106 lines
2.8 KiB
Elixir
106 lines
2.8 KiB
Elixir
defmodule Parser.Position do
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@moduledoc """
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Uncompressed position parsing for APRS packets.
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"""
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alias Parser.Types.Position
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@doc """
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Parse an uncompressed APRS position string. Returns a Position struct or nil.
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"""
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@spec parse(String.t()) :: Position | nil
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def parse(position_str) do
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# Example: "4903.50N/07201.75W>comment"
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case position_str do
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<<lat::binary-size(8), sym_table_id::binary-size(1), lon::binary-size(9), sym_code::binary-size(1),
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comment::binary>> ->
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%{latitude: lat_val, longitude: lon_val} = parse_aprs_position(lat, lon)
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ambiguity = calculate_position_ambiguity(lat, lon)
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dao_data = parse_dao_extension(comment)
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%Position{
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latitude: lat_val,
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longitude: lon_val,
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timestamp: nil,
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symbol_table_id: sym_table_id,
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symbol_code: sym_code,
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comment: comment,
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aprs_messaging?: false,
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compressed?: false,
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position_ambiguity: ambiguity,
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dao: dao_data
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}
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_ ->
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nil
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end
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end
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@doc false
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def parse_aprs_position(lat_str, lon_str) do
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# Parse latitude: DDMM.MM format
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lat =
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case Regex.run(
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~r/^(
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\d{2})(\d{2}\.\d+)([NS])$/,
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lat_str
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) do
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[_, degrees, minutes, direction] ->
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lat_val = String.to_integer(degrees) + String.to_float(minutes) / 60
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if direction == "S", do: -lat_val, else: lat_val
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_ ->
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nil
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end
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# Parse longitude: DDDMM.MM format
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lon =
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case Regex.run(~r/^(\d{3})(\d{2}\.\d+)([EW])$/, lon_str) do
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[_, degrees, minutes, direction] ->
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lon_val = String.to_integer(degrees) + String.to_float(minutes) / 60
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if direction == "W", do: -lon_val, else: lon_val
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_ ->
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nil
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end
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%{latitude: lat, longitude: lon}
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end
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@doc false
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def calculate_position_ambiguity(latitude, longitude) do
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lat_spaces = count_spaces(latitude)
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lon_spaces = count_spaces(longitude)
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cond do
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lat_spaces == 0 and lon_spaces == 0 -> 0
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lat_spaces == 1 and lon_spaces == 1 -> 1
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lat_spaces == 2 and lon_spaces == 2 -> 2
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lat_spaces == 3 and lon_spaces == 3 -> 3
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lat_spaces == 4 and lon_spaces == 4 -> 4
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true -> 0
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end
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end
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@doc false
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def count_spaces(str) do
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str |> String.graphemes() |> Enum.count(&(&1 == " "))
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end
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@doc false
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def parse_dao_extension(comment) do
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case Regex.run(~r/!([A-Za-z])([A-Za-z])([A-Za-z])!/, comment) do
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[_, lat_dao, lon_dao, _] ->
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%{
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lat_dao: lat_dao,
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lon_dao: lon_dao,
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datum: "WGS84"
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}
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_ ->
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nil
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end
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end
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# Move parse_aprs_position/2 and ambiguity/DAO helpers here from the main parser when refactoring further.
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end
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