Reduce grid resolution to 0.5 degrees (~6k points)

95k points at 0.125 degree resolution caused the GRIB2 extraction to
take too long. 0.5 degree (~55 km) resolution gives 6k points which
completes in under a minute. Can increase resolution later once the
extraction is optimized.

lib/microwaveprop/propagation/grid.ex

@@ -1,13 +1,13 @@
 defmodule Microwaveprop.Propagation.Grid do
-  @moduledoc "CONUS grid definition for propagation scoring. 0.125 degree resolution (~14 km)."
+  @moduledoc "CONUS grid definition for propagation scoring. 0.5 degree resolution (~55 km)."
 
   @lat_min 25.0
   @lat_max 50.0
   @lon_min -125.0
   @lon_max -66.0
-  @step 0.125
+  @step 0.5
 
-  @doc "Returns all grid points as `{lat, lon}` tuples covering CONUS at 0.125 degree spacing."
+  @doc "Returns all grid points as `{lat, lon}` tuples covering CONUS at 0.5 degree spacing."
   def conus_points do
     for lat <- float_range(@lat_min, @lat_max, @step),
         lon <- float_range(@lon_min, @lon_max, @step) do

test/microwaveprop/propagation/grid_test.exs

@@ -4,7 +4,7 @@ defmodule Microwaveprop.Propagation.GridTest do
   alias Microwaveprop.Propagation.Grid
 
   describe "conus_points/0" do
-    test "generates grid at 0.125 degree resolution" do
+    test "generates grid at 0.5 degree resolution" do
       points = Grid.conus_points()
       assert length(points) > 5000
       assert length(points) < 100_000
@@ -17,10 +17,10 @@ defmodule Microwaveprop.Propagation.GridTest do
       end)
     end
 
-    test "points are on 0.125 degree grid" do
+    test "points are on 0.5 degree grid" do
       Enum.each(Grid.conus_points(), fn {lat, lon} ->
-        assert Float.round(lat * 8, 0) == lat * 8
-        assert Float.round(lon * 8, 0) == lon * 8
+        assert Float.round(lat * 2, 0) == lat * 2
+        assert Float.round(lon * 2, 0) == lon * 2
       end)
     end
 
@@ -39,8 +39,8 @@ defmodule Microwaveprop.Propagation.GridTest do
   end
 
   describe "step/0" do
-    test "returns 0.125" do
-      assert Grid.step() == 0.125
+    test "returns 0.5" do
+      assert Grid.step() == 0.5
     end
   end