Specifies the API for using an SRTM dataset source.

A source downloads the raw contents of an HGT file — the square grid of samples that SRTM.DataCell parses — for a file name such as "N36W117". The built-in sources are SRTM.Source.AWS and SRTM.Source.ESA.

use SRTM.Source declares the behaviour and imports get/2, which performs the request with the same certificate handling and :timeout option as the built-in sources:

defmodule MyApp.MirrorSource do
  use SRTM.Source

  @impl true
  def fetch(hgt_name, opts) do
    opts = Keyword.validate!(opts, [:timeout, endpoint: "https://srtm.example.com"])

    get("#{opts[:endpoint]}/#{hgt_name}.hgt", opts)
  end
end

Pass it to SRTM.get_elevation/3, on its own or paired with the options it is called with:

SRTM.get_elevation(36.455556, -116.866667,
  sources: [{MyApp.MirrorSource, timeout: 5_000}, SRTM.Source.AWS]
)

Sources are tried in order, so returning an error rather than raising lets the next one take over.