fix terrainRGB algorithm (#616)

Author: vincentsarago

CHANGES.md

@@ -1,5 +1,9 @@
 # Release Notes
 
+## 0.11.5 (2023-03-22)
+
+* fix `TerrainRGB` (change interval from `1.0` to `0.1`)
+
 ## 0.11.4 (2023-03-20)
 
 * set FastAPI version lower than 0.95 (https://github.com/tiangolo/fastapi/discussions/9278)

src/titiler/core/tests/test_algorithms.py

@@ -4,7 +4,9 @@
 
 import numpy
 from fastapi import Depends, FastAPI
+from rasterio.io import MemoryFile
 from rio_tiler.models import ImageData
+from starlette.responses import Response
 from starlette.testclient import TestClient
 
 from titiler.core.algorithm import BaseAlgorithm
@@ -63,3 +65,46 @@ def main(algorithm=Depends(algorithms.dependency)):
         params={"algorithm": "multiply", "algorithm_params": json.dumps({"factor": 3})},
     )
     assert response.json() == arr.max().tolist() * 3
+
+
+def test_terrain_algo():
+    """test terrain algorithm deps."""
+    # Add the `Multiply` algorithm to the default ones
+    app = FastAPI()
+
+    arr = numpy.random.randint(0, 3000, (1, 256, 256))
+
+    @app.get("/", response_class=Response)
+    def main(algorithm=Depends(default_algorithms.dependency)):
+        """endpoint."""
+        img = ImageData(arr)
+        if algorithm:
+            img = algorithm(img)
+
+        return Response(img.render(img_format="PNG"), media_type="image/png")
+
+    client = TestClient(app)
+
+    # MAPBOX Terrain RGB
+    response = client.get("/", params={"algorithm": "terrainrgb"})
+    assert response.status_code == 200
+
+    with MemoryFile(response.content) as mem:
+        with mem.open() as dst:
+            data = dst.read().astype(numpy.float64)
+
+    # https://docs.mapbox.com/data/tilesets/guides/access-elevation-data/
+    elevation = -10000 + (((data[0] * 256 * 256) + (data[1] * 256) + data[2]) * 0.1)
+    numpy.testing.assert_array_equal(elevation, arr[0])
+
+    # TILEZEN Terrarium
+    response = client.get("/", params={"algorithm": "terrarium"})
+    assert response.status_code == 200
+
+    with MemoryFile(response.content) as mem:
+        with mem.open() as dst:
+            data = dst.read().astype(numpy.float64)
+
+    # https://github.com/tilezen/joerd/blob/master/docs/formats.md#terrarium
+    elevation = (data[0] * 256 + data[1] + data[2] / 256) - 32768
+    numpy.testing.assert_array_equal(elevation, arr[0])

src/titiler/core/titiler/core/algorithm/dem.py

@@ -128,7 +128,7 @@ class TerrainRGB(BaseAlgorithm):
     """Encode DEM into RGB (Mapbox Terrain RGB)."""
 
     # parameters
-    interval: float = 1.0
+    interval: float = 0.1
     baseval: float = -10000.0
 
     # metadata