Add gridtype attribute to REGIS contruction

nlmod/dims/resample.py

@@ -494,10 +494,22 @@ def structured_da_to_ds(da, ds, method="average", nodata=np.NaN):
         logger.info(f"No crs in da. Setting crs equal to ds: {ds.rio.crs}")
         da = da.rio.write_crs(ds.rio.crs)
     if ds.gridtype == "structured":
+        # assume an average delr and delc to calculate the affine
+        if "extent" in ds.attrs:
+            # xmin, xmax, ymin, ymax
+            dx = (ds.attrs["extent"][1] - ds.attrs["extent"][0]) / len(ds.x)
+            dy = (ds.attrs["extent"][3] - ds.attrs["extent"][2]) / len(ds.y)
+        elif "delr" in ds.attrs and "delc" in ds.attrs:
+            dx = ds.attrs["delr"]
+            dy = ds.attrs["delc"]
+        else:
+            raise ValueError(
+                "No extent or delr and delc in ds. Cannot determine affine."
+            )
         da_out = da.rio.reproject(
             dst_crs=ds.rio.crs,
             shape=(len(ds.y), len(ds.x)),
-            transform=get_affine(ds),
+            transform=get_affine(ds, sx=dx, sy=-dy),
             resampling=resampling,
             nodata=nodata,
         )

nlmod/read/regis.py

@@ -177,6 +177,7 @@ def get_regis(
             variables = variables + ("sdh", "sdv")
         ds = ds[list(variables)]
 
+    ds.attrs["gridtype"] = "structured"
     ds.attrs["extent"] = extent
     for datavar in ds:
         ds[datavar].attrs["grid_mapping"] = "crs"