Graham McIntire
2defa3db7a
- Unify haversine_km / deg_to_rad: Geo is the canonical home (atan2
form for antipodal stability); Radio, common_volume, rain_scatter,
ionosphere, terrain/srtm, terrain/elevation_client now delegate.
- Drop safe_min/safe_max wrappers in favor of Enum.min/max defaults.
- Move parse_float / parse_int to MicrowavepropWeb.LiveHelpers; eme,
path, and rover LiveViews import from there.
- Extract MicrowavepropWeb.LocationResolver from the eme/path
resolve_source / resolve_location duplicate. Standardize the kind
key and "Invalid grid square" error message.
- Convert Scorer cond chains (humidity, td_depression, sky, wind,
rain, pwat, pressure) to multi-clause guarded defs, matching the
existing classify_time_period style.
- extract_profile_fields uses a named map accumulator instead of a
6-tuple; build_path_conditions guards on %{temps: []} / %{dewpoints: []}.
- Collapse scores_file clamp/3 to max |> min.
- humidity_effect_label lives in BandConfig; map_live and path_live
both use it.
81 lines
2.9 KiB
Elixir
81 lines
2.9 KiB
Elixir
defmodule Microwaveprop.Propagation.CommonVolume do
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@moduledoc """
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Geometry for the "common volume" of a microwave QSO — the lens-shaped
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intersection of two circles of radius R around the endpoints.
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Rain-scatter requires both stations' beams to intersect a precipitating
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cell, so the cell has to live inside both 400 km-radius neighborhoods.
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This module provides the geometric primitives a classifier needs:
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* `in_common_volume?/4` — is a point inside both disks?
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* `bounding_box/3` — lat/lon rectangle that contains the lens
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* `area_km2/3` — area of the intersection, for coverage normalization
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Distances are spherical-great-circle (haversine) at mean Earth radius.
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"""
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@km_per_deg_lat 111.32
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@type latlon :: {float(), float()}
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@type bbox :: %{min_lat: float(), max_lat: float(), min_lon: float(), max_lon: float()}
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@doc "Is `point` within `radius_km` of both endpoints?"
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@spec in_common_volume?(latlon(), latlon(), latlon(), float()) :: boolean()
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def in_common_volume?(pos1, pos2, point, radius_km) do
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haversine_km(pos1, point) <= radius_km and haversine_km(pos2, point) <= radius_km
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end
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@doc """
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Lat/lon rectangle containing the common volume. Returns `:empty` when
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the two circles don't overlap.
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"""
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@spec bounding_box(latlon(), latlon(), float()) :: bbox() | :empty
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def bounding_box({lat1, lon1} = pos1, {lat2, lon2} = pos2, radius_km) do
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if haversine_km(pos1, pos2) > 2 * radius_km do
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:empty
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else
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lat_pad = radius_km / @km_per_deg_lat
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# Approximate longitude degrees-per-km at the higher-latitude endpoint
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# (narrower at higher lat, so more conservative).
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ref_lat = max(abs(lat1), abs(lat2))
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km_per_deg_lon = @km_per_deg_lat * max(:math.cos(ref_lat * :math.pi() / 180.0), 0.01)
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lon_pad = radius_km / km_per_deg_lon
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%{
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min_lat: max(lat1 - lat_pad, lat2 - lat_pad),
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max_lat: min(lat1 + lat_pad, lat2 + lat_pad),
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min_lon: max(lon1 - lon_pad, lon2 - lon_pad),
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max_lon: min(lon1 + lon_pad, lon2 + lon_pad)
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}
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end
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end
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@doc """
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Area (km²) of the lens-shaped intersection of two circles of radius
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`radius_km` centered at `pos1` and `pos2`. Returns `0.0` when the
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circles don't overlap. Uses the standard two-circle lens formula
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with the great-circle distance between centers.
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"""
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@spec area_km2(latlon(), latlon(), float()) :: float()
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def area_km2(pos1, pos2, radius_km) do
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d = haversine_km(pos1, pos2)
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cond do
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d >= 2 * radius_km ->
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0.0
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d <= 0.0 ->
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:math.pi() * radius_km * radius_km
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true ->
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r = radius_km
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# Lens area = 2 * [r² * arccos(d/2r) - (d/4) * sqrt(4r² - d²)]
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part_arc = r * r * :math.acos(d / (2 * r))
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part_tri = d / 4 * :math.sqrt(4 * r * r - d * d)
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2 * (part_arc - part_tri)
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end
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end
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defp haversine_km({lat1, lon1}, {lat2, lon2}), do: Microwaveprop.Geo.haversine_km(lat1, lon1, lat2, lon2)
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end
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