Implement #370 for SAR extension

Author: duckontheweb

pystac/extensions/sar.py

@@ -304,15 +304,17 @@ def observation_direction(self, v: Optional[ObservationDirection]) -> None:
     def get_schema_uri(cls) -> str:
         return SCHEMA_URI
 
-    @staticmethod
-    def ext(obj: T) -> "SarExtension[T]":
+    @classmethod
+    def ext(cls, obj: T) -> "SarExtension[T]":
         if isinstance(obj, pystac.Item):
+            cls.validate_has_extension(obj)
             return cast(SarExtension[T], ItemSarExtension(obj))
         elif isinstance(obj, pystac.Asset):
+            cls.validate_has_extension(obj)
             return cast(SarExtension[T], AssetSarExtension(obj))
         else:
             raise pystac.ExtensionTypeError(
-                f"File extension does not apply to type {type(obj)}"
+                f"SAR extension does not apply to type {type(obj)}"
             )
 
 

tests/data-files/sar/sentinel-1.json

@@ -0,0 +1,107 @@
+{
+    "type": "Feature",
+    "stac_version": "1.0.0-rc.1",
+    "stac_extensions": [
+        "https://stac-extensions.github.io/sar/v1.0.0/schema.json"
+    ],
+    "id": "sentinel-1-example",
+    "properties": {
+        "datetime": "2018-11-03T23:58:55.617217Z",
+        "start_datetime": "2018-11-03T23:58:55.121559Z",
+        "end_datetime": "2018-11-03T23:59:55.112875Z",
+        "platform": "sentinel-1a",
+        "constellation": "sentinel-1",
+        "instruments": [
+            "c-sar"
+        ],
+        "sar:instrument_mode": "EW",
+        "sar:polarizations": [
+            "HH"
+        ],
+        "sar:resolution_range": 50,
+        "sar:resolution_azimuth": 50,
+        "sar:pixel_spacing_range": 25,
+        "sar:pixel_spacing_azimuth": 25,
+        "sar:looks_range": 3,
+        "sar:looks_azimuth": 1,
+        "sar:looks_equivalent_number": 2.7,
+        "sar:frequency_band": "C",
+        "sar:center_frequency": 5.405,
+        "sar:product_type": "GRD"
+    },
+    "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+            [
+                [
+                    -67.071648,
+                    -64.72924
+                ],
+                [
+                    -65.087479,
+                    -56.674374
+                ],
+                [
+                    -68.033211,
+                    -51.105831
+                ],
+                [
+                    -70.275032,
+                    -59.805672
+                ],
+                [
+                    -67.071648,
+                    -64.72924
+                ]
+            ]
+        ]
+    },
+    "links": [
+        {
+            "rel": "root",
+            "href": "../../catalog.json",
+            "type": "application/json"
+        },
+        {
+            "rel": "parent",
+            "href": "../collection.json",
+            "type": "application/json"
+        }
+    ],
+    "assets": {
+        "noises": {
+            "href": "https://example.com/collections/sentinel-1/items/annotation/calibration/noise-s1a-ew-grd-hh-20181103t235855-20181103t235955-024430-02ad5d-001.xml",
+            "type": "text/xml",
+            "title": "Calibration Schema"
+        },
+        "calibrations": {
+            "href": "https://example.com/collections/sentinel-1/items/annotation/calibration/calibration-s1a-ew-grd-hh-20181103t235855-20181103t235955-024430-02ad5d-001.xml",
+            "type": "text/xml",
+            "title": "Noise Schema"
+        },
+        "products": {
+            "href": "https://example.com/collections/sentinel-1/items/annotation/s1a-ew-grd-hh-20181103t235855-20181103t235955-024430-02ad5d-001.xml",
+            "type": "text/xml",
+            "title": "Product Schema"
+        },
+        "measurement": {
+            "href": "https://example.com/collections/sentinel-1/items/measurement/s1a-ew-grd-hh-20181103t235855-20181103t235955-024430-02ad5d-001.tiff",
+            "type": "image/tiff",
+            "title": "Measurements",
+            "sar:polarizations": [
+                "HH"
+            ]
+        },
+        "thumbnail": {
+            "href": "https://example.com/collections/sentinel-1/items/preview/quick-look.png",
+            "type": "image/png",
+            "title": "Thumbnail"
+        }
+    },
+    "bbox": [
+        -70.275032,
+        -64.72924,
+        -65.087479,
+        -51.105831
+    ]
+}

tests/extensions/test_sar.py

@@ -7,6 +7,7 @@
 import pystac
 from pystac.extensions import sar
 from pystac.extensions.sar import SarExtension
+from tests.utils import TestCases
 
 
 def make_item() -> pystac.Item:
@@ -24,6 +25,7 @@ class SarItemExtTest(unittest.TestCase):
     def setUp(self) -> None:
         super().setUp()
         self.item = make_item()
+        self.sentinel_example_uri = TestCases.get_path("data-files/sar/sentinel-1.json")
 
     def test_stac_extensions(self) -> None:
         self.assertTrue(SarExtension.has_extension(self.item))
@@ -141,6 +143,24 @@ def test_polarization_must_be_list(self) -> None:
                 product_type,
             )
 
+    def test_extension_not_implemented(self) -> None:
+        # Should raise exception if Item does not include extension URI
+        item = pystac.Item.from_file(self.sentinel_example_uri)
+        item.stac_extensions.remove(SarExtension.get_schema_uri())
+
+        with self.assertRaises(pystac.ExtensionNotImplemented):
+            _ = SarExtension.ext(item)
+
+        # Should raise exception if owning Item does not include extension URI
+        asset = item.assets["measurement"]
+
+        with self.assertRaises(pystac.ExtensionNotImplemented):
+            _ = SarExtension.ext(asset)
+
+        # Should succeed if Asset has no owner
+        ownerless_asset = pystac.Asset.from_dict(asset.to_dict())
+        _ = SarExtension.ext(ownerless_asset)
+
 
 if __name__ == "__main__":
     unittest.main()