step 1: lock public api and pure core

tests/test_projection.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+import pytest
+
+from dpg_map.projection import (
+    WEB_MERCATOR_MAX_LAT,
+    clamp_latitude,
+    latlon_to_tile,
+    latlon_to_world,
+    screen_to_world,
+    world_to_latlon,
+    world_to_screen,
+)
+
+
+@pytest.mark.parametrize(
+    ("lat", "lon", "zoom"),
+    [
+        (0.0, 0.0, 0),
+        (47.9029, 1.9093, 15),
+        (-33.8688, 151.2093, 10),
+        (WEB_MERCATOR_MAX_LAT, 179.999, 4),
+    ],
+)
+def test_projection_roundtrip(lat: float, lon: float, zoom: int) -> None:
+    x, y = latlon_to_world(lat, lon, zoom)
+    roundtrip_lat, roundtrip_lon = world_to_latlon(x, y, zoom)
+
+    assert roundtrip_lat == pytest.approx(clamp_latitude(lat), abs=1e-7)
+    assert roundtrip_lon == pytest.approx(lon, abs=1e-7)
+
+
+def test_latlon_to_tile_returns_xyz_coordinate() -> None:
+    assert latlon_to_tile(0.0, 0.0, 1) == (1, 1, 1)
+
+
+def test_world_screen_roundtrip() -> None:
+    center = (47.9029, 1.9093)
+    world = latlon_to_world(47.91, 1.92, 14)
+    screen = world_to_screen(*world, center=center, zoom=14, width=800, height=600)
+
+    assert screen_to_world(*screen, center=center, zoom=14, width=800, height=600) == pytest.approx(
+        world
+    )