make stats and histogram optional #466 (#467)

* make stats and histogram optional #466

* update docstring and changelog

* update comment

* fix(docs): use PR for changelog

* Update tests/core/test_add_raster.py

* Update tests/core/test_add_raster.py

---------

Co-authored-by: Pete Gadomski <[email protected]>

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- Make computation of statistics and histogram optional for `core.add_raster.add_raster_to_item` ([#467](https://github.com/stac-utils/stactools/pull/467))
+
 ## [0.5.2] - 2023-09-20
 
 ### Fixed

src/stactools/core/add_raster.py

@@ -18,11 +18,15 @@
 BINS = 256
 
 
-def add_raster_to_item(item: Item) -> Item:
+def add_raster_to_item(
+    item: Item, statistics: bool = True, histogram: bool = True
+) -> Item:
     """Adds the raster extension to an item.
 
     Args:
         item (Item): The PySTAC Item to extend.
+        statistics (bool): Compute band statistics (min/max). Defaults to True
+        histogram (bool): Compute band histogram. Defaults to True
 
     Returns:
         Item:
@@ -34,27 +38,38 @@ def add_raster_to_item(item: Item) -> Item:
         if asset.roles and "data" in asset.roles:
             raster = RasterExtension.ext(asset)
             href = make_absolute_href(asset.href, item.get_self_href())
-            bands = _read_bands(href)
+            bands = _read_bands(href, statistics, histogram)
             if bands:
                 raster.apply(bands)
     return item
 
 
-def _read_bands(href: str) -> List[RasterBand]:
+def _read_bands(href: str, statistics: bool, histogram: bool) -> List[RasterBand]:
     bands = []
     with rasterio.open(href) as dataset:
         for i, index in enumerate(dataset.indexes):
-            data = dataset.read(index, masked=True)
             band = RasterBand.create()
             band.nodata = dataset.nodatavals[i]
             band.spatial_resolution = dataset.transform[0]
             band.data_type = DataType(dataset.dtypes[i])
-            minimum = float(numpy.min(data))
-            maximum = float(numpy.max(data))
-            band.statistics = Statistics.create(minimum=minimum, maximum=maximum)
-            hist_data, _ = numpy.histogram(data, range=(minimum, maximum), bins=BINS)
-            band.histogram = Histogram.create(
-                BINS, minimum, maximum, hist_data.tolist()
-            )
+
+            if statistics or histogram:
+                data = dataset.read(index, masked=True)
+                minimum = float(numpy.nanmin(data))
+                maximum = float(numpy.nanmax(data))
+            if statistics:
+                band.statistics = Statistics.create(minimum=minimum, maximum=maximum)
+            if histogram:
+                # the entire array is masked, or all values are NAN.
+                # won't be able to compute histogram and will return empty array.
+                if numpy.isnan(minimum):
+                    band.histogram = Histogram.create(0, minimum, maximum, [])
+                else:
+                    hist_data, _ = numpy.histogram(
+                        data, range=(minimum, maximum), bins=BINS
+                    )
+                    band.histogram = Histogram.create(
+                        BINS, minimum, maximum, hist_data.tolist()
+                    )
             bands.append(band)
     return bands

tests/core/test_add_raster.py

@@ -0,0 +1,176 @@
+import tempfile
+from typing import Callable, List, Optional
+
+import numpy as np
+import pystac
+import pytest
+import rasterio
+from rasterio.crs import CRS
+from rasterio.transform import Affine
+from stactools.core import create
+from stactools.core.add_raster import add_raster_to_item
+
+
+def random_data(count: int) -> np.ndarray:
+    return np.random.rand(count, 10, 10) * 10
+
+
+def nan_data(count: int) -> np.ndarray:
+    data = np.empty((count, 10, 10))
+    data[:] = np.nan
+    return data
+
+
+def data_with_nan(count: int) -> np.ndarray:
+    data = np.random.rand(count, 10, 10) * 10
+    data[0][1][1] = np.nan
+    return data
+
+
+def zero_data(count: int) -> np.ndarray:
+    return np.zeros((count, 10, 10))
+
+
+def test_add_raster(tmp_asset_path) -> None:
+    item = create.item(tmp_asset_path)
+    add_raster_to_item(item)
+
+    asset: pystac.Asset = item.assets["data"]
+
+    _assert_asset(
+        asset,
+        expected_count=1,
+        expected_nodata=None,
+        expected_spatial_resolution=60.0,
+        expected_dtype=np.dtype("uint8"),
+        expected_min=[74.0],
+        expected_max=[255.0],
+    )
+
+
+@pytest.mark.parametrize(
+    "count,nodata,dtype,datafunc,hist_count",
+    [
+        (1, 0, np.dtype("int8"), random_data, 256),
+        (1, None, np.dtype("float64"), random_data, 256),
+        (1, np.nan, np.dtype("float64"), random_data, 256),
+        (2, 0, np.dtype("int8"), random_data, 256),
+        (2, None, np.dtype("float64"), random_data, 256),
+        (2, np.nan, np.dtype("float64"), random_data, 256),
+        (1, 0, np.dtype("uint8"), zero_data, 0),
+        (1, None, np.dtype("uint8"), zero_data, 256),
+        (1, None, np.dtype("float64"), nan_data, 0),
+        (1, np.nan, np.dtype("float64"), nan_data, 0),
+        (1, None, np.dtype("float64"), data_with_nan, 256),
+        (1, np.nan, np.dtype("float64"), data_with_nan, 256),
+    ],
+)
+def test_add_raster_with_nodata(
+    count: int, nodata: float, dtype: np.dtype, datafunc: Callable, hist_count: int
+) -> None:
+    with tempfile.NamedTemporaryFile(suffix=".tif") as tmpfile:
+        with rasterio.open(
+            tmpfile.name,
+            mode="w",
+            driver="GTiff",
+            count=count,
+            nodata=nodata,
+            dtype=dtype,
+            transform=Affine(0.1, 0.0, 1.0, 0.0, -0.1, 1.0),
+            width=10,
+            height=10,
+            crs=CRS.from_epsg(4326),
+        ) as dst:
+            data = datafunc(count)
+            data.astype(dtype)
+            dst.write(data)
+
+        with rasterio.open(tmpfile.name) as src:
+            data = src.read(masked=True)
+            minimum = []
+            maximum = []
+            for i, _ in enumerate(src.indexes):
+                minimum.append(float(np.nanmin(data[i])))
+                maximum.append(float(np.nanmax(data[i])))
+
+        item = create.item(tmpfile.name)
+
+        add_raster_to_item(item)
+
+        asset: pystac.Asset = item.assets["data"]
+        _assert_asset(
+            asset,
+            expected_count=count,
+            expected_nodata=nodata,
+            expected_spatial_resolution=0.1,
+            expected_dtype=dtype,
+            expected_min=minimum,
+            expected_max=maximum,
+            expected_hist_count=hist_count,
+        )
+
+
+def test_add_raster_without_stats(tmp_asset_path) -> None:
+    item = create.item(tmp_asset_path)
+    add_raster_to_item(item, statistics=False)
+
+    asset: pystac.Asset = item.assets["data"]
+    bands = asset.extra_fields.get("raster:bands")
+
+    assert bands[0].get("statistics") is None
+    assert bands[0].get("histogram")
+
+
+def test_add_raster_without_histogram(tmp_asset_path) -> None:
+    item = create.item(tmp_asset_path)
+    add_raster_to_item(item, histogram=False)
+
+    asset: pystac.Asset = item.assets["data"]
+    bands = asset.extra_fields.get("raster:bands")
+
+    assert bands[0].get("statistics")
+    assert bands[0].get("histogram") is None
+
+
+def _assert_asset(
+    asset: pystac.Asset,
+    expected_count: int,
+    expected_nodata: Optional[float],
+    expected_dtype: np.dtype,
+    expected_spatial_resolution: float,
+    expected_min: List[float],
+    expected_max: List[float],
+    expected_hist_count=256,
+) -> None:
+    bands = asset.extra_fields.get("raster:bands")
+    assert bands
+    assert len(bands) == expected_count
+
+    for i, band in enumerate(bands):
+        nodata = band.get("nodata")
+        dtype = band["data_type"].value
+        spatial_resolution = band["spatial_resolution"]
+        statistics = band["statistics"]
+        histogram = band["histogram"]
+        assert nodata == expected_nodata or (
+            np.isnan(nodata) and np.isnan(expected_nodata)
+        )
+        assert dtype == expected_dtype.name
+        assert spatial_resolution == expected_spatial_resolution
+        assert statistics == {
+            "minimum": expected_min[i],
+            "maximum": expected_max[i],
+        } or (
+            np.isnan(statistics["maximum"])
+            and np.isnan(expected_max[i])
+            and np.isnan(statistics["minimum"])
+            and np.isnan(expected_min[i])
+        )
+        assert histogram["count"] == expected_hist_count
+        assert histogram["max"] == band["statistics"]["maximum"] or (
+            np.isnan(histogram["max"]) and np.isnan(statistics["maximum"])
+        )
+        assert histogram["min"] == band["statistics"]["minimum"] or (
+            np.isnan(histogram["min"]) and np.isnan(statistics["minimum"])
+        )
+        assert len(histogram["buckets"]) == histogram["count"]