ENH: Add zonation with layer range info to grid metadata

schema/definitions/0.8.0/schema/fmu_results.json

@@ -356,6 +356,21 @@
           "title": "Yshift",
           "type": "number"
         },
+        "zonation": {
+          "anyOf": [
+            {
+              "items": {
+                "$ref": "#/$defs/ZoneDefinition"
+              },
+              "type": "array"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "default": null,
+          "title": "Zonation"
+        },
         "zscale": {
           "title": "Zscale",
           "type": "number"
@@ -10146,6 +10161,32 @@
       ],
       "title": "Workflow",
       "type": "object"
+    },
+    "ZoneDefinition": {
+      "description": "Zone name and corresponding layer index min/max",
+      "properties": {
+        "max_layer_idx": {
+          "minimum": 0,
+          "title": "Max Layer Idx",
+          "type": "integer"
+        },
+        "min_layer_idx": {
+          "minimum": 0,
+          "title": "Min Layer Idx",
+          "type": "integer"
+        },
+        "name": {
+          "title": "Name",
+          "type": "string"
+        }
+      },
+      "required": [
+        "name",
+        "min_layer_idx",
+        "max_layer_idx"
+      ],
+      "title": "ZoneDefinition",
+      "type": "object"
     }
   },
   "$id": "fmu_results.json",

src/fmu/dataio/_model/specification.py

@@ -96,6 +96,20 @@ class CPGridSpecification(RowColumnLayer):
     zscale: float = Field(allow_inf_nan=False)
     """Scaling factor for the z-axis."""
 
+    zonation: Optional[List[ZoneDefinition]] = Field(default=None)
+    """
+    Zone names and corresponding layer index ranges. Note the indices
+    are zero-based; add 1 to convert to corresponding layer number,
+    """
+
+
+class ZoneDefinition(BaseModel):
+    """Zone name and corresponding layer index min/max"""
+
+    name: str
+    min_layer_idx: int = Field(ge=0)
+    max_layer_idx: int = Field(ge=0)
+
 
 class CPGridPropertySpecification(RowColumnLayer):
     """Specifies relevant values describing a corner point grid property object."""

src/fmu/dataio/providers/objectdata/_xtgeo.py

@@ -18,6 +18,7 @@
     PointSpecification,
     PolygonsSpecification,
     SurfaceSpecification,
+    ZoneDefinition,
 )
 from fmu.dataio._utils import get_geometry_ref, npfloat_to_float
 
@@ -383,6 +384,24 @@ def get_spec(self) -> CPGridSpecification:
             xscale=npfloat_to_float(required["xscale"]),
             yscale=npfloat_to_float(required["yscale"]),
             zscale=npfloat_to_float(required["zscale"]),
+            zonation=self._get_zonation() if self.obj.subgrids else None,
+        )
+
+    def _get_zonation(self) -> list[ZoneDefinition]:
+        """
+        Get the zonation for the grid as a list of zone definitions.
+        The list will be ordered from shallowest zone to deepest.
+        """
+        return sorted(
+            [
+                ZoneDefinition(
+                    name=zone,
+                    min_layer_idx=min(layerlist) - 1,
+                    max_layer_idx=max(layerlist) - 1,
+                )
+                for zone, layerlist in self.obj.subgrids.items()
+            ],
+            key=lambda x: x.min_layer_idx,
         )
 
 

tests/test_units/test_rms_context.py

@@ -497,6 +497,51 @@ def test_grid_export_file_set_name(inside_rms_setup, grid):
     )
 
 
+@inside_rms
+def test_grid_zonation_in_metadata(inside_rms_setup, grid):
+    """Export the grid to file with correct metadata and name."""
+
+    edata = dataio.ExportData(
+        config=inside_rms_setup["config"], content="depth", name="MyGrid"
+    )
+
+    assert grid.subgrids is None
+    meta = edata.generate_metadata(grid)
+    assert meta["data"]["spec"].get("zonation") is None
+
+    grid.set_subgrids({"zone1": 2, "zone2": 3})
+    meta = edata.generate_metadata(grid)
+    assert meta["data"]["spec"]["zonation"] == [
+        {"name": "zone1", "min_layer_idx": 0, "max_layer_idx": 1},
+        {"name": "zone2", "min_layer_idx": 2, "max_layer_idx": 4},
+    ]
+
+    # check that we get zones in order even though subgrids are not
+    grid.subgrids = {"zone1": [1, 2], "zone3": [5], "zone2": [3, 4]}
+    meta = edata.generate_metadata(grid)
+    assert meta["data"]["spec"]["zonation"] == [
+        {"name": "zone1", "min_layer_idx": 0, "max_layer_idx": 1},
+        {"name": "zone2", "min_layer_idx": 2, "max_layer_idx": 3},
+        {"name": "zone3", "min_layer_idx": 4, "max_layer_idx": 4},
+    ]
+
+    # test that various incorrect subgrid input causes error (in XTGeo)
+    with pytest.raises(ValueError, match="Subgrids lengths"):
+        grid.subgrids = {"zone1": [1, 2, 3], "zone2": [3, 4, 5]}
+
+    with pytest.raises(ValueError, match="not valid"):
+        grid.subgrids = {"zone1": [1, 2, 3], "zone2": [3, 4]}
+
+    with pytest.raises(ValueError, match="not valid"):
+        grid.subgrids = {"zone1": [1, 2, 3], "zone2": [5, 6]}
+
+    with pytest.raises(ValueError, match="Subgrids lengths"):
+        grid.set_subgrids({"zone1": 3, "zone2": 3})
+
+    with pytest.raises(ValueError, match="Subgrids lengths"):
+        grid.set_subgrids({"zone1": 1, "zone2": 1})
+
+
 @inside_rms
 def test_gridproperty_export_file_set_name(inside_rms_setup, gridproperty):
     """Export the gridprop to file with correct metadata and name."""