transforming cell corners for ESMF usage

transform_points_esmf.ipynb

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      "/home/pletzera/anaconda2/lib/python2.7/site-packages/Iris-1.10.0.dev0-py2.7.egg/iris/fileformats/grib/__init__.py:59: IrisDeprecation: The module iris.fileformats.grib is deprecated since v1.10. Please install the package 'iris_grib' package instead.\n",
      "  \"The module iris.fileformats.grib is deprecated since v1.10. \"\n"
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   "source": [
    "import copy\n",
    "import iris\n",
    "import ants.tests.stock as stock\n",
    "import ants\n",
    "import cartopy.crs as ccrs\n",
    "import numpy as np\n",
    "from ants.regrid import _ESMFRegridder"
   ]
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   "source": [
    "# Lets create a fictitious source.\n",
    "source = stock.geodetic((4, 4), with_bounds=True)\n",
    "sx_coord, sy_coord = ants.utils.cube.horizontal_grid(source)\n",
    "\n",
    "# Lets create a fictitious target by copying the source and replacing the coordinate system with a rotated one.\n",
    "target = source.copy()\n",
    "tx_coord, ty_coord = ants.utils.cube.horizontal_grid(target)\n",
    "tx_coord.coord_system = iris.coord_systems.GeogCS(semi_major_axis=6378137.0, semi_minor_axis=6356752.314245179)\n",
    "ty_coord.coord_system = copy.copy(tx_coord.coord_system)\n",
    "ty_coord.standard_name = 'grid_latitude'\n",
    "tx_coord.standard_name = 'grid_longitude'"
   ]
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   "source": [
    "# True lat-lon crs\n",
    "latlon_crs = ccrs.Geodetic()\n",
    "\n",
    "# Transform the coordinates of both source and target (which could be any crs) to a true lat-lon crs for usage with ESMF.\n",
    "src_crs = sx_coord.coord_system.as_ants_crs().as_cartopy_crs()\n",
    "tgt_crs = tx_coord.coord_system.as_ants_crs().as_cartopy_crs()\n",
    "\n",
    "# Get cell corners of the source as true lat lon points\n",
    "x_bounds, y_bounds = np.meshgrid(sx_coord.bounds, sy_coord.bounds)\n",
    "xyz = latlon_crs.transform_points(src_crs, x_bounds, y_bounds)\n",
    "sx, sy = xyz[..., 0], xyz[..., 1]\n",
    "\n",
    "# Get cell corners of the target as true lat lon points\n",
    "x_bounds, y_bounds = np.meshgrid(tx_coord.bounds, ty_coord.bounds)\n",
    "xyz = latlon_crs.transform_points(tgt_crs, x_bounds, y_bounds)\n",
    "tx, ty = xyz[..., 0], xyz[..., 1]"
   ]
  },
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   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
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   "source": [
    "# Now supply the source and target lat lons to ESMF as well as the source data for regridding\n",
    "regridder = _ESMFRegridder(source, target, method='conserve')\n",
    "# Initialise the target data\n",
    "target.data[...] = -1\n",
    "# Apply the regridding weights\n",
    "target = regridder(source)"
   ]
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   "execution_count": 6,
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     "text": [
      "[[ 0  1  2  3]\n",
      " [ 4  5  6  7]\n",
      " [ 8  9 10 11]\n",
      " [12 13 14 15]]\n"
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   "source": [
    "# Check\n",
    "print(target.data)"
   ]
  },
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   "execution_count": null,
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