Graham McIntire
51e390959c
277 @spec/@type annotations added to 58 files covering all public APIs: contexts (propagation, radio, weather, terrain, beacons, commercial), GRIB2 decoders, terrain analysis, duct detection, rain scatter, CSV/ADIF import, weather clients, and all Ecto schemas. Dialyzer passes with 0 errors.
82 lines
2.3 KiB
Elixir
82 lines
2.3 KiB
Elixir
defmodule Microwaveprop.Weather.Grib2.SimplePacking do
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@moduledoc false
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@doc """
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Extract a single value from GRIB2 simple-packed data at the given grid index.
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Formula: value = (R + X * 2^E) * 10^(-D)
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Where R = reference_value, E = binary_scale, D = decimal_scale,
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X = raw packed integer at the given index.
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"""
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@spec extract_value(map(), binary(), non_neg_integer()) :: {:ok, float()} | {:error, :index_out_of_range}
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def extract_value(%{bits_per_value: 0} = params, _data, _index) do
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{:ok, params.reference_value * :math.pow(10, -params.decimal_scale)}
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end
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def extract_value(params, data, index) do
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%{
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reference_value: r,
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binary_scale: e,
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decimal_scale: d,
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bits_per_value: n,
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num_data_points: num
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} = params
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if index < 0 or index >= num do
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{:error, :index_out_of_range}
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else
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x = extract_bits(data, index, n)
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value = (r + x * :math.pow(2, e)) * :math.pow(10, -d)
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{:ok, value}
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end
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end
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@doc """
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Extract multiple values from GRIB2 simple-packed data at the given grid indices.
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Returns `{:ok, %{index => value}}`. Out-of-range indices are silently skipped.
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"""
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@spec extract_values(map(), binary(), [non_neg_integer()]) :: {:ok, %{non_neg_integer() => float()}}
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def extract_values(%{bits_per_value: 0} = params, _data, indices) do
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value = params.reference_value * :math.pow(10, -params.decimal_scale)
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{:ok, Map.new(indices, fn i -> {i, value} end)}
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end
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def extract_values(params, data, indices) do
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%{
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reference_value: r,
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binary_scale: e,
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decimal_scale: d,
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bits_per_value: n,
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num_data_points: num
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} = params
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factor_2e = :math.pow(2, e)
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factor_10d = :math.pow(10, -d)
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results =
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Enum.reduce(indices, %{}, fn index, acc ->
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if index >= 0 and index < num do
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x = extract_bits(data, index, n)
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value = (r + x * factor_2e) * factor_10d
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Map.put(acc, index, value)
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else
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acc
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end
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end)
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{:ok, results}
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end
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defp extract_bits(data, index, bits_per_value) do
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bit_offset = index * bits_per_value
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byte_offset = div(bit_offset, 8)
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remainder = rem(bit_offset, 8)
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<<_skip::binary-size(byte_offset), _pad::size(remainder), x::size(bits_per_value)-unsigned-big, _rest::bitstring>> =
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data
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x
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end
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end
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