Graham McIntire
5a9359191f
Eliminates the external wgrib2 C tool dependency that blocked HRRR processing. Implements Lambert Conformal projection, simple packing (Template 5.0), complex packing with spatial differencing (Template 5.3), and GRIB2 section parsing — enough to extract point values from HRRR grid data using only Elixir.
70 lines
2.2 KiB
Elixir
70 lines
2.2 KiB
Elixir
defmodule Microwaveprop.Weather.Grib2.LambertConformalTest do
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use ExUnit.Case, async: true
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alias Microwaveprop.Weather.Grib2.LambertConformal
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# HRRR grid parameters (from GRIB2 Section 3, Template 3.30)
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@hrrr_params %{
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nx: 1799,
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ny: 1059,
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la1: 21.138123,
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lo1: 237.280472,
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lad: 38.5,
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lov: 262.5,
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dx: 3000.0,
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dy: 3000.0,
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latin1: 38.5,
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latin2: 38.5,
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scan_mode: 64
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}
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describe "to_grid_index/3" do
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test "first grid point maps to (0, 0)" do
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assert {:ok, {0, 0}} = LambertConformal.to_grid_index(@hrrr_params, 21.138123, 237.280472)
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end
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test "first grid point with negative longitude" do
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# 237.280472 in 0-360 == -122.719528 in -180..180
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assert {:ok, {0, 0}} =
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LambertConformal.to_grid_index(@hrrr_params, 21.138123, -122.719528)
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end
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test "Dallas area returns reasonable indices" do
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# Dallas TX: ~32.78, -96.8 (263.2 in 0-360)
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# HRRR 3km grid covers CONUS; Dallas should be roughly in the middle
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assert {:ok, {i, j}} = LambertConformal.to_grid_index(@hrrr_params, 32.78, -96.8)
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# Indices should be well within grid bounds
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assert i > 100 and i < 1700
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assert j > 100 and j < 900
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end
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test "handles negative longitudes correctly" do
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{:ok, {i1, j1}} = LambertConformal.to_grid_index(@hrrr_params, 40.0, -105.0)
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{:ok, {i2, j2}} = LambertConformal.to_grid_index(@hrrr_params, 40.0, 255.0)
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assert i1 == i2
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assert j1 == j2
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end
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test "returns error for point outside grid" do
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# London, UK — well outside CONUS HRRR domain
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assert {:error, :outside_grid} =
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LambertConformal.to_grid_index(@hrrr_params, 51.5, -0.12)
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end
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test "returns error for point south of grid" do
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# South America
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assert {:error, :outside_grid} =
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LambertConformal.to_grid_index(@hrrr_params, -10.0, -80.0)
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end
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test "edge of grid returns valid indices" do
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# Somewhere near the grid edge — northeast CONUS
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result = LambertConformal.to_grid_index(@hrrr_params, 45.0, -70.0)
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assert {:ok, {i, j}} = result
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assert i >= 0 and i < 1799
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assert j >= 0 and j < 1059
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end
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end
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end
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