Add fast tests for UTM conversions (#537)

Author: wgu9

.github/workflows/ubuntu.yml

@@ -50,6 +50,8 @@ jobs:
                   pip install --user .
             - name: Test import
               run: python -c "import samgeo; print('samgeo import successful')"
+            - name: Fast unit tests
+              run: python -m unittest tests.test_utmconv
             # - name: PKG-TEST
             #   run: |
             #       python -m unittest discover tests/

tests/test_utmconv.py

@@ -0,0 +1,124 @@
+"""Tests for the dependency-free UTM conversion helpers."""
+
+import importlib.util
+import math
+from pathlib import Path
+import unittest
+
+
+def _load_utmconv():
+    module_path = Path(__file__).resolve().parents[1] / "samgeo" / "utmconv.py"
+    spec = importlib.util.spec_from_file_location("utmconv", module_path)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+utmconv = _load_utmconv()
+
+
+class TestUtmconv(unittest.TestCase):
+    """Tests for samgeo/utmconv.py."""
+
+    def assert_close(self, actual, expected, tolerance):
+        self.assertLessEqual(abs(actual - expected), tolerance)
+
+    def test_degree_radian_conversions_round_trip(self):
+        for degrees in [-180.0, -45.5, 0.0, 37.25, 180.0]:
+            radians = utmconv.deg2rad(degrees)
+            self.assert_close(radians, math.radians(degrees), 1e-12)
+            self.assert_close(utmconv.rad2deg(radians), degrees, 1e-12)
+
+    def test_utm_central_meridian_for_edge_zones(self):
+        expected_degrees = {
+            1: -177.0,
+            30: -3.0,
+            31: 3.0,
+            60: 177.0,
+        }
+
+        for zone, central_meridian in expected_degrees.items():
+            self.assert_close(
+                utmconv.rad2deg(utmconv.utm_central_meridian(zone)),
+                central_meridian,
+                1e-12,
+            )
+
+    def test_latlon_to_utm_known_equator_point(self):
+        easting, northing = utmconv.latlon2utmxy(
+            utmconv.deg2rad(0.0),
+            utmconv.deg2rad(0.0),
+            31,
+        )
+
+        self.assert_close(easting, 166021.443096, 1e-6)
+        self.assert_close(northing, 0.0, 1e-9)
+
+    def test_latlon_to_utm_known_central_meridian_point(self):
+        easting, northing = utmconv.latlon2utmxy(
+            utmconv.deg2rad(-75.0),
+            utmconv.deg2rad(40.0),
+            18,
+        )
+
+        self.assert_close(easting, 500000.0, 1e-6)
+        self.assert_close(northing, 4427757.218472, 1e-6)
+
+    def test_latlon_utm_round_trip_for_northern_and_southern_points(self):
+        cases = [
+            (-75.0, 40.0, 18, False),
+            (151.0, -33.0, 56, True),
+            (179.9, 0.1, 60, False),
+            (-177.0, -79.9, 1, True),
+        ]
+
+        for longitude, latitude, zone, is_south_hemi in cases:
+            with self.subTest(
+                longitude=longitude,
+                latitude=latitude,
+                zone=zone,
+                is_south_hemi=is_south_hemi,
+            ):
+                easting, northing = utmconv.latlon2utmxy(
+                    utmconv.deg2rad(longitude),
+                    utmconv.deg2rad(latitude),
+                    zone,
+                )
+                round_trip_longitude, round_trip_latitude = utmconv.utmxy2latlon(
+                    easting,
+                    northing,
+                    zone,
+                    is_south_hemi,
+                )
+
+                self.assert_close(
+                    utmconv.rad2deg(round_trip_longitude), longitude, 1e-6
+                )
+                self.assert_close(utmconv.rad2deg(round_trip_latitude), latitude, 2e-5)
+
+    def test_southern_hemisphere_false_northing_is_reversible(self):
+        longitude = 151.0
+        latitude = -33.0
+        zone = 56
+
+        easting, northing = utmconv.latlon2utmxy(
+            utmconv.deg2rad(longitude),
+            utmconv.deg2rad(latitude),
+            zone,
+        )
+
+        self.assertGreater(northing, 0.0)
+
+        round_trip_longitude, round_trip_latitude = utmconv.utmxy2latlon(
+            easting,
+            northing,
+            zone,
+            True,
+        )
+
+        self.assert_close(utmconv.rad2deg(round_trip_longitude), longitude, 1e-6)
+        self.assert_close(utmconv.rad2deg(round_trip_latitude), latitude, 2e-5)
+
+
+if __name__ == "__main__":
+    unittest.main()