README.md

GDAL Reprojection with Dask Arrays

Reprojection of maps with coordinate referrence systems (crs), using GDAL's implementation with Rasterio and supporting Dask backed arrays for parallel computation.

Options for setting chunks or number of blocks in each dimension for easy dask chunking.

Also provides the 'geo' accessor for DataArrays

pip install gdal_dask_reproject

conda install -c chlochlo gdal_dask_reproject

Usage:

Import reproject from cc_reproject; then apply reproject with arguments for the input DataArray (containing Rioxarray compatible crs attrs and coords) and the destination crs desired.

If the input is a dask-backed data array then chunking is done automatically for the destination, matching the chunk structure of the input.

If the input is a np backed data array then the default will run a single reproject and return a np backed data array. But, setting the destination chunks or numblocks will return a dask backed array.

Note: the chunks input refers to the destination chunks; if this is provided without dst_shape, it will determine the dst_shape; if chunks and dst_shape are provided, the chunks in each dimension must sum to the provided shape.

Note on providing chunks when using an input that is already chunked: band chunking must match from src to dst; i.e. if the src band chunks are (1, 2) the destination must also have them in that order. If not, reproject will coerce the dst to match the src band chunking.

Note on using numblocks for chunking: numblocks is currently set to chunk the dst array by a math.ceil operation, so chunking an uneven dimension, like 3 bands for example, returns chunks (2, 1).

Kwargs are also available for passing through to rasterio.warp.reproject. For example, setting resampling. See below.

Example:

from cc_reproject import reproject

src = xarray.DataArray(np or dask array)
src_crs --> 'EPSG:4326'  # set in spatial_ref coords according to rioxarray compatibility
dst_crs = 'EPSG:3857'

reproject(src, dst_crs, **kwargs)

--> xarray.DataArray(np or dask)

reproject(xarray.DataArray(np), dst_crs, numblocks=(1, 2, 2), **kwargs)
--> xarray.DataArray(dask) chunked 1, 2, 2 times along the band, height, and width dimensions

Using the 'geo' accessor:

from cc_reproject import geo

my_data_array = xarray.DataArray(...)
my_data_array.geo.reproject(dst_crs, **kwargs)
--> reprojected xarray.DataArray

Adding kwargs for rasterio.warp.reproject

from cc_reproject import reproject
from rasterio.warp import Resampling

my_data_arr = xarray.DataArray(np or dask)
reproject(my_data_arr, dst_crs, resampling=Resampling.min)
--> reprojected xarray.DataArray(np or dask) resampled according to input

Support for multiband chunking

gdal_dask_reproject also allows chunking along band dimension for multiband rasters. You can add band_kwargs to apply specifically to each band chunk. band_kwargs is a dict with keys for each band chunk index, and values that are dicts of kwargs for each band index; for example: if 3 bands are split into 2 chunks 1, 2 in length, then keys would be 0 and 1. You can also set global kwargs differing from the ones set for specific band chunks. Any band_kwargs will overrride global kwargs for those bands specified, but the rest of the kwargs and the bands not included in band_kwargs will have the global settings.

from cc_reproject import reproject
from rasterio.warp import Resampling

# 3-band raster, for example
my_data_arr = xarray.DataArray(np or dask: shape = (3, 200, 400))
band_chunks = (1, 2)
band_kwargs = {
    0: {
        'resampling': Resampling.min
    },
}

# 300 and 600 tuples below are arbitrary chunk height and width settings. Using these, the returned DataArray will
# have the shape (3, 300, 600), based on summing the chunks specified for the destination.
reproject(my_data_arr, dst_crs, chunks=(band_chunks, (300,), (600,)), band_kwargs=band_kwargs, resampling=Resampling.bilinear)
--> xarray.DataArray(dask) 
    band chunk 0: band 1: resampled by min
    band chunk 1: band 2 and band 3: resampled by bilinear

Based on the work of Kirill Kouzoubov in OpenDataCube and with the desire to have a standalone GDAL dask reprojection package: (Note: all errors are my own).

Issue in rioxarray

ODC code