Adding ESMF.LocStream capabilities to xESMF

xesmf/backend.py

@@ -114,6 +114,38 @@ def esmf_grid(lon, lat, periodic=False):
     return grid
 
 
+def esmf_locstream(lon, lat):
+    '''
+    Create an ESMF.LocStream object, for contrusting ESMF.Field and ESMF.Regrid
+
+    Parameters
+    ----------
+    lon, lat : 1D numpy array
+         Longitute/Latitude of cell centers.
+
+    Returns
+    -------
+    locstream : ESMF.LocStream object
+    '''
+
+    if len(lon.shape) > 1:
+        raise ValueError("lon can only be 1d")
+    if len(lat.shape) > 1:
+        raise ValueError("lat can only be 1d")
+
+    assert lon.shape == lat.shape
+
+    location_count = len(lon)
+
+    locstream = ESMF.LocStream(location_count,
+                               coord_sys=ESMF.CoordSys.SPH_DEG)
+
+    locstream["ESMF:Lon"] = lon.astype(np.dtype('f8'))
+    locstream["ESMF:Lat"] = lat.astype(np.dtype('f8'))
+
+    return locstream
+
+
 def add_corner(grid, lon_b, lat_b):
     '''
     Add corner information to ESMF.Grid for conservative regridding.

xesmf/frontend.py

@@ -7,7 +7,7 @@
 import os
 import warnings
 
-from . backend import (esmf_grid, add_corner,
+from . backend import (esmf_grid, esmf_locstream, add_corner,
                        esmf_regrid_build, esmf_regrid_finalize)
 
 from . smm import read_weights, apply_weights
@@ -72,9 +72,40 @@ def ds_to_ESMFgrid(ds, need_bounds=False, periodic=None, append=None):
     return grid, lon.shape
 
 
+def ds_to_ESMFlocstream(ds):
+    '''
+    Convert xarray DataSet or dictionary to ESMF.LocStream object.
+
+    Parameters
+    ----------
+    ds : xarray DataSet or dictionary
+        Contains variables ``lon``, ``lat``.
+
+    Returns
+    -------
+    locstream : ESMF.LocStream object
+
+    '''
+
+    lon = np.asarray(ds['lon'])
+    lat = np.asarray(ds['lat'])
+
+    if len(lon.shape) > 1:
+        raise ValueError("lon can only be 1d")
+    if len(lat.shape) > 1:
+        raise ValueError("lat can only be 1d")
+
+    assert lon.shape == lat.shape
+
+    locstream = esmf_locstream(lon, lat)
+
+    return locstream, (1,) + lon.shape
+
+
 class Regridder(object):
     def __init__(self, ds_in, ds_out, method, periodic=False,
-                 filename=None, reuse_weights=False, ignore_degenerate=None):
+                 filename=None, reuse_weights=False, ignore_degenerate=None,
+                 locstream_in=False, locstream_out=False):
         """
         Make xESMF regridder
 
@@ -118,6 +149,12 @@ def __init__(self, ds_in, ds_out, method, periodic=False,
             If False (default), raise error if grids contain degenerated cells
             (i.e. triangles or lines, instead of quadrilaterals)
 
+        locstream_in: bool, optional
+            input is a LocStream (list of locations)
+
+        locstream_out: bool, optional
+            output is a LocStream (list of locations)
+
         Returns
         -------
         regridder : xESMF regridder object
@@ -135,15 +172,31 @@ def __init__(self, ds_in, ds_out, method, periodic=False,
         self.periodic = periodic
         self.reuse_weights = reuse_weights
         self.ignore_degenerate = ignore_degenerate
+        self.locstream_in = locstream_in
+        self.locstream_out = locstream_out
+
+        methods_avail_ls_in = ['nearest_s2d', 'nearest_d2s']
+        methods_avail_ls_out = ['bilinear', 'patch'] + methods_avail_ls_in
+
+        if locstream_in and self.method not in methods_avail_ls_in:
+            raise ValueError(f'locstream input is only available for method in {methods_avail_ls_in}')
+        if locstream_out and self.method not in methods_avail_ls_out:
+            raise ValueError(f'locstream output is only available for method in {methods_avail_ls_out}')
 
         # construct ESMF grid, with some shape checking
-        self._grid_in, shape_in = ds_to_ESMFgrid(ds_in,
-                                                 need_bounds=self.need_bounds,
-                                                 periodic=periodic
-                                                 )
-        self._grid_out, shape_out = ds_to_ESMFgrid(ds_out,
-                                                   need_bounds=self.need_bounds
-                                                   )
+        if locstream_in:
+            self._grid_in, shape_in = ds_to_ESMFlocstream(ds_in)
+        else:
+            self._grid_in, shape_in = ds_to_ESMFgrid(ds_in,
+                                                     need_bounds=self.need_bounds,
+                                                     periodic=periodic
+                                                     )
+        if locstream_out:
+            self._grid_out, shape_out = ds_to_ESMFlocstream(ds_out)
+        else:
+            self._grid_out, shape_out = ds_to_ESMFgrid(ds_out,
+                                                       need_bounds=self.need_bounds
+                                                       )
 
         # record output grid and metadata
         self._lon_out = np.asarray(ds_out['lon'])
@@ -312,6 +365,9 @@ def __call__(self, indata, keep_attrs=False):
     def regrid_numpy(self, indata):
         """See __call__()."""
 
+        if self.locstream_in:
+            indata = indata[np.newaxis, :]
+
         outdata = apply_weights(self.weights, indata,
                                 self.shape_in, self.shape_out)
         return outdata
@@ -341,7 +397,14 @@ def regrid_dataarray(self, dr_in, keep_attrs=False):
         # apply_ufunc needs a different name for output_core_dims
         # example: ('lat', 'lon') -> ('lat_new', 'lon_new')
         # https://github.com/pydata/xarray/issues/1931#issuecomment-367417542
-        temp_horiz_dims = [s + '_new' for s in input_horiz_dims]
+        if self.locstream_out:
+            temp_horiz_dims = ['dummy', 'locations']
+        else:
+            temp_horiz_dims = [s + '_new' for s in input_horiz_dims]
+
+        if self.locstream_in:
+            temp_horiz_dims = ['dummy_new'] + temp_horiz_dims
+
 
         dr_out = xr.apply_ufunc(
             self.regrid_numpy, dr_in,
@@ -355,20 +418,28 @@ def regrid_dataarray(self, dr_in, keep_attrs=False):
             keep_attrs=keep_attrs
         )
 
-        # rename dimension name to match output grid
-        dr_out = dr_out.rename(
-            {temp_horiz_dims[0]: self.out_horiz_dims[0],
-             temp_horiz_dims[1]: self.out_horiz_dims[1]
-            }
-        )
+        if not self.locstream_out:
+            # rename dimension name to match output grid
+            dr_out = dr_out.rename(
+                {temp_horiz_dims[0]: self.out_horiz_dims[0],
+                 temp_horiz_dims[1]: self.out_horiz_dims[1]
+                }
+            )
 
         # append output horizontal coordinate values
         # extra coordinates are automatically tracked by apply_ufunc
-        dr_out.coords['lon'] = xr.DataArray(self._lon_out, dims=self.lon_dim)
-        dr_out.coords['lat'] = xr.DataArray(self._lat_out, dims=self.lat_dim)
+        if self.locstream_out:
+            dr_out.coords['lon'] = xr.DataArray(self._lon_out, dims=('locations',))
+            dr_out.coords['lat'] = xr.DataArray(self._lat_out, dims=('locations',))
+        else:
+            dr_out.coords['lon'] = xr.DataArray(self._lon_out, dims=self.lon_dim)
+            dr_out.coords['lat'] = xr.DataArray(self._lat_out, dims=self.lat_dim)
 
         dr_out.attrs['regrid_method'] = self.method
 
+        if self.locstream_out:
+            dr_out = dr_out.squeeze(dim='dummy')
+
         return dr_out
 
     def regrid_dataset(self, ds_in, keep_attrs=False):
@@ -382,7 +453,14 @@ def regrid_dataset(self, ds_in, keep_attrs=False):
         name, dr_in = next(iter(ds_in.items()))
 
         input_horiz_dims = dr_in.dims[-2:]
-        temp_horiz_dims = [s + '_new' for s in input_horiz_dims]
+
+        if self.locstream_out:
+            temp_horiz_dims = ['dummy', 'locations']
+        else:
+            temp_horiz_dims = [s + '_new' for s in input_horiz_dims]
+
+        if self.locstream_in:
+            temp_horiz_dims = ['dummy_new'] + temp_horiz_dims
 
         # help user debugging invalid horizontal dimensions
         print('using dimensions {} from data variable {} '
@@ -402,18 +480,27 @@ def regrid_dataset(self, ds_in, keep_attrs=False):
             keep_attrs=keep_attrs
         )
 
-        # rename dimension name to match output grid
-        ds_out = ds_out.rename(
-            {temp_horiz_dims[0]: self.out_horiz_dims[0],
-             temp_horiz_dims[1]: self.out_horiz_dims[1]
-            }
-        )
+        if not self.locstream_out:
+            # rename dimension name to match output grid
+            ds_out = ds_out.rename(
+                {temp_horiz_dims[0]: self.out_horiz_dims[0],
+                 temp_horiz_dims[1]: self.out_horiz_dims[1]
+                }
+            )
 
         # append output horizontal coordinate values
         # extra coordinates are automatically tracked by apply_ufunc
-        ds_out.coords['lon'] = xr.DataArray(self._lon_out, dims=self.lon_dim)
-        ds_out.coords['lat'] = xr.DataArray(self._lat_out, dims=self.lat_dim)
+        if self.locstream_out:
+            ds_out.coords['lon'] = xr.DataArray(self._lon_out, dims=('locations',))
+            ds_out.coords['lat'] = xr.DataArray(self._lat_out, dims=('locations',))
+        else:
+            if not self.locstream_in:
+                ds_out.coords['lon'] = xr.DataArray(self._lon_out, dims=self.lon_dim)
+                ds_out.coords['lat'] = xr.DataArray(self._lat_out, dims=self.lat_dim)
 
         ds_out.attrs['regrid_method'] = self.method
 
+        if self.locstream_out:
+            ds_out = ds_out.squeeze(dim='dummy')
+
         return ds_out

xesmf/tests/test_backend.py

@@ -3,7 +3,7 @@
 import ESMF
 import xesmf as xe
 from xesmf.backend import (warn_f_contiguous, warn_lat_range,
-                           esmf_grid, add_corner,
+                           esmf_grid, add_corner, esmf_locstream,
                            esmf_regrid_build, esmf_regrid_apply,
                            esmf_regrid_finalize)
 from xesmf.smm import read_weights, apply_weights
@@ -207,3 +207,19 @@ def test_regrid_periodic_correct():
     assert np.max(np.abs(rel_err)) < 0.065
     # clean-up
     esmf_regrid_finalize(regrid)
+
+
+def test_esmf_locstream():
+    lon = np.arange(5)
+    lat = np.arange(5)
+
+    ls = esmf_locstream(lon, lat)
+    assert isinstance(ls, ESMF.LocStream)
+
+    lon2d, lat2d = np.meshgrid(lon, lat)
+    with pytest.raises(ValueError):
+        ls = esmf_locstream(lon2d, lat2d)
+    with pytest.raises(ValueError):
+        ls = esmf_locstream(lon, lat2d)
+    with pytest.raises(ValueError):
+        ls = esmf_locstream(lon2d, lat)