub classes for projected coordinates:
///
/// Class  | 2D/3D | Coords | Values   | x | y | z | m
/// ------ | ----- | ------ | -------- | - | - | - | -
/// `XY`   | 2D    | 2      | `double` | + | + |   |
/// `XYZ`  | 3D    | 3      | `double` | + | + | + |
/// `XYM`  | 2D    | 3      | `double` | + | + |   | +
/// `XYZM` | 3D    | 4      | `double` | + | + | + | +
///
/// And there are also specialized sub classes for geographic coordinates:
///
/// Class         | 2D/3D | Coords | Values   | lon (x) | lat (y) | elev (z) | m
/// ------------- | ----- | ------ | -------- | ------- | ------- | -------- | -
/// `LonLat`      | 2D    | 2      | `double` |    +    |    +    |          |
/// `LonLatElev`  | 3D    | 3      | `double` |    +    |    +    |    +     |
/// `LonLatM`     | 2D    | 3      | `double` |    +    |    +    |          | +
/// `LonLatElevM` | 3D    | 4      | `double` |    +    |    +    |    +     | +
abstract class BasePositionCoords extends Position implements Coordinates {}

/// A geospatial position as an iterable collection of coordinate values.
///
/// Such position is a valid [Position] implementation and represents
/// coordinate values also as a collection of `Iterable<double>` (containing 2,
/// 3, or 4 items).
///
/// See [Position] for description about supported coordinate values.
@immutable
class PositionCoords extends BasePositionCoords {}