interactive plotting with lonboard

xdggs/accessor.py

@@ -3,6 +3,7 @@
 
 from xdggs.grid import DGGSInfo
 from xdggs.index import DGGSIndex
+from xdggs.plotting import explore
 
 
 @xr.register_dataset_accessor("dggs")
@@ -115,3 +116,40 @@ def cell_boundaries(self):
         return xr.DataArray(
             boundaries, coords={self._name: self.cell_ids}, dims=self.cell_ids.dims
         )
+
+    def explore(
+        self, *, cell_boundaries="cell_boundaries", cmap="viridis", center=None
+    ):
+        """interactively explore the data using `lonboard`
+
+        Requires `geopandas`, `matplotlib`, and `lonboard` to be installed.
+
+        Parameters
+        ----------
+        cell_boundaries : str
+            The name of the coordinate containing the pre-computed cell boundary polygons.
+        cmap : str
+            The name of the color map to use
+        center : int or float, optional
+            If set, will choose this as the center point for a diverging color map.
+
+        Returns
+        -------
+        map : lonboard.Map
+            The rendered map.
+
+        Notes
+        -----
+        Plotting currently is restricted to `DataArray` objects.
+        """
+        if isinstance(self._obj, xr.Dataset):
+            raise ValueError("does not work with Dataset objects, yet")
+
+        cell_dim = self._obj[self._name].dims[0]
+        return explore(
+            self._obj,
+            cell_boundaries=cell_boundaries,
+            cell_dim=cell_dim,
+            cmap=cmap,
+            center=center,
+        )

xdggs/plotting.py

@@ -0,0 +1,53 @@
+import numpy as np
+
+
+def explore(
+    arr,
+    cell_boundaries="cell_boundaries",
+    cell_dim="cells",
+    cmap="viridis",
+    center=None,
+):
+    import geopandas as gpd
+    import lonboard
+    from lonboard import SolidPolygonLayer
+    from lonboard.colormap import apply_continuous_cmap
+    from matplotlib import colormaps
+    from matplotlib.colors import CenteredNorm, Normalize
+
+    if len(arr.dims) != 1 or cell_dim not in arr.dims:
+        raise ValueError(
+            f"exploration only works with a single dimension ('{cell_dim}')"
+        )
+
+    if cell_boundaries not in arr.coords:
+        raise ValueError(
+            f"cannot find the cell boundaries coordinate: '{cell_boundaries}'"
+        )
+
+    name = arr.name or "__temporary_name__"
+
+    gdf = (
+        arr.to_dataset(name=name)
+        .to_pandas()
+        .pipe(gpd.GeoDataFrame, geometry=cell_boundaries, crs=4326)
+    )
+
+    data = gdf[name]
+
+    if center is None:
+        vmin = data.min(skipna=True)
+        vmax = data.max(skipna=True)
+        normalizer = Normalize(vmin=vmin, vmax=vmax)
+    else:
+        halfrange = np.abs(data).max(skipna=True)
+        normalizer = CenteredNorm(vcenter=center, halfrange=halfrange)
+
+    normalized_data = normalizer(data)
+
+    colormap = colormaps[cmap]
+    colors = apply_continuous_cmap(normalized_data, colormap)
+
+    layer = SolidPolygonLayer.from_geopandas(gdf, filled=True, get_fill_color=colors)
+
+    return lonboard.Map(layer)