MONET Xarray Accessor

MONET can add georeferencing tools to xarray’s data structures through their accessor mechanism. These tools can be accessed via a special .monet attribute, available for both xarray.DataArray and xarray.Dataset objects after a simple import monet in your code.

Initializing the Accessor

All you have to do is import monet and xarray.

import monet
import xarray as xr

cmaqfile = monet.__path__ + '/../data/aqm.t12z.aconc.ncf'

from monet.models import cmaq

c = cmaq.open_dataset(cmaqfile)

c.O3[0,0,:,:].monet.quick_map()
_images/cmaq_o3_example_quickmap.png

Interpolation Methods

The MONET accessor provides several useful interpolation routines including:

  • getting the nearest point to a given latitude and longitude

  • interpolating to a constant latitude or longitude

  • interpolating to a vertical levels

  • remapping entire 2D DataArray or DataSet.

Find Nearest Point

To find the nearest latitude/longitude point you just need to use the nearest_latlon() method. In this example we will continue to use the CMAQ test file above. We will find the closest grid points to lat=20.5, lon=-157.4.

c.monet.nearest_latlon(lat=20.5,lon=-157.4)

<xarray.Dataset>
Dimensions:    (time: 48, x: 1, y: 1, z: 1)
Coordinates:
* time       (time) datetime64[ns] 2018-05-17T12:00:00 2018-05-17T13:00:00 ...
  latitude   (y, x) float64 dask.array<shape=(1, 1), chunksize=(1, 1)>
  longitude  (y, x) float64 dask.array<shape=(1, 1), chunksize=(1, 1)>
Dimensions without coordinates: x, y, z
Data variables:
  O3         (time, z, y, x) float32 dask.array<shape=(48, 1, 1, 1), chunksize=(48, 1, 1, 1)>

Notice that the length of the dimensions are now (time: 48, x: 1, y: 1, z: 1). If you wanted to only find the nearest location for a single variable you can use the accessor on the DataArray.

c.O3.monet.nearest_latlon(lat=20.5,lon=-157.4)

<xarray.DataArray 'O3' (time: 48, z: 1, y: 1, x: 1)>
dask.array<shape=(48, 1, 1, 1), dtype=float32, chunksize=(48, 1, 1, 1)>
Coordinates:
 * time       (time) datetime64[ns] 2018-05-17T12:00:00 2018-05-17T13:00:00 ...
   latitude   (y, x) float64 dask.array<shape=(1, 1), chunksize=(1, 1)>
   longitude  (y, x) float64 dask.array<shape=(1, 1), chunksize=(1, 1)>
Dimensions without coordinates: z, y, x
Attributes:
   long_name:   O3
   units:       ppbV
   var_desc:    Variable O3
   _FillValue:  nan