Fixed tangent-plane advection bug

Author: tkschuler

src/EarthSHAB/Forecast.py

@@ -358,8 +358,8 @@ def _advect(self, lats, lons, u, v, dt):
             # same arithmetic as utils.transform.{latlon_to_meters,
             # meters_to_latlon}_spherical, minus their NaN guards).
             cosc = self._cos_central
-            cx = (lons - self.central_lon) * 111000.0 * cosc
-            cy = (lats - self.central_lat) * 111000.0
+            cx = (lons - self.central_lon) * 111320.0 * cosc
+            cy = (lats - self.central_lat) * 111320.0
             x_new = cx + u * dt
             y_new = cy + v * dt
             lat_new = np.clip(self.central_lat + y_new / 111320.0, -89.999999, 89.999999)

src/EarthSHAB/config.py

@@ -22,8 +22,8 @@
 # for the evaluation suite. To run a current-day prediction instead, set a recent
 # forecast_start_time (cycle hour 00/06/12/18 UTC), set balloon_trajectory = None,
 # and download the forecast first with `python -m EarthSHAB.saveNETCDF`.
-forecast_start_time =  "2026-06-15 12:00:00" # Forecast start time, should match a downloaded forecast in the forecasts directory
-start_time = datetime.fromisoformat("2026-06-15 14:36:00") # Simulation start time. The end time needs to be within the downloaded forecast
+forecast_start_time =  "2026-06-16 06:00:00" # Forecast start time, should match a downloaded forecast in the forecasts directory
+start_time = datetime.fromisoformat("2026-06-16 14:36:00") # Simulation start time. The end time needs to be within the downloaded forecast
 balloon_trajectory = None # Only Accepting Files in the Standard APRS.fi format for now
 
 # Single forecast file path. The reader (EarthSHAB.Forecast.Forecast) opens
@@ -57,7 +57,7 @@
 )
 
 forecast = dict(
-    file = "/home/schuler/HAB-COM/GFS_DATA/NETCDF/gfs_20260615_12z_1p00_3h.nc",
+    file = "/home/schuler/HAB-COM/GFS_DATA/NETCDF/gfs_20260616_06z_1p00_3h.nc",
     forecast_start_time = forecast_start_time, # used to build the default file path above
     forecast_update_interval = 60,               # (s) After how many iterated dt steps are new wind speeds are looked up
 
@@ -80,7 +80,7 @@
     #                     re-anchored at the balloon each step.
     #   'tangent_plane' - spherical tangent-plane step about the fixed launch
     #                     anchor.
-    advection = 'tangent_plane',
+    advection = 'geodesic',
 
     # Wind-lookup backend tier (same trajectory within float32-cache tolerance):
     #   'numpy'  - (default) pure-numpy per-member sampling, float64. Matches

src/EarthSHAB/utils/transform.py

@@ -48,11 +48,11 @@ def latlon_to_meters_spherical(origin_lat, origin_lon, target_lat, target_lon):
     #target_lat_rad = math.radians(target_lat) # unused now
 
     # Calculate distance for latitude change
-    lat_distance = (target_lat - origin_lat) * 111000  # meters per degree of latitude
+    lat_distance = (target_lat - origin_lat) * 111320  # meters per degree of latitude
 
     # Calculate distance for longitude change
     #longitude_distance = (target_lon - origin_lon) * 111000 * math.cos((origin_lat_rad + target_lat_rad) / 2) #OLD OUTDATED TRANSFROM.  THIS FAILED OUTSIDE of 150 km due to Transform errors
-    longitude_distance = (target_lon - origin_lon) * 111000 * math.cos(origin_lat_rad)
+    longitude_distance = (target_lon - origin_lon) * 111320 * math.cos(origin_lat_rad)
 
     # If lat or lon is nan from the transform step being too close to the central coordinate, revert back to central coordinate distance
     if np.isnan(longitude_distance):

tests/test_savenetcdf_archive.py

@@ -80,11 +80,16 @@ def test_select_ranges_level_subset():
 # ── URL construction ────────────────────────────────────────────────────────────
 
 def test_cycle_file_url():
-    assert arch.cycle_file_url("20220822", 12, 0) == (
+    # cycle_file_url's res_token defaults to RES_TOKEN, which is frozen from
+    # config at import time. Pass res_token explicitly so the test asserts the
+    # URL format deterministically, independent of the res config declares.
+    assert arch.cycle_file_url("20220822", 12, 0, res_token="0p25") == (
         "https://noaa-gfs-bdp-pds.s3.amazonaws.com/"
         "gfs.20220822/12/atmos/gfs.t12z.pgrb2.0p25.f000"
     )
-    assert arch.cycle_file_url("20220822", 6, 27).endswith("gfs.t06z.pgrb2.0p25.f027")
+    assert arch.cycle_file_url(
+        "20220822", 6, 27, res_token="0p25"
+    ).endswith("gfs.t06z.pgrb2.0p25.f027")
 
 
 # ── Output filename ───────────────────────────────────────────────────────────
@@ -212,6 +217,10 @@ def test_live_step_hours_controls_forecast_hours(monkeypatch):
     nc_start = base.replace(hour=(base.hour // 6) * 6, minute=0, second=0, microsecond=0)
     monkeypatch.setitem(config_earth.netcdf_gfs, "nc_start", nc_start)
     monkeypatch.setitem(config_earth.netcdf_gfs, "download_days", 1)
+    # Pin res: hourly steps exist only on the 0.25° grid, so the test must not
+    # inherit whatever res config currently declares (a 0.5°/1° default would
+    # make step_hours=1 invalid and raise before the URL-building path runs).
+    monkeypatch.setitem(config_earth.netcdf_gfs, "res", 0.25)
     monkeypatch.setitem(config_earth.netcdf_gfs, "step_hours", 1)
 
     seen = []