# `Meridian.Pathfinding`
[🔗](https://github.com/code-shoily/meridian/blob/v0.1.0/lib/meridian/pathfinding.ex#L1)

Spatially-aware pathfinding wrappers around `yog_ex` algorithms.

Injects geographic heuristics and distance-based edge weight functions
into the core graph pathfinders.

# `a_star`

```elixir
@spec a_star(
  Meridian.Graph.t(),
  keyword()
) :: {:ok, map()} | {:error, term()}
```

A* shortest path using haversine distance as the heuristic.

## Options

  * `:from` — start node id (required)
  * `:to` — goal node id (required)
  * `:weight_fn` — function `(graph, from, to) -> number` for edge cost.
    Defaults to `Meridian.CRS.distance/3` if nodes have point geometries.

## Examples

    iex> g = Meridian.Graph.new()
    iex> g = g
    ...>   |> Meridian.Graph.add_node(:a, %{geometry: %Geo.Point{coordinates: {0.0, 0.0}}})
    ...>   |> Meridian.Graph.add_node(:b, %{geometry: %Geo.Point{coordinates: {0.0, 1.0}}})
    ...>   |> Meridian.Graph.add_edge_ensure(:a, :b, 100.0)
    iex> {:ok, path} = Meridian.Pathfinding.a_star(g, from: :a, to: :b)
    iex> path.nodes
    [:a, :b]

    iex> g = Meridian.Graph.new()
    iex> Meridian.Pathfinding.a_star(g, from: :missing, to: :also_missing)
    ** (ArgumentError) start node :missing does not exist in graph

---

*Consult [api-reference.md](api-reference.md) for complete listing*