I'm preprocessing HMASR data, the data contains multiple data files with format of netcdf, and each tile (1X1 degree) is a nc file. So I read it through xarray open_mfdataset() to mosaic it spatially and do transformation after this. The data after mosaicing is like 4050x9900x366 which is listed below:

Dimensions:    (Latitude: 4050, Longitude: 9900, Day: 366, Stats: 5)
  * Latitude   (Latitude) float64 27.0 27.01 27.01 27.02 ... 44.99 44.99 45.0
  * Longitude  (Longitude) float64 61.0 61.01 61.01 61.02 ... 105.0 105.0 105.0
Dimensions without coordinates: Day, Stats
Data variables:
    SWE_Post   (Day, Stats, Longitude, Latitude) float32 dask.array<chunksize=(366, 5, 225, 225), meta=np.ndarray>
    SCA_Post   (Day, Stats, Longitude, Latitude) float32 dask.array<chunksize=(366, 5, 225, 225), meta=np.ndarray>

The speed is acceptable so far, but it becomes desperately slow when it comes to write it to the geotif.

The raster I want to write shaped (Latitude: 4050, Longitude: 9900). Firstly, I tried to use xarray function to_raster to write it , and with resample to match the template(you can see it from the commented code), I found that the writing processes itself are slow enough, so I gave it up. It kept getting performance warning. I also tried the convert the data to numpy.array to output it with gdal, but it gives no improvement. I think the problem is linked with the dask or chunksize. As i have seen example of the larger size image writing without performance issue.

This is part of my code:

import numpy as np
import xarray as xr
from lytools import * # a customed package
from tqdm import tqdm
from osgeo import gdal
import rioxarray
import dask    
def SWE_merged_annually(self, indir):
    #### Below is code used to create the array that will be written to a GeoTIFF ####
    # mosaic
    ds = xr.open_mfdataset(indir,
    SWE_year = ds.SWE_Post.sel(Stats=0)
    SWE_peak_2000 = xr.apply_ufunc(lambda x: x.max(axis=-1),

    SWE_peak_dowy_2000 = xr.apply_ufunc(lambda x: x.argmax(axis=-1),
    # mask
    SWE_peak_2000 = SWE_peak_2000.where(self.classifi == 1)
    SWE_peak_2000 = SWE_peak_2000.where(self.Non_seasonal_snow == 0)
    SWE_peak_dowy_2000 = SWE_peak_dowy_2000.where(self.classifi == 1)
    SWE_peak_dowy_2000 = SWE_peak_dowy_2000.where(self.Non_seasonal_snow == 0)

    ##### Above is code used to create array to write to GeoTIFF #####
    ##### writing part ######
    outdir1 = "/Volumes/My Passport/组内数据/雪水当量/HMA_SR/SWE_peak_tiff/"
    outdir2 = "/Volumes/My Passport/组内数据/雪水当量/HMA_SR/SWE_peal_DOWY_tiff/"

    outfname1 = outdir1 + str(self.year_now) + '.tif'
    outfname2 = outdir2 + str(self.year_now) + '.tif'

    # scheme 1 writing with rioxarray
    # ds = rioxarray.open_rasterio(tif_template_yuan, masked=True).isel(band=0)
    # SWE_peak_2000_resample = SWE_peak_2000.squeeze().transpose('Latitude', 'Longitude').rio. \
    #         set_spatial_dims(x_dim='Longitude', y_dim='Latitude').rio.write_crs('epsg:4326').rio.reproject_match(ds,resampling=5) 
    # SWE_peak_2000_dowy_resample = SWE_peak_dowy_2000.squeeze().transpose('Latitude', 'Longitude').rio. \
    #         set_spatial_dims(x_dim='Longitude', y_dim='Latitude').rio.write_crs('epsg:4326').rio.reproject_match(ds, resampling=5)
    # SWE_peak_2000_resample.to_raster(outfname1)
    # SWE_peak_2000_dowy_resample.to_raster(outfname2)

    # scheme 2 write with gdal
    Lon = SWE_peak_2000.Longitude
    Lat = SWE_peak_2000.Latitude
    LonMin, LatMax, LonMax, LatMin = [Lon.min(), Lat.max(), Lon.max(), Lat.min()]
    N_Lat = len(Lat)
    N_Lon = len(Lon)
    Lon_Res = (LonMax - LonMin) / (float(N_Lon) - 1)
    Lat_Res = (LatMax - LatMin) / (float(N_Lat) - 1)
    SWE_peak_arr = np.transpose(np.array(SWE_peak_2000))
    SWE_peak_dowy_arr = np.transpose(np.array(SWE_peak_dowy_2000))
    ToRaster().array2raster(outfname1, LonMin, LatMax, Lon_Res, -Lat_Res,
                            SWE_peak_arr)  # this is a customed function supposed to write tiff
    ToRaster().array2raster(outfname2, LonMin, LatMax, Lon_Res, -Lat_Res, SWE_peak_dowy_arr)

The performance warnings are below, i get rid of it by add dask.config.set(**{'array.slicing.split_large_chunks': False}), but i'm not sure if it helps the progress substantially

PerformanceWarning: Slicing is producing a large chunk. To accept the large
chunk and silence this warning, set the option
    >>> with dask.config.set(**{'array.slicing.split_large_chunks': False}):
    ...     array[indexer]

To avoid creating the large chunks, set the option
    >>> with dask.config.set(**{'array.slicing.split_large_chunks': True}):
    ...     array[indexer]
  return self.array[key]

Anyone know how to improve the performance of this code. And hopefully with resample functionality.

  • I just finished writing 4 Geotiffs to my disk, it costs me 9 hours. I think it's abnormally slow, as each Geotiff is no more than 200MB. I have similar question when dealing with CMIP6 data, it's also about xarray and dask, I think it's conneted. I tried add some configuration to dask, it's also won't help.
    – 孟泽楷
    Mar 5 at 2:49
  • Nevermind, i finished runing it, it's very slow though. i check some github issues, lots of question tagged with performance have quite a few comments. I guess the it's just what it is.
    – 孟泽楷
    Mar 14 at 6:37


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