Allow float tile_buffer (#405)

* Add tests of the expected behaviour

* Add `tile_buffer` `float` support in `COGReader.tile()`

* :facepalm

Co-authored-by: Bernhard Stadlbauer <bstadlbauer@blackshark.ai>
Co-authored-by: vincentsarago <vincent.sarago@gmail.com>

CHANGES.md

@@ -55,6 +55,7 @@ with COGReader(
 
 * compare dataset bounds and tile bounds in TMS crs in `rio_tiler.io.base.SpatialMixin.tile_exists` method to allow dataset and TMS not compatible with WGS84 crs (https://github.com/cogeotiff/rio-tiler/pull/429)
 * use `httpx` package instead of requests (author @rodrigoalmeida94, https://github.com/cogeotiff/rio-tiler/pull/431)
+* allow **half pixel** `tile_buffer` around the tile (e.g 0.5 -> 257x257, 1.5 -> 259x259) (author @bstadlbauer, https://github.com/cogeotiff/rio-tiler/pull/405)
 
 **breaking changes**
 

rio_tiler/errors.py

@@ -13,6 +13,10 @@ class TileOutsideBounds(RioTilerError):
     """Z-X-Y Tile is outside image bounds."""
 
 
+class IncorrectTileBuffer(RioTilerError):
+    """Tile buffer is a float but not half of an integer"""
+
+
 class PointOutsideBounds(RioTilerError):
     """Point is outside image bounds."""
 

rio_tiler/io/cogeo.py

@@ -6,7 +6,7 @@
 import attr
 import numpy
 import rasterio
-from morecantile import Tile, TileMatrixSet
+from morecantile import BoundingBox, Tile, TileMatrixSet
 from rasterio import transform
 from rasterio.crs import CRS
 from rasterio.enums import Resampling
@@ -17,8 +17,13 @@
 from rasterio.warp import calculate_default_transform, transform_bounds
 
 from .. import reader
-from ..constants import WEB_MERCATOR_TMS, WGS84_CRS, BBox, Indexes, NoData
-from ..errors import ExpressionMixingWarning, NoOverviewWarning, TileOutsideBounds
+from ..constants import WEB_MERCATOR_TMS, WGS84_CRS, BBox, Indexes, NoData, NumType
+from ..errors import (
+    ExpressionMixingWarning,
+    IncorrectTileBuffer,
+    NoOverviewWarning,
+    TileOutsideBounds,
+)
 from ..expression import apply_expression, parse_expression
 from ..models import BandStatistics, ImageData, ImageStatistics, Info
 from ..utils import (
@@ -325,7 +330,7 @@ def tile(
         tilesize: int = 256,
         indexes: Optional[Indexes] = None,
         expression: Optional[str] = None,
-        tile_buffer: Optional[int] = None,
+        tile_buffer: Optional[NumType] = None,
         **kwargs: Any,
     ) -> ImageData:
         """Read a Web Map tile from a COG.
@@ -337,6 +342,7 @@ def tile(
             tilesize (int, optional): Output image size. Defaults to `256`.
             indexes (int or sequence of int, optional): Band indexes.
             expression (str, optional): rio-tiler expression (e.g. b1/b2+b3).
+            tile_buffer (int or float, optional): Buffer on each side of the given tile. It must be a multiple of `0.5`. Output **tilesize** will be expanded to `tilesize + 2 * tile_buffer` (e.g 0.5 = 257x257, 1.0 = 258x258).
             kwargs (optional): Options to forward to the `COGReader.part` method.
 
         Returns:
@@ -349,16 +355,25 @@ def tile(
             )
 
         tile_bounds = self.tms.xy_bounds(Tile(x=tile_x, y=tile_y, z=tile_z))
-        if tile_buffer:
-            x_res = (tile_bounds[2] - tile_bounds[0]) / tilesize
-            y_res = (tile_bounds[3] - tile_bounds[1]) / tilesize
-            tile_bounds = (
-                tile_bounds[0] - x_res * tile_buffer,
-                tile_bounds[1] - y_res * tile_buffer,
-                tile_bounds[2] + x_res * tile_buffer,
-                tile_bounds[3] + y_res * tile_buffer,
+        if tile_buffer is not None:
+            if tile_buffer % 0.5:
+                raise IncorrectTileBuffer(
+                    "`tile_buffer` must be a multiple of `0.5` (e.g: 0.5, 1, 1.5, ...)."
+                )
+
+            x_res = (tile_bounds.right - tile_bounds.left) / tilesize
+            y_res = (tile_bounds.top - tile_bounds.bottom) / tilesize
+
+            # Buffered Tile Bounds
+            tile_bounds = BoundingBox(
+                tile_bounds.left - x_res * tile_buffer,
+                tile_bounds.bottom - y_res * tile_buffer,
+                tile_bounds.right + x_res * tile_buffer,
+                tile_bounds.top + y_res * tile_buffer,
             )
-            tilesize += tile_buffer * 2
+
+            # Buffered Tile Size
+            tilesize += int(tile_buffer * 2)
 
         return self.part(
             tile_bounds,

tests/test_io_cogeo.py

@@ -17,6 +17,7 @@
 from rio_tiler.errors import (
     AlphaBandWarning,
     ExpressionMixingWarning,
+    IncorrectTileBuffer,
     NoOverviewWarning,
     TileOutsideBounds,
 )
@@ -257,6 +258,31 @@ def test_tile_invalid_bounds():
             cog.tile(38, 24, 7)
 
 
+def test_tile_with_incorrect_float_buffer():
+    with pytest.raises(IncorrectTileBuffer):
+        with COGReader(COGEO) as cog:
+            cog.tile(43, 24, 7, tile_buffer=0.8)
+
+
+def test_tile_with_int_buffer():
+    with COGReader(COGEO) as cog:
+        data, mask = cog.tile(43, 24, 7, tile_buffer=1)
+    assert data.shape == (1, 258, 258)
+    assert mask.all()
+
+    with COGReader(COGEO) as cog:
+        data, mask = cog.tile(43, 24, 7, tile_buffer=0)
+    assert data.shape == (1, 256, 256)
+    assert mask.all()
+
+
+def test_tile_with_correct_float_buffer():
+    with COGReader(COGEO) as cog:
+        data, mask = cog.tile(43, 24, 7, tile_buffer=0.5)
+    assert data.shape == (1, 257, 257)
+    assert mask.all()
+
+
 def test_point_valid():
     """Read point."""
     lon = -56.624124590533825